Hesitation/miss Under Load

Discussion in 'Fox 5.0 Mustang Tech' started by izodhalo, Nov 13, 2013.


  1. izodhalo

    izodhalo New Member

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    I have searched and found many issues similar but nothing quite the same as the problem I'm having. I'll post here to see if anyone can chime in if they have had the same problem and tell me what to check first.

    1990 LX 5.0 5spd
    106k miles
    Only mods are CAI and off-road H with flowmasters, and MSD distributor and streetfire wires.
    All mods done by previous owner

    I am getting quite a bit of hesitation or miss when the car is under load. It revs fine and drives fine with a constant, light throttle. But it seems like in any gear when you press the accel down, it will buck or hesitate or stumble. Noticed this morning that it actually drove good while still cold, then as soon as the temp starting to rise up, it started hesitating when a load was put on it. Once warm, it has NO issues starting back up. It also tends to idle a bit high at 1300 when coming to a stop, then it settles down to about 1000 or 950, still a bit high.

    Things I've tried:
    Adjusting the timing--It was set low when I bought it at about 8 degrees or so. I set it to about 13, saw hardly any change, except for when I first drove it when it was cold it ran great with no hesitation, then I took it on a trip and about 5 to 10 minutes in, the hesitation comes back. Set the timing back to about 10 and saw no change, possible a little more hesitation.
    Cylinder balance test came back clean with no codes.
    Normal scan came back with no codes.

    Any help would be appreciated, even if sending me to another thread I may have missed in a search. I want to isolate this problem and not just throw money away buying parts that are not broken.
    #1
  2. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    I would be suspect of that MSD distributor, they are horrible when it comes to reliability. If you have access to a stock one I would try that first and the MSD distributors are notorious for causing all sorts of drivability problems
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  3. izodhalo

    izodhalo New Member

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    I had been suspecting the MSD distributor as well but have been reading about many other things that COULD be the problem. I don't have a stock distributor to test out, ironically 10+ years ago my brother and I would probably have 3 or 4 laying around, and now not a single one. If it is the distributor, is there a good one to buy new, or is there a trusted rebuilt one? The stock ones are pretty hard to find in good shape. I have heard a few people say good things about Richporter's new ones, not rebuilt. And for my application, close to stock, I don't need to a $300 billet distributor, after all it's still on the stock coil.
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  4. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    Honestly if it isn't OE Ford I wouldn't even consider it. Some local junk yards or even Ebay as much as I hate to say it are good sources for those type of parts.
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  5. izodhalo

    izodhalo New Member

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    Come to think of it, I am not 100% sure it's a MSD distributor, but I know it's a MSD cap and probably rotar. I don't have the car with me right now so I can't take a closer look.

    Could the TFI module be causing the issues? The last time I drove it, it was hesitating/bucking/missing pretty much with any pedal movement. It has not shut off on me or refused to start after warming up, but it does run like crap.
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  6. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    If it is not an OE Ford Module than that certainly would be suspect. Any aftermarket module I have ever encountered has always given me trouble at one point or another.
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  7. izodhalo

    izodhalo New Member

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    I checked it out once I got home, and it seems to be a stock distributor and also Motorcraft TFI module, with a MSD cap and rotor.
    One thing I did do was adjust the timing a bit more. I set it to about 14, then drove it and it had a little hesitation but greatly improved, you could actually drive it. Pulled it back into the shop and bumped it to about 16 and set it, drove it and it did better, hardly any hesitation and WOT was great. All test drives were done when the engine was warm and at OT. I am wondering if it may be a spark problem now instead of the TFI or distributor now that I know they are Ford parts. I know they will wear out but I would suspect the MSD cap, rotor, and steetfire wires. I forgot to mention before that the previous owner had installed Mac equal length headers, and it looks like the design is hell on wires.

    Are these streetfire wires trash? Should I just get some nice Motorcraft 9mm wires? What about the types of plugs, regular Autolites fine?
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  8. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    Regular autolites are perfect. I have no experience with the street fire wires and while the motorcraft racing wires are ok, I like Taylor wires and love my moroso ultra 40s. I'm curious to know if maybe your balancer has spun or something of that nature. The car should be detonating at 16 base advance and the fact that it runs better and better makes me cxurios. I've seen it before. Might be worth the ten minutes to use a piston stop and verify tdc with the balancer pointer.
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  9. Decipha

    Decipha Member

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    16 on low grade should ping, out if your running premium you can probably squeeze 19 or so before you hear pinging

    although 14 on stock tune and heads is optimal

    i second the balancer, its probably off and your witnessing the effects

    its odd that the additional timing stops the missing, i recommend advancing until she starts pinging so you know where your at

    pull the plugs and see what they have to say
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  10. izodhalo

    izodhalo New Member

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    I am running 92/93 in it. I am going to check the plugs next like you said and see what they look like, then also check the balancer.

    Any other suggestions on what to look for and try?
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  11. mikestang63

    mikestang63 Mustang Master

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    check the balancer- look for rubber coming out,check the gap on the plugs, and when it is dark out open the hood and with the car running, take a spray bottle with some water and lightly mist the spark plug wires. If you see arcing, then the wires are crap and I'd replace them with a quality set like Taylor. Sometimes on really crappy wires you don't even need to spray them- you can see them arcing when it is dark.
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  12. izodhalo

    izodhalo New Member

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    I just got back inside. Jacked the car up and put it on stands, looked all around the balancer and it looks good. No rubber poking out. I took a pic of it just to be sure. Didn't see anything coming out the back or anything that looked suspect. Everything looked uniform. Put the car back down and started it up to check to see if I saw any arcing, didn't see any and tried spraying some water and didn't see anything like that either. My next step is to verify the TDC is where it is supposed to be on the balancer. Could the balancer have spun without messing up the rubber? I did manage to take out the #1 plug and it was an E3.42 plug. I haven't seen those before. Forgive me, I'm getting back into mustangs after a long time with just diesels, so I kinda forgot what it's like working with spark plugs.

    Are the E3.42 plugs any good. Looks like they would be a little tough to gap if you had to.
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  13. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    TDC location process courtesy of Michael Yount
    If you're trying to find ACTUAL tdc for cam installation/degreeing, follow the steps below:

    Positive stop – obtain an old spark plug for the Ford engine – most of us have at least one laying around. Put it in your vice, and with a tool of destruction you deem appropriate – cut off the ground tip and bust up the ceramic around the center electrode. Keep pounding to get the ceramic and center electrode removed so you’ve got a good ¾” or so of hollow space inside what used to be the ‘business’ end of the spark plug. If you happen to break the ceramic on the other end of the spark plug, don’t worry about it. Once you’ve got a nice hollow space in the tip of the plug, take a 5/16” tap, and cut threads inside that end of the plug. I found that diameter to go right in without any drilling required. Once you’ve cut threads, screw in a 5/16" bolt about 1.5” to 2” long. Then take your hack saw and cut the head off the bolt. Wouldn’t hurt to take your file/grinder and dress up the freshly cut surface so no sharp edges or shrapnel enter the combustion chamber. Also clean up the threads on the plug so that it easily screws into and out of the plug hole.

    Determining TDC – remove the passenger side valve cover. Rotate the engine (socket on crank bolt) until the #1 piston is down the cylinder on the intake stroke. Unscrew the spark plug in that cylinder, and replace it with the positive stop you just made. Only screw the positive stop in hand tight. Install your cam degree wheel and pointer (no easy task in some cases as harmonic balancer and other accessories will have to be removed). You may want to remove all spark plugs at this point because it will make it easier to smoothly turn the engine over in small increments. GENTLY rotate the engine clockwise until the piston comes to rest against the stop. Note the degree wheel reading. GENTLY rotate the engine in the opposite direction until the piston comes to rest against the stop. Note the degree wheel reading. TDC is exactly half way between these readings. Calculate where that position is on the degree wheel, remove the piston stop from the cylinder, and rotate the engine to TDC as you calculated it.
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  14. izodhalo

    izodhalo New Member

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    Used the crude method for checking for TDC (finger covering #1, bumping over and waiting for compression to push finger off) and it appears the timing is right. I don't have a piston stop right now and actually don't have an extra spark plug to do the method jrichker is talking about. With the engine at TDC, as far as I can tell, I took the cap off and the rotor was pointing near #1 plug wire. I am thinking about ordering a piston stop and trying to further verify TDC but I think the timing and the balancer are good, but it doesn't hurt to be 100% sure.
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