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1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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strexx
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Nov 27, 2009, 2:46 PM
Post #1 of 11
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1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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Ok, we just got a 1988 Jeep Cherokee. It has a 2.5L engine, 5 speed manual transmission.
List of symptoms include:
1. Slow to start, takes lots of cranking, and have to keep foot on accelerator pedal until it will idle on its own (which takes several minutes).
2. Extremely high idle when started cold, then dies... so we have to keep the pedal down some....
3. Idles fine once warmed up.
4. Taking off from a stop is okay, but it begins to hesitate/bog down, then it will buck like you're just learning to drive a stick. Often, pressing the clutch back in and revving it up, then releasing the clutch will make it stop bucking, but not for long. It does this in all the gears -- except, we've never had it going fast enough to even go into 5th gear. Driving on flat roads often requires upshifting and downshifting to stop the bucking and to help keep the speed up... Going up hills is a joke. Downshift, downshift, downshift, till it's barely even crawling up the hill. The heavier the acceleration, the worse the problem gets.
5. The warmer the Jeep gets (the longer it's driven) the worse the hesitation/bogging/bucking become...
There is no tach, so I can't tell what the RPM range is when this is occurring.
I don't know anything about the history of this Jeep, but it does appear that the entire exhaust system is new, including the catalytic converter. (No red-glowing catalytic converter, either, so I've pretty much ruled this out as the problem).
I haven't done anything to it yet, but I'm just looking for the most logical place to start and the most common causes of these symptoms. We're thinking fuel pump. I did replace the section of rubber line from the tank to the fuel filter with metal line to make sure it wasn't collapsing under pressure. And bypassed the fuel filter for a brief test-drive to see if the filter was clogged or clogging, but there was no improvement.
Is it possible that it's the TPS instead of a fuel supply problem?
Any suggestions are appreciated.
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Hammer Time
Ultimate Carjunky
/ Moderator
Nov 27, 2009, 4:01 PM
Post #2 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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Sounds more like an ignition misfire to me but it's impossible to tell from someone else's description..
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Loren Champlain Sr
Veteran
/ Moderator
Nov 27, 2009, 6:28 PM
Post #3 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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strexx; Couple of things jump out at me, here. This should be TBI (throttle body injection). With fuel injected engines, when you depress the throttle, you are giving the engine more air. Not fuel. If it helps starting by opening the throttle, that sounds to me that it is overfueling. Although rare, I have seen MAP (Manifold Absolute Pressure) sensors cause this. More common are the CTS (Coolant temp sensor) sensors. The MAP sensor reads engine vacuum. When it 'sees' a drop in vacuum, it tells the computer that you are accelerating, and then 'dumps' fuel. The CTS tells the computer the engine temp. If it thinks that it's -40F outside, it 'dumps' fuel. Either of these, or many other possiblities, could cause the extended crank symptoms. If it IS overfueling, it is very possible that the catalytic converter is plugged. Unfortunately, some diagnostics are going to be required to get to the 'cause'. If you have the equipment, we can supply a chart so that you can check the CTS resistance vs. actual temperature. The cat. can be checked with a pressure guage installed in the oxygen sensor port or a vacuum reading at idle and cruise speeds. But, need to find the cause before attacking the cat.
Loren
SW Washington
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strexx
New User
Nov 28, 2009, 4:13 PM
Post #4 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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It just seems to be starved for gasoline, in a nutshell.
the cat is brand new.
Installed new plugs today, and dumped in a bottle of injector cleaner.
Starts a little easier, smoothed it out a little running wise, and it idles much better, but the bucking problem is still there. At first, before it warmed up, it didn't buck until 3rd gear, but on the return trip from the test-drive after she was warm, the bucking was back in all of the gears.
Now, in addition to all of that, it started overheating today. In a matter of minutes, it was hot and boiling over into the overflow. Checked the obvious (fluid level, looked for leaks, checked the oil for water contamination, etc), then checked the thermostat... there was no thermostat. Installed one, with the new gasket. Still... overheats rapidly, just at idle, without even being driven.
There's a lot of other little stuff we're working on, too... no brake lights, heater core leaks (we assume, someone else bypassed it at some point), blower motor doesn't work, etc, etc. This one is definitely a challenge.
(This post was edited by strexx on Nov 28, 2009, 4:16 PM)
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Hammer Time
Ultimate Carjunky
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Nov 28, 2009, 4:18 PM
Post #5 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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I would start out with a cooling system pressure test. It could have a blown head gasket. Check your fuel pressure also.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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chickenhouse
Enthusiast
Nov 28, 2009, 6:47 PM
Post #6 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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Can you see coolant flowing in the radiator while it's running?;
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strexx
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Nov 29, 2009, 8:07 AM
Post #7 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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Did check for radiator flow, and it kinda "surges", coolant level drops below the point where you can still see it in the radiator, then it all comes flowing through and it pours out the radiator opening for 15 - 30 seconds, then goes back down. And it just keeps doing that. No other symptoms of a blown head gasket.
Don't have any way to check the fuel pressure, or would have done that already.
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strexx
New User
Nov 29, 2009, 8:45 AM
Post #9 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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If I had the cash to do that, I'd have done that.... which is why I'm here. Was just looking for suggestions.
Thanks for you time.
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Hammer Time
Ultimate Carjunky
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Nov 29, 2009, 9:51 AM
Post #10 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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We have given you suggestions. The suggestions were for testing which is how these problems are found. If you aren't equipped to perform the necessary tests, then you have no choice but pay someone else to do it for you. we can give you advice but we don't use crystal balls. We use test equipment and we pay dearly for it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Loren Champlain Sr
Veteran
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Nov 29, 2009, 7:44 PM
Post #11 of 11
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Re: 1988 Jeep Cherokee 2.5L Hesitates, Bucks, Extreme high idle & dies when cold
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>> coolant level drops below the point where you can still see it in the radiator, then it all comes flowing through and it pours out the radiator opening for 15 - 30 seconds, then goes back down. And it just keeps doing that. No other symptoms of a blown head gasket. >>
strexx; This sounds like you've got an air pocket in the system, or...you installed the thermostat backwards?
Although rare, could be that the water pump is faulty. The impeller on the water pump could be 'eaten' away from rust or (believe it or not) air in the system. Air bubbles will wear away metal. Also, again very rare, the impeller could be slipping on the shaft, not circulating the water. I'd remove the thermostat, get it full of water, and watch to see if you have good circulation. It should be a steady flow out of the upper radiator hose into the radiator.
 The top left of the picture is the top of the thermostat, and should be pointed towards the radiator.
Loren
SW Washington
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