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99 Running very rough

jeffreylane

NAXJA Forum User
Location
Memphis, TN
Forst off, thanks for taking time to read this. I have read around the forum for quite some time now, but like most forums I read, I don't really post much. Warning, this is a long post, but I don't want to waste anyones time being redundant an things that I habe already tried.. I have a problem that has been whipping me pretty good lately. We have a 99 XJ 4.0 (auto) that had been running fine. Now it is barely running. The problem started about a month ago. We live inside the city, so this vehicle was rarely seeing over 45mph for quite a while. There was a roar in the rear (bearing or driveshaft), so I took it out on the interstate and took it up to about 75mph for a few miles, a few times (speeding up, then lettinh off to 55) to try and diagnose the roar. After exiting, I noticed that it was stumbleing at yhe stops. It seemes to get worse in the few mile trip through town to the house. After getting home, it idled terrible, but would smoth out ok while dribing until letting off the gas. I checked compression. All cylinders look good and pretty close. Clockspring had recently went bad, so after research, I unplugged it. No change. When I say no change, there was no change at any point I changed a part. It has however gotten progrssively worse along the way. I checked the TPS and it was out of range (guessing shorted from the bad clockspring). Only run "slightly" better after relacement, but now it test within range. Swapped the map sensor, cam sensor, crank sensor, no change. Went throgh fuel injector wiring, replaced the wires, as some were meltrd together, but I think just the insulation. Did noid test, everything fine but #3. About a year ago #3 driver had an internal short to ground I guess, and stayed grounded i stead of pulsing. I simply jumpered the #3 ground over to #5 and it ran fine. Been running fine over a year now. All other injecttors are getting a pulse and a steady 12v. I am getting codes for tps over and over voltage, and 1,3 and 6 injector. It is running extremely rich, as the new (1 week)spark plugs are dark sooty black just drom being cranked diagnosing in the driveway. new fuel pressure regulator, although a cheap one, but no change at all. Fuel pressure guage is very erratic, with needle fluctuatung very quickly between about 45 and 50, and then motor hesitages more (already running rough) and it quickly fluctuates between about 41 and 51ish. No loss in coolant. Oil smells and looks fine. Exhaust is very strong with white smoke, but no smell of coolant. Maybe Fuel pump assembly? Can valves make pressure fluctuate and have good compression? This one is stumping me, and any help would be greatly appreciated.



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O2 and/or temp sensor.

I would not have gone cheap on the regulator/filter.

TPS + over voltage could be the clock spring.


I would go over your grounds/cables.
 
Solve the TPS codes. Only buy genuine Jeep engine sensors. Running extremely rich makes one suspect an exhaust mainold crack/leak, or the O2 sensors. Only buy NTK O2 sensors. If you have 49 psi, +/- 5 psi, of fuel pressure, the fuel pump is OK.
 
O2 and/or temp sensor.

I would not have gone cheap on the regulator/filter.

TPS + over voltage could be the clock spring.


I would go over your grounds/cables.
Thanks for the replies.
Would o2 aensor and temp sensor come into play on a cold crank? My understanding was that it ran in closed loop until it was up to operating temp, then used the info from the o2 sensor. I may be wrong on this though.
Both tested out fine with a meter.
I went cheap on the regulator/filter because it I don't figure this one out, all the good parts (suspension, axles, etc) will be pulles and I'll scrap the rest. Trying not to sink a ton of money into it guessing. I was just looking for any type if change with the cheap one, and there was no change at all.

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Solve the TPS codes. Only buy genuine Jeep engine sensors. Running extremely rich makes one suspect an exhaust mainold crack/leak, or the O2 sensors. Only buy NTK O2 sensors. If you have 49 psi, +/- 5 psi, of fuel pressure, the fuel pump is OK.
I still get the TPS ober/under codes, but TPS seems to check out fine with a meter. Smooth electrical curve. Sitting about 17% at idle. Unplugging o2 sensor causes no change either. Is the O2 sensor info being used on cold starts, or inly after it is up to operating temp?
I have looked over the manifold and don't hear any leaks, but I will look over it again after work.

It seems like it is just dumping way too much fuel. Took injector rail off, turned on pump and I did not have any leaking injectors or dribbles.

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Thanks for the replies.
Would o2 aensor and temp sensor come into play on a cold crank? My understanding was that it ran in closed loop until it was up to operating temp, then used the info from the o2 sensor. I may be wrong on this though.
Both tested out fine with a meter.
I went cheap on the regulator/filter because it I don't figure this one out, all the good parts (suspension, axles, etc) will be pulles and I'll scrap the rest. Trying not to sink a ton of money into it guessing. I was just looking for any type if change with the cheap one, and there was no change at all.

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Two schools of thought here....

Some rely solely on meter readings, sensor will read fine cold in your driveway, problem persists in real-world conditions.

I rely on symptoms, what is the engine actually doing.


Erratic fuel pressure is a problem, injectors will flow at 41lbs differently than at 50lbs.



If you are scrapping this one anyway...............may not want to chase this one down.
 
Two schools of thought here....

Some rely solely on meter readings, sensor will read fine cold in your driveway, problem persists in real-world conditions.

I rely on symptoms, what is the engine actually doing.


Erratic fuel pressure is a problem, injectors will flow at 41lbs differently than at 50lbs.



If you are scrapping this one anyway...............may not want to chase this one down.
Thanks. Trying to avoid scrapping it. It's a pretty decent XJ that was a daily driver up to this problem. It will hurt to not figure it out and have to scrap it. It is long armed, locked, geared, etc etc.

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Thanks. Trying to avoid scrapping it. It's a pretty decent XJ that was a daily driver up to this problem. It will hurt to not figure it out and have to scrap it. It is long armed, locked, geared, etc etc.

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You state that the XJ is rarely driven over 45mph, then you take it out on the hwy, my first guess is a dead spot in the TPS.


I'm still guessing, temp and O2.

Temp is cheap, I'd start there.
 
Inspect and test, use the results to diagnose, then buy parts. Cheap parts are cheap for a reason, and a fair number of cheap parts are faulty right out of the box.

All the OBD engine sensors can be easily tested with basic tools. Guessing the root cause, and/or throwing random parts at an undiagnosed problem seldom cures the problem, and it costs lots of money. The CHECK Engine Light trouble codes almost always point to the root cause of the symptoms, or will provide enough data to consider any alternate causes for the symptoms. ALWAYS post the CEL trouble codes. Keep in mind that you need to inspect and test the sensor wire plug, the wire harness, and any related fuses or ground connections. If the PCM cannot see a sensor, it reacts the same as if the sensor is faulty.
 
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I did swap the map sensor out with 0 change. It tested good with a meter, but swapped it anyways out of frustration. No change at all. So far, other than the codes, the only thing not testing out as normal is the erratic fuel pressure gauge.

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You state that the XJ is rarely driven over 45mph, then you take it out on the hwy, my first guess is a dead spot in the TPS.


I'm still guessing, temp and O2.

Temp is cheap, I'd start there.
When you say temp, are you talking about water temp or IAT? The water temp hand on the dash seems to function ok, if that means anything.

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Inspect and test, use the results to diagnose, then buy parts. Cheap parts are cheap for a reason, and a fair number of cheap parts are faulty right out of the box.

All the OBD engine sensors can be easily tested with basic tools. Guessing the root cause, and/or throwing random parts at an undiagnosed problem seldom cures the problem, and it costs lots of money. The CHECK Engine Light trouble codes almost always point to the root cause of the symptoms, or will provide enough data to consider any alternate causes for the symptoms. ALWAYS post the CEL trouble codes. Keep in mind that you need to inspect and test the sensor wire plug, the wire harness, and any related fuses or ground connections. If the PCM cannot see a sensor, it reacts the same as if the sensor is faulty.
I did test all the sensors before changing anything. I also hate to parts shotgunned without testung I am just running out of options. The TPS was originally out of range, being at about 70% at idle. After replacemant, the voltages and curve all look correct. I have also run new wiring to all 6 injectors, since I had a p0201, p0203, p0206 code. Also run new wires to water temp sensor, iat sensor, map sensor and tps, all with no change. This all started about a week after clockspring messed up, which is now unplugged (both plugs) with no change.
I can usually hold my own on a 4.0. I have a tube chassis crawler with a 4.0 that I built, cut down harness etc. Just,finishing up the swap in our yj (4.0 head and injection and auto tranny swap into cammed 4.2 jeep, cut down harness etc. I am way more familiar with obd1 though, and probably would have would have had it diagnosed in 30 min had it been obd1.

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