new engine, same problem

Hello Ford fans. I have a 91 GT 5spd with what seems to be a lean condition at low rpms. When taking off, the engine acts like its hitting a rev limiter that's set too low. It misses and pops and simply will not rev past 2,500 rpm regardless of how far the gas pedal is pushed. This usually lasts for maybe 1/4 mile, then it snaps out of it as if I flipped a switch. This problem began with the mostly stock original engine and would happen only once every couple of months. It had somewhere around 150k miles so I assumed the injectors were on their last leg and I replaced them with new stockers. The problem was stiil there but again, only once in awhile. I had replaced the stock fuel pump with a 190 and put on a adjustable regulator years before. I'd also put a sending unit type digital readout pressure gage in the car because it was easier than trying to run a real mechnical gage. Pressure has always been in the mid to upper 30's when cruising and then low 40's when I stood on it. I changed the fuel filter once a year. Not long after the new injectors were installed the motor finally let go. I had the engine professionally rebuilt with the normal upgrades. Bigger cam, aluminum heads, intake, ect. Nearly every component involved with running the engine has been upgraded or replaced, except the adj regulator, fuel pump and gage. The new engine ran great and I figured that one of those old parts was causing the problem. Then the problem came back. Again, it was just once in awhile. I've since changed the computer but it didn't help. The problem then started happening more frequently to the point that I parked it last fall. I'm now ready to get back on it. It idles fine and will rev when there is no load. The only thing I can think to do now is put another pump and regulator on. Any other suggestions? Sorry for the long thread.

Um, did you have it professionally tuned and or Dyno tuned???:rofl:
You may be having a timing issue or something??
My 98 was running real rich/lean (not sure wich) and it wouldn't stay started untill i reved it into red 2 times and then the puter would start working...:banghead:
I think you should have it tuned. A Mustang shop should definatly know what is wrong....??
TK

Humm, had the same problem in my van, idle fine but under load if would cut out and couldn't build rpms. This happened all the time though, not just now and then at certain rpms like your. For me it was a bad fuel filter. I would check that again, but it sounds more like something electronically controlled. Have you tried to pull any codes yet, with that type of problem, I'm sure the computer has got something to say.

The car hasn't been to any tuning shops yet. The way its running right now, I'd have to trailer it. Don't even know where I'd take it. I've thought about it but when it runs good, it runs good and I have more pressing issues to deal with than having a shop fine tune the engine. But that may still happen. I've checked and adjusted the timing several times, ranging from 10-15 initial. I did just remember that the coil is a stocker but it's not the original one. Back before the engine blew, a buddy gave me another coil to try but no luck. A new one is on the list, but the stocker seemed to be doing fine with me shifting at 6,000. The distributor is MSD. I had the tranny (tremec) pro-shifted and put in a 9" rear and basically ran out of money and patience last year. As far as codes, I'm not sure if there are any. The engine light doesn't come on while this is going on but the light may be burnt out. I did take it to a local Ford dealer but they're not too keen on messing with modified mustangs. They wanted me to leave the car but I didn't really want someone learning to drive my new pro-shifted trans. I told the manager it had a crash box and he thought I meant the car was a 4-speed. I took the car home with me. The only thing keeping me from taking all that electronic crap off and putting a carb on, is the money I've spent so far. I'd loose too much in trying to sell the stuff.

Just because the "check engine" light is not on, does not mean there are no codes being thrown. I suggest doing the self test and go from there. If you need directions on checking for codes, I can throw up a quick run through.

Sounds like something electrical. What I have learned about running codes on 5.0 EFI stangs at my work has gave me new appreciation for it. The only problem is you need about $2,000 in scanners and other devices. Those intial codes we all get from the cheap part store scanners are just the tip of the iceburg.

I know people hated hearing me call them to say thier bill is up to $200+ dollars and I'm still not done yet just finding the problem. But it takes hours to run one test, after another test. after another to trace down a problem. I'd hate to have to pay it too but sometimes you just have to do it.

I used one of those Snap on scanners once when I was working at the shop. That thing was great!

Yea the Snap-on Advantage is a great tool. I have used that one for a lot of testing. Great item for like $1500 LoL

Thanks for the input. There is a shop in my town that uses the Snap-On scanner and I know the guy that runs it. If they can't find anything, I'm going to go ahead and change the fuel pump and regulator. They've been on the car for at least 10 years. That may not fix anything but it's one more thing I can do before loading it on a trailer and hauling it somewhere.

Since some of you guys are into drag racing, here's my car's modest numbers to date. With the old motor, when it was in its prime, the car ran dead consistant 13.40's at 100 mph with gears, exhaust and 8" slicks. 60ft's were 1.70. With the new motor, it's ran 12.40 at 111mph with 1.65 60 ft. That was before I had the tranny re-done and on 3 year old 8" slicks. Between the new tranny and some fresh slicks, I'm pretty sure I can knock at least a couple tenths off that. Again, thanks for the help.

After looking the engine over again, I realized I hadn't changed quite everything. The sensor that goes on the back of the EGR valve was still the original. I went and got a new one from Ford and the car ran fine.... for a day. There is still an occasional pop or two while accelerating. It's closer to 3,000 rpms now but it runs alot closer to normal. I upped the fuel pressure some but it didn't help. Still haven't got it to the shop to check for codes.

From experience, a fault code doesn't always trigger the CEL. Go to Autozone, they'll run a basic scan for free. Your check engine light should illuminate when you turn the key on - like all the other dash idiot lights.

How about vacuum lines?? Pinched fuel line? TPS adjustment? Did you use the same cats?? Have you changed the ECT?

I just HATE these annoying misfire conditions!! Good luck - keep us posted.

Honestly, I've been kinda lazy the last couple weeks about trying to fix the problem. I've even put the car up for sale. It acted up fairly bad this morning when I started down the street but cleared up for the most part when I got out of town. There is another symtom that I thought I fixed last year. At times I can smell gas inside the car. The problem was a leaking seal around the gas filler neck at the tank. When I filled the tank up, gas would leak at that area. I replaced the seal and the problem went away. But I've started smelling gas again. I've been under the car several times, searching the fuel lines for a pin hole leak. It doesn't smell all the time though and only once while I was looking for the leak, did I smell gas. It was in the engine compartment but I can't find a leak. I've suspected fuel as being the source of the problem all along. I don't think there is anything wrong with the injectors or how they're seated in the intake. This problem existed when the car had all the factory stuff and I put a different fuel rail on with the new engine. Its gotta be the fuel line somewhere. I'm just missing it. The search continues.

Hello Ford fans. I have a 91 GT 5spd with what seems to be a lean condition at low rpms. When taking off, the engine acts like its hitting a rev limiter that's set too low. It misses and pops and simply will not rev past 2,500 rpm regardless of how far the gas pedal is pushed. This usually lasts for maybe 1/4 mile, then it snaps out of it as if I flipped a switch. This problem began with the mostly stock original engine and would happen only once every couple of months. It had somewhere around 150k miles so I assumed the injectors were on their last leg and I replaced them with new stockers. The problem was stiil there but again, only once in awhile. I had replaced the stock fuel pump with a 190 and put on a adjustable regulator years before. I'd also put a sending unit type digital readout pressure gage in the car because it was easier than trying to run a real mechnical gage. Pressure has always been in the mid to upper 30's when cruising and then low 40's when I stood on it. I changed the fuel filter once a year. Not long after the new injectors were installed the motor finally let go. I had the engine professionally rebuilt with the normal upgrades. Bigger cam, aluminum heads, intake, ect. Nearly every component involved with running the engine has been upgraded or replaced, except the adj regulator, fuel pump and gage. The new engine ran great and I figured that one of those old parts was causing the problem. Then the problem came back. Again, it was just once in awhile. I've since changed the computer but it didn't help. The problem then started happening more frequently to the point that I parked it last fall. I'm now ready to get back on it. It idles fine and will rev when there is no load. The only thing I can think to do now is put another pump and regulator on. Any other suggestions? Sorry for the long thread.
Change your o2 sensors i had a similar problem with no codes this cured it

Change your o2 sensors i had a similar problem with no codes this cured it

Please do not bring up old threads!