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**UPDATED FIXED**Help This is driving me crazy!!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 87BrnRsd, Aug 7, 2003.

  1. 87BrnRsd

    87BrnRsd 1/2 ton status

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    **UPDATED**
    Well, my friend who worked on it got it fixed. He said the timing was off by 20 degrees! /forums/images/graemlins/eek.gif I put my timing llight on it (with the tan and black wire unhooked), and it was dead on. Looks like my timing light from 1978 might not be working up to par. /forums/images/graemlins/blush.gif Other than that, he said that it had a weak egr valve. He said that it was stiking wide open, and the engine was running too rich. It is supposed to close with hard throttle, so the engine can run leaner, but it was stuck open therefore causing it to run rich, especially when hot. I didnt have to buy another egr valve though because he knew a way to by-pass it by sticking a hot needle in the vacuum line that comes from the map sensor. I dont know exactly what he did, but he got it fixed. /forums/images/graemlins/thumb.gif I am still amazed that my timing light was off by 20 degrees. /forums/images/graemlins/eek.gif /forums/images/graemlins/rotfl.gif
    -Harrison


    I have an 87 K5 with 700r4, and 350. It has fuel injection. I had my engine re-built and put it in myself about 2 months ago. I couldnt really drive it, but I got it registered today and insured and decided to take it out for a little spin.
    -Well, let me first say that I got a code maybe 2 weeks ago that the map sensor voltage was low. So I bought a new map sensor today and put it on. I started it up and it ran alright. I let it run for a little while then started down the road with it. It was running fine, then after maybe a mile or so, started running like crap. It was backfiring through the tbi, sputtering, black smoke was comming out of the exhaust, and it would cut off randomly at idle. I pulled over and looked at it but couldnt get it fixed. So I went home and pulled code on it. I got 4 codes. One said the Throttle Position Sensor voltage was low, the next said the MAP sensor voltage was low and vacuum high, the next said the MAP sensor voltage was high and vacuum low, and the last one said Oxygen sensor rich error. I knew it was running rich because it had black smoke comming out of the exhaust. After limping it home and getting the codes, I decided to go get some gas since it was on e. I limped it to the gas station maybe 2 miles down the road, and put $5 in it. I started it back up and it started running better. Not great, would not move right away from a dead stop, had to baby it a little, but much better than it was. It basicly runs bad from a dead stop, then smooths out and runs like it should after about 25. I took it on the highway after getting gas, and it ran fine.
    -I have noticed though that sometimes it will run fine, then all of a sudden it will just start running bad. Black smoke comes out of the exhaust, and it wont hardly idle. It idles alright, then the engine starts shaking and slows way down like its gonna cut off, then come back to life, and keeps doing this. I just dont get it. I know the timing is set right and that the distributor is in the truck perfectly. I talked to a friend of mine who is the service manager at my local chevy dealership, and he said it sounds to him like a bad ground, bad wiring somewhere, or a bad computer. He said to bring it buy his house next week and he will take a look at it for me. I was just wondering in the meantime, if yall had any ideas why it runs good sometimes and really bad at others. Thanks for looking,
    -Harrison
     
  2. yunit

    yunit 1/2 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    Vacuum leak or bad ground or short.
     
  3. Blue85

    Blue85 Troll Premium Member

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    This could be a vacuum leak that happens intermittently, screwing up the MAP reading. Look for bad hoses, including brake booster.

    It sounds more like electrical trouble to me. It could be the ground strap from the block to the chassis. If the ground is not good between the engine and computer, the signal levels appear to drift to the computer and all of the sensor reading can get garbled.

    How can it backfire without having bad timing? Could the pickup coil be bad or could there be an intermittent connection from the distributor?

    Other than that, check all of the electric connections around the engine compartment. If you know somebody else with one, maybe you can borrow another computer that is known to be good.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    IIRC, low voltage readings (since you are having two of them) sometimes indicate that something else in the system is not right for the rest of the engines operating parameters...IE manifold pressure readings are way off compared to what they should be based on TPS values, or the engine RPM is way too high vs. TPS readings, etc. Coolant temp may be wrong for how long the vehicle has been operating (bad sender) and so on.

    You *really* need a scanner on it for something like this, along with the correct service manual. It could be something very easy, but unless you stumble upon it by chance, you will be pulling hair out trying to find the cause.

    Obviously check easy stuff...vacuum leaks, connections, components, etc. Since the engine was swapped, perhaps a connection got kinked, or burned, or a sensor got cracked.

    If you've got a laptop, winALDL might be for you. Try checking over on www.thirdgen.org and searching the forums there for low voltage codes might be something common that has already been covered.

    Are you getting the "ECM ok" code when you check??

    Computers and proportioning valves are most likely the two most misunderstood/oft replaced components, that are almost never the root cause of a problem.
     
  5. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    How is this for inspiration! That SAME EXACT CRAP happened to me with my old 454. I tried for 4 months to determine what the problem was. I had WinALDL... I had professionals look at it... I had replaced EVERYTHING... I had tried praying... NOTHING... and I do mean NOTHING fixed it.

    I really wish you have better luck finding your issue than I did with mine... but PLEASE come back and tell us what you did to fix it! /forums/images/graemlins/grin.gif

    -Dan
     
  6. 87BrnRsd

    87BrnRsd 1/2 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    Thanks for the replies! I will check the grounds and vacuum lines as best as I can. I think its in the electrical system. I started it up last night and it idled perfectly. I started it up today and it ideled perfectly for about 3 seconds, then stumbled and almost cut off, then idled fine for about 3 seconds then stumbled, and kept on doing this. This is how it usually doed. If I cant find the problem, my friend at the chevy dealership is going to look at it for me. Im taking it to his house next week, and he said he will bring a good computer for it and see if that is it. If anyone can find it, it would be him. I will let yall know if we figure it out, and what is causing this. Thanks again.
    -Harrison
     
  7. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    I might try running a 12-14ga. ground wire directly from the engine block to the ECM case. This would resolve ALL thoughts of a bad ground... and could be done relativly quickly. /forums/images/graemlins/thumb.gif

    -Dan
     
  8. Confedneck

    Confedneck 3/4 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    how about that throttle position sensor, do you own a volt meter? if you do, with key on engine off check the voltage at the tps, should be about .5-.8 volts i believe..
     
  9. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    TPS voltage @ rest should be 0.540v +/- .075v /forums/images/graemlins/thumb.gif
     
  10. Blazin Ed

    Blazin Ed Registered Member

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    PLEASE let us know if you get this problem resolved! I'm experiencing the same exact problem right now that I just posted and it's driving me nuts. My problem is that it idles just fine but as soon as you put it in gear black smoke comes out the exhaust and it wants to die. Good luck fixing it!

    Ed
     
  11. Confedneck

    Confedneck 3/4 ton status

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    Re: HELP!!!! THIS IS DRIVING ME CRAZYYYYY!!!!

    [ QUOTE ]
    TPS voltage @ rest should be 0.540v +/- .075v /forums/images/graemlins/thumb.gif

    [/ QUOTE ]
    wow i was close eh? not too shabby of a guess...good luck with this problem and keep us posted.. /forums/images/graemlins/ears.gif
     
  12. 87BrnRsd

    87BrnRsd 1/2 ton status

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    Re: **UPDATED**Help This is driving me crazy!!!!

    We have an update!
    -Harrison
     

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