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Thread: Extreme richness at startup and idle.

  1. #1
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Extreme richness at startup and idle.

    Ever since I got the engine running on the stand it has been very rich on startup. It did run clean but has stopped doing that. If I can make it run long enough to heat up the O2 sensor it cleans up but then cuts out wot about 2000 rpm or a little higher. I had read a code thirteen so I removed the baro solenoid and tested. Its working. I hooked the map sensor directly to the intake and disconnected the battery to be sure the code thirteen went away. It didn't change anything. I verified that the AIS was operating, the pintle withdrew to full open and then returned to ful close. I have a stock FPR which is putting 60 psi in the rail. The thing I noticed on the OTC 4000 E is that at startup the injector pulse width is about 7.2 ms. When the engine idle cleans up it goes to 2.4 ms.
    Could the O2 sensor be causing the richness? It's the single wire type.
    I can't get an ohm reading on it. Should I be able to?
    The ECM is an 87 T2.
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  2. #2
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Extreme richness at startup and idle.

    What happens when you unplug the 02 sensor? 7.2 ms is rockin fuel! Even 2.4 sounds high to me at idle but I'm going purely off memory here.

    Guessing this is all stock set-up?

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  3. #3
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Extreme richness at startup and idle.

    It seems to have no effect. I dont understand why the ECM is coming up with that number, something is creating that response. I have the fuel pump controlled by a switch. If I turn the pump off the engine will continue to run cleanly on the pressure still in the fuel rail but if I turn the pump back on it goes back to very rich. I could imagine if the FPR is somehow loading to much pressure at the injectors and they are leaking??? The injectors are 33lb. Codes are 33, 35, 36, 41.

    So I fixed a broken wire on my OTC and went out to the shop to test it armed with a pen and pad to record data. At first when I started up the engine, the readings looked the same as before. The map was 29.1 Ihg, I had seen that before but it didn't make sense, so I removed the vac line from the map and looked at the data. Something changed! I plugged the hose back on the map, now suddenly the engine was running clean, the map volts .88 at idle, map Ihg 10.4 (varying) O2 volts .82, IPW 1.6-1.9. It varied with throttle changes.
    I had pulled a vacuum on the map before I used it, it was solid at 15Ihg but the engine still wouldn't go full throttle.
    I'm calling it a bad map.
    Last edited by jeff1234; 08-08-2023 at 04:53 PM.
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