How did the problem start? Is this after a repair? Verify and test ohms engine, body,battery grounds. Seems to be trying to correct a very rich condition. Fuel old? Fuel pressure? Air intake restricted? OEM spark plugs? compression test?

 

- Initially, the Jeep started shaking, buckling & knocking under load above 2000 RPM - say 25-30 MPH.

- All sensor signal and isolated ground wires averaged around 6-7 ohms (good). Main engine grounds look good.

- Fuel was fresh at the time and near empty. Recently added 5 gallons of premium (~7 months later).

- Fuel pressure was in spec (engine off). Fuel injectors upgraded to Bosch due to original injector body leaks after cleaning. (Lots of grime/tar build-up probably masked that problem). Leaks/fire hazzard prevented further testing. The leak-down test seemed ok at the time. Pressure did drop slowly but discounted due to the injector leaks.

- No intake restrictions. No apparent exhaust blockage based upon no rattling/odd sounds AND rear CAT temp being ~100 degrees higher than the front temp. (Other threads said the front would read hotter if the CAT was blocked, etc).

- Using Jeep NGK FR5-1 7252 plugs, not Champion. Jeepster reviews indicated these worked just fine. NGK designed these specifically for NGK V-Power Spark Plug is designed specifically for '87-02 Wrangler YJ and TJ 2.5L(and 91-98 4.0L) engines. Anyway, it's highly unlikely these would cause the problems I'm experiencing.

-Compression: As I recall, all readings after the top-end rebuild varied no more that ~15% with the lowest above 140 PSI, probably more. Engine has around 97K miles. Cyl walls looked good - no discoloration or material wear marks. Still see lots of cross-hatching.

Any further thoughts?

Thanks. -Steve

 

If has miss at 1000 rpm on 2.5
Check if Injector harness has a pair cross up

Typically people have an urge to put 3 on 4 and 4 on 3

Since intake valves really time fuel entry not injectors it still runs OK but tends to have a miss around 1k rpm

Sent from my SM-S902L using Tapatalk

 

Already checked twice. #3 YL/WT agrees with FSM diagrams.

Thanks. -Steve

 

Looks like you hit everything I was thinking. I'll grasp at other thoughts, Check temp at each exhaust port/manifold. Inspect O2 and crank sensor wiring for chaffing or burns? crushed exhaust pipe/muffler? could you have lost a cam follower? Pull each plug wire one at a time, does any one plug wire NOT affect running? Cam and crank timing ok? Timing chain slip? Brake booster or vacuum, but that would cause a lean mixture. But maybe it's trying to adjust? Check for carbon tracking in distributor cap and rotor. I'm out of ideas, kinda hard when you can't hear or see it. A very good contact cleaner is Deoxit. Oil based lasts a long time, just an FYI as you had some connector issues. After more thought pinch off the vacuum line to the power brake booster, massive vacuum leak would cause hard starting and went pedal feathered would cause more fuel as the ECU would read throttle position.I'll try to lookup more info on the 2.5L.

 

Check temp at each exhaust port/manifold.

I'll do this when I get a chance... couldn't hurt, but I seriously doubt anything unusual here given the history above.

Inspect O2 and crank sensor wiring for chaffing or burns? crushed exhaust pipe/muffler? could you have lost a cam follower? Check for carbon tracking in distributor cap and rotor. Brake booster or vacuum, but that would cause a lean mixture.

No problems here.

Pull each plug wire one at a time, does any one plug wire NOT affect running? Cam and crank timing ok?

All wires, plugs, cap & rotor all new. I can double check wire resistance and plug gaps again. I doubt this is the problem as misfiring is minimal if non-existent at idle. Problem seems to be flaky wiring/senor signal related - especially when trying to increase RPM.

Cam and crank timing ok? Timing chain slip? But maybe it's trying to adjust?

Cam timing controlled by ECU. CPS and CKP are working. Chain has minimal slack per rotating crank back and forth at damper bolt. If it had more, I'd have pulled the cover to check further. However, I will put #1 cyl at TDC and check rotor position just to be sure. While at it, I'll double check spark plug gaps and wire resistance.

A very good contact cleaner is Deoxit. Oil based lasts a long time, just an FYI as you had some connector issues.

I used CRC's QD Electronic cleaner. I'll apply again at all sensor connectors - especially the coil and CPS. These wires had lots of grime but were clean at the contacts.

After more thought pinch off the vacuum line to the power brake booster, massive vacuum leak would cause hard starting and went pedal feathered would cause more fuel as the ECU would read throttle position.

I'll try again. I did spray all the vacuum hoses with cleaner which had NO effect on RPM's, etc. Also, all hoses are clamped or wire-twisted.

Who knows, it's always possible something went bad after earlier checks.

Thanks. -Steve

 

Steve
Has this motor ever had head gasket problems? If any coolant/antifreeze got to the CAT it is done. And the fact that the problem started during a big load on the engine, I would disconnect the front of the CAT and hold the pipes a part with an old screw driver or chisel. The CAT with this rich of mixture should be smoking hot like 2000 to 2500 degrees.
I have also researched that aftermarket CPS are problematic, only Mopar ones seem reliable. Don't know personally.
ECU loose mounting screws can cause intermittent grounding issues.
I have had rodents chew/eat the engine wiring harness, requires a very bright light and lots of patience, really SUCKS.
Do you have the service manual for your jeep? If so I would check that every engine compartment ground is in fact there. Then clean, test, reinstall.
Sorry I can't help more but long-distance troubleshooting is a crap shoot at best.
Let me know when you find it.

 

Steve
Has this motor ever had head gasket problems?
ECU loose mounting screws...

Nope

Steve
The CAT with this rich of mixture should be smoking hot like 2000 to 2500 degrees.

As mentioned earlier, CAT & muffler seem fine - no dents, sounds, rattle, smoke, temps good (3-400 degrees if I recall). Don't see the need to pull apart.

Steve
... aftermarket CPS..

Nope. Mopar CPS. Replaced all other sensors BUt the CPS and oil pressure.

Steve
Do you have the service manual for your jeep? If so I would check that every engine compartment ground is in fact there. Then clean, test, reinstall.

Yup, all look good. Haven't removed/cleaned engine block ground. Can't hurt I guess.

UPDATE:

Ran a few quick tests again today.

- Brake vacuum assist is good.
- RPM COULD go above 2500 RPM this time...
- The same 3 Error codes thrown again after wiggling the main harness.
- Went away after more jiggling. but knocking continued.
- Once Knocking/Bogging started, IAT temp jumped, spiked to 240.
- Other readings also went nuts/varying as usual.

- While checking exhaust manifold temps, # 3 seemed cooler than the others. Earlier temp readings were better before knocking/bogging. Could be due to timing advance and other OBD-II reading fluctuations... There was even a brief period of NO RPM or timing advance readings! This seems to suggests there IS a wiring problem somewhere.

The only connectors I didn't check were the two branching off of the main harness into the bulkhead/firewall. I was unable to separate them (corrosion??) and am wondering if this might be the problem source.
Sprayed some contact cleaner into them as best I could. Will repeat and try to separate them for further inspection.

-Steve

 

A friend's 2.5L YJ was doing something similar to this; ended up being a section of wiring harness close enough to either the exhaust manifold or downpipe to partially melt insulation. Sometimes it would jiggle enough to short itself and start acting up, sometimes it would settle in a good spot and run for a while. Took him months to find the bad spot. It sucks to do, but you should really try to trace yours end to end. Either visually, or by touch when you can't get an eyeball or mirror on a section. Can't rely on multimeter readings if it's just bad insulation, as you're never sure when it's touching something it shouldn't.

 

I opened up the harness nearest the exhaust pipe and tranny. Dirty wires but didn't see anything overly suspicious. Heading to Home Depot tomorrow to get non-adhesive hi-temp tape to wrap a few wires just to be sure and close it all up after cleaning the wires off for a final inspection.

I'll probably pull the harness and open it all up from just before the fuel rail behind the back of the engine as that's closest to the exhaust manifold.

Sure wish I could get the harness junction connectors pulled apart where they head into the bulkhead. They are just plain stuck. Nothing I tried would free them up. It would sure make inspecting the main harness a LOT easier non to mention being quite suspicious at this point.

-Steve

 

Steve,

Rock auto has a lot of the connectors, much cheaper than Jeep. I think your on the right track. I don't know how much Jeep/Chrysler charges for the engine harness but it might be worth pricing. I usually end up soldering and heat shrinking the problems, but I can solder to NASA standards. I have the feeling the junction connectors are stuck because the are corroded together or melted. Making headway.

 

Saved the Rock Auto link. Unfortunately, they have the 2 stuck harness connector parts that I may need...
Wish I could get them separated! Applying another round of contact cleaner today... after getting some tape.

Agreed - soldering is the best method. I have Hakko's SMD and Soldering stations and a Aoyou desoldering gun.
Great to have - using these to rewire my entire boat to the pilot house console. Love then switches and breakers (OCD).

What a PITA this problem has become! 8 months of on/off searching for a resolution which has gone nowhere.
I'd take it to the Jeep dealer for an hour of diagnostics if not for the wiring harness being suspected!

Thanks for your suggestions. Have a great day. -Steve