Long story short, I got given a 90 XJ Limited with a 4.0 and a mopar competition cam that needed a new computer. Put a new ECU in, turns out it needed alot more than that. Ran like garbage, backfiring through the intake, low idling, sputtering while accelerating, as welm as slow accelration. so we did some basic maintenance, new sensors, had to do some cooling system repairs as well as delete the bs Bendix 9 ABS brake system, cause we had literally no brakes. (If you ever have to do the conversion, just set it on fire)

Ran better, good enough to drive it from its grave down to my house, but the backfiring issue was terrible. Tinkered with it, replaced some more sensors, gave up and took it to the shop. Blew my timing chain on the way.

So we redid the timing set, new chain and gears, ran SO MUCH BETTER. Normal idling, good acceleration. It still backfires (not as bad) but only until it gets up to operating temps.

Ideas? Suggestions? Bear with me, I am new to the forum, and this is my first jeep. ✌🏼

Parts replaced

MAP Sensor
TPS sensor
CPS Sensor
Timing Set
O2 Sensor
Distributor
Plugs, Wires
Bendix 9 abs delete, WJ booster installed
Ignition Coil system

 

I’m no mechanic but...

Is it possible that the cam is the problem? Not saying that it is, just wondering if its reasonable to consider it...

Also

Have you thought of replacing/testing the coil?

I’ve heard that if it backfires through the intake then its likely a timing/spark issue. If it’s backfiring out the exhaust then it’s a carb or air-flow issue.

So maybe even the distributor was not installed properly or the timing is off.

Maybe the crank position sensor?

I’m guessing that you’re fuel injected so if your backfiring out the tail pipe then you may want to consider injectors and/or their wiring or even a new catalytic-converter, I’ve been told that they can cause weird drive ability issues too.

I’ll watch to see how it unfolds...

Stay with it.

I was given a 95 Cherokee with a serious spider infestation and a rabbit had chewed through the wiring on the top of the motor. Took me a few months but its my daily driver now. It still needs work but I’ll keep at it till it’s where I can drive it coast to coast and camp and fish along the way. Im in no rush and I’m enjoying the process.

Be patient, it’ll get there...

 

That's what I replaced that i forgot to mention, the ignition coil system is all new because we had a no spark issue and just threw parts at it, it turned out to be the crankshaft position sensor. (CPS).

I suppose it's entirely possible that the Cam could be the issue, but I know it didnt run like this before my buddy parked it. I just didnt really want to go that far in, I also have no idea how to diagnose that. .

As far as the distributor being off, it only goes in correct or 180 off. We put it in wrong the first time and it ran like crap.

Not giving up, I've been daily driving her with no problems I'm just pretty sure backfiring isnt good for the intake, even if itits only occasionally.

 

Compression tested, engine is making a healthy 150 across all cylinders.

Checked for vacuum leaks, I couldnt find any. Checked plug wires, all good.

It only backfires through the intake until it warms up, then it's mostly fine. Still have no idea what the issue is.

Possibly a lean fuel issue?

 

Put the Parts cannon away for a while.

Go to www.cruiser54.com and perform Tips 1,3,4,5, and 12 before doing anything else.

 

Wall of text, but alot has happened since I've posted here and the Jeep has now become undriveable. Shop doesnt know what's up, I dont know what's up.

Put down that parts cannon, went amd did all your tips. It did not fix my issue, so I replaced the only thing I hadnt replaced yet, the fuel pump. While I did that my buddy replaced a leaky power steering hose and tried to wash the engine a bit.

Once the pump was in, I went to drive it home and the issue was a million times worse. Non stop popping through intake, redlining rpms, no shifting and not going over 10mph. had to limp it home. Reset the ecu, amd it now shifted, but still had little to no power and was popping back through intake.

I got frustrated and put it in a shop nearby that does Renix jeeps all the time. The guy pulled dizzy and reindexedd with your tip (the only thing I didnt do) and he called and said it fixed the problem.

I informed him it was running pretty decent before we changed the fuel punp; minis the backfiring through intake before warmed up.

He didnt beleive me and was shocked. Said he was gonna take it for a few more drives the next day and make sure it wasnt an intermittent problem. I didnt hear from him for a whole week, until today.

Dizzy did not fix the problem. It ran decent for a good minute, then started backfiring through the intake all kinds again. He hooked up to a mt2500 and read the data, voltage tested everything, getting voltage to where it needs to be. Everything he can tell it's a healthy jeep, but boy oh boy is it undriveable. He didnt charge me anything because he couldnt figure it out. It's now back at my place.

so my question is...what do I do now? Is it possible maybe water got into my TPS or IAC? I hear they are super water sensitive..but I figure if they werent working it would show on the data? Literally every way I can think of says this Jeep is healthy, but once you try to go it just doesnt work.

 

Washing the engine is the first thing that screams "water is somewhere that it should not be". It should have dried up, unless something got wet and fried. Start going through everything and drying it out, use dielectric grease wherever possible.

Ok, just a question or two.

Will the Jeep still idle properly? Just starting it, not driving at all.

The ECU you replaced it with, did you get it from a reliable source (known running vehicle) or a junkyard where it was sitting?

 

Could be a faulty pump right outta da box. Test fuel pressure.

 

I am wondering about the ECU also.

 

Put the other one back in then.

 

As far as the ECU, it came brand new. I bought a new one from rock auto. I've cleaned and dried everything out, and it's been gone through at the shop as well. WHEN it was running and idling, it would idle inconsistent but after we went through all the connections cleaned and DE'ed em, the idle smoothed out.

Fuel pressure is good at the rail, perfect psi even when I unplug the regulator.

I say WHEN it was running, because when I just drove it home from the shop it started up no problem. Parked it, Went to crank it over , and Now I have no spark.

I still have the old ECU, but I can guarantee it is bad. The jeep went for a swim before I owned it (years ago) and fried the ECU which is the whole reason it got parked in the first place.

 

I wonder about the coil and ICM getting dunked in water and corroding. Ever take it apart like in Tip 3?

 

We did clean the ICU connectors and coil connectors when we replaced the coil a few months ago. It has not been done since my buddy sprayed the bay with a hose. I will get right to that and report back on if it fixes my no spark.

It's just weird cause it literally worked 3 hours ago

 

Unplug the cPS and plug it back in.

 

Lost daylight and didnt get around to pulling the coil, but I pulled the throttle body on a hunch and found this. It was not noticeable until I pulled the body completely.

is this a symptom, or a cause of the backfire? It being a cause makes sense to me, once the gasket warmed and expanded from being at operating temps it sealed a bit better and the backfires would stop. Once the gasket blew completely the backfires made it undriveable.

I'm not entirely sure if that makes sense though correct me if I'm wrong.