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Old 11-03-2012, 02:27 PM   #1
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Unhappy 4.0 engine stalling

Hi everyone...
I have a annoying problem with my TJ. It's very hard to diagnostic, because DRB scan tool show no error codes

First I need to explain the problem. After driving for so long, say 20-30km, it starts to act up as if it was running out of fuel. Backfiring, cutting out, loss of horse power ect... It does it whether you try giving it a little gas or the whole petal. But it only does it after being driven for awhile and its hot outside. When the temperature outside cools off and during the winter it doesn't act up at all. When it's not acting up it runs great and no problems. Sometimes I can put it in neutral and turn key off and back on and it fixes for a short time. Other times I have to actually pull over and turn the jeep off and let it sit for approx 10 mins and it's back to normal again for a short time. It's not showing any warning lights inside of any kind. All gauges are at normal places and throwing no codes. There are no vacuum leaks that have been found after several times looking and listening. My theory is something is getting too hot I just can't figure out what. If someone could please help me I would for ever be grateful.
And there is occasionally problem with throttle body - when i stay and want to drive - adding a little gas and the engine miss for a half or one second and then go with power. Looks like the engine power is delayed from the added gas on the petal. Occasionally have the same problem when driving slowly, i quickly add much gas and the engine power is delayed in cca. one second.

I have new TPS, changed MAP sensor / new distributor cap, rotor and ignition cables too. No codes on DRB II. Everything looks good, i checked wiring harness, cleaned the connectors, blah, blah..

But the problem is still here and gets annoying and hard for my "bucks"
I have ideas, it is the crankshaft position sensor?, or camshaft sensor? Or fuel pump, or filter. The air filter is new, throttle body and air intake manifold is cleaned.

Any tips guys, please help with this shit

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Old 11-03-2012, 02:34 PM   #2
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Had a similar issue with my YJ, it turned out to be a bad coil.

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Old 11-03-2012, 02:43 PM   #3
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1995 Jeep Grand Cherokee Laredo. Need Help please. Tried everything. - JeepForum.com

This guy here have the same problem, changed everything and no results
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Old 11-03-2012, 07:01 PM   #4
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I am having the same problem in my 1997, but mine would do it hot or cold. Took it back to where I got it and they said it was the fuel pump. Your issue might also be vapor lock if its only doing it when hot.
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Old 11-03-2012, 07:30 PM   #5
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Thanks a lot man, this helps.
I must check the fuel pressure, and i try to clean the fuel system too. Must replace the fuel filter.

The vapor lock thing i hear first time - go to study about it [http://en.wikipedia.org/wiki/Vapor_lock]

Not only in hot, but in cold temperature the symptoms come rarely than in hot. And when hot must wait a long time to cool down 15-30 min. / In colder temp. i wait a 3-4 minutes and go fine again. But not long, only a few kilometres. But this is a problem with something get hot when i drive it.

When i drive slowly, or go offroad - there is no stalling and i drive fine nonstop - only a gas delay problem here.
The stalling come up only when i drive fast onroad - up to 2000rpm permanent.

Thanks for tips...
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Old 11-10-2012, 07:18 AM   #6
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Problem diagnosed !
Bad fuel pump. Bad ignition distributor.

Fuel pump after a few miles at high rpm loss the pressure when overheating and this cause the stalling, no power and misfire.
Distributor have big "allovance" on the axle of the distr. to sides [no up-down] and this cause 10-25% time-shifts in ignition.

What you mean about this ?
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Old 01-16-2013, 04:15 PM   #7
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just to throw it out there... most the time when I see RPM related problems it is either;

1. Spark Plugs
2. Distributor Cap & Rotor
3. Coil

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