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What would cause TBI engine to sputter, hesitate, skip and misfire/backfire

Discussion in 'The Garage' started by afroman006, Dec 19, 2003.

  1. afroman006

    afroman006 1/2 ton status

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    This thing with the burban is killin me. Fairly inconsistently while accelerating it will start sputtering, hesitating, misfiring and any other way an engine could run bad. I've "looked" for vacuum leaks but came up with nothing but I still need to try the propane torch idea. Is there ANYTHING else that could be causing this? Burb is 91 w/ TBI 350 and 4L80E.
     
  2. James670X

    James670X 1/2 ton status

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    I would throw some GM combustion chamber cleaner down it and then drive it for a bit to clear it out. Once you've done that give it a complete tune-up (change spark plugs, cap, rotor, spark plug wires (if it needs them), PCV valve, oxygen sensor(s), & air cleaner) and then I would check the timing and change the oil and oil filter as well (make sure you do the combustion chamber cleaner step first though), then it should run like a champ.
     
  3. woody9

    woody9 1/2 ton status

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    understand that the dist-shaft bearings may contribute to such behavior..... how many miles on it?
    Sounds like you've checked the obvious.. (vac leaks, etc).
    How many miles on the sensors? Was the control unit RESET when you installed new ones? (O2, TSP, temp, etc)
    Just some ideas.. haven't PERSONALLY experienced too much of this YET on my 91, but then again, only 193,000! /forums/images/graemlins/wink.gif
     
  4. K5Jimmy

    K5Jimmy 1/2 ton status

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    Had a similar prob while accellerating...checked everything I could think of...turned out to be a plug wire that looked good to me...it was fairly new, not discolored or touching anything, good connection,etc....I thought it had jumped time or had a wet distributor... and it only did it under a pretty good load and especially when I nailed it from a some...it just started alla sudden one day...hope yours turns out to be something as simple... /forums/images/graemlins/grin.gif
     
  5. Triaged

    Triaged 1/2 ton status

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    If it is only on acceleration it could be your TPS. You need a analog volt meter to check it. You want to make sure that the needle on the volt meter moves smoothly and doesn't skip around when you move the throttle.
     
  6. paulefoster

    paulefoster Registered Member

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    Same thing happened to my Jimmy and it finally died and I still can't find the problem. I lost ignition altogether and can't find the problem. I've tried new ignition switch, new computer, etc. Once I touched the radio button and the darned thing came on for a short time. I think it may have to do with an alarm system that was factory installed but I can't find any wiring diagram that includes the audio alarm. I have the GM service manual and wiring diagram etc. What I need is a GM mechanic for this one. I'm sorry I have no help for your problem but this is how mine ended up. I have never run across such and aggravating problem. I've tried everything I knoe except bypassing the computer which I think I can do. Anyone have suggestions for this one?
     
  7. afroman006

    afroman006 1/2 ton status

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    Where can I get this cleaner? All the tune up stuff has already been replaced in search of the problem ($$$ /forums/images/graemlins/angryfire.gif) Here's what I'v replaced in the last few months:

    Cap and rotor
    plug wires
    sparkplugs
    catalytic converter
    O2 sensor
    mufler
    air cleaner
    ignition module
    ignition coil
    thermostat

    I think that's about it. The truck has 200000 miles on it but the PO told me the engine only has 9k. I think only the shortblock has 9k on it cause all the accesories look like they've been around the block a few times. Does the fact that its sporadic indicate anything? Thx for the suggestions.
     
  8. BurbinOR

    BurbinOR 3/4 ton status

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    Sounds like a sensor is giving a bad reading, causing the computer to try to compensate. EVERYONE with FI needs some kind of scanner - like one I have from www.autoxray.com - to read what is going on with the engine sensors. I had an issue exactly like this with my TPI K5 a couple of years ago that threw no codes but had your symptoms. Turns out it was the manifold air temp sensor reading 100 degree air on a 30 degree morning /forums/images/graemlins/eek.gif - your issue is not this because TBI doesn't have intake air temp sensing, but it could be coolant temp sensor bad, TPS (throttle position sensor) bad. Really only way to diagnose this stuff without throwing money at it is by scanning. You've already replaced all kinds of tune up parts so that's good in it's own way, but sounds like another sensor to me. /forums/images/graemlins/confused.gif
     
  9. Thunder

    Thunder 3/4 ton status

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    Have you checked for trouble codes stored on the computer(ECM)?
    Scanning for trouble codes should be the first thing you do when having driveability problems.
    If you dont know how to scan codes go here:GM trouble codes and scanning info
    All you need is a wire or paper clip.
    it will help to know if you have any codes stored.

    BurbanOr couldn't be more right. If you have FI get a scanner. They are only around $150 for the: AutoXray with the GM OBDI
    By the time you go buying and needlessly replacing good sensors you could have easly payed for a scanner. The scanner wont tell you everything that is wrong with your engine but it does tell you what is right and if all sensors are operating in their proper range which really helps narrow down the problems. A scanner saves a lot of time, money and frustration.I have upgraded mine it has more than payed for its self Plus I can use it on all my cars no matter what the make.


    If you have not changed the fuel filter. Do so. It may not be the problem but if it is plugged it may be part of it. They are cheap and easy to install. You should change the filter yearly on FI
     
  10. afroman006

    afroman006 1/2 ton status

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    Well, imagine that. I'm getting a scanner for x-mas /forums/images/graemlins/thumb.gif. Just a few more days away I think I can last that long. Thx
     
  11. R72K5

    R72K5 Banned

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    even could be module also, but yeah distributor bushings wear is a good possibility, yhou have a coupel different options, either remove distributor and inspect condition, and have module tested or simply replace it, or take vehicle to dealer and let them hook it up to the almighty FI machine and see if they can find the cause(s)

    i stick with carb vehicles /forums/images/graemlins/laugh.gif

    good luck
     
  12. crazy427

    crazy427 1/2 ton status

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    /forums/images/graemlins/ears.gifHave you checked the fuel pressure?low fuel pressure from a bad regulator, clogged fuel filter or bad fuelpump can also cuase that sort of problem. wheni changed my truck over to a holley 670 tbi i didnt adjust it correctly when i initally installed it and got a hesitaion problem that was similar. after i adjusted it everything was cool /forums/images/graemlins/cool.gif
     
  13. James670X

    James670X 1/2 ton status

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    You can get the GM combustion chamber cleaner at any auto parts store and if they do have it your local GM dealership should. I would do what the other people on here are saying and just go get your hands on one of those scanner tools because chances are it could be something pretty obscure.
     
  14. TJS

    TJS 1/2 ton status

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    Sounds like you are loosing signal to the injectors. What controls this you ask. It is a pickup coil in the distibutor.
    They are windings that deteriorate over time. I see that you replaced the module. When you had the cap off was there greenish cruddy stuff inside the cap and on the inside base of the distributor?? If so the pickup coil is bad. You need to pull the dist. knock the roll pin out and pull the shaft to get at the clip that holds the pickup coil on. Pry the clip off (ok if it breaks, new part comes with new one).Replace the pickup and also check the magnets on the shaft, I have seen them crack. Note before knocking the roll pin out mark the orintation of everything. Also when pulling the shaft lube it up nice and slowly working it out.
    I have done many of these on TBI trucks. Should take you about an hour or so.
    T.J.
    www.tjsperformance.com
     
  15. afroman006

    afroman006 1/2 ton status

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    How do I go about checking fuel pressure? I'm thinking it is the distributor though, because sometimes when I romp on it this god-awful ratcheting/clicking sound comes from the engine (I assume its the distributor) As a side note my 97 Z71 w/ 200k does the same thing to a lesser extent. How much would a brand-spankin new AcDelco distributor run me? Thx
     
  16. crazy427

    crazy427 1/2 ton status

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    You need to remove the fuel line feed from the back of the throtlebody and put a guage in between. /forums/images/graemlins/thinking.gifalso that loud racheting noise you hear could be pinging or ignition knock from a lean fuel condition.
     
  17. fortcollinsram

    fortcollinsram 1/2 ton status

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    The best way ot check the FP is to get a dynamic pressure reading with the motor running. Go to Napa and get part number 2-18421 or 2-18422 (can't remember whicho ne it is but I think it is the 2-18421) and it plugs in the supply line AT the trhottle body and has a 1/4" NPT port to plug in a pressure gauge...I have this adapter on my 454 TBI and have a AutoMeter gauge mounted on my hood...

    Take the cap off the dist. and try to wriggle the rotor shaft side to side...If there is a good bit of play, time for a new dist. also check to see if the rotor is hitting the electrodes on on the distribtor cap. A new GM performance parts dist can be yours for like $140 and has everything (dist., cap, rotor, gear, ignition module)

    That is the one I have in my 454 and it is a great buy in my opinion...

    Chris
     

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