beserk

Hi there all..

Coming to you from Australia, I need help with my jeep, and the search has gone international.

Have owned 3 xjs over 10 years. Theres alot of jeep hate in Australia, but I love the things.

My current issue has me completely stumped, and unless your a complete jeep enthusiast, i doubt anyone else could pinpoint the answer. You need to know about crank position sensors, that sometimes you need to wiggle the shifter to turn it over, or bash the dash to get the speedo working haha. Xj specific stuff.

Anyway. My issue.

1996 RHD 4.0 lt auto. 200,00KMS.

I have a horrible miss Im chasing. Its pretty damn specific. Ive search the entire web, and these forums, and still cant pin point it. I need xj specialists.

So the miss starts once to operating temp.
When cold, or hot, starts fine.
Idles fine cold or hot.
When started cold, and running normally, i leave my house, boot it to the floor, and it runs as it should. As the symptoms start, I can plant my foot halfway, and there is power. As I go to 3/4 or flat pedal, there is LESS power, like it is bogging down. Ease back to half pedal, and the power comes back and increases. After about 5-10 mins, it starts missing badly, and gets worse quick to the below standard.

Symptoms are:

Foot flat - It completely pauses, before backfiring out the exhaust, stuttering bucking, no power at all, just bucking like a pig.

Foot planted half way:
Surging forward and backwards. No backfiring, but lack of power still.
Consistant surging forward and back.

Light acceleration :
No symptoms. On a flat road cruising along at 90kmh, no miss, nothing.
As soon as you start putting your foot down, you start the surging, and going into the above 2 categories.

Once its got to this stage and I limp it home, Planting the foot in neutral, it will only go to 2000-3000 rpms, at stutter and backfire and wont go any further.
But if I rev it smoothly and a bit slower, it well rev through the entire range.
Plant it : popping, backfiring sputtering.
Slower acceleration : climbs entire rev range.

Just to screw me and a buddy that were trying to diagnose it even more....
Once we got it bucking on the road, got it home, planted foot fast and it was sputtering and backfiring only to 3000rpm....I shut it off for 5 seconds.
Turned it back on. Symptoms gone. Plant foot and screams through the whole rev range. Take it back out on the road, after 5 mins, symptoms return. Come home, plant it....sputtering, backfiring. Turn it off for 5 seconds.....gone.

I'm pulling my hair out on this, and need help desperately.

This is a list of things I have tried so far. I currently own 6 xjs and a zj.
4 of the xjs are parts cars. As much as i worry swapping in older parts, id prefer that than cheap chinese crap. Ive also changed multiple times to completely try and rule them out. If a replaced part was also faulty, i may expect slightly different symptoms.

New Crankshaft sensor x3 ( now have a genuine one in there)
New camshaft sensor x2 (oem)
New leads x3
New sparkplugs x 3 ( have brand new champion copper in now)
New upstream oxygen sensor x 2
New air intake sensor ( cleaned both sensors and mount point)
New Map sensor ( brand new Trident)
New TPS sensor x3
New fuel pump x 3
New fuel filter
New coil x3
New cap and rotor x3
New coolant temperature sender sensor x2
New PCM
New injectors and rail ( thoroughly cleaned )
New MAF sensor
Drained entire tank and refilled.
Removed throttle body and cleaned entire thing
manifold and throttle body cleaner used
Fuel injector and octane boost run through fuel
No symptoms of heatsoak, I run twin electric thermo fans, have hood scoops and rear of bonnet raised. Its cool as under the hood. Engine temps on the gauge are good, never overheats.
No cracked head symptoms, no oil in water, no water in oil, no overheating, not losing any water, compression seemed good.
We tried to measure fuel pressure with a tyre gauge as its all we had, got about 40-45psi.
Alternator and battery seem got, pumping about 13.7-14.0 volts at idle.
Contact cleaner in all connectors
Redid all ground points.
No apparent vacume leaks.
No CEL.

As you can see, ive gone full parts cannon on this thing. More like parts machine gun.

NOTHING, changed any of the symptoms.



Went and bought an OBD2 reader today and cleared stored codes, as we had been disconnect a heap of stuff. Performed more drives and tests, and got it to misfire. Engine is throwing no codes on obd2 reader or the 3 turn key trick.

Im literally out of ideas at this point.

The reason I am so desperate to get this fixed, is I have my young son coming to stay with me for xmas. I only get to see him 4 times a year because my ex wife moved him 1000kms away

But ive got a roof top tent, and he loves camping and 4wding with me, and he has been banging on to me about it on the phone. Ive been at this thing for the last month solid, trying to remedy it before he comes.
I've got 1 week left. I went 10 hours straight on it yesterday, without stopping, without eating.

The miss is still there....

I feel I'm so close. I dont think its a catastrophic failure. I dont think its something to complex. But Im lost.
Anything you guys could suggest would be greatly appreciated. I'm going to paste on a few other forums, as I need all the help I can get with 1 week to go.

So in a nutshell.

Jeep misses, backfires, stutters loses power.
Only does it once warmed up after 10 mins of driving.
A turn off, turn back on restart will fix problem, for another 5-10 mins.
Very light throttle, barely any missing at all, no symptoms.
More the pedal is pressed, worse symptoms get.
Starts and restarts fine
Idles fine.

I apologize that this was a bl@@dy novel, but i really need help, and I know from experience of searching the web, as much information as possible is best.
Personally I think there is a few specific symptoms and signs that differentiate it from all the other threads Ive researched.

But the main reason is so that in a weeks time, I can put a smile on a small boys face, by letting him steer it on the beach, and taking him camping at xmas.

Sincere thanks in advance.

doublechaz

When it misses, is it a specific cylinder, or all of them randomly?

With the parts cannon fired, I would say it is likely an adjustment thing rather than a broken sensor.

I had a Subaru that acted somewhat like what you describe that turned out to be a jumped timing belt so the cam off. My Jeep is an 88 so I'm not sure what yours is like mechanically. 88 has a thing like a distributor that needs to be aligned correctly for spark timing to be right. There is also an adjustment to the crank sensor on an 88 to get it lined up with mechanical top dead center. Do these things translate over to your 96?

I expect someone with more specific knowledge for the OBDII generation will be along soon.

beserk

Thanks for the reply.
When missing, it sometimes sounds like it is running on 5 or less cylinders.
But im getting no codes on the key trick, or OBD2 reader.
Spark plugs all looked okay and the same when I replaced them.
As far as im aware, timing cannot to changed on a 96. It is set when installing the distributor
Also crank sensor has no adjustment on a 96, which im pretty confident is OBD2.
At first I thought it was intermittent. But then I realised it had a pattern the more I test drove it.
I wondered about split wiring, or a short. But figured it doesnt do it on corrigated roads, over bumps, round corners.
Then also the fact it had a consistent pattern doesnt line up with an intermittent wiring short.
My last guess was it was happening once engine components got to temp. As i Can get the temp gauge up pretty fast by leaving fans off from cold, and although the engine reads hot on the temp gauge, it doesnt do it...after 10 mins, it starts its misfire, and it doesnt matter how could i get it running with twin fans, the issue persists.
Which led me to believe it was engine components getting to temp and hot, not the actual engine.

But when I realised that turning it on and off again cures the problem, was kinda left feild. That if a component was failing at temp, that turnng it on and off again, that part would still be at exact temp. Only thing I can think there is that turning it off, resets the computer, temporarily removing whatever is causing the issue at start up. But it appears again pretty quickly in 5-10 minutes.

Im wondering if closed loop/open loop is an issue. I just did the key trick, and its throwing a 21 which is 02 sensor, which I've had before. I've tried 3 different sensors with no change. As far as im aware its only the upstream sensor on a 96 that controls air fuel ratio. The downstream 02 sensor only monitors cat operation, doesnt affect fuel trims, only throws a cel light.
I've also disconnect the upstream sensor and run it, thinking it would stay in open loop, but no change at all, same symptoms. Disconnected temp sensor, no change, same symptoms.

Forgot to mention i checked cat, and its not blocked either.

beserk

A bit more info from today, when data streaming with the OBD2while driving, we were able to watch a few things. The main one was open/closed loop and also short term fuel trims, and long term fuel trims. It shows live data from a few other things, but im not sure where to start.
I wonder if I need to research where those parameters should be, and try to check them while driving.

Im going to uppercut myself in the face if its something like a Bl##dy fuse.
( have checked and replaced all fuses and relays BTW)

cruiser54

Ever monitored fuel pressure while these shenanigans were going on?
Ever verify, inspect, clean and refresh every engine harness ground there is?

Here's the one for the fuel pump.

cruiser54

beserk

Is that a rear ground point for the fuel pump, inside the cabin in the rear? You could definately be onto something there.
A few weeks back, I was snatching someone out of a deep puddle. The strap wouldnt reach, and I had to dump my rear end in the puddle also.
I was not happy, as the rear carpet in the boot got wet, and I had to dry it for days.
It is quite possible that maybe water got to that point, and I have a bad earth......
This is why i came to the US forums for advice! That is something I have totally overlooked, and could possibly be the culprit

I havent got a fuel pressure gauge, and the scanner I have only gives short term fuel trim, and long term fuel trim, in percentage figures.
Quite frankly, they are all over the place, so unsure how to make sense of them yet.
All engine grounds Ive undone, cleaned and checked. Ive never known about the rear one.
Many thanks.

cruiser54

We'll help you out even though you drive on the wrong side of the road and your toilets flush backwards. Not to mention Vegamite..... I eat that stuff. Only person in the US that does......

beserk

Haha cheers buddy.

I've ran jeep xjs over here for over 10 years. Theres so much jeep hate in Australia. They all love Nissan Patrols, and toyota landcruisers over here.
But the look on there faces when a jeep that cost the price of their tyres alone, outwheels them is priceless. Let alone when I have to recover one.
It makes it all worth it.
There i am in my sub $2000 xj, towing a $40,000 4wd up the beach, or out of a bog. I get a kick everytime.
I dont think many aussies have actually driven jeeps let alone an xj. They just hate on them.
After wheeling one, and seeing how capable they are, i can totally see why they are one of the favoured offroad beasts in america.
So jealous of some of the setups I see over there. I just ordered rear shackle location brackets from your neck of the woods, the postage near killed me, but no one in Australia sells them.
Its for my upcoming build of another bone stock 96 I have sitting here with 150,000 kms on the clock.

Again, thanks for your help. Thats why we are allies , because australia depends on you hahaha

cruiser54

I have owned at least 6 KL60 Patrols.

agreen

Let's try this again. (I accidentally scrolled down too far to a "related post" and wrote my reply to a year old thread.


(Cut/paste to the right spot: )

What helps me is using a Bluetooth OBD2 scanner and an app called "car scanner". You can datalog what your sensors are seeing in real time. I found an intermittent TPS issue this way.

I got an ELM327 scanner for about $10 US, and the app is free.

Here's a picture of my TPS being funky. Notice how at one point while driving it just wouldn't go below about 17%. This TPS was relatively new, but it wasn't a Mopar TPS.

4.3L XJ

So this happens only when warm, not when cold?

beserk

correct, only when warm, after about 10mins.
Cold, its as good as gold

4.3L XJ

OK mate, here is what I think is what is happening. When the engine is started when cold, it runs rich independent of what the O2 sensor says. Once the engine temp sensor indicates the engine is warm enough, the electrical voltage from it signals the ECM to start running off the data, or voltage, from the O2 sensor. I think the data is wrong ro bad new sensor, aggravating I know. The same thing happens when you have shut it off for awhile. It starts up rich and switches to the O2 sensor.

Having said that, here is a question you need to answer. Is there a crack in your exhaust manifold. Common problem and can mess with the results, though it often makes them run rich instead

Shumpa@aol.com

My Sons 2000 Sport appears to run rough during our summer months intermittently.
it appears to be fuel line fuel vapor locks as the fuel line WAS close to the hot block.
moved the fuel lines within the engine compartment. No more rough running wen hot.
just a thought as it appears you have rebuilt the machine.
steve