[KK95GT]

Looking for some diagnostic help on my ’95 GT 93,000 mile 5.0 motor with a stock intake system (except for K&N filter) and a Mac shorty / Flowmaster cat-back exhaust. In other words, a basically a stock original motor w/o many mods.

The car runs great except above 3000 RPM at wide open throttle. About 2000 miles ago I had some intermittent starting problems so the fuel pump, idle air control valve, ignition control module (not the computer), ignition coil, and fuel filter have all been replaced. (Replacing the ignition switch finally fixed the problem….). The car has been fine up to about a month ago.

For normal everyday driving the car is fine. If you run it up to 4500 at part throttle it’s fine and it will run continuously (cruise) at 4500 without a problem. It’s when you punch it and try to rev it above 3000 RPM that it has a problem. In other words, it will run up to 4500 fine with a part throttle but if it’s WOT (floored from a take off) it will run up to 3000-3500 RPM and then act like it’s running out of fuel above approximately 3000 RPM. It will start to die and loose power at 3000-3500 but momentum will carry it up to about 4500 (starts acting up about 3000 but will still rev up to 4500) but by then it’s dying enough to slow itself back down. If you hold it WOT it will continue to slow itself back down just like it’s running out of fuel. If you back off to part throttle at any point it’s fine and will run at 3000, 3500, 4000, what ever you want, but as soon as you step back down to WOT it acts like it’s loosing it’s fuel flow and begins to die again. I really don't believe it's a fuel issue though so the best way to describe it is to say it feels just like a rev limiter is kicking in or the advance is being pulled waaay too far forward or something. It's like it's a rev/vacuum controlled type issue.

No check engine light is showing and the fuel pressure regulator seems to be operating ok (I have a fuel pressure gauge mounted on the rail and at idle the PSI bumps up with the vacuum line disconnected like it should). With a new fuel pump and fuel filter, new ICA, and new ICM in the car and the regulator appearing to work I don’t really know where to go from here. It strikes me as a computer control/signal issue or some sensor like maybe the throttle position sensor type issue. I just hate to just throw money at new parts (particularly the computer) and hope something fixes it.

Anyone had this problem and know how to fix it!

Thanks.

[mustang5l21]

i had the exact problem, it was the filter hooked onto the end of the pump, it was cloged. i changed it with a new one and never looked back. i did replace the pump before the problem and it already cloged so maybe check that cuz fuel presure was ok when i checked under the hood just f'ed up when driving like you explain.

[mr_jcm3]

Hey
I had a 83 carb that did the same thing come to find out it was my wires breaking down and could not carry the current i replaced my wires and it was back to normal hope this helps

[92lxcan]

Check the plug end boots,make sure there not burnt from the headers and grounding out at high rpms.

[88Stang]

This sounds like the same problem I'm having, only you described it better. Does it happen only when the engine is warmed up or all the time?

[KK95GT]

The car is a mainly a weekend/after work driver and I'm not always driving it hard each time I take it out so it may go for awhile before I actually take notice/remember that it's acting up again and I need to do something about it. It's one one those remembering what it did this time vs last time deals so my memory of the specific conditions gets a little fuzzy.
But answering your question, it seems to do it hot or cold although I'd say more when it's cold. Also, I can't say that it necessarily does it every time I rev it WOT, but it seems like most every time.......

Also, when I try to get the OBD KOEO codes, using the check engine flash method I get a very faint flash, then a three and a three, a 4 second pause and then a one, three, and three. I don't have any codes shown in my books or CD referencing a 33 or a 133 code.

Along the code line, the 94-95 has the OBD-1 which I believe is the EEC-IV (compared to the 96 and newer OBD-2 / EEC-V) and my Haynes manual only shows 3 digit trouble codes. I've found 2 digit codes for the EEC-IV which reference the 33 trouble code as an INSUFFICIENT EGR FLOW here online but they may not be for a Mustang. Anybody have any thoughts regarding codes? Any idea if an EGR valve could cause this problem?

[meangreen92]

I've always thought the SN-95s to have tree-digit codes, while Foxes had two digits.
EGR isn't used at WOT, but it wouldn't cost nothin' to pull the valve and see if if might be sticking open.
If I was going to throw parts at it, I'd start with the filter. I hope it's not the screen in the tank.
I've got a rail gauge too, but I wish I'd gotton the remote type, which you can monitor while driving...

[89GTVert]

I had a similar problem and it turned out to be the EGR not working right. As Meangreen said, check that while you are there.

[92lxcan]

Check the o2 sensor wires,make sure there not burnt.It happen to a buddy of mine.His car had the same symtoms.
Goodluck!!!!!!

[KK95GT]

EGR appears to be ok. I pulled the vac line and operated it manually and that caused a fault code. Doing that helped me finally figure out the codes!!!
I've been reading the 3 3 1 3 3 as a two digit 33 code with a 1 for a separator. It's actually a 111 111 1 111 111. The pauses are alot shorter than the book descibed them. When I got the 334 for the EGR fault that I created by disconnecting it, it let me see how quick the 3 and 4 actually flash. 111 IS A PASS CODE. So as far as the computer is concerned, whatever is causing my problem apparently is not showing up in the computer.......

[KK95GT]

I did put new plugs in this weekend. Didn't help.

Someone suggested plug wires but I really don't think it's plug wires. The MSDs are not that old and they're the good Heli-Core (solid-wire) ones. Boots all look ok. It's just real hard to believe they've gone bad this quickly.

The thing that doesn't make sense in terms of being wires is that the car will cruise along fine at 3500, 4000, 4500 whatever, with no problem. If it was wires or something actually physically broken, I wouldn't expect it to run smooth like it does any time except WOT. Whenever I floor it and go to wide open throttle then it starts to bog. Let back off, it's fine.

Wide open throttle seems to be the key, that's what's triggering the problem somehow. The car basically runs fine anytime except WOT.

[meangreen92]

You wouldn't, by chance, be running Bosch Platinums, would you? If so, replace them with some Motorcrafts.

[90-7up+92-LX]

Originally Posted by meangreen92

You wouldn't, by chance, be running Bosch Platinums, would you? If so, replace them with some Motorcrafts.

If you are runnin the Bosch's def replace them bc they burn too hot because of the either 2 or 4 connection points. you only need one ie motorcraft

someone should have told you not to run them whane you bought them if thats what you are running...

[KK95GT]

Yeah that's what I pulled out, the Bosch Platinum double tip ones that the previous owner had put in.
Installed Autolite #25 copper cores. Didn't make a difference though, at least not with this particular issue.

I've read that the Platinums are strictly a low maintenance item, not a performance item and that they actually have alot more resistance to them than the stock types.

[meangreen92]

How about the TPS setting? If you have an analog meter, you can check it's full range of motion to make sure it doesn't have a dropout, like a crackly old volume knob...
I would think you'd have some CM codes if it were leaning significantly out, on you.
Those SN-95 processors will pull alot of timing out too. If it's muggy out, and especially if the gas isn't of the best quality, I hear it's really noticeable.