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Last cry for help

FastEddie505

NAXJA Forum User
Location
Michigan
1999 xj 4.0l

New 02s up and down. Stream
When cold the jeep will run so bad and have a miss at idle will through a code for to rich will have a cyl 3 misfire code all new parts on spark side and new tps iac cts , injectors , header, as soon as it switches from open to closed loop it won't miss and everything will smooth out, will get a few backfires in intake if it gets loaded up changing gears (auto) . Not a clue where to look next I did put a pcm from a 98 in it not sure if the open loop is that much different but worth mentioning.
Thank you in advance
 
1999 xj 4.0l

New 02s up and down. Stream
When cold the jeep will run so bad and have a miss at idle will through a code for to rich will have a cyl 3 misfire code all new parts on spark side and new tps iac cts , injectors , header, as soon as it switches from open to closed loop it won't miss and everything will smooth out, will get a few backfires in intake if it gets loaded up changing gears (auto) . Not a clue where to look next I did put a pcm from a 98 in it not sure if the open loop is that much different but worth mentioning.
Thank you in advance

Problem was there before all the new parts? Fuel pressure look correct? 96-99 all used the same injectors and fuel pressure, so shouldn't really be any mismatch there. I don't know how long the PCM waits to go into closed-loop mode, but heated o2 sensors should be warmed up and working in less than a minute.
 
1999 xj 4.0l

New 02s up and down. Stream
When cold the jeep will run so bad and have a miss at idle will through a code for to rich will have a cyl 3 misfire code all new parts on spark side and new tps iac cts , injectors , header, as soon as it switches from open to closed loop it won't miss and everything will smooth out, will get a few backfires in intake if it gets loaded up changing gears (auto) . Not a clue where to look next I did put a pcm from a 98 in it not sure if the open loop is that much different but worth mentioning.
Thank you in advance

Where did the 98 pcm come from? Why did you replace it? Sounds like a computer problem to me but I'm no expert. Have you checked cylinder 3? Fouled plug? A slight leak could cause it to miss and it might get better as the engine warms and coolant escapes the cylinder. You could post this on NAXJA or cherokeeforum and I'm sure one of those wizards could help you much better than i.

Sent from my SM-G930V using Tapatalk
 
The PCM's are very specific on application!
 
The new pcm came off a part out xj never did see it run but I replaced the oem pcm because of high idle problems. I did change #3 plug was rich on plug most likely because of miss, oil is not milky and not burning coolant out of exhaust, no cracked valve springs and sea foamed it twice to clean valves . May try to patch up old busted pcm and swap it out. Weather has finally broke in Michigan so it's a race to get it up and running.
 
Do both PCMs share the same part numbers? -- If not then they are not a match and can't just be swapped around without being re-programmed


Done a compression test to rule out something physically wrong in the engine?

I chased a miss for awhile, ignored the guys who told me to compression test it -- Should have listened, had a stuck exhaust valve -- thing threw all sorts of codes
 
any cracks on exhaust manifold and between the o2 sensors? cracks will make it think its running lean and will dump more fuel. Then when the exhaust temps raise it the metal expands and closes the cracks so its not letting in air in
 
Checked compression and I'll good there , looked at the exhaust and intake again for cracks and found nothing. The pcm I believe are different numbers and I'll have to look into that. I'll start there also need a new throttle body I have air getting sucked in around the butterfly valve shaft.
 
Checked compression and I'll good there , looked at the exhaust and intake again for cracks and found nothing. The pcm I believe are different numbers and I'll have to look into that. I'll start there also need a new throttle body I have air getting sucked in around the butterfly valve shaft.
 
Start at the beginning, actual data required, no random guessing allowed. What Check Engine Light Trouble Codes are, or were, present ? Have you inspected the O2 sensor heater fuses ? You installed NGK/NTK O2 sensors, and not Bosch sensors, right ? Were the OBD engine sensors with genuine Jeep parts or with cheap Chinese clone parts ? Have you tested all the sensors or have live data from your OBD-II scanner ? Have you inspected and tested the sensor wire harnesses for cut insulation, melted insulation, and failed wire splices ?
 
What Tim said, plus check for vacuum leaks. They can cause rich codes. Failing map sensor hose or failing map as well. Eyeballing a vac leak is not how you do it. Smoke machine or use carb cleaner.
 
What Tim said, plus check for vacuum leaks. They can cause rich codes. Failing map sensor hose or failing map as well. Eyeballing a vac leak is not how you do it. Smoke machine or use carb cleaner.

Ok can we get into this a little -- make it a teaching moment

What is the proper way to test for a vacuum leak without a smoke machine?

I've always thought that you sprayed starting fluid around the vacuum lines while engine is running -- if you had a leak the engine would race -- Is this correct?

Starting fluid, propane from an unlit torch, brake cleaner -- What else works?

Doesn't brake cleaner harm plastic and rubber?
 
I made my own smoke machine with a small air compressor paint can and a cigar. Only smoke that came out of anywhere was around butterfly valve shaft on side of t.b. p0122 p0123 p0172 . Some will come and go but almost always is the too rich code and tps low voltage code . Checked harness for .5v and it had .6v with key off. I watch the live stream of both my o2 on my obd2 scaner and they seem to be doing well , I had replaced my tps about 2 1/2 months ago
 
Again, genuine Jeep OBD parts and NTK O2 sensors, or whatever crap Chinese clone parts AutoZone or Advance sold you ? It really does make a difference.






P0122 JEEP - Throttle Position Sensor Circuit Low Input

Possible causes

•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection

P0123 JEEP - Throttle Position Sensor Circuit High Input

Possible causes

•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection

P0172 JEEP - Fuel System 1/1 Lean Fuel System Rich

Possible causes

•Faulty front heated oxygen sensor
•Ignition misfiring
•Faulty fuel injectors
•Exhaust gas leaks
•Incorrect fuel pressure
•Faulty Mass Air Flow (MAF) sensor
 
Again, genuine Jeep OBD parts and NTK O2 sensors, or whatever crap Chinese clone parts AutoZone or Advance sold you

Tim, I'm relatively new to XJ wrenching. Have 98 xj and FSM which I'm reading. Could you elaborate on the foregoing a bit for me please.

1. Jeep OBD (on board diagnostic parts?) - what parts fall into this category?

2. What are Genuine Jeep parts? Mopar? Sources? (Really dumb question I know.)

2. I recently replaced TPS (had code read at AdvanceAutoParts) and and been running horrible. Great now. Would you recommend replacing with genuine jeep TPS (keep advance unit as emergency spare)?

Thanks for any response, sorry if derailing thread too much.
 
Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy genuine Jeep engine sensors and top quality replacement parts. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.

OBD -I or -II sensors are the ones monitored by the engine computer. Genuine Jeep parts can be purchased on-line from Dealerships, either from their website with a 30% discount, or on eBay and Amazon. Don't fall for "OEM parts" in the description, make sure they are Mopar parts.

Only use NTK O2 sensors, never use Bosch.



You could test the TPS, but I would return it or throw it out.

TPS failure may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

The TPS is mounted on the throttle body. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage) that represents throttle blade position. The sensor is connected to the throttle blade shaft. As the
position of the throttle blade changes, the resistance of the TPS changes. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5volts. This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:
-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction witha slow engine return to idle speed symptom.
 
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OBD -I or -II sensors are the ones monitored by the engine computer. Genuine Jeep parts can be purchased on-line from Dealerships, either from their website with a 30% discount, or on eBay and Amazon. Don't fall for "OEM parts" in the description, make sure they are Mopar parts.

Only use NTK O2 sensors, never use Bosch.

Thank you very much for your reply.

I got it. I want my Jeep to be as reliable as possible so MOPAR it is. Ordered a MOPAR TPS off ebay. Twice the price of Advance.

Ignition section of FSM has nice description of all sensors in ignition system linked to PCM.

I have three dealerships that are convenient to me. I checked their websites. All have form that must be filled in to order parts and then they will reply. Seems cumbersome and I did not see any mention of 30% off. Do they all offer the 30% discount?
 
Not to go OT, but an IAC Motor/Slug will cause rich idle, stumbling, flooding at idle, lean idle, misfire codes and a host of other ignition/fuel delivery related codes.

Once up to speed, the engine will operate normally.

Most people don't think of this part, but if you go to the junk yard, they are all missing.
 
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