homebrew said:
Ok so my dad gave me his 89 XJ 4.0 Auto. First of all it idels really low like 250. Drives on the street ok, but wont go any faster than 45-50. was going to drive it home, drove about 4 miles on the freeway at 45 and decided it would be better to tow it. So I ended up just towing it home.
The engine is fairley new. What can I use to flush the tranny? Im sure the tranny hasent been touched in at least 6 years. I think that may be part of the problem.
So in short I am asking what I need to do what should I check, what is causing this.
My 87 was just like that when I first aquired it over 2 years ago.
First off don't waste time and money on the tranny, they are bullet proof. Plenty of other stuff does need to be done. First off track down an FSM (Factory Service Manual) for the 89, Renix engine. If you can't find one PM me, Ecomike or 5-90.
Do the following. Pull and clean every ground wire connection on the engine block (2), firwall (2) and the battery clamps and posts.
If you don't have one, get a multimeter. Most of the Renix sensors and computer controls can be tested with a simple ohm-DC volt / multi meter. I have paid as little as $4 for a good one at harbour tools. They are available just about every where, radia shack, auto parts stores, wally world....etc.
Then with the meter and FSM start testing the conputer sensors such as throttle position sensor, intake air temperature sensor, coolant temperature sensor, O2 sensor, etc.
How old are the plugs, wires, rotor and cap? Rotor and cap go first, then the wires, then the plugs in my experience.
Also try and buy or borrow a fuel pressure and vacuum gauge. They will come instructions. You can learn a lot by measuring just the engine vacuum at idle, during acceleration, deceleration, and at various higher rpms. Fuel system pressure will tell you have a problem with fuel pump, fuel filter or fuel pressure regulator.
Get a can of good gas additive like seafoam, Techron from Chevron, or similar, for cleaning the fuel system and injectors and run it while testing and working on these other sensor and tune up items and issues.
Read up on how to remove, clean, lubicate and reinstall the Idle Air Controller and the throttle body.
And lastly dig up any history on the jeep you can and add it all to this post.
Don't buy and replace any parts until you have tested them and verified that they are toast with a multi meter, with the possible exception of the rotor and cap.
Pull the spark plugs, check the part number, spark gap and appearance and look up some pictures to see if thier condition can tell you anything.
Buy (or go to the library and borrow) a service manual like the Haynes guide for Jeeps. They run about $17 and they are worth it. Be sure and get a copy of the Renix (computer and sensors) service manual (contact, PM, me or 5-90)
Lastly your symptoms are just like mine were, and the Tranny and the fuel pump and fuel system had nothing to with my problem. It was a combination of other old worn out parts and issues.
Lastly read up here at
about these beasties, you won't find any better help or information anywhere else on the internet.
One last thing, check the exhaust system, or take it to an exhaust shop and ask them the to pressure test the Cat and Muffler and see if one or both of them are plugged up.