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OK I'm Hacked. MPG stuff.

Discussion in 'The Garage' started by Grim-Reaper, May 14, 2003.

  1. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    OK I\'m Hacked. MPG stuff.

    Ok so most of have read my burb thread. I'm getting 10 mpg in a 454 burb with TH400, 3.73 gears and 31 inch tall tires. Engine has 72k on it. It has been maintained fairly well by the PO.

    The MPG is true. I verified the miles with my GPS so it's not odometer error.

    Now everybody here says 10mpg hwy is normal. Well I think there is more and here is why. I also hang out on a RV forum for Airstreams. These guys with 27-31ft 16,000lb motor homes are pulling 11-12 on the hwy with CARBS and I should be able to pull at least that in a vehicle with the same engine (with FI) and tranny and 10,000 less pounds!

    Ok I'm going to see what I can do with it. I want 14mpg hwy. I know people that were pulling 18 out of 350 FI 4x4 1/2 ton burbs. I think it has 14 in it. The truck Managed 9mpg with 7500lb of K5 on a trailer behind it with 4 bad plug wires.

    What has been done to this point.
    New cap and button
    Wires
    O2 sensor
    plugs.

    I have a serge I'm chasing at hwy speeds. I am really starting to believe it's a bad Cat. Plugged cat can explain several problems I have. The truck has a heat up problem at idle with the A/C on. Truck shifts really hard at times. BOTH exhaust manifold gaskets are blown and blown bad. It all can be explained with excessive back pressure.

    If the engine can't get rid of the exhaust it's going to cause low intake vacuum. Low intake vacuum will cause misreading of the MAP sensor as well as incorrect readings for the O2 sensor. This will get it into a visious cycle and possibly cause it to run rich and further plug the cat.

    Low manifold vacuum will also cause the transmission to think that I'm using a lot of throttle (TH400 no electronics on it all works with manifold vac) and it will firm up the shifts thinking it's under a heavy load.

    Here are my plans for this weekend.
    Finish tune up. I haven't had a chance to set timing and install a PCV. I also want to check every vac line on the truck and check for vac leaks at the throttle body.

    Rig up the truck for testing including a Vac gage I can read while driving. Add some pig tails from O2 sensor, Map Sensor, TPS and run them inside so I can monitor them with my VOM while driving. See if I can round up a Lap top and down load some EFI monitoring software.

    I'm going to try to find a peice of 3 inch exhaust pipe and pull the cat. Run it for a week without it and see what changes. Then I'll get a Free flowing Cat to install on it and we can see how much a cat eats.
    Change over to Full synthetic motor oil as well

    Now the point of this thread is for me to hear some of your ideas to try a few and for me to share the end results. I also want to hear some results of upgrades and products others have used to try to make some MPG and performance gains and see their results.

    What I plan to do is a tech write up for the site and see what results I can come up with. This will take a couple months at least but the hope is to provide some good solid information for others.

    I plan do do this in steps so I can run at least 150miles after each change to get some good MPG figures. That's roughly a week between each change I try.

    This will lead up to part of a build up of my Ultimate tow rig. We (My family) plan to do some cross country traveling with our camper. This is what this truck was bought to do as well as serve as my DD. So like many of you this truck is serving multiple needs.

    Some things I am investigating is a bolt on over drive if I can swing it. Also looking at some ignition upgrades. Maybe a Jacobs or MSD set up.

    Ok, lets hear some ideas? What sort of upgrades would you like to see some tests on and I'll see what I can do about providing them. What products have you used and what are your results with them good or bad.
     
  2. ftn96

    ftn96 1/2 ton status

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    Re: OK I\'m Hacked. MPG stuff.

    All I can offer Grimmy is keeping the exhaust close to stock after you get those mannies and CAT taken care of AND

    That 400 not having lock up is where you are loosing a fair amount of efficiency on top of 3.73's and 31's..... hmmmm

    I'd think that a 3.42 with those 31's would get you "closer" to the 14 MPG.

    Keep us updated. /forums/images/graemlins/wink.gif
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Re: OK I\'m Hacked. MPG stuff.

    Use/borrow a laptop and run WinALDL to record as you drive around, then open up the history in Excel to view all the important data over the entire time...
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    Add some pig tails from O2 sensor, Map Sensor, TPS and run them inside so I can monitor them with my VOM while driving.

    [/ QUOTE ]

    Idea isn't bad, but as you allude to, you are kind of duplicating your efforts if you get a laptop. I'd *seriously* consider spending your time building one of the winALDL laptop cables, instead of pigtails to try and do it with a VOM. Besides, if you are thinking of it, cutting/splicing of wires is never a good idea if you don't have to. Since the ALDL connector is in the cab (wouldn't be if it was a Ford : ) it only makes sense to use the existing data port. Besides, I still don't believe TBI trucks didn't get VSS, even 465 equipped. Since you have a TH400 that doesn't have TCC, thats the same as a 465 to the ECM. You hooking some sort of device up to the ECM will prove that once and for all, since vehicle speed is something you'll see with a scanner, or winALDL and the like.

    TPS won't matter, TPS is a "static" measurement. Doesn't change depending on if you are driving or sitting still, the TPS voltage is based on throttle position, and thats it. So thats something you can test sitting in the driveway. X volts throttle closed, Y volts WOT.

    I've seen tests somewhere (GM manual?) that tell you how to troubleshoot a plugged cat. I can check my '88 camaro manual if you like, but I *believe* it was an actual backpressure tester, which tapped into the exhaust pipe upstream and downstream of the converter.

    Of course some GM vehicles have cat converter temp that you can extract from the ALDL, but trucks I'd guess do not. Any time I've heard of plugged cat converters, sluggishness slowly increases with driving time and engine load, as does heat coming from it.

    If the problem was constant, as a cat converter problem *should* be, affecting all the other readings (VSS, TPS, MAP, O2) you should start seeing codes. If you are not, more than likely it's not a constant problem, and that surge is probably somewhere else.

    Whenever I hear someone mention surge, EGR is the first thing I think of. You've checked it out?

    How about front air dam? Still present? If not, that's one of the FIRST things I'd like to see you report on, putting it on, and what difference, if any, it makes. Of course, .25-.50 MPG won't really be detected, but in conjunction with a few other changes, it will all add up. I know there is conjecture on what the air dam was for, but frankly, I've run with and without one, and cooling was no better nor worse, and MPG didn't change much, if any, either.

    The fender "seals" as well COULD be influential as well, still present?

    Another one I'd like to see is synthetic diff lube. If it works for the engine, it should help the diff as well.

    I'm sure a bunch of people are going to look at what you are going to do, and suggestions others make, and say that it's a waste of time. To those people I ask if they've ever been hiking, and had to actually carry some weight for some time. Every little bit removed helps, and if you can change 4 things that remove .25MPG inefficiency off of that vehicle (whether it be parasitic drag, wind drag, ignition, fuel, whatever) you've made measurable progress.

    The one thing I'm going to say is going to be a waste of time and money is any aftermarket ignition system (not individual components, like an aftermarket coil.) Unless you go from stock components that are in *good working order*, you will never know if an aftermarket system works as claimed. I'm not trying to start a pro/con argument for those ignition systems, but the GM system doesn't drop off at any reasonable RPM, and no aftermarket ignition company posts dyno data that's against known good stock stuff, and only replaces ONE component. If it helps with idle and startup, great. That doesn't affect mileage unless your idle is already piss poor. That would be my absolute last gasp to try and achieve higher MPG, because the data I've seen so far, indicates that money spent elsewhere brings more gains.
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    All I can offer Grimmy is keeping the exhaust close to stock after you get those mannies and CAT taken care of AND

    That 400 not having lock up is where you are loosing a fair amount of efficiency on top of 3.73's and 31's..... hmmmm

    I'd think that a 3.42 with those 31's would get you "closer" to the 14 MPG.

    Keep us updated. /forums/images/graemlins/wink.gif

    [/ QUOTE ]
    Well I bought it to move things. the 3.73 are going to have to stay. That's why I'm looking at a overdrive. Gearvendors and a couple other companies make a over drive unit that will bolt onto the back of the TH400. They run these in motor homes so they can take the power.
    I honestly expect at least 1mpg once I get the serge gone. That will be the easy one to get. The next 1 mpg I don't think will be a big problem either. It may fall in place with this serge being solved.

    The 8600 GVWR means I don't have to smog this truck. But I do plan to keep it on the up and up.
     
  6. mdm365

    mdm365 1/2 ton status

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    Re: OK I\'m Hacked. MPG stuff.

    grim I would love to see how a jacobs would work for you. I have not had any luck with msd the modules they always seem to go out on me.I will keep and eye on this post.my bro has a turd that was getting bad mpg the dealer told him it was the o2 sensor ond he replaced it with no prevale later we pulled the cat and it was about 90% blocked so we gutted the cat.We hit that one the truck is doing much better now. mike /forums/images/graemlins/thumb.gif
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Re: OK I\'m Hacked. MPG stuff.

    FWIW, I agree about the ignition stuff, GM HEI is just fine and I don't think upgrades are necessary on anything resembling stock.

    Some other random thoughts beyond the obvious stuff your already looking into... ATF in the t-case? Probably a 208 or similar (i.e. not 205) so I guess so. Synth (at least in the rear) is supposed to help by some small measurable amount, I'm told that's why the factory is going that way. Running higher pressure in the tires, but you posted before about proper pressure, still... Wax, smooth finish, remove luggage rack, anything to cut drag, not sure how much if any the rear deflectors help.

    More significant and costly. Best low rpm torque (MPG focused) cam and intake you can find (Edel?). Maybe Tri-Ys? Matched chip? Regear (OD?) to put engine rpm at absolute peak at your typical speed? TH350/700R4 for less parasitic loss? Setup to maximize on premium? (higher timing among other things, hey you didn't say you were concerned about cost per mile, just MPG )

    Yeah, it all adds up. Some of this is probably pointless, certainly beyond the PODR, but, it all adds up...
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Re: OK I\'m Hacked. MPG stuff.

    Oh, and be sure to get one of those magnet things that goes on the fuel line along with one of those things that goes in the breather to spin the air going in. I saw on TV that those things give you 15-30% increase in mpg EACH. That alone will get you to 14 mpg! /forums/images/graemlins/rotfl.gif
     
  9. bowtiepower00

    bowtiepower00 1/2 ton status

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    Re: OK I\'m Hacked. MPG stuff.

    I would put a set of headers on it, along with new exhaust. Single 3" would be the most efficient, but duals would work as well. If your feeling rich it's hard to beat a Banks kit. I've done headers by themselves, and everything from the manifolds back by themselves, and the improvements were small, but when combined they make quite a difference. I would avoid synthetic in the engine, higher milage motors get funny when you switch them over. I would use synth in the diff and tranny though. An open element K&N or some kind of cold air system should make a difference as well. I've been doing a lot of research on building and tuning TBI motors, and thirdgen.org has a GREAT TBI tech section that includes computer tuning. TBI throttle body spacers, injector spacers, and air horns are worth some improvement. If you decide to touch the motor, a new manifold and even cam would give you some improvement as well. I wouldn't mess with a jacobs system, I've read too many horror stories about them, but MSD makes bolt-in coils and modules for the small-cap dist. The under/overdrives are great, but spendy. Another option would be a 4L80e, but that will cost just as much if not more. Putting a little taller tire may help as well.
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: OK I\'m Hacked. MPG stuff.

    dyeager535:

    Yeah I found the VSS. It's in the dash. I have a factory manual for the truck and it lists it's location. The discription of the VSS says it's behind the speedometer. It sounds like a seperate modual . I'll be investigating more. This may be a good one to use when people convert older trucks to FI. Speaking of older FI conversions....I have FI on it's way for the 75. So some of this is also a lesson for me in GM FI for that conversion.

    As for the taping in. No cutting. just stripping back a wire and sticking it into existing plugs. This trick was outlined on 3rdgen site. The goal is the lap top but it's not something I will have this weekend. Will have to work with what I have right now.

    TPS.: I'm looking for a momentary interuption like bad connection as well as proper set up. The PO had a pressure washer and he used it often on the engine. I'm looking for any moisture damage indications.

    Plugged cat:
    Its a bead style converter. I have had multiple people tell me they are restrictive and prone to becoming more restrictive with age. So even if there isn't really a problem there is plenty of room for improvment.

    Hasn't thrown any codes but one of the disadvantages of a MAP sensor bassed FI is they don't actually monitor the air flow in like a MAF. All my previous FI vehicle ran a MAF so I'm familure with their logic process. With a MAP It just monitors intake vacuum. Well knowing that, a partly plugged up converter might not thow a code. It may just operate under the premmis that I'm hauling some weight. Lots of throttle but not lots of RPM. Run rich in the process as well. If the heat is packing infront of the converter throwing off the reading on the O2. That reading would again match what the map sensor is saying and asume "load".

    I'm going to hit the local muffler shop and see if they have a way to test the cat. The volocity of the exhaust exiting the tail pipes just doesn't seem to be as much as I would expect from such a large displacement motor. My 3.0 Supra seems to push out a lot more air at a 750 rpm idle then this 7.4 does. It may be an illusion though.

    A mechanic buddy said check the MAP sensor. I plan to do that as well. His comment is that the Map is what he found caused the problem the most after ruling out a bad O2 and installing a clean fuel filter. Did the filter Monday and no change. This goes back the the PO and his pressure washer. I know he did in a alternator with it. Checking al sensors that could also have sufferend from high pressure water.

    Well no Air damn on the truck but I do like them and I am looking for one for cosmetic reasons as well as any other gains it might provide. I don't think the 2wd trucks got them. Think that was a 4x4 thing to help with the increased ride hight. Every one I have ever seen had tow hook notches. Again this leads me to conclude that it was a 4x4 thing. I have tow hooks that I will be installing so looking for a 4x4 version. I do plan to atempt to see if I find any increase in MPG or hwy cooling once I find one.

    As for the fender seal.....It's bone stock and complete. Everything it rolled off the line with is present and accounted for. This truck has 72k original and documented miles. The PO was maticulous and took VERY good care of this vehicle. He is in his mid 80's so no hot doging. He however did not drive it much in the last 2 years. He put less then 1k on it in the last 1.5 years.

    EGR I plan to test this week. No idle problems so I don't think I will find a problem. My understanding is they usualy stuck open and causing a idle issue or the controler failed and should throw a code. No codes.

    As for the ign upgrades. Good point. I'm going to start by making double sure the truck is at 100% STOCK before I mess with any of that. Then I may see if I can get a "put your money where your mouth is" deal going on that.

    First thing is curing the serge and that's this weekends primary goal.

    Thanks for the input! Very thought provoking stuff. Keep it coming.
     
  11. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    Oh, and be sure to get one of those magnet things that goes on the fuel line along with one of those things that goes in the breather to spin the air going in. I saw on TV that those things give you 15-30% increase in mpg EACH. That alone will get you to 14 mpg! /forums/images/graemlins/rotfl.gif

    [/ QUOTE ]

    I just replaced the speakers. I was going to wrap the fuel lines around the magnets a few times. The magnets are a LOT bigger then the ones they use so I should get at least 45% gain I'll let you know how it work. /forums/images/graemlins/thumb.gif
    /forums/images/graemlins/rotfl.gif
     
  12. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    I would put a set of headers on it, along with new exhaust. Single 3" would be the most efficient, but duals would work as well. If your feeling rich it's hard to beat a Banks kit. I've done headers by themselves, and everything from the manifolds back by themselves, and the improvements were small, but when combined they make quite a difference. I would avoid synthetic in the engine, higher milage motors get funny when you switch them over. I would use synth in the diff and tranny though. An open element K&N or some kind of cold air system should make a difference as well. I've been doing a lot of research on building and tuning TBI motors, and thirdgen.org has a GREAT TBI tech section that includes computer tuning. TBI throttle body spacers, injector spacers, and air horns are worth some improvement. If you decide to touch the motor, a new manifold and even cam would give you some improvement as well. I wouldn't mess with a jacobs system, I've read too many horror stories about them, but MSD makes bolt-in coils and modules for the small-cap dist. The under/overdrives are great, but spendy. Another option would be a 4L80e, but that will cost just as much if not more. Putting a little taller tire may help as well.

    [/ QUOTE ]
    I have heard great things about the Banks products form the motor home crew. Significant power improvments as well as MPG gains. It has 3 inch exhaust factory and it looks mandrel bent. Looks very free flowing for stock. Now how well that muffler moves air is another story.
     
  13. BurbinOR

    BurbinOR 3/4 ton status

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    Re: OK I\'m Hacked. MPG stuff.

    Overdrive is where it's at but the initial cost is tough to overcome. My 91 Burb with 6" lift, 35" X Terrains, 4.11 gears and a 4L80E tranny pulled down 14.1 mpg on a trip from Portland down to the beach over spring break, loaded with lots of stuff. FI is awesome as you know.

    Make sure your timing is set right. I had surging in my 89 S15 that was eliminated by setting the timing back to 0. Map sensors are cheap, and even if it doesn't solve the problem you now have a spare, always a good idea. O2 sensor same deal, always a good idea to replace them since you're doing a tune up. $50 will handle both sensors and give peace of mind. Cats that they put in these things were the original bead style, and a new hi flow model will help immediately no matter what.

    Keep us posted.............
     
  14. Thunder

    Thunder 3/4 ton status

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    Re: OK I\'m Hacked. MPG stuff.

    I would ditch the cat. If it has more than 60000 on it I'm sure it is getting pluged. Those bead type cats dont flow as well as the honeycomb type. A low back pressure muffler will be a big help too. A flowmaster force 2 cat back system would be even better /forums/images/graemlins/wink.gif
    Get the velocity stack (air flow enhancer) fromturbocity.com These have helped fuel milage every truck I have put them on. The stock air cleaner spacer is pretty restrictive. That 454 needs all the air it can get. They work best with good exhaust.
    Dont know how your air intake system is. But a cold air intake system will also help improve milage a little.
    Anything you can do to help your engine breathe better will help.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    Yeah I found the VSS. It's in the dash. I have a factory manual for the truck and it lists it's location. The discription of the VSS says it's behind the speedometer. It sounds like a seperate modual . I'll be investigating more. This may be a good one to use when people convert older trucks to FI.

    [/ QUOTE ]

    VSS was used for cruise control as well, so even if the ECM didn't use it, it could still be present. In any case, all cars used VSS to help with fuel management, so for FI trucks not to have it, makes no sense whatsoever. You need VSS for correct FI swaps, so you don't have to do much research on that /forums/images/graemlins/smile.gif

    [ QUOTE ]
    TPS.: I'm looking for a momentary interuption like bad connection as well as proper set up. The PO had a pressure washer and he used it often on the engine. I'm looking for any moisture damage indications.

    [/ QUOTE ]

    Again, anything you'll see at cruise you'll see at idle. You might have a bad harness wire, but other than that, checking it at idle is going to do you fine. Jiggling wires while sitting there and being able to focus on that task instead of driving, is easier and more reliable. TPS changes so fast and so often, for so little throttle movement, you'll be looking at all kinds of readings, normally.

    [ QUOTE ]
    Well no Air damn on the truck but I do like them and I am looking for one for cosmetic reasons as well as any other gains it might provide. I don't think the 2wd trucks got them. Think that was a 4x4 thing to help with the increased ride hight. Every one I have ever seen had tow hook notches. Again this leads me to conclude that it was a 4x4 thing. I have tow hooks that I will be installing so looking for a 4x4 version. I do plan to atempt to see if I find any increase in MPG or hwy cooling once I find one.

    [/ QUOTE ]

    Should take a peek at the slosh.com blazer brochures, see what the '81+ 2wd trucks had on them. You might be right that the 2wd's didn't get them, but tow hook and non-tow hook versions exist, I've got one of each. The other way to look at it, instead of height, is the front axle on 4wd trucks. Lots of turbulence there that doesn't exist on a 2wd front setup.

    [ QUOTE ]
    First thing is curing the serge and that's this weekends primary goal.

    [/ QUOTE ]

    Straight out of the '88 Camaro Manual, with the 5L TBI motor:

    Surges and/or chuggle

    Definition: Engine power variation, under steady throttle or cruise. Feels like car speeds up and slows down, with no change in the accelerator pedal.

    Use scan tool to verify VSS reading matches speedometer
    Check for:
    Intermittent EGR
    Ignition timing
    Inline fuel filter
    Fuel pressure
    Generator output voltage outside of 9-16 volts
    TCC operation (not applicable for your tranny : )
    Inspect O2 sensor for contamination from fuel, or use of improper RTV sealant. Sensor may have white, powdery coating and result in a high but false signal voltage (rich exhaust indication) The ECM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
    Remove spark plugs. Check for cracks, wear, improper gap, etc. You already changed them, SHOULDN'T be an issue. I've had new plugs that were bad, so double check that perhaps.

    If you need more on the surge/chuggle issue, let me know, as this manual has the troubleshooting chart for EGR, VSS and Fuel pressure.

    I need to get my own scanner /forums/images/graemlins/smile.gif

    Also has section on poor fuel economy, what about your thermostat? Like you said, well maintained, but what temp does it run at (really?) Another good reason to have a scanner, you can compare the gauge to the temp the ECM is seeing.

    Only other things listed worth looking into for fuel economy is "AC compressor always on?", which could also be from the defroster being left on. Check air cleaner element. Timing. Check compression. Dragging brakes.

    I'd love to see MPG results with a header swap as well /forums/images/graemlins/smile.gif
     
  16. doctor4x4

    doctor4x4 1/2 ton status

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    Re: OK I\'m Hacked. MPG stuff.

    Just had 2 post my $.02 worth with a post this technical
    so here goes
    beg borrow steel a set of 33 or 35 " tires see your increase
    next check all your injectors
    next i like the gearvendor idea
    also ya i agree get that trrqu converter to lock up
    + what u said 2 begin with LET IT BREATH !!!
    finnally find that motors power band peak and keep it there
    well ill shut up now
    and if all else fails go get a diesel
    /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/thumb.gif
     
  17. yellowK20

    yellowK20 Well Lubricated Premium Member GMOTM Winner

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    Re: OK I\'m Hacked. MPG stuff.

    Grim, your right 14 mpg is about what you should get My 86 K20 has a tbi 454 with headers,3" duals with crossover 2-chamber 40 series flowmaster's , 14" open element K&N air cleaner, 1" throttle body spacer, NV4500 5-speed 4.10 gears 4" lift and 315-70-16 BFG mt's it gets 14-17 Mpg highway and about 11 mpg towing and in town . I know I have overdrive but my truck is heavier with lower gears big tires a lift and it's fourwheeldrive I'm sure you could get 14 highway out of your Burb /forums/images/graemlins/truck.gif
     
  18. Blazer1970

    Blazer1970 1/2 ton status

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    Old Mission, MI
    Re: OK I\'m Hacked. MPG stuff.

    I didn't read this 100%, so if this has been covered don't flame me. I think that bad exhaust manifold gaskets or doughnuts can cause extra air to get pulled into the exhaust stream. This would especially be true with the manifold gaskets since it could be trying to scavenge from the cylinders that are not on the exhaust stroke. This fools the O2 sensor into reporting a lean condition and effectively makes the engine run rich. I would also check the distributor real close for bushing wear, as I have heard of this causing all kinds of crazy problems on TBI trucks.
     
  19. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    [ QUOTE ]
    First thing is curing the serge and that's this weekends primary goal.

    [/ QUOTE ]

    Straight out of the '88 Camaro Manual, with the 5L TBI motor:

    Surges and/or chuggle

    Definition: Engine power variation, under steady throttle or cruise. Feels like car speeds up and slows down, with no change in the accelerator pedal.

    Use scan tool to verify VSS reading matches speedometer
    Check for:
    Intermittent EGR
    Ignition timing
    Inline fuel filter
    Fuel pressure
    Generator output voltage outside of 9-16 volts
    TCC operation (not applicable for your tranny : )
    Inspect O2 sensor for contamination from fuel, or use of improper RTV sealant. Sensor may have white, powdery coating and result in a high but false signal voltage (rich exhaust indication) The ECM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
    Remove spark plugs. Check for cracks, wear, improper gap, etc. You already changed them, SHOULDN'T be an issue. I've had new plugs that were bad, so double check that perhaps.

    If you need more on the surge/chuggle issue, let me know, as this manual has the troubleshooting chart for EGR, VSS and Fuel pressure.

    I need to get my own scanner /forums/images/graemlins/smile.gif

    Also has section on poor fuel economy, what about your thermostat? Like you said, well maintained, but what temp does it run at (really?) Another good reason to have a scanner, you can compare the gauge to the temp the ECM is seeing.

    Only other things listed worth looking into for fuel economy is "AC compressor always on?", which could also be from the defroster being left on. Check air cleaner element. Timing. Check compression. Dragging brakes.

    I'd love to see MPG results with a header swap as well /forums/images/graemlins/smile.gif

    [/ QUOTE ]

    Yeah I plan to check all of the above. My manual goes into some good detail on how to test with the VOM. Like somebody else pointed out the MAP is cheap. Even if it doesn't fix it it will give me a spare so I may just buy one.

    The PO was good about documenting thigs. The thermostat was recently replaced. Going down the hwy with A/C off I'm running about 190 with ambiant around 75-80 deg. With the A/C on I'm running between 195 and 210 with 80-85 ambiant. I have been experimenting with it. Seems in line with a 195deg thermostat. But yes I do want to get it on a scan tool of some sort and see what the ECM says the temp is. Let me check with a Chevy head buddy of mine. See if he has one for his 94 and if it would be compatible with my 88. Might barrow a spare laptop we have at the office this weekend and see if I can build a ASDL connector. One of thes sites has the information on how to do it.
     
  20. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: OK I\'m Hacked. MPG stuff.

    [ QUOTE ]
    I would ditch the cat. If it has more than 60000 on it I'm sure it is getting pluged. Those bead type cats dont flow as well as the honeycomb type. A low back pressure muffler will be a big help too. A flowmaster force 2 cat back system would be even better /forums/images/graemlins/wink.gif
    Get the velocity stack (air flow enhancer) fromturbocity.com These have helped fuel milage every truck I have put them on. The stock air cleaner spacer is pretty restrictive. That 454 needs all the air it can get. They work best with good exhaust.
    Dont know how your air intake system is. But a cold air intake system will also help improve milage a little.
    Anything you can do to help your engine breathe better will help.


    [/ QUOTE ]
    Thanks I'll check in with Turbo city. I want to get a base line of STOCK working at 100%. Then I can test out a few upgrades and get some real data as to what the improvements are in real world use.

    I take a lot of these claims that some manufactures make with a grain of sale. Stuff like the K&N. Yeah you take out a crusty used filter and put in a new one you going to see improvement. You get the idea.

    Anyway this is the type of stuff I want to hear good or bad. Thanks for the info. Now On my list of items to look into now. I have had their name dropped several times and so far it has all been good comments.

    As for those questioning my intake and exhaust.

    Intake is stock air cleaner assembly with K&N. Might switch to a Amsoil airfilter (amsoil dealer buddy of mine has been all over me about it). The preheat flap does appear to function correctly. The stock 4 inch snorkle to the grill intake for cold air intake. No add ons at this point. It's exactly the way it rolled off the assembly line.

    Exhaust: Stock Y pipe with what looks like twin 2.25-2.5 inch tube down into a 3 inch collector. Stock bead style converter. Stock muffler it rolled off line with. Stock tail pipe set up that goes from 3 inch pipe into twin 2.25-2.5 pipes both exiting on driverside.

    Now this is the family hauler. We plan to run this thing cross country with 4k of trailer behind it a couple times a year. As such high on the list is whatever exhaust work I do on it has to be near stock volume inside the truck. I have done the 40series flowmasters and I guess I got old and can't handle the noise anymore. Both the wife and I grew real tired of not being able to have a conversation with out yelling. So let me know how loud the mufflers everybody keeps recomending are. I'm not opposed to changing the muffler at all but I want quiet. The 40's droaned horribly in the K5.
     

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