94 gt no power sputtering at higher rpm

[carnutz]

I have a 94 gt 5.0 L that was very fast until a few weeks ago. 76mm mas air, 75mm tb, cold air, ported intake, 3.73 rear.

Now it has very little power (for a mustang) and acceleration is very slow after 3000 rpm. It is also sputtering at higher rpms. I have tuned and replaced coil, cap, rotor, plugs, fuel filter, checked plug wires,
Replaced some old vacuum lines checked fuel pressure. Still can hardly spin tires and very slow with sputtering at rpm’s above 3500. No computer codes.

Pleas help I thought I was a good mechanic until now!

 

[HISSIN50]

Were any new parts added to the car right before she got sluggish?

I'd get ignition module (on the passenger side fender, sitting in a heat sink under the MAF) tested. Have them do it a few times to heat it up (simulating underhood conditions).

Do you run plat plugs? They alone can do it.

Have you been able to watch fuel pressure as the car starts sputtering?

Good luck.

 

[carnutz]

No new parts I have a new cobra intake I was going to put on, but lucky for me I have not installed it yet or I would have thought it was that.

I just took it for a test ride on the highway and it is most noticeable going up hill at WOT at high rpm 3500-4000. POS will not go past about 4500rpm . Not really sputtering but more of a power on/off in about 1/2 second intervals rrmm quite rrmm quite rrmm. I am starting to think I need to remove the tank and look at the pump not a fun job.

 

[HISSIN50]

Going at it from another perspective, is it possible you have an exhaust restriction? This would namely be the cats.

I'd toss a vac gauge on a manifold vac nipple and rev it to 3K and hold it. Watch the gauge - if the vac reading starts to fall off after 20-30 seconds, that suggests a restriction. Been there and done that.

If it was the fuel pump, I'd have figured it to have gotten worse or you'd hear some pinging............. Lean codes would be a sign too, yet you have none......

Good luck.

 

[carnutz]

well it's not the fuel pump or the MAF. I am going to do some vac testing next.

BTW. I am seeing a higher temp then normal not over heating just running hotter then normal ??

 

[carnutz]

Ok I don't know what could be the problem.

I am thinking it is the stock h pipe it is over 12 years old. anyway I have a nice set of flowmasters and the stock cats can't help. Unless they gutted the cats when they installed the new cat back system?

 

[HISSIN50]

Unfortunately, it takes a little bit of diagnostics and thinking to narrow down the possibilities. Otherwise, tossin parts at things costs a bit of cash and actually takes more time (I can rule something out faster than I can replace it).

Good luck.

 

[carnutz]

Thanks! I have only been replacing the parts I think are causing the problem after doing diagnostics and thinking about it. Unluckily I have bee wrong so far.

It is soooo slow I am talking 8+ seconds 0-60 and if I leave it in 2nd it won't go over 4800 rpm and it must take 10 sec to get to 4500. I don't know about the 10sec but it takes what seams like forever. And if I push it to fast WOT under high load it sputters RRMMM silence RRMMMM silence on and off very fast a few times a sec but only under high load at WOT or close lets say ¾.

I have a 2000 grand marquee that is now much faster then the mustang with about 220hp and 1500 lbs. heaver. This car was doing 0-60 in about 5sec not that long ago then it started to slow down one day, just kept getting slower and slower all in about 2 days. Before this I had a vacuum leak that gave me an erg code I did not fix for months I didn’t care car was running fine and very fast. I am thinking that I messed up the cats by not fixing the egr in time I only fixed the egr after it started to slow down not only was the egr out but the vacuum line that ran the egr and air system was bad.

Well I am down to 2 things that I think might be the problem cats or injectors. If anyone has any comments post you answers I am stumped. and now my car is in ICE after the storm we just had.

This is some problem in 20 years I have never had a problem so hard to fix !!!!

 

[webslinger67]

let me ask you this...

did you work on your car for an extensive amount of time, like months, and just start it up and let it run a little bit to warm it up and shut it off? how about do you get a back fire every now and then?

that is what i did on my 90 gt, and now that you have the same problems i do... nothing over 3000 rpms will this car pull..... it wont even hit redline.... i am starting to think cats on mine are plugged to..... and they are the stock ones , with flowmasters out the back.....

sigh..... will try this test tomorrow....

maybe our resident expert can give us an opinion on this, i really hate my car being like this....