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Discussion Starter #1
Have a 97 T-Bird 4.6 sport w/ about 250000 miles. Had since new. Recently it will not run and cannot determine cause. Will run all day at idle but nearly shuts down with any acceleration. Has no power and eventually stalls. Has 40 lbs fuel pressure, good plugs and wires, added new fuel and fuel cleaner/water remover. has spark on both coil packs but spark is erratic (checked with a timing light on each wire) on all wires. Also simultaneously with the problem the battery loses its charge - coincidence or part of the problem? I hve not done a compression check yet that is the next thing to check. I do not believe that there is any intake manifold leaks / problems as I replaced that as part of diagnosing the problem (heater hose nipple was cracked). No unusual noises.
Any suggestions? I'm thinking possibly computer or alternator/voltage regulator.
 

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I think your right, it sounds like the alternator (in general, specifically the voltage regulator, which is internal). Mine wasn't charging if reved over around 3200 rpm, and eventually it ran real bad. I used a volt meter on the battery and reved it up and saw it drop down to battery voltage, and replaced the alternator. The battery light was coming on when not at idle when I had this problem.

I would also try unplugging the MAF at the airbox and see if that helps it run any better, that is an easy thing to do and check the voltage at the battery with the car not at idle.
 

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Discussion Starter #3
Thanks. Forgot to mention that checked voltage at battery at idle and it was 13.8 and dropped only slightly when all accessories like lights etc were turned on. Will not rev at all in fact when accelerator is pressed will run slower, stumble and nearly stall. Will only limp at about 10 mph for short distance and then stall. Check engine light never appears and no trouble codes are present. This has been really frustrating since this is my son's daily driver.
 

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Everyone says "Did you clean the MAF?"... so I'll say it. Make sure the MAF sensor is clean. If it doesn't help, unplug it like Bangster said; if it runs better then there's a problem with the sensor itself and you will need a replacement.

Also be sure the crankshaft position sensor plug is nice and tight, look under the a/c compressor near the bottom of the block on the passenger's side for that one.

Possibly a clogged exhaust? ... Just a thought.
 

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Clogged fuel filter? You mentioned replacing fuel but not the filter.
That's what I was thinking too...
That or ECM..
 

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Discussion Starter #7
I will have to try the MAF. haven't done it yet since I have been busy and it is quite cold and breezy outside. The crankshaft position sensor appears to be tight and in fact it was replaced this summer due to a no start problem. I guess I need to check the wires for continunity as well. Once we can get it out I have a friend that works for the company that rebuilds the computers and he offered to check out the computer.

Keep the suggestions coming.
 

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Discussion Starter #10
Would be surprised to see a clogged cat since this is only a couple years old this being the third one on the car since new. I do appreciate the suggestions though. We will be working on it in earnest again this weekend since it is too late at night when we get home. Disconnecting the MAS only made it worse.
 

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Don't count out the fuel filter. I had very similar symptoms on my 5.0 when I first installed it, had 35-ish psi of fuel pressure in park, but could not give it more than about 40% throttle without it bucking and popping. Turned out that I had a pinched fuel line. Don't need very much fuel in park so it didn't show up in the pressure test.
 

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Don't count out the fuel filter. I had very similar symptoms on my 5.0 when I first installed it, had 35-ish psi of fuel pressure in park, but could not give it more than about 40% throttle without it bucking and popping. Turned out that I had a pinched fuel line. Don't need very much fuel in park so it didn't show up in the pressure test.
+1 I've had similar problems in the past with a plugged filter...
 

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+1 I've had similar problems in the past with a plugged filter...
Xinfinity it totally sounds like a clogged fuel filter. Pressure may check good, but volume will not be great enough under a load, besides they are very cheap and part of good PM.
-Rob
 

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Discussion Starter #14
Had the computer checked and it checks out OK. Haven't been able to get it back in due to it being bitter cold outside and now over 40 inches of snow on the ground. Looks like a real difficult piece to get back in though!!!!
 

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PCM is a pain the first couple times, no doubt. +1 on fuel filter now that I think about it...

Easy and quick to change (if you have the quick disconnects), cheap...
 

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Clog Cats may just be it.. Easy way, once it warms up some? is jack up the car, loosen off the Nuts holding the exhaust to the Exhaust Manifolds and start the car up..
 

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Discussion Starter #17
Would clogged cat or fuel filter cause eratic spark? When I put a timing light on every plug wire every one (both sides) it shows erratic spark. Will investigate both filter and cats a(but cats not that old and maybe have 30 - 50 K miles. I am also thinking about replacing the camahaft sensor (crank sensor was replaced last summer and appears to be tight.
 

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technically a 4.6L car has 4 coils, each coil triggers two spark plugs (IE Waste spark) so each spark plug is `fired' every 180 degrees of crank rotation So that's why you may be getting an erratic spark
 
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