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Old 09-02-2006, 11:48 AM   #1
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Engine Driveability Problem

1997 4.0 automatic.

Engine has begun being difficult to start and keep running while cold.

Starts, then stalls.

Won't restart for several minutes, and when it does, it stalls easily, and needs some throttle in neutral to stay running.

As soon as it's a little warm (3 minutes of running) it's fine again for the rest of the day.

No MIL (Check Engine Light), though it tests fine when the key ignition is turned on.

Ideas?

Bob

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Old 09-02-2006, 08:52 PM   #2
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Might be a TPS going out, dirty Throttle body, or the engine temp sensor that runs to the cpu. Let me think on it over night, Been up all day repairing my computer and have to work at 0300. I have a few possibilities on the edge of my brain but they just aren't coming out atm. I will post anymore ideas if no one beats me to it.

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Old 09-02-2006, 11:55 PM   #3
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fuel pump/filter or injectors maybe. mine tends to act the same way, just not as severe as stalling out.
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Old 09-03-2006, 12:07 AM   #4
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I should have added that this came on suddenly, from one day to the next, as opposed to something that has progressively gotten worse over time.

My Volvo years back slowly developed this type problem, and cleaning the throttle body cured it. It also didn't set a MIL.

I guess because the Jeep started doing it suddenly, I didn't think about carbon/sludge on the throttle body and thought it might be a component failure. Maybe not.

An air temp sensor failure probably wouldn't set a code, either, since the computer doesn't know the temp sensor is wrong. Hmmm...

If it's a water temp sensor, fuel consumption even after hot should be affected, but doesn't the cluster gauge use the signal from the same computer water temp sensor? If that sensor went bad, the temp gauge should be screwed up as well.

Just thinking out loud...

Keep the great ideas coming with my thanks,
Bob

Bob
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Old 09-03-2006, 12:18 AM   #5
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You may simply have gotten some bad gas. Condensation in large underground tanks does accumulate, and if you got some of the bottom of the tank, you could have gotten some water. Try running a couple of bottles of "Heat", in your tank. May not hurt to check out the throttle body as well, giving it a good cleaning.
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Old 09-03-2006, 06:23 AM   #6
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OK there a few things that can cause this. If your computer for some reason isnt throwing codes, it could be a TPS, O2, or MAP sensor. I have seen cpu's not throw codes but it is rare. You could also have a bad EGR valve, Throttle body gasket cold leak, and as khenderson pointed out Fuel pump/pressure regulator, and we cant forget the fuel filter also. Bad gas or gas with to high of a percentage of ethonol will do it also. I have seen worn or unhooked vacum lines cause it but usually along with this come a lean run condition or a rich run condition depending on which line it is (similar to when you have a leaking brake booster, when you step on the brake the engine idle drops). Blue is right also, it might not be a bad idea giving the TB a good cleaning wouldn't hurt anything The sensor mounted on the side of the throttle body operates through a pinhole in the houseing very easy to plug.
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Old 09-03-2006, 10:03 AM   #7
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GREAT list to check from everyone. Thanks!!

I think the first thing to do (after I spray some carb cleaner around the intake/TB gaskets at idle looking for leaks) is remove and thoroughly clean the TB while carefully observing gaskets/hoses and such for vaccuum leaks/disconnects. At 80K it's probably in need of cleaning even IF it isn't "the problem."

Then I'd know it was good before I started throwing parts at it.

The fact that there is no MIL is probably a good clue in itself.

A leaking EGR would mess up idle so that's a decent place to start (though removing them to check is often a pain due to corrosion)

The "bad gas" is also an obvious, but often overlooked cause since we assume gas is so uniformly good these days.

I'll pass along what I find as I work through it, but I have a great start.

It's too easy to forget basic diagnostic skills as we grow more dependent upon MIL codes to tell us what to do. Kind of like cash registers telling check-out kids what change to give, so now they've forgotten how to do very simple math!

Bob

Quote:
Originally Posted by Odhinn
OK there a few things that can cause this. If your computer for some reason isnt throwing codes, it could be a TPS, O2, or MAP sensor. I have seen cpu's not throw codes but it is rare. You could also have a bad EGR valve, Throttle body gasket cold leak, and as khenderson pointed out Fuel pump/pressure regulator, and we cant forget the fuel filter also. Bad gas or gas with to high of a percentage of ethonol will do it also. I have seen worn or unhooked vacum lines cause it but usually along with this come a lean run condition or a rich run condition depending on which line it is (similar to when you have a leaking brake booster, when you step on the brake the engine idle drops). Blue is right also, it might not be a bad idea giving the TB a good cleaning wouldn't hurt anything The sensor mounted on the side of the throttle body operates through a pinhole in the houseing very easy to plug.
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Old 09-03-2006, 10:19 AM   #8
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I know this sounds a little tacky, but we use to check EGR's by tapping on them with a hammer to start. Usually it will knock it loose and the car will then idle. Similar to the technicale diagnostics we use to use on the 90 model camero and firebird Mass airflow sensors, exceot with them we used the back of a screwdriver. This definately doesn't take the place of a good inspection of the valve, but as you stated Bob they are a bit of a pain in the butt to work with.
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Old 09-03-2006, 02:37 PM   #9
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Quote:
Originally Posted by Odhinn
I know this sounds a little tacky, but we use to check EGR's by tapping on them with a hammer to start. Usually it will knock it loose and the car will then idle. Similar to the technicale diagnostics we use to use on the 90 model camero and firebird Mass airflow sensors, exceot with them we used the back of a screwdriver. This definately doesn't take the place of a good inspection of the valve, but as you stated Bob they are a bit of a pain in the butt to work with.
Great idea for the other jeeps but the 4.0 does not use an EGR valve.
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Old 09-03-2006, 03:45 PM   #10
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My bad I guess I was thinking of the 4.2
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Old 09-04-2006, 09:15 AM   #11
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Quote:
Originally Posted by jeepersandcreepers
Great idea for the other jeeps but the 4.0 does not use an EGR valve.
GREAT, We've eliminated one possibility altogether without getting dirty!

The 258" was a great engine, but the 4.0 is even better!

Actually, The 4.0 has been SO reliable and trouble-free, I have almost been able to forget it's in there, so no need to get THAT familiar w/ it.

Only required maintenance to 80k has been a radiator (leak at plastic), serpentine belt idler bearings (and A/C compressor pully bearing) so far.

Thanks, all...

Bob

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