cold engine stumble

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  1. #1

    Default cold engine stumble

    So I have a 96 MKVIII. only when the engines cold ( I live in FL so relatively cold) If I jump on the gas say pulling out of the work parking lot. I get a stumble and it continues to stumble as long as I keep my foot in it. If I back off and ease back on the throttle it runs right up to 70MPH with no effort, just when Push past say half way on the go pedal. This issue goes away with 2-3 minutes. Say at the next light on the way home it jumps up and dances.

    I do occasionally get code P0411 but I know the secondary air pump is shot, i pulled it and bench tested its a deader for sure. Found a rebuilt at rock auto just haven't done it yet.

    Any ideas

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  3. #2

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    The Mark VIII's factory tunes are usually pig rich on cold start up. There is both a temperature threshold and a timer to switch to a leaner AFR.

    It sounds like you may be experiencing an anomoly that causes the engine to either run leaner or richer than what it likes at cold start ups. My guess is to the lean side. It could be a myriad of things, the least of which would be the secondary air system. The MAF may need cleaning or there could be failing fuel injectors. It could possibly even be a vacuum leak.

    I would start with the simplest (clean the MAF sensor) and progress from there to any suspect that would upset the air/fuel mixture.

    Is the P0411 code the only code you get?

  4. #3

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    yes the only code i've ever gotten has been the P0411. It occurs also on cold engine (less than 4 miles on it) When sitting at the red light with foot on brake. The stumble happens only on dead cold, first pulling out of work or park entrance and accelerating to hi way speed first run up. If i ease into the first access (no traffic) by the second red light it doesn't happen. I noticed this morning that the temp guage begins to move before i get to the light so maybe its a temp sensor thing?

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  6. #4

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    Quote Originally Posted by baylensman View Post
    ... so maybe its a temp sensor thing?
    Certainly possible, and inexpensive enough to replace. I don't recall whether the '96 has a single ECT sensor or two. If it does have two, the one with two wires in the harness connection is the one that is connected to the PCM. The other is simply for the coolant temp gauge.

    Since the '96 is OBD2, you can datalog and get live data to give yourself something to look at to help diagnose the problem.

  7. #5

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    Quote Originally Posted by driller View Post
    Certainly possible, and inexpensive enough to replace. I don't recall whether the '96 has a single ECT sensor or two. If it does have two, the one with two wires in the harness connection is the one that is connected to the PCM. The other is simply for the coolant temp gauge.

    Since the '96 is OBD2, you can datalog and get live data to give yourself something to look at to help diagnose the problem.
    I've put in a new fuel filter and air filter as they were on the list anyhow and i had them on the shelf, no noticeable change. I will pick up a can of MAF compatible cleaner this week. What should i look for in the data logging. i'm new to OBD. I do have a code read with data logging capability in the car. i'm an old points and floats kind of guy. You know tune by ear and feel with a screw driver and wrench.

    The other day I kept my foot in it for a longer distance, almost 1/2 mile (no traffic early in the a.m.) the sputtering started to mix with brief periods of better running, by then i was doing almost 70 mph when i backed off the car ran fine again. It was very similar to an old 72 I had, on a cold mornings the car would sputter at anything over 1/3 pedal till the choke started to move open. kind of like sputter sputter sputter rev sputter sputter, with the rev getting longer and more frequent until up to temp.
    Last edited by baylensman; 07-18-2017 at 08:24 AM.

  8. #6

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    Quote Originally Posted by baylensman View Post
    What should i look for in the data logging. i'm new to OBD. I do have a code read with data logging capability in the car.
    If it were me, I would look at short term fuel trims, coolant temps, load, MAF counts/voltage, and rpm. Possibly spark, O2 sensors, throttle position and vehicle speed.

  9. #7

    Icon7 Lincoln goes sideways!!!!

    Quote Originally Posted by driller View Post

    I would start with the simplest (clean the MAF sensor) and progress from there to any suspect that would upset the air/fuel mixture.

    Is the P0411 code the only code you get?
    Well I did pull the air box and clean the MAF. I also decide to clean the throttle body. The odd headed bolt that holds the end of the violin case was finger tight I thought. Turns out it was not even in the hole of the TB, so the air inlet was pulling in dirty and hot air from the back of the motor. This was messing up the EEC I'm sure. Well I throughly cleaned the TB and operated the plates by hand and also did deep inside as well as the back of the blades.

    I put it back together CORRECTLY and took it for a quick ride. This is the first time since i've owned the car that it has lit the tires without turning off the traction control! When I left the park I actually went sideways!

    Don't know if the cold engine stumble is gone yet. I will drive to work later this week and be able to try it,but so far its progress.

    I also recovered my visors so they look great. Headliner next!
    Last edited by baylensman; 07-24-2017 at 11:49 AM.

  10. #8

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    Good news!

    Let's hope your issues are behind you.

  11. #9

    Icon7 At last and other improvement benefits!

    So I finally had the chance to drive a bit further. The stumble is gone! I can feel a bit of a pulse now, I guess plugs and wires next. You'd think they'd last longer than 137K miles! I also noticed something else, the trans used to shift weird at speed. If i was rolling along at say 45-50MPH more or less coasting with traffic and hit the gas the car would hit hard almost a bang like the U joints were out of the TC disconnected. It never slipped just the bang. Well since fixing the Throttle body/violin case issue the shift at speed when i hit the gas to pass is much smoother! no more bang. So I guess I don't need U joint yet!

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