HELP - 1991 Jeep Cherokee Laredo 4 X 4 Engine won't start

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guzzimike

guzzimike

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OK, here's the situation...

1991 Jeep, 4.0 Liter /6 engine. Been working OK till yesterday.

The Jeep won't start. Cranks all day long, engine won't fire.

It is NOT the computer. Swapped it with another from a running, same year Jeep, and it was OK.

If I remove the Air Filter into the throttle body and pour a bit of Gasoline, the engine starts and STAYS running...but the momentr I turn it off, If I leave it OFF for more than a minute, the Engine will not start.

It's almost as if I gotta prime the throttle body with fuel to get it going.

My question:

Ist this time to replace the entire Throttle Body or

Is it something like the Throttle Positioning Sensor..?

Or, is it something else..?


Thanx..




This Picture below is what the throttle body on my Jeep looks like -

When I pour the fuel directly into the butterfly valve, after I crank the valve open a bit by hand...If I then crank it, it starts and stays running.

The Throttle positioning sensor is the plastic Doo-Hickey on the Right. I don't know what the Doo-hickey on the top could be..


!BcYwV9!BGk~$(KGrHqQOKjgEq45Q)lW7BK0Sy18Te!~~_12.JPG
 
With the 4.0L a common problem when this happins is the crankshaft position sensor, I had it happin to mine and use to have them come in all the time with this problem,
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I think the part is close to $75 I might have a used one that still works laying around, I'll check but I doubt it. Will PM you if I do.
 
Crankshaft Position Sensor 4.0L
41985206


The crankshaft position sensor is mounted in the transmission housing at the rear of the engine block.

REMOVAL


  1. Disconnect the Crankshaft Position Sensor (CPS) electrical connector.
  2. Remove the CPS mounting screw.
  3. Remove the CPS.
INSTALLATION


  1. Install the CPS flush against the opening in the transmission housing.
  2. Tighten the CPS mounting screw.
  3. Connect the electrical connector to the CPS
Crankshaft Position (CKP) Sensor Operation
42264867


Disconnect the engine speed sensor electrical connector from the wiring harness. Check the resistance of the sensor by placing an ohmmeter across terminals A and B (marked on sensor connector). With the engine at normal operating temperature, the ohmmeter should read 200 ±75 ohms. Replace sensor if ohmmeter readings are not within specifications.
Crankshaft Position Sensor Crankshaft Position Sensor4638128$98.45 Contact Dealer For Most Current Part and Price Information. LaborSkill
LevelMfg.
WarrantyStandardCrankshaft Position Sensor ReplaceB0.40.6
This is all the info I could pull up off our old information databse. Hope this helps. if you have any questions. PM ME
 
Is you check engine light on? If it is scan it but more than likely if it's not then it's the crankshaft position sensor
 
But first things first since it sounds fuel related, check your fuel filter, jeeps are bad about clogging up.
 
guzzimike said:
If I remove the Air Filter into the throttle body and pour a bit of Gasoline, the engine starts and STAYS running...but the momentr I turn it off, If I leave it OFF for more than a minute, the Engine will not start.

It's almost as if I gotta prime the throttle body with fuel to get it going.



When I pour the fuel directly into the butterfly valve, after I crank the valve open a bit by hand...If I then crank it, it starts and stays running.
Click to expand...

Does sound like a fuel delivery issue rather than the crankshaft position sensor since it does start and run if primed
 
The doo hickey on the top appears to be the idle air control valve. Sometimes you can take it off and spray brake parts cleaner into it to clean it and then spray penetrating oil into it. They sometimes stick. It "should" at least start though because that valve controls the idle . If you can get it running, check your fuel pressure. There should be a port on the fuel rail for this. It seems that the throttle body is not pulling fuel. You may have a bad fuel pump. Fuel pump relay? Hope this helps.
 
moparornocar72 said:
But first things first since it sounds fuel related, check your fuel filter, jeeps are bad about clogging up.
Click to expand...

No "Check Engine" lights.

I have not checked the fuel filter in years.

Would me "Priming" the Throttle Body overcome any "Drag" in the flow of fuel that could be caused by a clogged Fuel Filter..?


BTW, now the engine has sat for about an hour. I just checked it, and it starts and runs well...Went for repeated runs, cycling the "Start" Sequence...all seems OK.


I hate it when this happens.

Just in case, I replaced the 3 Relays ( # 50732) that have been on there since Day One - when I bought the Jeep new, in 1991 (330K Miles ago).

These relays are for the Fuel Pump, Starter and Aux Electric Fan.
 
With most OBD vehicles, turn key to run, make sure Check engine lite on, crank engine, if crank sensor is working the check engine lite will go out while cranking. If it stays on more likely the crank sensor is done. If I am not mistaken there was a TSB for a update crank sensors You have a lot of great detail in the previous replys!!
 
Hopefully you don't have it happin again. 4.0 is a great motor just the sensors and relays go out far to often. If u need anything else or diagrams/ instructions pm me
 
Sound fuel related.
My vote is fuel pressure regulator, weak fuel pump, or possibly something within the ignition circuit.
Initial turn of the key always causes fuel pump to kick for a few seconds.
Fuel pressure regulator could be bleeding down, so this few seconds of "priming" is not getting fuel pressure up to speed.

Do you hear the pump hum with key?
Do you have a fuel pressure gauge to see if the hum is getting fuel pressure up on the rail?
Does fuel pump run when key is in "start" position? ( need a friend listening at filler neck )

If ignition switch is not sending signal to pump to prime for start, OR regulator is bleeding off prime, AND vehicle does not make pump run with key in START position, it could be possible that you have a combination that yields no pressure at the rail, and no pressure coming if the car does not make the pump run while in start. This would explain why "priming" gets enough fuel to get the vehicle to fire, and then when you release the key to "run" the fuel pump kicks in?

To test, a fuel pressure gauge that verifies pressure is up at rail after key to on position would be first. Is pressure up where it should be (condition of pump) and does pressure stay up for a bit (condition of regulator). Follow that with a test (with buddy) to see if the fuel pump runs in "start" position.
 
No "Check Engine" Lights.

I hear the Fuel Pump when I first turn the key, then the fuel Pump stops (this is all normal, it's always done so)...

Then if I go to the START Key Position, it just cranks and cranks with NO engine start.

It's gotta be sone kind of Fuel Regulator system, as it works fine when primed manually.

Then, If Primed by hand, it runs OK, even if I Stop and Start repeatedly, as long as it doesn't sit for too long with the engine OFF.

If it sits for an hour or so, it's See-Ya...No more start.


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One easy test is when you have the no-start condition, try turning the key on and off a half dozen times without actually cranking the engine. This will help build up pressure to the fuel rail. If it now starts, it's probably the pressure regulator, weak pump, or a clogged filter. You can also put a gauge on the rail and check it that way, assuming you have the tools.
 
cudamark said:
One easy test is when you have the no-start condition, try turning the key on and off a half dozen times without actually cranking the engine. This will help build up pressure to the fuel rail. If it now starts, it's probably the pressure regulator, weak pump, or a clogged filter. You can also put a gauge on the rail and check it that way, assuming you have the tools.
Click to expand...

Tried it, No Go...

Oh, well...


Thank you all, guys..


The Jeep issue will have to wait till later on in the next week to get sorted out, as I have an out-of-town job going on for the next couple of days.


Thank you all again for your time, your help and excellent suggestions.


This is a great site with good people. 8)

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I have the same problem with a Camry ( daughter drives it ). It acted up for weeks before the check engine light ever came on. It stays on now. The problem is a air temp sensor in the air filter box. 52 bucks for a 2 wire thingy about the size of a lipstick.
Engine starts every time when cold and runs fine until it gets warmed up. Then it begins to hesitate at take off. Turn it off and it may refuse to start for as much as half hour.
The sad part is the previous owner put one of those K&N air filters on it and removed the original box. This expensive POS sensor is dangling from the wires under the hood. I doubt a new one would last very long. :(
 
RedFish said:
I have the same problem with a Camry ( daughter drives it ). < snip > Engine starts every time when cold and runs fine until it gets warmed up. Then it begins to hesitate at take off. Turn it off and it may refuse to start for as much as half hour. < snip >
Click to expand...

Hi RF. My Jeep actually does not start when cold.

It will only start cold if I put some gasoline into the throttle body.

Then it stays On for as long as I want to run it, and if I stop the engine for say 10 -20 minutes, it will start again with no problem, even for repeated starts..

However, if the engine sits turned OFF for more than one hour or so, it will not start again.

Slightly different issue than your daughter's car, I think..

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see if u can check the fuel pressure and check if there is a fuel regulator.
 
yeah the symptoms are different. If the problem is electronic controls related it may or may not set on the check engine light.
There are some pre elctronics conditions that will cause your symptom also...
Spark plugs loose in the holes or their electrode burned away ( gap too wide ).
Leaking head gasket(s) or intake gasket(s). Small amount of water getting into one or more cylinders. Just enough to prevent firing until you chase it out with a heavy dose of fuel.
 
You need to get or borrow a fuel pressure gauge. Ther is a fuel pressure regulator on the injector fuel rail at the front of it. This could leak off PLUS, built into the fuel pump is a check valve to allow the pressure side of the syst. to hold fuel pressure in the complete syst. In otherwords, the pressure regulator (seals up) the return side of the fuel syst. and the check valve in the fuel pump (seals up) the pressure side of the fuel syst. when the engine is shut off. Leaking at either one of these will cause it to loose all the pressure in the fuel rail and make it hard to start after it sits. You would be able to see this if you had a gauge on it and watched it after you shut it off. You can pinch off the rubber fuel lines on the return or pressure sides with the gauge on it to try to figure which one is the problem child!
 
Put the temperature sensor (not sender) in the freezer for a while. Quickly re-install it and try to start the engine. It will tell the computer to send extra fuel. I have had a lot of trouble with these sensors. Cheaper than buying the spray that freezes stuff.
 
OK - Solved it.

It was the Ignition Coil.

It had an intermittent fault.


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