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Thread: Car runs fine for 2 minutes then starts hesitating

  1. #1
    Join Date
    Feb 2019

    Car runs fine for 2 minutes then starts hesitating

    Good afternoon, been fixing up the 93 SC. I've been slowly making progress but something new always pops up, guess that's the norm with an old car.. The last thing I have is the car starts no issues, you can drive it around for maybe 2-3 minutes, accelerates really good no hesitation or anything, but after 3 minutes the car doesn't want to accelerate, can't get pass 1500 rpms while driving, and if car is parked it sometimes can get pass the 1500 rpm sometimes it can't. If I turn of the car for a couple of minutes same thing happens, car runs fine then after 3 minutes it's starts hesitating.

    Car has new fuel pump, fuel filter, air filter, ECU, ignition switch, starter solenoid and cam sensor. I'll do a fuel pressure test I this week to see if it has the correct fuel pressure, but it's strange that it runs fine the first 2 to 3 minutes. I'm thinking fuel pressure regulator? Anyone has any ideas?
    Last edited by marcosrodoca; 04-09-2019 at 03:20 PM.

  2. #2
    Join Date
    Jan 2010
    Bossier City, LA
    I'm more thinking something that doesn't come in until it goes closed loop - I'd be checking O2s first.

    Then MAF, TPS, and IAC sensors.

    Someone who tunes may have better suggestions; but it sure does sound like something that doesn't get looked at when open loop (cold).


  3. #3
    Join Date
    Dec 2007
    Salem OR
    Ralph is on it... Took a quick look in the emissions/diags manual, and for 'lack of power/misses under load' it says this about that:

    - Throttle position sensor
    - Plugged/bad injector(s)
    - Bad fuel pressure regulator

    For the TPS, I'd want to know if there is a 23, 53, 63 when reading codes. Be sure to do a proper code read on warmed up engine, full goose test, etc.

    For injectors, I'd run a cylinder balance test via a code reader (easy), or test on/off car according to convenience (maybe not easy). If they are legacy, I'm a big fan of new or properly serviced replacements.

    For the FPR, pull the vacuum line on it and check for raw fuel. Put a fuel gauge on it you can safely monitor while testing. Check pressure while running and after a shut down to see what the bleed off drop time amounts to. Report results, or search previous threads, etc. for info on what means what.

    I would read codes and put a fuel pressure tester on it regardless at this point.

    Otherwise, I'd wonder if the cats are plugged, but I doubt it would matter if the engine was cold/warm, so....

  4. #4
    Join Date
    Feb 2019
    Was able to work and drive the car a bit after work. So first thing I did was check fuel pressure, cold car, no key yet, checked pressure and it was 0PSI. Put key on pressure jumps to 40PSI then quickly bleeds to 0PSI. Turn the car on and at idle car stays at a steady 38PSI with vacuum at about 18mmHG. Went for a drive, did a couple of WOT and car went beautiful, about three WOT later started to hesitate, checked the pressure it was down to 12 PSI with vacuum at about 13-14 mmHg, a couple of seconds later car dies. Start car back steady idle pressure of 38PSI, try to WOT and car doesnt pass the 1500RPMS, fuel pressure drops to about 10-12PSI and boost goes to about 5PSI (when trying to accelerate).

    Ran the code scanner, finally got some codes, doing KOEO got code (212-Ignition module circuit failure/SPOUT circuit grounded), and doing KOER got code (225-Knock was not sensed during KOER test) (i think the car isnt completing the KOER test, i do WOT when indicated and code 225 is the last thing to show up, tried doing the test a couple of times and read code reader manual).

    Found an old thread which user had similar issue, he stated that he wasnt able to WOT and changing crank sensor fixed the problem, you guys think changing the crank sensor is worth a shot?

  5. #5
    Join Date
    Dec 2007
    Salem OR
    Those numbers point to an issue w/fuel pressure I would worry about first. Fuel pressure should hang steady with key on and climb along with boost, not fall on it's face at all when the engine is running.

    About that new it the right one, is it sucking air at a fitting, is there something inside the tank that is blocking the pump inlet? Crushed line, bad filter/not installed correctly, etc. Maybe it's just the fuel pressure regulator.

    212 is a stored code/Continuous...confirm you clear all stored codes when testing, then test again & see if it comes right back, if not, then it's not actionable at this time. Might need a hammer-to-the-block to test against the 225 code

    Crank sensor quick test is to see if the upshift light is on while cranking to start - if so, that points to a bad crank position sensor. Be sure to check the balancer to see if it wants to leave home.
    Last edited by KMT; 04-10-2019 at 09:41 PM.

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