Loosing power @ WOT above 3000 - need help

[KK6695GT]

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 2000miles ago I had some intermittent stating 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.

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.

 

[wytstang]

Sound like an ignition problem, does it do it when hot or all the time?

 

[KK6695GT]

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 faith 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.

 

[KK6695GT]

x

 

[kruegs74]

sounds like plug wires to me. some times you can take a spray bottle full of water and soak the wires down and you will actually see them shorting out or the engine might even start to misfire at idle. im a ford tech and i see it all the time.

 

[KK6695GT]

They're MSD 8MM replacements which are a couple years old but don't really have many miles on them. I'll try to take a look at them at night.

This feels more like a definite cut out though, more than just a miss. Like a loss of fuel or the timing is being pulled waaay too forward or something. Almost like a rev limiter is kicking in earlier than it's supposed to be. Seems like either an RPM, vacuum, or computer controlled thing because letting off the gas will allow it to pick back up but as soon as you go back to WOT it will want to die again.

 

[KK6695GT]

x

 

[KK6695GT]

I put new plugs in this weekend. Didn't help. I really don't thing 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.

Also, the computer isn't showing any fault codes. I'm getting a 111 so whatever is happening, the computer doesn't seem to be picking it up.

 

[HISSIN50]

I think Danny and others have the right idea. I hate throwing parts at things, but if you happen to have a spare coil around, I'd toss it on and try it. Your symptoms fit how a coil sometimes fails.

Platinum plugs (I probably missed where you talked about plugs) can also cause an issue just like you're having. It faills into the same logic as the coil - a weak spark under severe demand and high RPM's.

Good luck.

 

[KK6695GT]

Put the old coil back in - no help.
Cleaned the MAF and put a paper filter in - no help.
TPS low/high voltages check out ok.

 

[KK6695GT]

Thought I’d dig this thread back out and re-run it. I’ve seen this problem listed before here and in other threads, maybe worded a little differently, but essentially the same problem. Have never seen any solutions listed though….

The only thing I can think of at this point is that I need a new computer. I’ve driven the car for a couple months now and the car works fine in every way, except when I have it floored (wide open throttle). I can consistently run the car up and down to and from 5000 RPM and it will hold at 5000 RPM as long as I want with no issues at part throttle. For that reason, it just can’t be the normal wires, fuel pump, fuel flow, injectors plugs, plug gap, that type of problem. It has to be a computer or sensor signal to the computer problem. The car runs fine, as long as it’s not floored. When it’s floored it bogs and will slow down and keep slowing down as long as I keep it floored. Drop back to part throttle, and it picks right back up.

Other than replacing the TPS which tests ok or the computer which really should have no way of being able to change its own settings (both of which I hate to just throw money at and buy for the sake of change), at this point I’m still at a loss for a solution.

Anyone had this problem and an explanation as to what solved it?