Weird Tuning Issue.... Rough Idle, Trys To Stall On Right Turns.

Discussion in 'Fox 5.0 Mustang Tech' started by ratio411, Jun 30, 2012.


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  1. ratio411

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    Engine is a stock 5.0 with bolt ons.
    RJM harness, MAF system, with all non-essential systems deleted from harness by RJM, with EGR resistor built into harness.

    GT 40 intake, 65mm TB, and 70mm MAF sourced from a 95 5.0.
    MAC headers, OR-X

    Fresh tune up.
    New fuel tank and pump
    Recent module and coil
    Recent injectors
    Recent O2s
    No vac leaks, strong vacuum on gauge.
    No misfire on wires, or injectors, new plugs.
    No codes

    About the only sensor that has not been inspected and cleaned/replaced is the IAT.

    The car was idling very rough, but intermittently. No one cylinder showed a misfire or bad injector. It wandered, and we went to the IAC. It is working and only had very slight oil (it is recently new) coat, not clogged or dirty.

    Then we did the tune-up. That temporarily quelled the issues. For a short time, it ran smooth and strong.

    It is still running MUCH better most of the time, but the ghost in the system comes back intermittently.

    Idle drops, gets rough, and the car comes very close to stalling on right turns.
    Not every right turn, and never on a left turn, hill, or bump. Only right turns.
    The problem is more pronounced by far when the engine is up to operating temp.

    No mechanical noises, smokes, smells, etc.

    If it does stall, it starts right back up, and runs perfectly smooth for a few minutes. It never starts right back up and go right into the rough idle that just stalled it.

    It does it worst on hot days. The idea of vapor lock did cross our minds???

    Fuel pressure 38 psi on gauge, vacuum unhooked.

    Engine smooths out as RPM goes up.

    Any ideas?
    We have done alot, I may have forgot something.
     
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  2. ratio411

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    I should clarify...
    The problem happens intermittently, is worst at operating temp, and a hot day makes it even worse.
    Then, a right turn when it is happening is when it can stall.

    My first post made it sound almost like the whole problem only happened on a right turn...
    It happens anytime, but heat, outside temp, then right turn are the 3 most aggrivating to the problem, and in that order.
     
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  3. jrichker

    jrichker StangNet's favorite TOOL
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    It sounds like a loose fuel pump baffle may be the source of the dying on RH turns.

    The baffle can be epoxied back into place. The problem is to precisely locate the baffle in its old location. That can be tricky.

    JB Weld is suitable to secure the baffle IF you clean the mating surfaces of the baffle and tank. Acetone is the recommended cleaning agent. Be sure to locate the baffle correctly and then epoxy it in place. Some strong magnets may be helpful to hold the baffle in place, and can even be left in place if you happen to cover them with the epoxy. Then let it sit overnight after putting gas back in it so that the epoxy has a chance to completely cure. Put the tank some place warm since this will speed the epoxy cure and strengthen the bond.


    The other possiblity could be a failing ignition switch. The ignition switch is especally suspect if you notice things like radio, A/C & heater blower and wipers doing strange things when the engine dies.
    There was a FREE recall on Ford ignition switches. They overheat and sometimes catch fire. That burns up the steering column and sometimes the car interior. Since this is very old information, you may not be able to get the switch replaced for free anymore. The auto parts stores sell the switches for $13-$15.

    Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly



    See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. The checklist is right here in the Stangnet 5.0 Tech forum and you don’t have navigate to some other unknown web site. It‘s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

    The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.
     
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  4. ratio411

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    We figured it out.

    The fuel pump (less than 3 months old!) failed.

    When the car was cool, the fuel pressure seemed fine, but apparently when it got hot, the pressure was dropping.
    I am guessing at this point, because the pressure was right when we checked it, but after about a week, it ran worse and worse, and another check showed the PSI at 20# cold, and almost down to 10# when hot. So it apparently was quickly degrading.

    Anyway, we could hardly believe it was the pump, so we put in another fuel filter, and checked the regulator using a couple different methods, and it kept checking out okay. We replaced the pump and sock, and we were back in business.

    No codes ever showed, and the rough running was the only real symptom.
    The only other thing we had to do was loom spark plug wires #5 and 6 further apart. The idle smoothed out, so apparently they were stealing spark energy from one another as they fired back to back.

    Car is running great again.
     
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  5. ratio411

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    Oh, and this was an engine swap 5.0 HO into a Fox Fairmont...

    We have a guess as to why the pump failed.

    The EFI (TBI on the old non-Mustang Foxes) gas tank that we used for the swap, had a low psi pump (plastic) from the factory, and the return line did not pour over the pump for cooling, like the high psi Mustang pump setup. Therefore we figure that the pump was overheating. This time around, we re-plumbed the return line to spray over the pump as a cooling mechanism. Hopefully that will keep the new pump alive.
     
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  6. ratio411

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    Now the car is sending up a PIP malfunction code. :(

    Swapping in the distributor from my 87 GT to see if it clears up.
    (New symptoms are high rpm instability, popping)
    No such codes on my GT...
     
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  7. ruin41

    ruin41 New Member

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    Hi ive got a 90 fox mustang 5.0 that i chucked a turbo on late last year. It didnt seem to be 100% before i turbo'd it and surely was 100% worse with the turbo on. Tried just about everything and like you left the IAC to last, not realising that these things have huge amounts of carbon going through the inlet from the EGR system and no fuel to clean it off. Not only was the IAC absolutely covered in carbon but the bulb was carboned solid to the brass frame of the fitting and thus reading the block temperature rather than passing air temp. Along the way i read about the TFI being recalled due to overheating issues and changed that. This made a huge difference and the other huge improvement came from cleaning the MAF sensor. My symptoms were very similar to yours surging idle, excess fuel consumption and intermittently not running right, like not running on all 8 but nothing found wrong and no fault codes other than the missing EGR stuff i took off. Hope something here is helpful.
     
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  8. ratio411

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    The PIP was bad.
    My son now has my distributor, and I have his.
    Gotta love kids. ;)
     
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  9. Noobz347

    Noobz347 Stangnet Facilities Maint Tech... Er... Janitor
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