[89StangGT]

Well it was a beautiful day so me and my buddy washed up the car and took it out today, got on it a bit here and there, ran great, stopped and got something to eat, left there, got back on the road and got up next to another mustang, from about 40mph i put it in 3rd and layed into it and it just broke up and miss fired horrible, we both looked at each other like wtf? so we turned down a side street and free reved it and as soon as it got to about 4500 it did it again. just driving normal keeping the RPMs down it was fine, then we took off in first and i very slowly got into it and ran it up to about 5500 rpm and it was fine. its only when you jump on it hard that it breaks up and miss fires horribly. Anyone have any idea what it could be? Its a stock motor in a 89 GT.

[neverfastenough1]

Have you tried to do a self test to see if you get any codes? Was the engine warm? It runs richer cold. Missing though I would think it was running lean. Your o2 sensors are ignored at WOT so I am guessing that is why it runs fine otherwise. Try running that self test to see what you come up with. Any kind of boost? Could be something as simple as a fuel filter or plugs.

http://www.muscularmustangs.com/test1.php

[89StangGT]

yeah the motor was warm, it was about 98 degrees out yesterday. no type of boost. my air fuel gauge isnt hooked up so i cant tell if it was running lean lol, but Ill try that sites suggestions. It pisses me off Im susposed to go to the track tonight with a bunch of buddies =[

[neverfastenough1]

That sucks. Hopefully it is something simple.

[nolife]

I've been fighting with the same thing for about a month now. Mine does it under full load about 30% of the time. Very frustrating.
I recently switched to an Autolite from a Motorcraft plug in the same temp range, Even though I've pulled and looked at them 3 times in the past month, I am still thinking this may be my problem. I think I'm going to try a colder plug since I have boost even though these do not show signs of overheating, well actually, they only have a few hundred miles on them so they show no signs of anything.

Make sure you report back when you find the problem, maybe your solution will be something I have not tried already

[Zak]

Did you wash the engine bay as well?

This happened with my Mercedes just after I washed the car and under the hood.. started misfiring I let it dry, thought maybe an electric fault cuz of the water.. didn't go away. I'll cut it short, the valve cover was leaking oil into some of the spark plug wells and screwed up the contact between the plugs & wires. Changed the cover gasket & plugs, runs OK now.

With my Mustang however, it was a different finding. I pulled out the distributor and found a few distributor gear teeth broken - switched to MSD billet with steel gear. Check it out, could be your case. Also, check the wire connection to the coil. Hope that helps.

[usmcsawgunner]

im gonna second the fuel delivery problem.....check the fuel filter and lines and stuff....could be just an old fuel filter...you could even put that baby on at the track if you wanted to....get'em motivator

[vfast]

1st off those A/F gauges are worthless so don't rely on them.....another thinh=g it might help is you can't read a plug with just driving around and then turning it off.....what you need to do it do a 1/4 miles or so WOT and just as you let off kill the engine..this will give you a more truer reading....
list of things to check I'll start with free to cheap
1. TPS voltage
2. timing
3. fuel pressure?..bad fuel filter
4. dist cap-wires..look and replace if nec.
5. dirty maf..using k/n oil reside will get on maf wire
6. vacuum leak..use some seafoam to find
7. tfi
8. partial plugged egr

[8A_Honda]

Did you ever find your problem? I'm having the same issue right now. I have Autolite's and wondering if they're garbage.

[nolife]

HAHAHA, I replied in this thread as well noting I had the same problem with my 88 GT. I too put in Autolite plugs about a month before this problem (104 for use with GT40Y head). My car does not do it as much as it did before though, must have fixed itself. I still don't trust those Autolites and I am still thinking it might be an injector. Since I have boost I thought a colder plug might be a good choice but Autolite 104 is supposed to be equivelent to the Motorcraft plugs I replaced and they worked fine. Maybe they are "almost" equivelent.
I tried to read codes but my EEC4 connector does not seem to be wired the same as the different examples I've seen or like my 91 GT is wired. Maybe something was different when the conversion to mass air was done.

[8A_Honda]

Well, I've never used anything but NGK's and always thought of Autolite as being "cheap" but seeing everyone recommending Autolite's, I decided to try them out (but can't remember which one's I have so need to take them out and check to see which ones I have). Can't remember if my sputtering was done before or after the plugs were installed but I know I had to make a road trip and the car kept dying on me. I managed to see an Autoparts store a mile down the road and walked the mile to get a distributor cap cause the inside of mine was looking pretty crappy. Fixed the problem for the most part and got me back home but still had the problem somewhat. So bought wires, no luck, changed headgasket cause there was water in the oil, that didn't fix it, changed the coil from my parts car, that didn't fix it, changed the fuel filter, that didn't fix it, checked the fuel pressure and guessing that's okay. Checked the codes and came up with an 82 and a 41 but not thinking either of those are causing the issues. Changed the tps sensor today and no luck.

It's only doing it under wot for the most part and figuring that if the plugs are cheap as hell, they may not be igniting all the fuel that's being dumped into the cylinders. I had the plugs gapped to .050 I believe and figured that was too wide so narrowed them to .043 and still no luck. I had an Eclipse I had modded and when I got it to the point to where I'd turn the boost up past 15 psi, it'd start cutting out on me really bad. They were new plugs but they were dual prongs. Changed them to single prong NGK's and never had the problem again. So wondering if I'm having the same problem with the Stang although not boosted.

Nolife, what's your gap? How are you checking for your codes? Does your check engine light work? Mine doesn't and it's an 88 as well. I had to use a test light. I stuck a paperclip in the Self-test In, to the SIG-RTN and then put the clip of the test light onto the + of the battery and the test light into the Self-test Out. That gave me my readings. Hope that helps you out. Counting was a pain in the butt, trying to make sure I was counting them correctly.

http://www.fordfuelinjection.com/?p=13

Anyway, hope to hear some results as to any solutions in this thread. A buddy of mine here in town is also having the same exact problem. Neither of us really care to be dumping money into the cars and not fix the problem.

[nolife]

I initally had them at 42 like the ones I took out but during my troubleshooting, I regapped them to 35 based on some info I got on the turbostang forums based on the boost I am running. My check engine light comes on during the inital key on like every car does giving the impression that it is attached and something is going on but I've never seen it on other then that. I don't remember off hand which ones but my wires in the test plug do not appear to be in the order or the color they should be so I could not get the voltmeter to read any codes in the 10 or so minutes I tried. I'll check the link you gave and will revisit that. Overall I did everything you did except for the fuel filter as my pressure was reading fine. I have two fully running fox bodies so it is easy for me to swap stuff around for testing. I even swapped out my MSD with the stock iginition. The only thing I did that MIGHT have resulted in an improvement was untwist and rearrange the spark plug wires so they were not crossing over and under each other. I still have all of my emissions equipment including the two air bypass valves and with my SC and its inlet, there is not a lot of room on the passenger side to make the plug wires neat but I did.

Again though, my full throttle high rpm problem random sputter seems to have gone away so maybe in my case it was bad gas or a vacuum leak that I may have fixed without knowing while doing other work on the car.

[8A_Honda]

Bought some NGK's this morning. I'll post an update later today hopefully.

[8A_Honda]

Well, I changed to NGK's. No luck fixing the problem. Freakin-A!!! Wondering if the original poster of this thread ever fixed the problem. I'm beginning to run out of ideas here aside from just replacing the whole motor, sensor, and everything electrically.

[ujslost]

seems like fuel delivery to me, also try cleaning your mass air meter.

[8A_Honda]

I'm speed density.

[ujslost]

Ok that black box on the fire wall next to the vaccum tree. I forget what its called off the top of my head BAP i believe. Make sure the vac line is plugged into it and that it doesnt have a leak.

[IcantDo55]

Ohm out the wires.

[8A_Honda]

I don't think it's gonna be the wires if it was doing it with the old wires and the new ones. Did a few things today. I'll try and post the results tomorrow though. Later!

[8A_Honda]

K just to donate to the thread, my problem was the distributor. Swapped one out with a buddy of mine yesterday and it cleared up. Not sure what part of it was bad cause I have a new module on the side of mine that didn't fix it. Could've been the pickup coil maybe? I dunno. Regardless, I'll have a new distributor tomorrow. Wasn't gonna tear apart the whole thing just to replace a pickup coil and still have the problem.