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homebrew

NAXJA Forum User
Location
Bremerton, WA
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.
 
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 NAXJA 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.
 
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Ok so I took the air intake hose off the TB was filthy, I cleaned it with some spray started it up and it ran awsome,sounded real strong now it is ideling a little high around 1100-1250. I have a chiltons. How is the tranny controled electric or vaccum?
 
homebrew said:
Ok so I took the air intake hose off the TB was filthy, I cleaned it with some spray started it up and it ran awsome,sounded real strong now it is ideling a little high around 1100-1250. I have a chiltons. How is the tranny controled electric or vaccum?

The tranny is electronically controlled. Unless you have specific tranny problems, I second the advice to leave it alone. If the fluid looks dirty, you can drain and refill, but skip the power flushing and fancy stuff.

It sounds as if you've touched on your other problem, but not solved it. The high idle could be a dirty idle air controller (little electrically controlled plunger in the throttle body). Careful further cleaning (never force anything) might help. Check also for vacuum leaks. The throttle position sensor may also be a suspect, but a thorough cleaning of the throttle body comes first. Do not attempt to correct the idle by adjusting the throttle plate. The engine management system should set idle speed, and the throttle adjustment, once disturbed, can be hard to get right again if you've messed with it.

You should also check to make sure that the throttle linkage is free. My old 87 had some idle problems that turned out to be in the accelerator pedal pivot, and later the same problems returned and turned out to be in the bell crank attached to the side of the engine. When diagnosing throttle problems, make sure you operate the throttle at the throttle body itself, and if the high idle does not occur, look for binding somewhere.

And do the whole routine that Ecomike suggests. Old Renix systems are fairly sensitive to voltage issues, so make sure that every connector and every connection is clean and good.
 
Matthew Currie said:
It sounds as if you've touched on your other problem, but not solved it. The high idle could be a dirty idle air controller (little electrically controlled plunger in the throttle body). Careful further cleaning (never force anything) might help.

Don't forget to give the IAC a drop of very light machine oil on the threads before reinstalling it, after cleaning it.

Check also for vacuum leaks.

He had a low Idle before He pulled the air filter hose assembly, now with that off he has a high idle, I am thinking the air filter is clogged, needs replacing and is probably soaked with pluged CCV system motor oil!

When diagnosing throttle problems, look for binding somewhere.

Like a shifted floor mat hung under the accelerator pedal?:cheers:
Mine still does that once in a while, time to glue it in one place I think.

And do the whole routine that Ecomike suggests. Old Renix systems are fairly sensitive to voltage issues, so make sure that every connector and every connection is clean and good.

Yep, like a 0.1 volt change on the throttle possition sensor results in something I like a 250 RPM change in the idle speed, that sensitive. I posted my actual test data on that here somewhere about 2 months ago. I was shocked at how sensitive it was. Even a 13 ohm ground resistance from the engine to the battery was bad news. That surprised the hell out me too. On top of that the computer can sometimes compensate, but as the engine heats and cools a bad ground can change resistance and make the computer think the gas peddle has moved due to the changing ground resistance!
 
JoshRountree said:
If you want to do anything to the tranny, I'd just drain and refill, or pull the pan and replace the filter. No flush though.
The reason they saying to not flush, is many have reported serious problems with working Trannys that had no problems until after they were flushed.

Also check and read up on the proper tranny fluid for your year if you change fluid. If the fluid smells new and is red, leave it alone. If it is a dark brown with a burnt smell to it then do drain it. If it is milky white, you have major Tranny fluid and radiator problems (like engine coolant in the tranny fluid).

From the sounds of your first efforts, the Tranny and Exhaust system may be OK. It may just be a matter of cleaning the throttle body (which you just did) cleaning all the grounds, fixing all the vacuum leaks, replacing the CCV (Crankcase ventilation system tubing, small line from the Valve cover to the intake manifold), and replacing the air filter. Then the very last thing to is reset, calibrate the TPS sensor to read 0.80 to 0.82 volts from the pin B to pin C, power on, engine off (don't start it). The TPS is held in place with two torqs screws, loosen them and rotate the TPS until you have 0.80 to 0.82 volts. But get those grounds cleaned before you touch the TPS. You want less than 1 ohm of resistance from the engine block to the battery and from the firewall to the engine block. Then start, run, stop, start run, stop, 3 times while the ECU computer relearns and resets the Idle speed!

Then enjoy your new toy!
 
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Alright there are 2 different connectors in there both with the same color color wires. 1 rectangle looking 1 square looking. Which one do I test?? Also what setting should my multi meter be on?
 
Added confusion.

I had the ignition on with engine off. There is a wining sound coming from the right side along with this the tach jumps up and down. What might be causing this?
 
I tried adjusting the TPS now it wont even start. What did I do wrong?
 
homebrew said:
Alright there are 2 different connectors in there both with the same color color wires. 1 rectangle looking 1 square looking. Which one do I test?? Also what setting should my multi meter be on?
Use the three pin, flat rectangular connector. It is the Idle speed to the ECU Computer. The four pin square connector talks to the Transmission.

There are some threads in this forum that go into great detail on TPS testing and setting. Search "Throttle Position sensor idle speed renix" and it should come right up, also use the advanced search and use "Ecomike" for the poster in the search.

Use the DC volt scale on the Multi meter, something between 2 and 10 volts for the scale.

Got me on the whining sound, follow the sound, locate it and if neccesary post a photo of the sound source.

Perhaps the whine is the fuel pump? Mine whines, but only for 3 to 5 seconds then it cuts off. If it is the fuel pump whining it should cut off after 3 to 5 seconds.
 
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Definitely check the exaust after it has sat for a while. Mine actually had a mouse nest in the Catalytic converter! Poor mice :-( Luckily, Alberta is the only province in Canada that it's legal to run without one, so, i didn't have to get a "payday loan" to replace it. I just have straight pipe to the muffler.

I feel kinda guilty though, what with my province being against Kyoto in a big way, and me still polluting even more. I think I will burn:flame:.
 
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