gray89xj

Hi guys, finally decided to ask the people with experience, as the title states I am having some issues with my jeep. I have looked high and low for people with similar issues, especially the starting problem, and have not had much luck.

First off, it is a 89 Cherokee Laredo with 203,000 miles on it, automatic, 3" lift, 32" MTRs, and 4.10s, blah blah blah. This jeep was bought by my father in 1996 or thereabout and this has both of us stumped.

The Problem(s):

When cold, it will usually crank and fire just fine, and comes up to about 800 rpm where it should be. But, then it dies. If you crank it over again, it starts up and revs to about 1500 rpm, then slowly comes down to about 700 rpm, running well. If you give it gas on first startup to keep it running, it will idle very low if you let your foot off and will die randomly, such as when you stop to go from reverse to neutral.

When warm, it will start right up, idling low (about 450-500) at first and then slowly come up to 50 rpm idle.

Sometimes, however, about every 4 cold starts (or whenever it feels like it seems) it will do what it does on the first start normally, but it will do it every time. However, if I drive it about 3 minutes or so, it will idle fine.

Things I have done:

All of this has had no lasting effect on my starting issue, the swapped out ECU worked right on the first start but no change since.

I am stumped.

In addition, about 3 weeks ago, the transmission has started shifting late, as in shifting at 3500 latest at WOT and not downshifing under heavy throttle, even when running about 1800 rpm. I have adjusted the kickdown cable numerous times and adjusted the TPS to transmission specs with no change to either the engine or the transmission.

Engine makes no noises and has good oil pressure, transmission was a remanned unit about 12 years ago.

Any ideas or suggestions?


Also, is it normal for these jeeps to only want to do 70 going uphill on the interstate with 32"s even with 4.10s? Guessing it probably is.

cruiser54

Where did you get the TPS? It could have failed.

Ever done my sensor ground test? #5. Connector refreshing? #3, Complete ground refreshing? #1, Trans plug refreshing? #10, MY TPS instructions? #8.

Click on the "Pink Link" below in my signature. Complete write-ups for the procedures, with photos, are in the posts corresponding to the numbers above. Keep us posted.

gray89xj

Thanks Cruiser! I have done most of the stuff you suggested but since I am off work today I will redo it and see what happens. I have cleaned the dipstick ground before and have a #4 cable running from there to the firewall ground bolt. All the grounds I have checked read about 1 ohm with my Harbor Freight cheapo multimeter, but that thing reads some resistance just between the two leads. The TPS procedure I followed appears to be identical, but I'll check it anyway.

I got the TPS from Oriley Auto Parts, and though it may be causing my transmission issue, it did not change the starting behavior at all when I put it in, replacing the obviously bad original TPS sensor.

I'll report back with results.

89cherokee2gtmudy

I'm curious what your problem is. My 89 with 194xxx has been randomly stalling also. Sometimes stalls when I put it in drive after its been sitting. Also liked to stall if its crawling along about 5 mph and it will stall when I let off gas and try to turn.

cruiser54

Ever cleaned your throttle body?

gray89xj

Well, I am reporting back. I got the transmission issue fixed! It was nothing electrical though. Apparently the ratcheting part in the kickdown cable stuck. I noticed the throttle didnt seem to be opening as much as it should, so I took off the intake hose, and waddya know, it wasn't! I messed with the cable and got it working again, so now I have full throttle and with the kickdown cable working and the TPS adjusted it shifts right again!

Now for the starting problem. Went out to move the jeep to the driveway, didn't want to idle at all. Seems to be doing this more frequently. Then I got to work.

Sensor Ground Test Results:
TPS: 1.2 Ohms to ground wiggle test passed
IAT: 1.1 Ohms to ground wiggle test passed
MAP: 1.1 Ohms to ground wiggle test passed
CTS: 1.2 Ohms to ground wiggle test passed

Went through and cleaned relays, all sensor connectors, coil connectors, trans connectors, headlight connector, etc.

Refreshed dipstick grounds, Have the negative battery cable, 2 grounds for fuel injection, and a 4 Guage cable that goes to the firewall ground bolt all nicely cleaned and tightened on the dipstick stud. However the negative battery cable has terrible insulation and reads 1 Ohm from the battery to the engine block, could this be my problem? TPS adjusted by Cruiser's instructions for automatic transmission. However, even after all of this, when I went to start it up it still did not want to idle, just like it did before all this work. The ECU memory (if it has it) should have been reset when I had the battery disconnected for about half an hour too. Drive it around the block, and oh look, it will idle. But it is idling low, about the first line on the tachometer. Gah....

What do I try now? Going to replace the negative battery cable tommorow if that will help.

cruiser54

Do the battery cable. The rEnix ECU doesn't reset bTW.

Check the hose from the throttle body to the MAP very closely. A bit of a vacuum leak and the MAP thinks you're opening the throttle and requests more fuel.

gray89xj

Well, I replaced my ground cable today, no change. I got out my dad's vacum tester and the MAP line doesn't leak. However, while I had it out, I hooked it up to my engine. At regular idling speed (about 750 rpm, it decided to run right on the second start today) I am only getting 13-14 inches of vacuum. Could that be my problem? I sprayed starting fluid at all the vacuum ports and as much of the intake manifold as I could get at from the top with no change, could it be leaky rings?

89cherokee2gtmudy

Yes I have. Made it idle better and run smoother

gray89xj

Well today it was in a good mood starting right on the second try. The first time I started it today it didn't die and slowly came up to a normal idle over about 15 seconds, but died as soon as I put it in reverse. On repeated key cycles (the cycle restarts when you turn the key off and back on) it just died on the first start. It definitely seems like something electrical.....
Anyway, I recorded a video to show exactly what it is doing.

cruiser54

Adjust your TPS on the "engine" side (flat connector) per my instructions.

gray89xj

Just finished doing that, made no appreciable difference. However I messed around with the idle air control. If I unplug it the idle air control when it is idling correctly it will start right up every time. It almost seems like the idle air control can't open fast enough on the first start and the computer overcompensates on the second start, even though the idle air control is brand new (and didn't improve things over the original) This is reinforced by the fact that if you give it a little gas for the first 10 seconds or so and then let off it won't die and will idle correctly. On the starts where it won't idle perhaps for some reason the idle air control isn't opening at all. I replaced the idle air control because when I put it in a spare throttle body while plugging the hole in the throttle body of my jeep, it moved in response to the amount of air I let n manually but did it very slowly. I wonder if my idle air control wiring is messed up, but it seems like it would be fairly durable running directly from the computer to the stepper motor...

Any thoughts?

cruiser54

Never hurts to through all the connectors in the engine bay while you're at it. Look inside them for retracted pins and the like.

What happens if you do a key cycle or two before starting? On, off, on, off, then start.

gray89xj

Key cycles do not effect it at all. Already checked out all the plugs but I messed with the IAC plug tightening up the pins and putting dielectric grease in there. No change. For now I just waited until it was idling good and then just unplugged the IAC and left it unplugged. It will now start and run every time but of course the idle varies based on how warmed up the engine is now of course. The problem definitely has something to do with the IAC as otherwise it runs great.

67 GMC

This is a tough one since you can get it to run. I looked through your post and didn't see much testing on the fuel side. How about checking fuel pressure on the rail and also the leakage test? I would think it would run rough though. Did you recently run down your gas tank to empty? If so, change the fuel filter while you're at it.

In my experience, if it's CPS or other electrical issue, the engine dies like you've turned it off suddenly. Your Jeep sounds more like a slow death which makes me think of vacuum or fuel leakage or obstructions.

Keep posting.