Jeep Grand Cherokee

[deadman1474]

I am working on a 93 jeep grand cherokee with a 4.0 liter straight 6 in it. When it is cold it wont start with out a fight. But after it starts up it runs like a champ. I have recently replaced the cap and rotor, spark plugs, and spark plug wires. The car has 150,000 miles on it right now and after you start it it runs great. The check engine light is not on. (But the ABS and AIR BAG lights are). I was thinking coolant temperature sensor but it does not seem to fit with the car starting running great after. And after you run it if you kill it and restart it starts fine only when the engine is cold. Thanks Cody

[Brianstick]

Is it fuel injected or carb?

[deadman1474]

fuel injected

[Brianstick]

It sound like the computer is delivering too lean off a mixture to the engine when it is cold. There are sensors on the engine to tell the computer what mixture to deliver to the engine at various temperatures. In the old days they had automatic chokes that they used to controll mixture with a temperature sensor on the intake manifold that worked pretty well. Check in your service manual under the troubleshooting section.

[deadman1474]

The service manual is something that I am going to have to buy.

[Brianstick]

It's probably just a bad sensor. Knowing which one is the trick.

[84zmike]

Try tuning the key on and listening to the fuel pump once it stops running then try to start it if it doesn't then turn the key off and on again a few times letting the fuel pump stop each time before you try and start it if this works you need a new fuel pump as it is "loosing its prime" and the only fix is a new one

[Sparky#1]

Originally Posted by deadman1474

I am working on a 93 jeep grand cherokee with a 4.0 liter straight 6 in it. When it is cold it wont start with out a fight. But after it starts up it runs like a champ. I have recently replaced the cap and rotor, spark plugs, and spark plug wires. The car has 150,000 miles on it right now and after you start it it runs great. The check engine light is not on. (But the ABS and AIR BAG lights are). I was thinking coolant temperature sensor but it does not seem to fit with the car starting running great after. And after you run it if you kill it and restart it starts fine only when the engine is cold. Thanks Cody

Does the truck crank strong or is it lazy ? Also what type of oil are you running ?

[Go1lum]

150k on a 4.0 is brand new. Sounds like a temp sensor. ( hard starts with 4.0's are so common). Also maybe sign up on like pirate4x4.com and search. or www.naxja.org

[deadman1474]

Originally Posted by Sparky#1

Does the truck crank strong or is it lazy ? Also what type of oil are you running ?

It cranks fine and as soon as you get it started it runs great great oil pressure altho I am not sure what kind of oil is in it.

[Sparky#1]

Originally Posted by deadman1474

It cranks fine and as soon as you get it started it runs great great oil pressure altho I am not sure what kind of oil is in it.

If the oil is too heavy that could be an issue and check your oxygen sensor.

[84zmike]

Another thing came to mind with the EPA the way it is now there are winter blends for gasoline as well as Diesel so if you have a tank of summer fuel it will be hard to start or if you have a tank of winter blend and the Jeep is in a heat garage same issues......

[STwelder]

150000 miles on it...... check the timing on it. Its easy and you don't need a book, you can call auto zone or advance auto and the will tell you the timing degree over the phone.

[joeaus]

I have had several of these Jeeps, 4.0 is barely broken in at 150k. I believe it is the temperature sensor. Good luck.

[UCHOG]

The issue seems to me is it's the "Idle Air Control Valve". Since the engine is an EFI, there is a small electric motor on top of the plentum, (where the carb would normally sit) which has a fan blower inside. Over time, and 150,000 miles, the shaft on the electric motor will carbon up, not allowing the fan to engage, thus, not forcing air inside of the engine, making a cold engine difficult to start.
It is easy to resolve by either cleaning the motor or by simply replacing the unit. Look for a couple wires on top of the plentum.

[Magnetic Mechanic]

Didn't the 93's have obd1? If so you can eliminate sensors as you would get a check engine light on fail. Does the fuel pump relay come on with the ignition, or is it responding to the oil pump switch? Could also be a bad pressure relief in the fuel manifold, i think that can fail w/no code.

[Billdacat]

I sort of agree with UCHOG on the idle air control motor. In your case I would post this question on the Jeep Unlimited Forum....
http://www.jeepsunlimited.com/forums...splay.php?f=50

[Magnetic Mechanic]

Please let us know what you eventually find to be the problem

[rustywrangler]

Guess I will throw my 2cents. Go over to Jeepforum.com and check out their FAQ section. This is covered in there. Sounds like the air controler as well. Don't go to pirate4x4. They will eat you alive with this kind of question.

Here is a good link to the OBDI testing, even if you do not have a check engine light it still will record stuff sometimes: http://www.jeepforum.com/wiki/index....k_Engine_Codes

[SaW]

Originally Posted by rustywrangler

Guess I will throw my 2cents. Go over to Jeepforum.com and check out their FAQ section. This is covered in there. Sounds like the air controler as well. Don't go to pirate4x4. They will eat you alive with this kind of question.

Here is a good link to the OBDI testing, even if you do not have a check engine light it still will record stuff sometimes: http://www.jeepforum.com/wiki/index....k_Engine_Codes

Some good advice right there. They don't really love newbies over there