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Stumbling, missing, cutting out... what the hell is wrong with this car?

We've kicked this around on our local message board for a few months now and just when I thought that I had licked the problem, back it came. So maybe someone here has some ideas!

Car: My ever popular 1998 Slowstang GT. Automatic, lightly modified, etc. and so forth. Mileage presently sitting around 70,XXX give or take.

Late last year it started stumbling / missing / cutting out on me under low to moderate throttle. Enough to be noticeable but not enough to cause me a great deal of concern.

Then it started doing this at WOT. Car roars into action, then sputters and pops as the RPMs race up the tach. You hear it as well as feel it, but the car does continue accelerating, albeit not as quickly as I would prefer.

Have replaced the ignition wires with FRPP 8mm wires about 15,000 miles ago. Wires do not show any sign of arcing or external breakdown.

Have replaced the plugs with Bosch Platinum and good old fashioned Autolite coppers. No dice. Same problem.

Have replaced the Cam Position Sensor, cleaned the MAF element and swapped the K&N filter out for a paper filter. Nada.

BluestangGT loaned me a pair of coil packs. Same problem.

Have a brand new Crank Position Sensor on the workbench but haven't put it in yet because I haven't felt like fighting with the stupid A/C compressor just to get to it.

Have NOT replaced injectors or fuel pump. Check Engine light is NOT on. Bulb is NOT burned out either. ;-)

Any ideas? I am tired of throwing money at this problem with nothing to show for my efforts.

Reply to
Tungsten
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Have you checked the TPS? I didn't see it mentioned, looks like you checked everything else.

Reply to
WraithCobra

Have you changed the fuel filter?? Could be a bad filter or possibly clogged injectors? Not sure, but hope that helps. Erik D. '94 white lighnting

Reply to
Erik D.

yes, and did you check the fuel-pressure ? Buy/borrow a fuel pressure tester. You can get one for around 40 dollars. carefully screw it on the schrader valve (DO NOT OVERTIGHTEN) and measure the pressure. Check it with the engine off and the key switched to on. Should hold pressure for a while.. then check it withthe engine running.. play with the regulator and see if it works by removing the vacuum of it.. it should increase fuelpressure once the vacuum is no longer there. You seemed to have checked the ignition.. IF the pressure is not good your pump is bad or the regulator is bad

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Reply to
Rein

Have you cleaned your mass air flow sensor.. or maybe it needs replacing?

Kate

Reply to
SVTKate

Even though your Check Engine Light is NOT on, it will still hold codes.

Try pulling Codes and post them here.

-ERIC

Reply to
Katmandu

Ah, you know... I have not checked the TPS. I'll add that to my list of stuff to look at this weekend. For some reason I had convinced myself that the TPS most likely wasn't a culprit ... but watch that be exactly the wrong conclusion to have come to. ;)

Reply to
Tungsten

Replaced the fuel filter last fall as well but that doesn't mean it is not due for another replacing already. It's possible that I got some crap in the gas tank and it's clogged the filter up.

I've been thinking "clogged injector" myself but I'm hoping that isn't the case. I have run a few bottles of fuel system cleaner through the car over the past few months and that hasn't done any good. If it's an injector, it may be clogged too badly for that to help - or may just be on the fritz period.

Reply to
Tungsten

A buddy of mine is bringing a FP meter over this weekend and we were going to check those things. He thinks it's the FPR too.

Reply to
Tungsten

Yep, cleaned it, tested it, seems to be working fine. Probably the only thing under the hood that is right now. ;-)

Reply to
Tungsten

This is a long shot but on my 94GT i had misses for 6 mos until the distributor shaft finally broke completly. sTopped dead then.

Reply to
Glenn Grant

Anything with a 4.6 xOHC in it is distributorless... but I did have that problem in an '83 GLX convertible (3.8L) once...

JS

Reply to
JS

I just recently had a similar experience with my 99, but not as severe. I had it hooked up to the computer and the codes indicated it was a bad DPFE switch (which I believe works in conjunction with the TPS). Cost me $75 + tax for the part from the dealer and another $20 in labor to have my local Stang mechanic to replace it properly. Runs as good as new. If you've noticed that your gas mileage has taken a nosedive, also, then it could very well be the same problem.

Hope that helps.

Reply to
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