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Tbi- Help!

Discussion in 'The Garage' started by AJENSEN383, Nov 2, 2006.

  1. AJENSEN383

    AJENSEN383 Registered Member

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    Hi guys i am a newbie to posting to this form although i have been reading alot from here and learning alot...

    I do have a problem though,I have an 1988 k1500 it originally had a 305 tbi with a 5 speed and replaced it with a 355 for more power (slightly bigger cam, but nothing major 204/214 @ .050, and headers, other than that it is stock)...I swapped to a 350 injectors,and knock sensor but everything else i kept from the 305 including the chip (1227747 computer).. Driveability is pretty terrible... I can start it up in the morning and drive it for about 1/2 mile with no problems, then it seems to go lean and spit and sputter and have a huge miss to it, but when i floor it it will clear up and run better...It seems that it is only at light to mid throttle, or anytime i put a load on it, it will run this way..It does throw a lean code everytime i drive it as well, but it does run real bad in closed loop mode in the morning too..I did notice that since the 350 is in it, morning start up is only at 1,000rpm and with the 305 it was somewhere around 1500 or so then drop down slowly...

    DO you guys think that i need to go to a 350 chip? Can i just swap computers with one from a 350tbi?? Does the BCC code matter?? Could i use a computer from a 350tbi and automatic??.. Any help would be appreciated, since i am going outof my mind here!!!

    Thanks
    Jeff
     
  2. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Hey Jeff!

    Can you get me more details on the camshaft? Specifically the lobe separation angle?

    Its a common problem where guys will toss in a cam that isn't EFI friendly and have a lot of valve overlap. At lower rpms, the valve overlap will allow fresh air to pass from the intake valve straight out the exhaust valve, which the 02 sensor then picks up, and reports a super lean condition. The ECM then pours the fuel on in an attempt to compensate, which makes the engine run terrible. It also can wash piston rings, and prematurely wear your piston bores, rings etc.

    To test this theory, simply unhook the 02 sensor and see what happens. The engine will run a bit lean, and the timing won't be optimal, but you want to see if it drives better or not.

    Also, yes, I would highly reccomend that you install a 350 chip into the `7747, along with a 350 EST module (big flat square module just to the side of the throttle body). The 305 chip will have it running lean all the time, and will not run the best timing for a 350 either (esspecially a cammed one)

    The EST module from a 350 looks for a slightly different signal from the knock sensor as compared to a 305, so its best to swap them as a matched pair.

    If worse comes to worse, you may need to go to www.moates.net, buy a G2 adapter, and a spare `7747 ECM, along with a BURN1 programmer, and a few chips. You can then start burning your own chips for the setup, and get it running the best it can.

    Finally, yes, you can run a 350 with auto chip, but it will not idle as high as it would on a standard truck, and you will need to make the ECM think that the transmission is in gear all the time so it will enter highway mode, PE mode etc.
     
  3. AJENSEN383

    AJENSEN383 Registered Member

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    Hey Russ,

    Thanks for getting back to me...When i was building this engine for the truck i was considering the computer at the time, so i did choose the cam accordingly, the catalog says its a computer friendly one...Anyway, the cam is a 204/214 @ .050 .420/.442 lift and 112 LSA, so it does sound stock at idle...Also, it does have 2.02/1.50 valves in the heads, and a good valve job, but other than that they are stock.. Compression is right at 9.0:1

    I already changed the EST module to next to the TBI , and last night i disconnected the O2 sensor, and that made it quite a bit worse actually.

    Any other suggestions would be helpful...Thanks

    Jeff
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    I believe your 305 knock sensor will also be different from the 350, was that changed as well?
     
  5. AJENSEN383

    AJENSEN383 Registered Member

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    YEP, the knock sensor was changed already
     
  6. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Ah, good stuff, so we can rule out a mechanical cause then! Glad to see someone did some homework before dropping in a normal performance cam, then wonders why it doesn't work, lol

    Now, the best way to approach an EFI issue is to take a look at the symptoms, and break it down into a few possiblities. A couple possiblities come to mind, in order of their likelyhood:

    1) Incorrect prom providing 305 fueling on a 350, causing a lean condition
    2) Vaccum leak
    3) Low fuel pressure
    4) Timing problems

    Now, it should be easy to eliminate most of these possiblities without spending any money, so thats always best to check first.

    Put a vaccum gauge on the engine and make sure you're sitting at about 18 - 20 inches of vaccum. You want to hook up to a nipple on the baseplate of the throttle body, not a ported vaccum source on the side of the throttle body housing, and try spraying some carb cleaner along your intake gaskets, around the baseplate of the throttle body, and around vaccum connections with the air cleaner installed. If your engine picks up RPMS anywhere, then you've found a vaccum leak.

    Next, check your timing. With your aftermarket cam, and 305 prom, you probally want to advance the base timing a bit. Stock is 0 degrees with the EST bypass unplugged, but try closer to 6 - 8 degrees. If your idle quality suffers, back it off to around 3 - 5 degrees. Stock timing in the proms are extremely conservative, and I personally found my truck (which didn't have an EFI friendly cam at the time) ran best around 6 degrees intial timing.

    Next check to make sure you've got around 12 PSI of fuel pressure, and a nice spray pattern off the injectors. You can put a national pipe thread T-adapter between the injector pod and fuel line, then put a gauge on the adaptor. You can check the spray pattern by aiming your timing light at it. It should be a cone shaped pattern that strikes the throttle body just a few 16ths of an inch above the butterflies. If you've got any big drips, then the injectors are not in that great of shape.

    Finally, put a 350 prom in that thing. I can't imagine that a stock 350 / 5 speed prom should be too tough to find, or you can get the adapter I mentioned and burn your own.

    If none of that works, then it may be time to get a scanner, and see what the ECM is seeing. Maybe your CTS is outta whack, or the truck is detecting knocking at an idle and backing the timing way off. Kinda hard to tell without the ECM telling you. An ALDL cable for scanning a TBI truck costs something like 20 - 30 bucks shipped on Ebay, and just require a laptop, and some free software off the internet called WinALDL.

    Good luck, and keep us posted!
     
  7. sweetk30

    sweetk30 professional hooker Premium Member

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    i would sugest a custom chip for your setup. tbi likes more info than stock stuff. try www.tbichips.com he is on ebay also. 110% great guy. and his site is super for good info. i would bet the 305 chip is messing with ya big time. thats were i would start first.
     
  8. AJENSEN383

    AJENSEN383 Registered Member

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    Thanks Russ, when I was building the engine, I wanted torque and driveability more than a lumpy cam. I have the lumpy cams in my hot rods

    Here is a normal day of the trucks operations to give you the full effect..hahaha

    Start up in the morning and drive off ( do not let it idle but a few seconds, If I let it idle for a few minutes the symptoms will come sooner)

    It runs great for about ½-1mile through all the gears ( even 5th) …

    Then, it just starts losing power, stumbling, and jerking to the point of shaking the truck. I could hear a pfffft in the Throttle body before it jerks hard. If there is a hill forget it, I will just about be at a dead stop if a hill is involved. I basically have to floor it so I can go anywhere when it runs like this. When I floor it, it will clean up a little and go but not 100%. All this is happening with no SES light on ( It is still on open loop mode, since it is not warmed up)… Then the SES light comes on ( pulled the code and it’s a lean code 44) and the herky jerky motion kind of goes away so it’s atleast somewhat driveable. I can get the SES light to turn off if I leave off the throttle completely or use very very little throttle. Once the light goes out, it runs better but if I start from a stop sign and run through the gears I could feel that it is holding back ( running lean) unless I floor it, then it feels strong. Also, at about 2,000 rpm it will fall flat on its face, then pick up at about 2500, then fall flat, then pick up etc…

    If I drive it on the highway, and get it into 5th and just cruise it along, the light will stay on constantly unless I floor it. Although sometimes when I floor it, it will detonate extremely bad ,almost like gears grinding. I have been around vehicles my whole life and never heard anything like that before. Its not your typical detonation ping. Its pretty scary sounding.
    Anyway, my next course of action was to check fuel pressure, change the fuel filter, run some fuel injector cleaner, and check vacuum. If they do not do much, then I will go out and get a chip for it…I have checked all the local junk yard around here and the only 5-speed trucks they have are V-6 or 305 trucks, the 350 trucks are all automatics. Has anyone used a guy on e-bay that sells chips for $59? It has a picture of the chip and "MORE POWER" in the background. His feedback looks good.

    I know this post is long, but I thought I would give you a blow by blow of what is happening. This has been going on for the past year or so..At first I thought it was because I had the 305 injectors on it, but I swapped in 350 injectors earlier in the year, along with all the other 350 electrical components. Doing that seemed to make more power overall, but still have the issues mentioned above.

    Last thing..About 6 years ago while I still had the 305 in it and it was all original, I had a problem with the computer. It would spit raw fuel in the muffler and while I was driving along (barely) would ignite in the muffler and obviously go ka-boom. It blew apart the muffler after a few dozen times of doing that…The only way to not do that was to disconnect power to the computer, then re connect it.. I took apart the computer and found that there was a lady bug inside it, so I took it out and cleaned out the dust and put it back together and it worked fine after that. About a year after that I pulled the 305 to put in a carbed 350..Then our area passed the emissions testing law, so I had to put the TBI back on ( I left all the wiring in tact, just for that reason.. nothing was hacked up, or removed just disconnected).. Since then it has been running like this.

    BTW- The timing is set at 6 degrees,and i had disconnected the knock sensor awhile back thinking that it was detecting something and backing way off on the timing,but it made no difference)


    Thanks a lot guys for all the help & suggestions, I really appreciate it
    I will keep you updated!
    Jeff
     
  9. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    You know Jeff, just straight up sounds like a lean running engine to me. They will pop and spit, have next to no power, and detonate something horrible.

    It makes perfect sense if you break down your description above. First, it runs better when it first starts becuase EFI pours extra fuel in when the engine is cold. It does this to act like a choke would on a carbed engine, allowing the engine to start easier, and be able to drive immediately after starting on a cold day. Next, it gets better when you floor the truck becuase it goes into something called Power Enrichment Mode (PE Mode) Basically, at this point the ECM totally ignores the 02 sensor, and dumps the fuel in as fast as it can to prevent leaning out at WOT (which can be fatal to the engine with regards to detonation etc)

    Get yourself a correct stock chip for the 350 / 5 speed before you do anything else. I started my TPI truck off on a set of 305 injectors instead of the 350 injectors. I was anticipating a rich idle, so I tried to confuse the ECM by telling it that it had larger injectors than it did. 22 lb/hr instead of 19 lb/h. My truck behaved much like yours does right now, except it wasn't driveable at all.

    Finally, once you get it up and running reasonably with the 350 chip, you will have to do tuning on it to get it running like a stock engine. There is simply no way around it with a speed density injection system like TBI is. Its calibrated for the stock engine's flow, vaccum, fuel consumption and timing characteristics, and by adding a new cam etc, you've majorly changed all those characteristics without telling the ECM.

    However, you cannot just buy some aftermarket chip, and expect it to be good. Those chips typically just bump the timing up in a few places, but don't touch the fuel curves etc. Even datalogging and sending Brian your information will not get you a perfect chip. Granted, it will be a lot closer, as Brian is pretty good at what he does, but if you want a perfect chip that'll make the pipe sniffer tech's jaw drop come emissions testing time, you need to do it yourself. Datalog every time you drive, and burn a new chip after each drive.

    Heck, to get you started, I'll send you a 7747 ECM that already has been modified with a Moates G1 adapter, and a low profile ZIF fitted with a 28 pin flash chip already programmed with a stock 350 / 5 speed prom for the cost of shipping, and the chip (about 5 bucks).

    All you'd need then to get programming would be a 85 dollar programmer called the BURN1 from Moates.net, a 20 dollar ALDL cable, and a cheap laptop that has a USB slot, and Serial cable slot.

    PM me if interested!
     
  10. AJENSEN383

    AJENSEN383 Registered Member

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    Hey Russ, thanks for all the info. Sorry i didnt getback to you sooner,i havent been around a computer all weekend... Thanks for the offer for the computer, but since i am pretty new to the computer controlled aspect i really dont know what this is " I'll send you a 7747 ECM that already has been modified with a Moates G1 adapter, and a low profile ZIF fitted with a 28 pin flash chip already programmed with a stock 350 / 5 speed prom"... IS that all i would need to see how it works with the stock 350 chip?.. Im sorry i am not a registered member, so i cannot PM you.. I can give you my e-mail,if you want to correspond that way. I really appreciate the offer of you sending me one ready to go.. Thanks

    jbs71383@hotmail.com

    Jeff
     
  11. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Email Sent!
     
  12. randy88k5

    randy88k5 1/2 ton status

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    Hi Jeff,

    Im just starting to get into PROM burning myself. Well, I'm more in the research stage. Thirdgen has a wealth of information. Start by reading the intro guide, and follow a lot of the links. It is weeks, if not months of research.

    http://www.thirdgen.org/techboard/diy-prom/288763-prom-tuning-guide-book.html

    Maybe sign up for GMECM's mailing list (link is in the previous address)

    Good luck. Oh, also check the "Injection Section" section of the forum here on this site, as a few of our members are actively into chip burning. I wish I could say more, but I don't really know enough yet to start. Good luck...
     

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