HELP: Weird 89 cherokee starting/running issues

So I had what (hopefully not) appears to be a lack in judgement buying an 89 xj. The truck is badass- its got a lift, sway bar and 33 inch tires so you can understand what compelled me. It has a new motor however, apparently out of an 94.
The truck had obviously been driven hard, I managed to get it for super cheap because i got it the day the last owner was moving, unfortunately for this reason i never got a test drive.
Enough talk- onto the problem
So the truck has no problem starting (assuming the battery is charged) cold. It even idles smoothly. However, when I put in in reverse, the truck stalls/dies and then won't start up again. I have a bit better luck putting it in drive, but at best it won't run for to long.
I have replaced the spark plugs (which were shot!), also i checked the rotor on the distributor cap and it seemed alright.
-I haven't checked the fuel pressure as i don't have the right tools, however when i pressed the valve some shot out, so that should be good enough?
-I tried adjusting the TPS, it idled a little higher however it didn't seem to have much effect, however when i reved it backfired a bit (oh shit)
-When it is idling, if you rev it it comes back down slowly (like the throttle body/sensor is sticking?)
-When trying to start it hot, it will sputter/fire every 5 seconds or so, perhaps not all cylinders are firing?
-I still haven't changed the oil, its really dirty

ANY ideas would be appreciated! Hopefully you guys have experiance with this.

Other background- My DD is a 92 4dr 4L, I want to be able to tear it up with this rig on the weekends!
Please help me out!!! Thank you in advance.

I assume it ran okay after the engine swap? Just wondering if this is related to the swap or a new problem? The last person I saw who had stalling in reverse discovered the bellhousing bolts were loose. Might want to crawl under there and check that.

Also have a good look at the ground strap that runs from the back of the valve cover to the firewall. That tends to rot out and when that ground goes away all kinds of things start failing. Sounds like he kept the original engine computer and harness (you mentioned adjusting the TPS). CPS sensor could be marginal too.

As far as i know, the engine was running great after the swap, however I don't know how much to trust from the A****LE that sold me the rig.

Thanks for the tip about the ground at the back of the valve cover, hopefully its that simple (though I doubt it!)

When you say the bellhousing, do you mean where the tranny connects to the engine? Bellhousing sounds kind of generic, though i'm pretty sure I know what you're talking about.

I should also add that it randomly shot out oil yesterday onto the ground, it hasn't leaked any oil since... perhaps thats evidence toward the bellhousing issue??

The jeep obviously has numerous problems, but I can fix the other ones quite easily if I can just get it to run consistently. Thank you so much for your help!

check and see if the computer got wet.

To check spark-pull off a wire will its running and hover it over the plug, listen to it fire it should be a very fast popping noise

to check for fuel-find the PSI line, make sure everything is out of the way and not hot, get a rag and hold it against it and pull the line off at the fuel rail. Crank it...if fuel is flowing well then it LIKELY should not be a fuel issue. Make sure to check spark before fuel.

Also maybe anyone else can elaborate on this...If it starts popping and backfiring that should be a timing issue...

W/ how inconsistent everything seems...to me it really sounds like an electrical problem, computer style.

and go under it and just for poopy and giggles check out the transmission thoroughly like make sure the lines aren't kinked, make sure the connectors are good and clean make sure everything is tight, and next time it runs check the fluid level in the trans.

I mean if your intelligent enough you should be able to see if that thing has been hacked together or not...if its hacked I would suggest getting out from underneath the car in more than one way...know what I mean? You may run into a lot more grief than it is worth

First thing is to determine what you actually have. The 94 was OBD-I, the 89 was a Renix, different intake, throttle body, TPS, computer, CPS, flex plate, tranny computer, wiring harness all were different, so which ones did he keep and which did he upgrade is the first thing you need to determine.

Also check that the vacuum line from the intake to the MAP sensor is still connected and not leaking.

Cold versus hot symptoms may be related to the CTS or MAT sensors (air and coolant temp). Bad O2 sensor can cause erratic running. They can all be tested with an ohm/volt meter, multi-meter, compared to factory specs, posted here.

The MAP and TPS are usually key to backfiring during acceleration of deceleration of engine throttle, but a dying O2 or CPS can this too.

jcolindunn said:

When you say the bellhousing, do you mean where the tranny connects to the engine? Bellhousing sounds kind of generic, though i'm pretty sure I know what you're talking about.

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Yes, I meant where the tranny bolts up to the engine block.

Ecomike said:

First thing is to determine what you actually have. The 94 was OBD-I, the 89 was a Renix, different intake, throttle body, TPS, computer, CPS, flex plate, tranny computer, wiring harness all were different, so which ones did he keep and which did he upgrade is the first thing you need to determine.

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Any tips on how to identify this?

As for the engine, I know it used to run really well, however all these problems have arrised from a combination of abuse, poor maintenence and sitting for the last 2 months.

Oh, i suppose i forgot to mention that the truck had been sitting for 2 months.... i've got a feeling he XXXXed it over a bit over on may long haha, if any of you guys live in alberta you probably know that May long weekend is the craziest offroad party of the year.

Also any good tips for beginners dealing with this electrical/mechanical shit? This is really my first project, i'm 19 and never really had to do more than an oil change and the odd tune ups here and there.

Thank you all so much for your help, this has at least given me a couple leads.

The Renix TB has a bolt on flange for the intake hose, 92 and up use a hose clamp. The 92 up TPS won't work with the Renix computer. As for stalling, I'd check the Idle Air motor passage and see if it's clogged, the pintle moves, etc.

Most of the 92 up sensors don't interchange with Renix IMHO as Chryco re-engineered a complete OBDI setup, vs the Renault Bendix engineered system earlier. Even the fan control is different - it sends a varying volt signal for the computer to switch the fan, Renix uses a on-off thermo switch.

It will sort out, and then you can understand if the prior owner achieved DSPO status.

Here she is right here... cross your fingers for me:eeks1:

UPDATE:
So my buddy and I did some research and a bit of tinkering with the TPS. We loosened it, etc. to no real gain, except higher revs when idling. Simply to experiment we decided to take it off, and see what difference that made. In all our wisdom, we attached it upside down.... the jeep now starts up faster then my DD, only it idles at 2000 rpm. The truck can also be put into gear reverse AND drive without stalling!! This doesn't sound to bad, only this has put the engine off time! now when i put it in gear, the engine knocks! We reinstalled the tps right side up, and it was back to the original problem of no hot starting!
The inconsistent starting appears to be a result of the tps at this point, i'm picking up a new sensor today. Logically, this makes sense to me as the TPS has something to do with mixin up the air and fuel properly i believe. Any thoughts on this?
Hopefully if i'm real lucky the new tps will solve all the starting issues, and hopefully the timing will go back on to get rid of that damn new engine knock, and pigs will start flying and we can all go for a free ice cream and unicorn rides...
-I have changed spark plugs/wires/rotor
-I haven't got around to changing the oil yet, logical next step.
-Still haven't got in to the CPS, will check it after new TPS, hopefully the TPS will resolve the issues.

EDIT: I should also add that there is no more backfiring, unless you put the TPS back on right side up.

Any thoughts on the new knocking/timing issue? It would make sense to me if its cause the TPS is buggered because its obviously sending all the wrong messages to the computer, just wondering if you guys had dealt with that before?

Oh and BTW the engine and parts are mos def 94

I'm gonna have this truck purrrrrring all day long with your guy's help! thanks everyone.

Sorry, but what is buggered is your testing method. You can learn anything useful by installing a TPS backwards, except how to recognize when someone else has installed it backwards.

You need to buy and use a multi meter (Volt and ohms tester). Get an old style analog meter, it works better on certain tests like TPS noise testing.

On 94 versus 87-90 Renix, where is ECU located? Did you find it? It could still be a Renix-HO hybrid with the older computer and older flex plate and older CPS.

Is it automatic or manual?

What does the TPS look like? the 87-90 and 91+ TPS is completely different.

When ever you make changes like you did (backwards TPS install, new TPS, and so on), you need to disconnect the battery for a while, to clear the junk out of the computers memory or you will continue to get irrelevant, odd, useless running results while the computer slowly, painfully replaces lots of old bad data with new sensor and performance table data that it uses to run the engine.

Ecomike said:

When ever you make changes like you did (backwards TPS install, new TPS, and so on), you need to disconnect the battery for a while, to clear the junk out of the computers memory or you will continue to get irrelevant, odd, useless running results while the computer slowly, painfully replaces lots of old bad data with new sensor and performance table data that it uses to run the engine.

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Oh well thats good to know, at least I unhooked it. I just picked up the part and I'm about to go change it, wish me luck. Thanks for the other advice about the testing method, I just haven't got around to buying a voltmeter yet.

Ecomike said:

On 94 versus 87-90 Renix, where is ECU located? Did you find it? It could still be a Renix-HO hybrid with the older computer and older flex plate and older CPS.

Is it automatic or manual?

What does the TPS look like? the 87-90 and 91+ TPS is completely different.

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I'm gonna check the ecu now. The TPS is definitely the 91+, and its an automatic transmission.

So last night i replaced the TPS. The good news is that the engine now starts right up all the time now. It even fires faster then my DD xj.

the bad news is that there is now an engine knock under load. When the truck is put in drive/reverse, the engine has a nasty knock every 4 or 5 seconds, anyone know what this might be from?

The engine knock wasn't there when she wouldn't start hot.

91 up TPS isn't adjustable and if you do have it on a RENIX system then you are not getting signal to your tranny computer either how about some pics of the engine compartment clean preferably and people could help you identify these things much easier, no offense but it defenitly sounds like your completely unfamiliar with the way of the cherokee, i've just finished my own RENIX/HO swap but it sounds like someone really screwed your up...SO LETS HAVE SOME PICS. And yes you need a volt/multi meter with the RENIX especially, test test test is the key or you'll have the whole system replaced and it will still run like $h*!. There should be a flat 3prong and a square 4prong plugs where your TPS hooks to your wiring harness if you still have the pre90 injection and there should be acomputer above you gas pedal for the engine and another (smaller) on the back side of the lower dash panel on the passenger side this is for the AW4 auto Tranny. If you dont have these and the computer is buy the air box then maybe he swaped every thing wiring and all, BUT i dougt it that is way harder of a job. AGAIN PICTURES, VOLTMETER, AND PICTURES. Also the TPS 87-90 should be adjusted at 0.800 volt output. Hope that helps and HELP US HELP YOU.

I thought I had an engine knock and it turned out to be a cracked exhaust manifold. with the backfires and other stuff it has been through latley it may be that or a exhaust gasket ,,, or any other number of things (most will mean you are screwed) hope your knock is a simple fix.

Loose torque convertor bolts can also cause a knocking noise. Something to check if the engine was out recently. They should be installed with locktite.