miss at 3500 under load...
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Old October 7th, 2007, 09:00 PM   #1
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miss at 3500 under load...


OK I know my ignitions pretty well, but I aint too proud to ask for help.

My dad always said someone who knows something well knows when to ask questions.

I thought yall might have a shortcut through the troubleshooting.

I have not yet replaced the cap, rotor, plugs, wires, coil, module, or distributor yet.

the car runs GREAT under light load at normal driving speeds.

I set the timing to the final position today and its smooth as it can be and gets to speed with a purpose.

only one issue right at about 3200-3500 RPM underload (accellerating or hitting passing gear):

a miss of some kind and when I get back below 3200 or so I can get on it all I want untill it goes back up to 3200 or so.

this is confusing to me, it doesnt miss under load at a powerbrake, or anywhere under 3200 RPMs.

I thought there might be a Mustang specific issue to explain this.

I was thinking I needed a stronger spring ratio for the mechanical advance, because it was hitting full advance too soon, only to find out there is no mechanical advance.

I dont have the time to troubleshoot it today, and since I just got out of surgery a few days ago, its prolly not a good idea anyway.

My best guess is the module or distributor....

Any suggestions Y'all?

Thanks

Daniel

EDIT: this is a speed density, 1988 GT HO drivetrain, stock.
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Old October 8th, 2007, 09:05 AM   #2
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I drove it to work today and no new issues.

lit up second gear (even with the miss) when I went to pass a truck...that was fun

It seems to be intermittant....but temperature seems irrealavant, does it cold or hot.

I am going to replace the cap, rotor, wires and plucgs this friday, and the module too if I have the money.

I am hoping its not the Distributor itself....

Daniel
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Old October 8th, 2007, 11:54 AM   #3
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MSD 6AL box
MSD TFI coil
MSD cap and rotor
MSD 8.5mm Super conductor wires
and bosch, motorcraft or accel spark plugs..

the cap and rotor maybe bad, or a spark plug wire would be in the wrong spot causing it to run 2 cylinders down..
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Old October 8th, 2007, 05:49 PM   #4
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[quote="Speedstang302"]MSD 6AL box
MSD TFI coil
MSD cap and rotor
MSD 8.5mm Super conductor wires
motorcraft spark plugs..
quote]

X 2

I am looking for performance upgrades in March when I get back, right now Ill start troubleshooting in the next few days.

I know its not 2 wires, that would miss under load in a power brake too....

Im starting with the cap and rotor and going to wires and plugs.

Hopefully that will help for now.
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Old October 9th, 2007, 01:20 AM   #5
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Before you spend too much money, try replacing the plug wires first. I had the same problem and I found out that the wire boots on the mustang are real close to the header manifolds. I went through a number of wires until I found a boot that didn't burn through.
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Old October 9th, 2007, 04:52 AM   #6
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what kind of wires is that? i bought the msd 105 dollar ones....seem to work ok but still to close to the manifold for me....
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Old October 9th, 2007, 09:57 AM   #7
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If the problem is intermittent, when does it do it? Has there been moisture when you have experienced this problem? I wouldn't be looking at swapping over to an MSD ignition unless you have money to throw away. It is totally unneccessary at this point. The factory TFI system is a good system. I'd be looking at cap, rotor, plugs and wires for starters. Leave the module alone. The symptoms you are experiencing are not symptoms of a bad ignition module. Its very doubtful that its the distributor itself.
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Old October 9th, 2007, 10:34 AM   #8
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I had a similar issue and I believe it was because of my spark plug wire routing. I had a couple of places where the wires were crossing over each other. Again though, it could be anything in that spark path.
I have a rant about spark plug wires as well. I've had a few expensive pairs and some relatively cheap sets and some generic brands. I can not say that any one of them was better then the other. Too me, the price had nothing to do with the quality. Maybe on a 7000+ rpm car it makes a difference.
I have a set of Bosch 8.5 plain old gray for $40 and they have been going fine for a few years. My only complain with them is the wires for 4 and 8 are a little too long.
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Old October 9th, 2007, 12:01 PM   #9
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Originally Posted by Darrell
If the problem is intermittent, when does it do it?
I guess intermittant is a bad word for what I meant....

If I take it easy and run it up to 3500-4000 RPM, it does fine.

If I put it under loead (heavy accelleration or in passing gear) it starts jerking at about 3200 (give or take a few hundred RPM)

what I meant by intermittant is that it doesnt happen EVERY time I hit that speed, but only under load.

After the advice on here, Ill try the wires first, and go from there, these wires arent new and they ARE awful close to the headers.

Ive had excellent luck with Accel and MSD wires in Header applications. Ill start with the MSD Superconductors.

I will be up to bending and lifting and such this weekend, so Ill get on it then (besides Friday's payday)

Thanks everyone, I will post up results as soon as I have them.

Daniel
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Old October 9th, 2007, 08:08 PM   #10
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i havent had any problem with my msd superconductors, and darrel i just told him msd 6al box would be nice upgrade, never said he original is the problem..
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Old October 9th, 2007, 08:17 PM   #11
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Originally Posted by Speedstang302
i havent had any problem with my msd superconductors, and darrel i just told him msd 6al box would be nice upgrade, never said he original is the problem..
Yeah I understood.

I am planning alot.... Ive used MSD on everything else Ive built and I Love it.

I like the way the original ignition runs too, so Im not planning anything right now.

Got to have a good running car before you can mod it.

Daniel
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Old October 9th, 2007, 08:45 PM   #12
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Originally Posted by Darrell
If the problem is intermittent, when does it do it? Has there been moisture when you have experienced this problem? I wouldn't be looking at swapping over to an MSD ignition unless you have money to throw away. It is totally unneccessary at this point. The factory TFI system is a good system. I'd be looking at cap, rotor, plugs and wires for starters. Leave the module alone. The symptoms you are experiencing are not symptoms of a bad ignition module. Its very doubtful that its the distributor itself.
+1 If the tach goes falls to 0 quickly as the car misses then raises back to normal, it might be the module.
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Old October 9th, 2007, 08:48 PM   #13
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Originally Posted by usmcsawgunner
what kind of wires is that? i bought the msd 105 dollar ones....seem to work ok but still to close to the manifold for me....
why would you pay 105 buckd for a set of wires
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Old October 9th, 2007, 09:51 PM   #14
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mine were $95, but i have a discount there and they were $65..
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Old October 9th, 2007, 10:48 PM   #15
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Originally Posted by JBIGBOOTSY
+1 If the tach goes falls to 0 quickly as the car misses then raises back to normal, it might be the module.
The Tach stays pretty much where it is just jumps around alittle....like a normal miss....

I'll get yall some answers this weekend when i replace the wires.

Daniel
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Old October 10th, 2007, 12:23 AM   #16
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Originally Posted by DRFDIGGER

I guess intermittant is a bad word for what I meant....

If I take it easy and run it up to 3500-4000 RPM, it does fine.

If I put it under loead (heavy accelleration or in passing gear) it starts jerking at about 3200 (give or take a few hundred RPM)

what I meant by intermittant is that it doesnt happen EVERY time I hit that speed, but only under load.

After the advice on here, Ill try the wires first, and go from there, these wires arent new and they ARE awful close to the headers.

Ive had excellent luck with Accel and MSD wires in Header applications. Ill start with the MSD Superconductors.

I will be up to bending and lifting and such this weekend, so Ill get on it then (besides Friday's payday)

Thanks everyone, I will post up results as soon as I have them.

Daniel
It could very well be wires and/or plugs. Electricity will always take the path of less resistance. Under light load that path could be thru the wires and spark plugs. Under heavy load that path might be thru the insulation to the valve cover, block or headers. Keep us posted.
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Old October 10th, 2007, 11:15 AM   #17
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Will do. I should be able to get some wires on Friday, I also have the following to do (busy weekend):

both Ft brake lines
both ft rotors/calipers/pads
GT rocker trim

some kind of cohesion with the color of the car...lol (prime grey )

so I should be a busy dude this weekend, everythings been backing up since surgery last wednesday. Doc says I can start working Friday so its on...lol

Daniel
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Old October 15th, 2007, 12:10 PM   #18
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OK Heres what I did:

MSD 8.5MM Superconductor wires
New Cap
New Rotor
New Ft brakes, rotors, bearings and brake lines


First of all, I found a wire with a nasty spot on it, hiding down on the boot.

Miss identified.

Now no miss at all, but a problem persists:

up around 4-5000RPM I get some hard Predetonation....

I got the Timing set on Factory settings (10 deg which seems quite HIGH in my opinion) and everything is new except the coil and module.

I would say that the timing was awful high and it was at full advance before it could get up there...but everything is at factory settings so it should be running right... I think it's got to be an electrical (ECM) issue or something...perhaps the module?

the car runs GREAT even when its predetonating, but I let off of it as soon as I hear it and I know it shouldnt do that, even at 4-5000 RPM.

I will be back under the hood today and getting the driver's side GT rocker trim finished up so I will have more info later...

but any Ideas?

Thanks Everyone

Daniel
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Old October 15th, 2007, 12:24 PM   #19
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Try running some higher grade gas. What spark plugs are in the car? Do you live in a high altitude area? What is the engine temp when this occurs? How about outside air temp?
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Old October 15th, 2007, 02:12 PM   #20
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Outside Ait Temp: about 55-60 deg
Engine temp: Normal, 1 notch under halfway up.
Stock Motorcraft Spark Plugs

Athens/Ardmore, AL....dont think we'd be classified as High altitude, but we arent LOW altitude.... we are 5 miles South of the Tennessee Border.

Running 87 OCT right now, I will try running 93 in it on the next tank, but my budget wont let me do that more than once...lol

this was last night around 9:00 or so.

Does it every time Im on it above 4000... prolly what was causing the other issue to be so bad at certain RPMs...

Daniel
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