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  1. #1

    Default Surging (contiued...and continued, and continued)

    The History: I have posted various threads on this problem over the past few months. Each thread took me a step down the road, and with each step I thought that I would surely find my answer. So here I sit with many new parts and an old problem.

    The Problem: Intermittent surging. It generally happens when I am keeping a steady throttle, and is more noticeable at low speeds (10 to 15 MPH). There are short surges forward...each lasting about a second. It just jumps forward, then falls off, then jumps forward again, and falls off, etc. At constant throttle at 50 or 60 MPH you can just barely notice it, when it occurs, which again is not all the time.

    The “Fix” so far: I have replaced spark plugs, spark plug wires, rotor, and distributor cap. I replaced the idle control valve, EGR valve, rebuilt the TBI including fuel pressure regulator, and fuel filter. I put a couple of bottles of Seafoam through the fuel system. I have not replaced the fuel injectors, but I looked into the throttle body at idle and I see no leaks, just a fine mist. I have had the fuel pump replaced and I have put in a new oxygen sensor. I also checked to make sure the throttle plates weren’t loose.

    About all I can think to do is replace the injectors, or have them rebuilt. Are there any other ideas out there? Has anybody run into this?

    This is a 95 Suburban k1500 with a 5.7L and 208,000 miles.

    ---------- Post added at 09:16 PM ---------- Previous post was at 09:11 PM ----------

    I forgot to say that it idles smoothly. RPM's are solid. This is just when underway.
    '95 Chevy Suburban 4x4 LS 5.7L

  2. #2
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    Sounds alot more like a spark problem, more so a fuel problem at this point. I would have the crank position sensor checked.. im not to sure which parts store can test it but i know they can.
    Mike

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  3. #3
    Jr. Engineer McMahan's Avatar
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    Have you checked to see if it is throwing any codes, my 98 Z71 was doing the same thing and turned out the PCM had corrosion in the pins so I just had it replaced and that fixed the problem

  4. #4

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    Quote Originally Posted by murdog94 View Post
    Sounds alot more like a spark problem, more so a fuel problem at this point. I would have the crank position sensor checked.. im not to sure which parts store can test it but i know they can.
    Thanks for the idea Murdog94! I will check it out.

    Quote Originally Posted by McMahan View Post
    Have you checked to see if it is throwing any codes, my 98 Z71 was doing the same thing and turned out the PCM had corrosion in the pins so I just had it replaced and that fixed the problem
    No codes. I just rechecked. According to my manual, 96 and after have the PCM, but my 95 has the ECM. Would a bad ECM/PCM always show itself by setting a code?

    ---------- Post added at 08:39 PM ---------- Previous post was at 06:57 PM ----------

    Quote Originally Posted by murdog94 View Post
    Sounds alot more like a spark problem, more so a fuel problem at this point. I would have the crank position sensor checked.. im not to sure which parts store can test it but i know they can.
    Since a spark issue is indicated, what about the ignition control module? It is original.

  5. #5
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    There is a chance but if the motor is running properly most of the time then it usually is good. Right now im leaning more twards a bad crank sensor, or possibly even the entire distributor. My 1988 had a very similar problem, and after doing everything that you have i ended up doing the distributor, and after i had it timed it was running great! but as i said troubleshoot the crank sensor first.

  6. #6

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    Quote Originally Posted by murdog94 View Post
    There is a chance but if the motor is running properly most of the time then it usually is good. Right now im leaning more twards a bad crank sensor, or possibly even the entire distributor. My 1988 had a very similar problem, and after doing everything that you have i ended up doing the distributor, and after i had it timed it was running great! but as i said troubleshoot the crank sensor first.
    I went to a couple of parts stores. AutoZone shows a crank sensor for $232. Yikes. The other parts store doesn't show one, and said that if the vehicle has a crank sensor, it would not have a distributor. Now I am confused. I have a distributor. Where is this crank sensor located? I want to make sure I have one. AutoZone has a pretty good repair section and it has a test procedure.
    Last edited by bimmer84; 06-27-2011 at 11:13 AM.

  7. #7

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    Have you disconnected the EGR valve vacuum hose to see if it affects the problem? My '91 Sierra did the same thing, and when I disabled the EGR, it went away. I just drove it with the Check Engine light on (30k miles with no problems) because I didn't want to spend the money on a new EGR valve. You say you replaced the EGR valve -- did you use a factory unit, or aftermarket? I've had some problems with non-GM EGR valves not calibrated to work the way they should. Hope this helps.
    Good Luck and God Bless

  8. #8

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    Quote Originally Posted by Revredneck View Post
    Have you disconnected the EGR valve vacuum hose to see if it affects the problem? My '91 Sierra did the same thing, and when I disabled the EGR, it went away. I just drove it with the Check Engine light on (30k miles with no problems) because I didn't want to spend the money on a new EGR valve. You say you replaced the EGR valve -- did you use a factory unit, or aftermarket? I've had some problems with non-GM EGR valves not calibrated to work the way they should. Hope this helps.
    Good Luck and God Bless
    Thanks for chiming in Revredneck. I'll try that. It was an aftermarket EGR, not factory.

  9. #9
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    It is the cam postition sensor sorry. is is mounted under the rotor on the distributor and how the motor advances the timing. However i didnt even really think about the EGR since that usually will set off a code. As i said i wouldnt really buy anything since there are tests for most of them in repair manuals.

  10. #10

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    ok Murdog, that makes more sense. I don't find a cam sensor, but I do find an ignition control module, and I think that may be what you are talking about.

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