I recently got my newly overhauled 4.0 running like a top! Then out of nowhere it starts loosing power on take-off. Then, started idling high (1100-1200 rpms). I noticed the TPS reading on my REM II engine monitor dropping (went from 12% to 10, then on down as low as 6%) while I was stopped at a red light with my foot off of the accelerator and brake pedal depressed.
Because of this I changed out the TPS to my spare. When I started it back, the rough-running, lose of power that I was experiencing on take-off before was now occurring all of the time.
I pulled the battery cables and replaced the ECU with a spare - no change.
I re-installed the previous TPS - no change.

Looking at the REM readings as I've been driving, seems that the Ignition Advance was a bit high on acceleration (up to 42 degrees).
Checked timing with timing light at idle - firing at about 7 degrees BTDC
Dial Vacuum gauge shows around 15 Hg vacuum with a shaky needle.
Fuel pressure is good (31 with regulator / 39 regulator unplugged)
EGR transducer and/or EGR solenoid may be defective (vacuum test IAW manual), but still ran the same when by-passed.

***QUESTION*** - Could Crank Position Sensor cause timing to be off enough to make it run like this, or would it just be start/no start situation? CPS is relatively new with few miles on it.

 

Here are my readings at IDLE (800 rpm), 2200 rpm and around 2580 rpm.

800 RPM IDLE


2200 RPM



2580 RPM

 

Retorque intake manifold bolts and check for vacuum leaks there.

How does it run with the TPS disconnected?

 

How clean and shiny are the ground connections at the dipstick tube stud?

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.

All the components listed below ground at the dipstick tube stud:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition Control Module, Fuel Injectors, ECU main ground (which other engine sensors ground through, including the Oxygen sensor, Knock Sensor, Cruise Control and Transmission Sync signal. All extremely important stuff.

 

I will retorgue again, checked it maybe two months ago by spraying starter fluid around manifold-head connection to see if it would surge, nothing then, but one of the exhaust manifold bolts was loose. I'll go back and check them all.
Runs the same with the TPS disconnected. Could it just be a coincidence that it started running like crap while I was swapping pit the TPS?

 

I refreshed all of my grounds, cleaned down to metal the dipstick connection and replaced the connectors (cut wire about an inch back from the end and crimped in new wires & connectors with shrink tubing)
I refreshed all connectors in the engine bay with connector cleaner, added 4-gauge cable to braided ground location and hooked the other end to manifold.
I'm thinking maybe next I need to run through Tip#5 and check the sensor wiring?
I want to eliminate the C101, but I dont have a soldering gun that is fast enough to effectively solder the joints while they are installed. QUESTION *** - Will this work using connectors and shrink tubing?

***QUESTION*** - The engine harness that runs across the top of the engine with injector / sensor connections had fallen onto the top of the engine near the exhaust manifold. It got pretty hot, but on inspection nothing was melted. Is there anything that this could have done in the harness that I can't or didnt see? Since there was no melting of fusing of wires I kept looking).