98 LSC Stalling/bogging problem

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Dave 88 LSC

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I just purchased a 98 LSC with 85k miles. Very clean car.

Iver already put about 3000 miles on the car and this problem has appeared 4 times.

Once in a while, after prolonged period of driving, or sitting in traffic in extreme heat (90+) the car will drop RPMs if I press the gas pedal more than 20%. If I go light on the pedal it is fine and will go up to 60-80 MPH, but flooring it just cuts timing or fuel and it will drop the RPM down.
If I shut the car off for 10-15 minutes everything is back to normal. I drove to vermont, 600mile round trip without problems.

I would say its more heat related.

I have changed a Mass Air sensor, Fuel Filter. Cleaned the connector to TPS, Cam sensor.

Fuel pressure is at 30-31 with vacuum and steady 40 with regulator vacuum line off. I checked this when running normal and when the problem occurs. But not under load.

No codes. No check engine lights.

I am thinking a bad TPS? Cam or Crank sensor? Heat related?
Car starts great every time, never stalls, no miss, gets 25 MPG on the highway. This happens at random.

One thing, the first time it happened car wouldn't go past 1500 RPM, second time not past 3000, last time it happened I was able to get to 4000 and drive normal speeds using 10-15% of the gas pedal.


Any ideas?
 
Have you done the simple stuff...like check your plugs and gap?
 
Have not checked plugs yet.... but wouldn't the problem be consistent if plugs were bad?
 
fuel filter plugged? plastic fuel line crimped at filter? hot fuel pump getting ready to wear out? just some thoughts..
 
Green Machine said:
fuel filter plugged? plastic fuel line crimped at filter? hot fuel pump getting ready to wear out? just some thoughts..
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New air and Fuel filter. Lines looks good.

Fuel pump possibly, but as said before, car drives fine most of the time. Pressure is at 30-31 at idle with vacuum. I do not want to dump $400 in pump repair and have the problem come around a week later.
 
If it's the pump, drop a Focus pump on stock sending unit..$100
 
I was thinking about a 190lph Walbro pump fr a 98 Cobra. 255 is overkill anyhow.

Pump is all that's needed, I don't know why people change the whole white box that's inside the tank.

Focus SVT pump I assume? Is it a direct replacement?
 
Dave 88 LSC said:
I was thinking about a 190lph Walbro pump fr a 98 Cobra. 255 is overkill anyhow.

Pump is all that's needed, I don't know why people change the whole white box that's inside the tank.

Focus SVT pump I assume? Is it a direct replacement?
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Mustang pumps dont fit right. Get the Focus SVT pump. Drops right in. Also a 255 is a great match if you plan on doing a tune and exhaust in the future.

Does sound like a fuel pump heating up to me. Another thing it could be is IAC getting stuck open when its DC is turned off.
 
If it gets worse and gets to where it is doing it all of the time I would focus on the cats being stopped up, but like I said only if it starts doing it all the time. I had a 93 start out doing the same thing and then it just got to where it was so clogged up that it just would'nt even run. I had a feeling it was the cats because my dad had just had one do the same thing about 5 months prior so the first thing I did was cut them off (because I had plans for the driver manifold so I cut it off too) and it cranked right up. But it started out doing the same thing as you are explaining. I even changed the fuel pump!!! But good luck bro!!!
 
Trying to see if anyone was in my shoes again.
3k miles have past since I last ran into this problem. Mostly local driving and highway. But yesterday I got stuck in stop and go traffic for 2 hours, in 40 degree weather. Once the road opened up I wasnt able to go past 4500RPM with full throttle. It would go fine with 40-50% throttle input, but past that it would just bog and not want to rev.
No funny smells, no drips, no codes.
Fuel pressure is fine when that happens. cats do not glow, nor do they feel extra hot, from the inside of the car that is. 10 minutes after I shut the car down, all is back to normal.

I guess I'll start by changing TPS, then Crank Sensor, Cam Sensor, and go on and on?
 
Could be a bad coil or boot. Have you checked these parts?
 
What a strange problem.
I wouldn't put a pump in it, not yet anyhow.
If it was a miss it would happen more often then your seeing, plugs never hurt, but I doubt its the problem.
Sounds like your going down the right road by changing the TPS.
Your trouble shooting it the same as I would.
Good luck.
 
Dave 88 LSC said:
I am planning to change the plugs. Any specific plug? Gap?

How do I know if the coil or boot is bad?
Thank you.
Click to expand...

as for plugs, autolite or motorcraft only. NO BOSCH they are crap and blow out/fall into the cylinder=BAD DAY. i forgot the number for the autolite coppers i wanna say XXX but might be wrong (and i was). is your check engine light on? have that code pulled, see what cyl is missing and swap that coil with another one, when you do the plugs (and take note of what coil went where) clear the code (disconnect battery) and when the light comes back on see if the miss moved, if it did than replace the bad coil, if not continue diagnosing....
 
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Thanks for Spark Plug advice.

As for codes, No codes so far. I wish there was a code, I would know what to change right away.
I already changed out Mass Air sensor with no change.

I narrow this problem to Heat under the hood effecting something.
 
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