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1999 Chev K2500 Suburban (Old Body) 5.7 / auto started running rough at accelleration, under slight load (hills, trailer, starts). No codes or MIL light. Replaced plugs & wires (only owned truck for half year, 250K miles), EGR code showed, so cleaned & worked fine for a few hrs, then rough again, with code 1345. Found distributor lock was loose, tightened bolt, but rough running is getting worse. Will replace Rotor & Distributor cap since I don't know history of tune-ups, but what else to do? I did NOT pull distributor and only disconnected wire harness to check connections to cam sensor and crank sensor. Now with the running rough at its worst, pulling a code for lean condition, but no longer a 1345. Parked at home and waiting for advise.

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  • tjbritz
    tjbritz Dec 05, 2012

    I usually do naerly all work myself, but everything I read and get comments on points in 5 or 6 directions, I'm definitely shadetree-type and frugal, but would a trip to certified dealer be cost-effective to reset Cam Pos sensor in addition to dealer price of labor & any needed parts? (I can't believe I'm asking that question, but this is December Minnesota, and I no longer have shade from the tree, much less daylight at all anymore)

  • tjbritz
    tjbritz Dec 05, 2012

    No codes appearing for TPS.

  • tjbritz
    tjbritz Dec 05, 2012

    As I think about ignition switch, it taked a slow delay to engage starter, thought maybe the bendix had a dead spot so bought a starter, just in case (not installed yet). Found the ground straps were corroded of, so replace one from firewall to bolt on top of intake manifold. Starter engages quicker now, but still kinda slow

  • tjbritz
    tjbritz Dec 09, 2012

    Replaced rotor & cap, cap contacts were heavily oxidized. Put it back together, instantly ran crappy again for 30 seconds. Shut it down, put reader on it to see if there was a code yet, nothing. Restarted, and it ran smooth as silk, no hesitation for about 3 mins idling & revving. Took it for a 5 min test drive and the stumbling returned. Code P0174 appeared. I\'m now thinking that the fuel filter has a load in it that blocks fuel under demand, so that\'s my next step. I\'ll also clean the mass airflow sensor w brake cleaner, and check for any vacuun leaks. I\'m not sure how to test fuel line pressure, but if this doesn\'t work I\'m going to a certified Mech anyway to rescan Camshaft Position sensor, etc. That visit will tell me if I need to install fuel pump. Am I missing anything?

  • tjbritz
    tjbritz Dec 10, 2012

    Fuel filter changed, no difference: runs smooth for about 3 mins then starts to stumble...very subtle, but progressively worsens. Debating whether to purchase a fuel pressure tester for $40, since I think I have to take it in anyway to scan the camshaft sensor. Of sourse, if I did get the tester then the dealer wouldn't be able to blow smoke up my skirt about a fuel pump if I didn't really need it...

  • tjbritz
    tjbritz Dec 10, 2012

    Haven't found a vacuum leak yet, though very few hoses. Haven't heard unusual hissing, but haven't done any fuel enrichment testing around manifold or injectors.

  • tjbritz
    tjbritz Dec 13, 2012

    Took it into GM Cert mechanic today, verdict: plugged cats. Everything else I did was spot-on to help troubleshoot & determine the problem. Interesting note: the mechanic said if I had 50-55 lbs pressure in fuel rail (static, KOEoff) I was 'golden'. Any more pressure and there would be other problems. Engine will run well with 47-53 lbs pressure, he said. I checked with the Service Manager about the discrepancy between his info and what is said here on the net, and he backed up the mechanic's info He reaffirmed that 55 lbs is perfect for the 5.7L that is in my 'Burb'. So that still leaves me a little perplexed, but these guys are good at what they do. It just costs a lot to take it there so I save my more perplexing issues for them and they haven't screwed me yet.

  • tjbritz
    tjbritz Dec 13, 2012

    Oh, no vacuum leaks, TPS checked out, no additional programming of Cam Position Sensor needed, and Cam & Crankshaft Position Sensors checked out fine.

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  • Cars & Trucks Master
  • 21,873 Answers

If you can determine the ignition system is ok, I would look at fuel pressure and the fuel filter. If the distributor was loose you may have to check base timing.

Posted on Dec 05, 2012

  •  Stephen
    Stephen Dec 05, 2012

    Any good repair shop should be able to handle the timing check as well as further diagnosis.

  •  Stephen
    Stephen Dec 09, 2012

    No I would say you are on the right track.

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TPS will make it run bad and worse as time goes by. Fuel regulator will not let it run or it will pour out black smoke on heavy acelleration. I would check all the vacuum lines first, this is the most likely cause of rough idle, besides a tune up. Vacuum leak....

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something is blocking either the manafold or in the cadlack converter. see if pipe is getting hot befor cadalack converter or after. just had same prob on customer car and found that a section of honey comb in cadalac onverter hade broken off and was blocking the exhaust when it ran for about 5 mins. we replace the cadalac onvert and the customer notified us 3 days later car was running fine.

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