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Old 09-06-2009, 04:26 PM   #1
mtoliverjr
 
Join Date: Sep 2009
Vehicle: 1991 Ford Mustang LX 5.0
Location: Texas
Posts: 37
Default v85.0 engine randomly dies

EDIT: Random dying resolved, page four contains detailed info on the sluggishness experienced once warm. Problem isn't present on fresh ECM mapping, but once 40 miles occurs it starts to deteriorate in performance.



The car drives decently, other than what feels like a small power loss coming from somewhere and a semi-severe on and off bog past 4000 rpms.

The real issue is that sometimes (very randomly), the car will drop power. Most of the time I can simply turn it back on, but somtimes it'll only crank as long as I hold the key and give a decent amount of gas.

Thus far I've replaced a fuel pump, fuel pressure regulator and distributor. The plugs were gapped a little too high so they were adjusted closer to .50. All these changes improved the performance of the vehicle, but the random shutting down continues.

I know the car is running rich under load. There were some vacuum leaks allowing unmetered air into the car, but those have been plugged.

I'm planning to switch out the 02 sensors as well as clean out the iacv. I'd pondered a weak battery. The plugs and 02 sensors looked good upon inspection and we'd really thought the distributor was the solution, but the problem persists.

For about 6 months the ball joint connecting the header ending into my h-pipe was several pancaked, allowing outside air to rush into the exhaust about a foot above the 02 sensor. When i replaced the headers/hpipe, i forgot to swap the 02s out.

Any advice other than checking idle or switching 02s? Thanks in advance for your replies, I apologize for lenthiness
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Last edited by mtoliverjr; 09-24-2009 at 11:06 PM.
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Old 09-06-2009, 05:07 PM   #2
mtoliverjr
 
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Forged 302 bored .030 over
gt40 heads/angled plugs
trw 30 pistons
bbk headers/hpipe
mac slash exhaust
cold air maf
trickflow tbody
ngktr5 plugs
24lb injects
255lph walbro
tr3550,4:10s
new batt cables
oem ECM


needs chip/tune, some trans work and a freon recharge

Last edited by mtoliverjr; 09-06-2009 at 05:46 PM.
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Old 09-06-2009, 05:46 PM   #3
mjr46
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so your saying when it cuts out , it'll crank but won't start??
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Old 09-06-2009, 05:49 PM   #4
kennebellgt
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Its probably your tfi module, Im almost positive thats it.
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Old 09-06-2009, 06:00 PM   #5
mtoliverjr
 
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The car most often cranks up fine and runs. Every now and again it'd drop power, but I could start it right back up. With the replaced distributor that particular problem hasn't resurfacd.

However, twice now it's dropped power and not been able to crank effortlessly. It's seemingly required steady gas until the engine picks up over 1500 rpms, then I just release clutch in 1st to get the thing moving and out of other people's way

the obvious possibles seem like burned out o2s or a fading tps. I'll read up on what the tfi module controls

I'm not sure what the module that's located on the Distributor is referred to, but the new distributor we installed last night came with a new Module

Last edited by mtoliverjr; 09-06-2009 at 06:02 PM.
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Old 09-06-2009, 06:09 PM   #6
NoGo95GT
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It's either tow things: the TFI module or the Hall Effects Sensor(stator) inside of the dizzy. You can remove the TFI module and have it tested at Autozone/Oreillys for free. As for the stator, you can either rebuild it, or buy a reman. dizzy. I have read that it is a pain to rebuild, but it is doable. When mine went bad, I just replaced it. I think the rebuild kit is less than $50 and a reman dizzy is $150.
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Old 09-06-2009, 06:21 PM   #7
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i put on a new distributor yesterday, entire assembly w/ module. it drives smoother but still dies randomly. I think o2s are a reasonable culprit. it had a real rich mixture for a long time due to no thermostat during late fall to summer. maybe the engine is guessing in place of faulty info and just dropping too lean occasionally
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Old 09-06-2009, 06:24 PM   #8
mattdel
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o2's will not cause the car to die & lose power. if they are performing out of range or poorly, the PCM knows it and disregards their input.
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Old 09-06-2009, 06:33 PM   #9
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what things would cause it to die/lose power, and not want to start back up? the engine disregarding their information and "guessing" seems like it could lean out and die, or run so rich that it dousing spark.

could it be as simple as a tune? i would think the o2s should be replaced, though they look fine, given that 6 months of mixed air rushing over them as well as a ridiculously rich running engine thanks to never warming up properly

I was told not to worry about the battery/alternator, but I guess it'd be worth a look while buying the other necessary parts
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Old 09-06-2009, 06:40 PM   #10
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first post sounds like weak spark to me. i'd start with a coil.
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