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Did search need help on TBI 87 with lots of mods....(UPDATE!)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Batmanjr, May 11, 2003.

  1. Batmanjr

    Batmanjr 1/2 ton status

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    <font color="red"> IF you've already read this, please look at my last post! Thanks! </font>
    Posted this alot earlier and everyone told me to put the EGR and knock sensor back on, well I did!!!!! And no help! It's idling sortof wierd, kind of like a surge, but not too bad, the problem comes when I rev it up slowly and it hits about 3500-4000 RPMs(No Tach, GUESS!), It starts to backfire through the TB.... Also, If I stomp on the gas hard, It just dies! I replaced all the sensors when it was rebuilt! Other problem is that the CEL stays on, but the darn computer has NO codes!!!!! HELP!!!!!!!! Here are the mods I've done:

    Rebuilt 350 with stock cam and crank, Flat top pistons and bored 30 over other than that, it's a stock engine....
    Edelbrock performer aluminum intake
    1" riser block
    Holley 650 CFM TB
    K&amp;N air cleaner
    Dynomax headers
    MSD pro Distributor
    MSD 6 Coil
    8 Mil wires
    High flow oil pump
    High flow water pump
    The ECM is stock
    /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif
     
  2. MousePowrd

    MousePowrd 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    If it is backfiring that means it could be running lean, so look at your fuel system. Check the fuel pressure to make sure your pump isnt plugged or dying. Also change the fuel filter.

    If it has done this since the engine was first started you may have the distributor timing off, or maybe even the cam timing. Since you have no codes it is not a sensor. Are the plugs white (lean) or black (rich) ?

    definitely recheck the timing to make sure it is correct
     
  3. wrathORC

    wrathORC 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    Do a spark plug check. In other words, let it idle for about fifteen minutes to get all the crap off the plugs. Then run it at the stuttering stage for 15-30 seconds. You'll probably want to do this while driving so as to not make the motor cry about revving like that without a load.

    If I had to guess it's a coil or coil wire. My second guess would be an ingnition control module.


    You can scrap the EGR. The computer will never know it's gone. However, it does expect to see a knock sensor there.
     
  4. Bhintz

    Bhintz 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    if you didnt get this get it JET fuel pressure regulator. my friend went through what you did got that and it purred like kitten. because from the factory it comes a little line and w/ all the upgrades it needs more fuel and I would recommend getting a custom chip, there like $330 will help out a lot. /forums/images/graemlins/thumb.gif
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Re: Did search need help on TBI 87 with lots of mods....

    [ QUOTE ]
    Other problem is that the CEL stays on, but the darn computer has NO codes!!!!!

    [/ QUOTE ]
    If my tired brain is functioning properly tonight, I seem to recall that the factory service manual lists this as a symptom of a defective computer. /forums/images/graemlins/eek.gif /forums/images/graemlins/frown.gif
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: Did search need help on TBI 87 with lots of mods....

    You need to hook a scanner up to it. Will tell you real quick if the data from the ECM (and everything else) is good or not.

    Second, did you make sure the TPS is adjusted correctly since you changed the TB? A scanner will tell you that too.

    Of course, you'll need a factory service manual as well. Might as well take it to a shop if you aren't willing to get those items.

    And although technically not a sensor, I believe a messed up park/neutral switch, incorrectly adjusted TPS, or messed up VSS for examples, can screw up performance while not throwing codes.
     
  7. Thunder

    Thunder 3/4 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    [ QUOTE ]
    You can scrap the EGR. The computer will never know it's gone. However, it does expect to see a knock sensor there.

    [/ QUOTE ]

    The computer will know if the EGR is missing. It tests for EGR operation at highway cruise speeds.
    Highway speeds is when the most EGR flow is commanded. When cruising on the highway, the computer will pulse the EGR solenoid so that vacuum will pass and go to the EGR valve. After commanding the solenoid on, it will look
    for signs that the EGR valve openening and closing.It used the MAP sensor to look for a drop and increase in manifold vacume If it does not see the change in MAP,sensor readings it knows that exhaust gas is not flowing even though the ECM is commanding it. This is when the light comes on and the computer throws a code 32.

    If the computer is not throwing any codes:
    You should at least get a code 12 when you put it in diagonstic mode. Code 12 shows the ECM is functioning and not recieving a distributor reference signal wnen the ignition on.
    If it isn't showing a code 12 and the CEL is light the ECM(computer} is probabally bad.
    The engine will run with a bad ECM. It runs on a pre programed set of operating specs. But It wont run very well.

    I was looking at your engine mods
    Flat top pistions and a stock cam?
    the flat top pistions raised the compression ratio.Maby 9-10 to 1 ??
    The stock cam is a low comperssion cam(short duration)made for 8.2 to 1 comp ratio.
    Running higher compression than the cam is spec for will cause pre detonation and knocking. That is probabally why the knock sensor and EGR were dissconnected.
    You should talk to an engine builder to see if they could tell you what they think the compression ratio is and get a cam made for it.
    I am sorry to say this but it looks like whoever built that engine didn't put a whole lot of thought into it.
     
  8. MousePowrd

    MousePowrd 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    Also when you turn on the key to the "run" position, the SES light should come on. If it doesnt the ECM is not working
     
  9. 4DiggerDan

    4DiggerDan 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    [ QUOTE ]
    I was looking at your engine mods
    Flat top pistions and a stock cam?
    the flat top pistions raised the compression ratio.Maby 9-10 to 1 ??
    The stock cam is a low comperssion cam(short duration)made for 8.2 to 1 comp ratio.
    Running higher compression than the cam is spec for will cause pre detonation and knocking. That is probabally why the knock sensor and EGR were dissconnected.
    You should talk to an engine builder to see if they could tell you what they think the compression ratio is and get a cam made for it.
    I am sorry to say this but it looks like whoever built that engine didn't put a whole lot of thought into it.






    [/ QUOTE ]


    Holy shnikee's... You've got flat-tops with stock TBI heads... Thats NOT GOOD!!! When I do the math, figuring that its got a deck clearance of .015" (avereage for a 350) and head gaskets with a compressed thickness of .043" (also average) at .040" over, (also average for a TBI rebuild) that would put you at 10.78:1 for a final compression ratio. In other words... Thats a BOMB!!!

    Especially with a stock cam. If you were up around 292 degrees advertised duration, you'd be okay. But then that much duration won';t work with a TBI unless its been converted to a mass airflow sensor (instead of a MAP sensor.) Which I dunno if you can even do with a TBI. I know you can with TPI's, and LT1s already are using a MAS...

    Yep, your engine builder poohed the scrooch on that one... I think you should keep driving it and we'll all start a pool. I bet that the rod bearings are the first to go, and I bet they don't make it 45 days /forums/images/graemlins/smile.gif
     
  10. MousePowrd

    MousePowrd 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    I thought stock TBI pistons were flat tops with valve reliefs?
     
  11. wrathORC

    wrathORC 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    I don't think so, I think they were actually those medium-recess "flat tops" with reliefs. The genuine flat tops are slightly domed with 2 or 4 eyebrows (reliefs) which usually have an equivalent to a 6.1-6.6cc dish.

    We can figure out the compression ratio if you can tell us what pistons and what heads you've got. I don't know what the head cc is on TBI 350s.
     
  12. Thunder

    Thunder 3/4 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    As far as I know all stock truck TBI pistons are dished .067" with either 4 or 2 valve reliefs.

    TBI 350 heads are 76 cc
    TBI 305 heads are 58 cc
     
  13. Batmanjr

    Batmanjr 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    Alright,
    I appreciate all the help first of all.
    Second of all, the pistons I have look just like the ones I took out of the engine..... They have the 4 relief eyebrows and the only thing is that I was told they were flattop pistons... (Don't flattop pistons have 4 eyebrows???)
    I don't think I'm running 10+:1 Compression ratio! The engine has been running for 6 months, so the pool idea is shot! I will more than likely check the timing AGAIN, and put an out of tank fuel pump on the frame rail!
    QUESTION: Will a 9 PSI pump work, or do I need something higher?
    I like the idea of an adjustable regulator, but $300 I don't have!
    Some day, I would like to add a chip as well, but the money has to come first!
    This engine was rebuilt by me, and the cam will come later as well, but the rest of the engine is stock! I wanted to keep the inside of the engine mostly stock for now, cause if I break something later on the trail, I don't want to be buying specialty heads and cranks twice! Stock is good enough! I was mostly looking to add little power improvements too help... The ECM does throw a code 12, but here is what the CEl is doing exactly:
    Key to Run, light comes on and never goes off, it's not as bright as it could be, but on on.... If I start the truck, the light never changes.... Turn truck off. Clear codes by disconnecting battery, turn key to run, light goes on and never goes off again.... Check codes with paper clip, turn key on to do so, light comes on like always, but the ECM makes light get brighter to flash code 12, and only code 12.... As long as key is turned, light is on and never goes off!!!!
    I will probably be getting rid of the TBI spacer and adding a fuel pump. Is a generic pump alright, or do I need a fancy one from Jegs/Summit? Thanks all! /forums/images/graemlins/ears.gif
     
  14. MousePowrd

    MousePowrd 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    A 9psi pump is barely enough, just get a stock replacement from Summit and you should be ok. TBI requires 9-13 psi. Maybe you have a wire grounded somewhere causing the light to stay on, I dunno.
     
  15. wrathORC

    wrathORC 1/2 ton status

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    Re: Did search need help on TBI 87 with lots of mods....

    If it's stock with flat top pistons (6.2cc dish due to reliefs) and 76cc heads then it runs at 8.5:1 static compression ratio.

    Flat tops have 4 reliefs only when they're universal pistons, ie you can use them on either side of the motor. Expensive pistons only have two reliefs.

    You need 12-13psi. My Dad found out when you try to run on 8-9psi it makes it hard to start. Once it's running it wasn't a problem... but it was hard to get to that point. Just replace the in tank pump (under $100 from the local auto parts store), it's not that bad of a job. Easier to remove the box than the tank.

    As far as your check engine light, I've only seen that happen twice (stayed on). One time it was a junk computer (chip was good, computer bit the dust) and the other time there was a short on the back of the circuit board caused by a metal tang used to hold wires up in the dash. Hopefully someone else can come up with a better scenario.
     
  16. Thunder

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    Re: Did search need help on TBI 87 with lots of mods....

    Thats all I can think of Short or bad ECM.
    Take a look up under the glove box at the ECM and make sure everythings plugged in and no shorts.
    Flat top pistons are just that. Flat with the valve reliefs.
    The stock TBI pistons have a slight depression(dish) on the top with the valve reliefs in it.
    As for the backfireing thru the TB It Could be the fuel pump FI can do some wered things without enough fuel. A lean fuel mixture can cause that.
    Might want to check the TB gasket too.
     

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