This one has been stumping me and everyone I've talked to for awhile now, so let me start with all the information I know....

It's a 1987 GT 'Vert. I got it in May (first V8 Stang, and first EFI hot rod). The guy I got it from had some work done to it, but didn't know anything about it. He had the engine rebuilt and it had around 500mi on it when I got it. When the engine was built he said he "thinks" they put in a cam and a chip. I assume that if it has a cam it's probably the regular e303, but who knows, right? No, he doesn't have receipts or remember where it was done (car was in storage for 5 years between the work being done and me getting it). I already checked the ECM and found no chip plugged into it. I just put replaced the rusty Flowmasters with new 40-series hoping that might help, but didn't. Other than that it's stock, as far as we know.
I drove it for a few months not quite running right (I've been laid-off for awhile now, so repairs happen when the money comes). It had a slight stumble, but nothing obnoxious. When I finally could afford a tune-up I put in Accel shorty plugs (1 heat-range lower than stock as reccommended based on the cam), MSD cap & rotor, Accel 8.8 wires, & a new fuel filter, (air filter is good). While changing things I found cylinder number 4 wire was not plugged-in all the way which would explain the stumble. Immediately after the tune-up it ran much worse. Idled ok at first, but stumbled bad with any throttle in mid-range, but a WOT took off like a bandit. I did the wires one at a time so I knew they were right, & double-checked anyways. I re-checked plug gap, checked cap & rotor, checked for fuel leaks, checked for vacuum leaks, and adjusted timing (initial set at 22 deg). After talking to a friend I exchanged the plugs for stock heat-range. Seemed to help, but still have a problem.
Now & still...
It starts up & idles fine for a few mins then it stumbles slightly, then the idle will drop out & almost stall and surge back again. It'll drop 3-4 times getting lower each time. Usually it'll stall on the third or fourth time but on the rare occasion that it doesn't it then idles fine. If I take right off driving it'll drive great for a few miles (almost seems like about the amount of time it takes for the ECM to finish its tests) and then it will stumble real bad at part-throttle. It takes off good with high throttle and runs like a raped ape at WOT, but at cruising speed (about 1800-3000rpm) it stumbles AWFUL. The weird part is if you just leave it like that after a few miles it will suddenly clear up and run great the rest of the trip no matter how long it is. Also, when it starts running bad if I shut off the key (clutch & roll) & start it back up it will start the whole process over with running good then acting up again. The "Check Engine" light works, and doesn't come on. O2 sensors are in place & not likely to be the problem I think. I just tested & adjusted my TPS and it is fine with .985v with idle set at around 900rpm.
One crazy theory I heard was that with a stumble like I had to start with that the oil may get contaminated by unburned fuel leaking past the rings and will cause problems. I changed it and it did smell like gas. I think it helped (ran good for a day or two), but it didn't last. I've changed the oil twice more since then with no improvement.
I love my Stang, but it's my only transportation. Anybody got any good ideas?!? I'm beginning to think of maybe a faulty ECM, but that's $130 of non-returnable testing if it doesn't help.
Pics are available at http://www.motortopia.com/spdrcr/cars (although, I need to get some new ones posted!).

 

wow i thouhgt my stang had problems man good luck with yours

 

what are the numbers on the back of the ecm
mabey someone put a mass air computer in it or the other way around
but you need to know about the cam thats important
try the fuel pump from what you have said it sounds like a similar problem a fellow stanger of mine had a new pump fixed it this cat spent hundreds of $ on his car
it was a speed density car and at idle it sounded like it had a mild cam in it at times thats what he thought it was cause it was a sd car turns out it was a weak pump did you say what the fuel pressure was didnt say how many miles it had on it
besides if your gonna play around with it a new fuel pump wont hurt im laid also but tell yer wife you need a pump or you cant drive your car thats what i told mine only i didnt have a prob lol
but give it a try best of luck man
Nitrousd85 OUT

 

well it sounds like to me that you have an sd car with a maf cam in it if it does have the e303 in it , it will cause your car to do the exact thing you are talking about here , and no matter what you do it will never change unless you change that cam out or convert to mass air .does the car have a maf sensor on it , if so is it pluged in ? if not it will do this also .
you really need to know what type of fuel injection the car has in order for us to help you better .

 

I doubt it's the ecm or the cam cuz it wasn't like this before. When I first got it it was a slight stumble all the time, but very little. Then, after the tune-up it became intermittent. I just got done checking the codes again with the same result as before. KOEO: 82 Thermactor Circuit Integrated Control Circuit (emissions crap, but I'll be removing the A/C Comp & Smog junk end of this week anyways). Continuous: 22 MAP Sensor Out Of Range (I had disconnected it a few minutes prior to see if it was an issue). KOER: 42 Oxygen Sensor Indicating Rich Right Side (smells a little rich, but can I do anything about that?). That's it.

Not sure what you mean by that? All 1987 GT's were SEFI Speed Density, unless you're asking if I've changed it, which I haven't been able to afford to...yet.

Is there any way to find out what cam is in it without tearing it down? I doubt it, but if you know of a way, share the info!

I agree with you Nitrousd85, it's possibly the fuel pump. I've got a pressure gage I'll have to dig out of storage. Now that you mention it (can't believe I didn't remember this) I had a Jimmy that had intermittent problems due to a faulty fuel pump. I'll check that out later this week and let you guys know. Thanks for the help so far!

 

hope the pump fixes it feller good luck

 

well if it is stock sd and has an a letter cam in it this will cause the problems you have as the letter series frpp cams are a 112 lobe seperation and the sd injection in our stangs utilize a lobe seperation of 114 degrees seperate . i was asking if you were sure if it was sd or converted to maf or running a mass air ecu with no mass air meter , as you said all this stuff was done before you got the car and the guy you got it from didn't know or remember what was done to it . and the only way i know to find out what cam it is is to pull it , but mjr46 might no of a way to find out with out pulling the cam as he is a everyday tech .
i was trying to help you out there with the what type of injection it had i ment the ecu (located behind the passenger side kick panel in the car behind the plastic trim .