It won't rev past 4800 RPM, I'm TOTALLY out of ideas

tireburner163 · May 30, 2003

It won't rev past 4800 RPM, I'm TOTALLY out of ideas. PLEASE HELP!!!!

Hi fella's. I've got a 1991 Mustang GT vert, 5-speed. I bought it wrecked, and I've been fixing the damage. The motor has done this since day one. Here's my problem, it WILL NOT rev past 4800-5000 RPM's, it's like it hits a brick wall, just will climb fine then slam into it, sounds just like a rev limiter,. It hits it an WILL NOT got any further. It's driving me nuts!!!

I've replaced the distributor, TFI module, coil, plugs, plug wires, new cap and rotor, valve springs, tried two different known working EEC's, put a aftermarket tach on it to verify that stocker was correct (it was). It shows 42psi of fuel pressure at WOT. I checked the firing order several times, it's right

About the only thing I haven't done is replace the fuel filter or replace my whineing fuel pump, but I'm showing good fuel pressure so that can't be it.

Does anybody out there have the slightest clue what could be wrong with my motor???

Please help,
Josh, aka the tireburner

L&M Service · May 31, 2003

a shot in the dark here but try inspecting and then cleaning the MAF sensor element with carb clean.

4play · May 31, 2003

tired valve springs?

tireburner163 · May 31, 2003

I replaced my MAF with a known working MAF. I also installed new valve springs.

Neither one fixed the problem

Swampfox · May 31, 2003

Just a thought, Make sure that 347mm TB is opening all the way, I had a problem like that before but it was on a carbed engine, the secondaries werent opening but about 1/2 way and it acted like you describe

Mouse · May 31, 2003

Another shot in the dark, but you never know if someone stuck a fat cam in there and didn't check valve spring coil bind.

tireburner163 · May 31, 2003

doesn't idle like a aftermarket cam

speed demon · May 31, 2003

Plugged convertors. Undo the pipes at the manifold and watch the revs fly...

Trevor

DCstroker · May 31, 2003

I second the cats. A coworkers Kia had a clogged cat and it wouldn't pull past 3000RPM's. Drive the car at night aggressively then hop out and look at the cats. I bet they'll be cherry red.

tireburner163 · May 31, 2003

Yea, it could be the cat thing...............if it had any.

Sorry guys, it's had a off-road H-pipe for a while now.

Everybody starting to see why I'm going nuts?

DCstroker · May 31, 2003

Well that throws a wrench into things. I think the car had too many miles on it when you put the synthetic blinker fluid in it.

BSL · May 31, 2003

Just a thought. Have you tried to rev higher with the MAF unplugged? Maybe eliminate either mechanical or electrical.
Strange since the pcm changed. Maybe recheck the throttle plates, cable, and for airflow restrictions.
good luck man

Musclestang · May 31, 2003

is it getting 42 pounds of fuel when it acts up ?

tireburner163 · May 31, 2003

I don't think it's the TB not opening, because it doesn't just rev then gradually slow down and stop, it revs strong till 4800, it's like it just slams into a brick wall. I sounds just like a rev limiter, in fact that what I thought it was at first.

Yes I am getting 42psi even at WOT with it bouncing off 4800 RPM.

Also it does it any time. Sitting still, under load, doesn't matter.

Yes I've tried reving it with the MAF unplugged, no change

K. Devlin · May 31, 2003

This may sound real dumb but I have experienced similar problems with my 91 vert 5 speed.

I found it was not as pronounced as yours, but I had a difficult time reaching the rev limit, especially as the gears went higher.

I saw there was a hp gain by bumping the timing. Everyone knows you may get a little extra, but for some reason my car did not like it? I don't know why but when I moved the setting back to the stock position it revved fine.

I just had some engine work done. I put a set of ported stock heads, intake and new exhaust on the car. The mechanic bumped the timing up and I noticed it did the same thing as before. I moved it back and now it really seems to rev better?

I don't think I am crazy, it just seems to work better at the base setting. By the way, my car has rarely been rained on and had about 26,000 miles on it when I made these observations.

Don't know it it will help, just my 2 cents!

Sinful · May 31, 2003

its the spout connector there?

look at the plugs too. check every single one of them for lean/rich condition

5speedlx · May 31, 2003

coil ?

brad · May 31, 2003

dang josh.. still not working huh?

guys we've replaced EVERYTHING on this car.. ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

redrumpony · May 31, 2003

Did you replace the computer?...James

redrumpony · May 31, 2003

what about the flux capacitor?....James

redrumpony · May 31, 2003

Did you test the EGR. sometimes if it is clogged it will act as though the engine is starving for fuel....James

SprchrgdPony · May 31, 2003

Fuel? My old S/C 94 GT wouldnt pull past 5000rpm and only make 3-4psi max, noticed the FP was 34-35psi @ idle, so i bumped it up to 43-45psi @ idle, and the motor pulled hard til 6200 and started seeing 8-9psi again.

just a thought. Not sure if you have an adjustable regulator or not.

jmac5032 · May 31, 2003

Your piston return springs are shot.

speed demon · May 31, 2003

Try the undoing the exhaust anyway, it could have water, or a rats nest in the pipes. Also I've seen stock tachs up to 1000 rpm off, could it just be the tach?

speed demon · May 31, 2003

One more thing, do a volume test on the fuel pump. Might be putting out enough pressure, but due to a pinched line not enough volume.

Trevor

wrathchild · May 31, 2003

that sucks. is the distributor new or rebuilt?

It won't rev past 4800 RPM, I'm TOTALLY out of ideas

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