desertdog

Soliciting second opinions. 1990 XJ starts and usually idles, but engine starts sounding like only 5 cylinders are working when I drive it. Often will accelerate real nice then start sputtering as soon as trans upshifts to 3rd. I replaced the cap, rotor, plugs, and wires. Guess I should check spark in case it's the coil. Also I fiddled with the vacuum lines, which are a mess as the PO took out the stock airfilter and re-did it all with electrical tape and random pieces of hose...honestly
I don't know what is what with the emissions and vacuum. I did un-clog the PCV line, and checked vacuum on the EGR and that solenoid thing by the left fender. So I am suspecting some sort of vacuum or computer issue, pending a spark check to eliminate the coil. Oh and I changed the fuel filter too, but no different. Could be injectors I guess. Ideas?

Dan_in_WA

See what (if any) codes are stored in the Powertrain Control Module.

Is your "Check Engine" light in working order? When you've turned the key to "on" but aren't yet cranking it over, this is the Bulb Test for the dash lights - thats why they all come on. I'll assume it is...

Turn the ignition key On-Off-On-Off-On, and watch for the flashes of the Check Engine light. The light will flash out 2-digit codes for your '90.

Example: Code 24 will be flash-flash, pause, flash-flash-flash-flash.

It will start with the lowest numerical code, and work its way up until it flashes code 55, which is the end of test.

Do you have a manual on it?

Post back with what you find. Hope this helps!

Dan

freegdr

if im not mistaken 90s are renix this will not be abled to be scan for codes

tjwalker

Cannot pull stored codes from RENIX (87-90). That capability started in 1991. With a RENIX, you can only pull "real time" data and that requires specialized equipment.

1. Verify fuel delivery. With a 90, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator (be sure that line is pulling good vacuum and is DRY), with the FPR line disconnected, your pressure should jump to approx. 39 psi. Verification of fuel delivery is easy to do with a gauge (rent one) and needs to be ruled in or out early in the troubleshooting process.

2. Test AND adjust your throttle position sensor. Extremely important to a smooth throttle tip in. Your vintage IS adjustable and that should not be overlooked.

3. Here is a link to testing a lot of things on your 90, including engine management sensors. Bookmark it.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

4. Testing compression on all cylinders is never a bad idea and doesn't take long. It is a good "snapshot in time" of the internal condition of the engine. The compression spec. for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

5. Ponying up a few bucks and getting this engine on an engine analyzer is valuable in isolating a problem with a specific cylinder. Worth the money if you don't get this running better.

desertdog

I have the Haynes book. I am slightly confused because it goes from discussing all the engine sensors for a V6 to the 1991-on years. I sort of speculate maybe most of the sensors are the same on the V6 and I6....they look the same, are located the same, so maybe you test them the same? I intend to send Haynes an e-mail asking for clarification, but sounds like what we know so far is that there are no codes available for Renix engines. After sleeping on it I developed a theory that maybe it's the crank position sensor, because the trans was rebuilt recently and re-installed by complete morons. I just had to take off the transfer case and put in a new seal since all the trans fluid was escaping....so maybe they dingled up the CPS during the install. Anyway, thanks for the suggestions all, and wish me luck!

tjwalker

87-01 are all 4.0 inline 6 cylinders.

What you are seeing is one of many mistakes in the HAYNES manuals. I love Haynes underwear, I hate Haynes manuals. They are notorious for their inaccuracies. Chiltons is a little better, but the best documentation for working on your Jeep is the FSM (factory service manual). Can sometimes find a good deal on these on ebay.

This does not sound like a crank sensor problem. Procedure for adjusting throttle position sensor:
--------------------------

TESTING/ADJUSTING THE THROTTLE POSITION SENSOR (87-90)
*thanks to Joe Peters from NAXJA for this

For the AW4 automatic equipped vehicle the TPS has input to BOTH the engine management ECU and the transmission management TCU. If it is bad, not adjusted correctly, or has bad spots in its range of movement it will SCREW with you!

Unplug the 4-wire connector from the TPS; key ON, measure voltage between "A" positive and "D" negative. This value will be your "reference" voltage, so please write it down. Reference voltage is what the ECU or TCU is providing the sensor, supposedly 5.0 volts but seldom will you get that amount.

Ok, you now know your reference voltage value. Now, plug the 4-wire connector back in; key ON, measure the voltage between "B" positive and "D" negative--you have to back probe the connector to do this, use two small paper clips with one leg straight to slip into the back of the connector along the wire. This is the "output" voltage, and the value must be 83 percent of reference voltage. If it is not, loosen the two torx screws and adjust the TPS until it is that value. If you can't get it to adjust to that value, replace the TPS and start over.

Once you have the TPS correctly adjusted, check the output voltages through its full range of movement. This is where you need an analog--needle--type meter rather than a digital meter. When you move the throttle through its full range from closed to WOT you want to see a smooth sweep of the needle. Any hesitations/jumps indicates problems in the TPS and I guarantee you they will show up as problems in the engine or transmission's performance.

IF you have a super digital meter (read that as EXPENSIVE like a Fluke) then you can likely use that instead of the analog, but the lower price digital meters have too much buffering built in and they will mask many problems.

desertdog

Replaced TPS as the old one was missing the cover and dirty inside, which I'm sure can't be good for the resistor strips. Adjusted per instructions, and now the jeep idles very nicely. Also runs smoothly in park up to 4000 rpm. But in drive, as soon as it shifts to third I get sputter. Not as bad as before, but still not right. I noticed when adjusting the TPS that the supply voltage seemed to jump occasionally without me moving anything. Could it be a problem with the computer? What else should I look at, as the problem is clearly related to the relationship with engine and trans.

tjwalker

I think with what you're seeing, I would be sure that the connector for the TPS is clean. Spray it a few times with electrical contact cleaner (available anywhere) and a dab of dielectric grease on it before reinstalling.

If symptoms continue, I'd consider swapping in a new TPS.....they aren't too expensive.

desertdog

Yeah it's a new unit. Got it at Kragen for $48. I am thinking about going to the JY to look for an ECU....but I will clean the connector as suggested.

firefighter4511

i would start off by checking your fuel pressure to the rail. Find out if your fuel pump is good before you start jumping to electrical problems

desertdog

checking the fuel pressure will be my next step, then working my way through the sensors. are there any of those that can be advisably by-passed? just wondering....

tjwalker

No. Don't even try. The engine management system works in "concert" with input signals from all of the sensors.

Test and replace the faulty hardware as necessary...........

desertdog

how about the egr? can i get rid of that?

so interesting news: there were two wires hanging down by my transmission and on a whim i twisted them together. now the jeep runs! I appreciate all the help, especially from tjwalker and 5-90, definitely the RENIX gurus.

Tomxj48

What was the wire to? Im having a very similar problem and its a totaly weird problem that myself or any of my mechanically inclined friends cant figure out.

desertdog

Tom,

I don't know for sure but I surmise it's for the TCU or the neutral switch. And it didn't really solve my problem, cuz the next time I drove it it was back to runny crappy. There are two sets of two wires each down by my trans. One is plugged in, and the other two are just dangling. In the Haynes book it gives a diagram of continuity checks for the neutral switch, and it looks to have six conductors, so maybe neither of the things I'm looking at are that one. I wonder if the two loose wires got pulled out of the connector...need to take a closer look. I am also getting very suspicious of the EGR, as the engine will idle fine and then every once in awhile almost die. The stuttering USUALLY seems to kick in in 3rd or 4th gear, but has done it in the low gears too.

So far I have learned more than I ever thought possible about engine sensors and emissions.....thanks to the guys on the forum here, at NAXJA, and a few other places.

Here's a synopsis: Haynes manuals don't discuss engine sensors for RENIX Jeeps, 1987-1990.

Here are two links to more info: http://www.lunghd.com/Tech_Articles/...iagnostics.htm

http://www.pirate4x4.com/tech/billav...ion_manual.pdf

Definitely invaluable for RENIX owners. Mine is tricky because the stock airbox has been removed so I need to go through the entire vacuum system and make sure everything is correct.