for many years my $500.00 d1 has baffled many shops and lr pros.
here is where it stands today.

I can recreate the issue and resolve it (4 times in a row) in the following set of circumstances.

Perfect running vehicle until i drive it either at 65-70 for 30-50 miles OR i drive is in town staying in 3rd as to keep rpm's at least 2500-3500 for a few miles.

it sets over night then will start fine the next day but will not run above 2000 rpm's. It is as if the ECM has info that prevents normal operation even though fuel trim, TPS, MAF and other OBDii data shows no issues other than retarded timing advance (result of stall condition) and occasionally throwing a p0340 (camshaft CIRCUIT issue) I have spent several hundreds on wire harness inspections and no issues found.

IMPORTANT... The fix
To get the truck to get back to normal operation I have to remove the battery Leeds from the battery and short them together for a minimum of 5- 15 minutes and then all is well.

When it is in the failure state I have swapped with another ECM and get the same condition, and visa versa. When it runs well and i swap ECM it continues to run well. So I assume that excludes the ECM as a culprit.

the only sensors I have not replaced are the 2 knock sensors and I really do suspect what they may be doing to cause this problem...

SOO.... please all you OBDii brains... what can you add?

Thanks

 

Oh one more thing.. the last shop it was in stated that he saw no indication of the timing chain stretching (on his data collection) and no unusual sounds from the front of the engine

 

That ECM doesnt have a constant feed. You could unhook it and stick it on a shelf for a decade and it wont lose a thing.

Unplug the vss and see if that makes a difference. Also check both the cam and crank sensor wiring near the plug yourself.

 

"That ECM doesnt have a constant feed. You could unhook it and stick it on a shelf for a decade and it wont lose a thing. "

Of course you are right, so what I am doing must be discharging a capacitor (or something) because if I do not let it sit with the battery cables shorted it will not recover from it's running issues.. the question is - what values am I changing and why is it needed?

The VSS was never a suspect since it will not run past 2000 rpm even while sitting in park, but ... what can it hurt to try.. I will try that.

I have inspected the wires at the crank sensor due to the heat and the last shop checked at the cam sensor..

I also had them inspect the flywheel for metal debris that could bugger the circuit but all looked well.

Next?
Thanks

 

Maybe I wasnt clear. There is no need to discharge the capacitors since the ecu basically disconnects itself from the battery automatically about 30 seconds after key off. Its unique to GEMS, most stuff doesn't do that

Maybe also check every reluctor tooth on the flywheel. I think youre on the right track there

 

VSS was my first thought as well based on your note of "retarded timing advance" which is also what happens when the VSS goes bad and the ECM believes the truck is traveling above a specific speed (I can't remember exactly what that speed is but it is something >100 mph.

I'm not entirely confident this is the problem, but unplugging the VSS should have no effect on the performance of the truck other than losing the speedometer. If your other symptoms go away you will have isolated the problem.

Bottom line, unplugging the VSS is free and easy so give it a shot. Nothing to lose.

 

I was not present when the shop pulled of the inspection cover so who knows how deep or far they went. I may have to get dirty yet.

If teeth are missing I should get another code I think, but still wonder what could upset the cam sensor circuit.

Robert, what do you think is causing me to think the shorting of the battery cables is getting it back to normal? Could I be getting errant voltage on a ground that has nothing to do with the ECU? And shorting it clears it off the ground.. I have seen that on home cable systems from hot chassis conditions. Of course that raises the question of what sensor can hold voltage?

I think that the cam sensor ground wire is only shared with 2 temp sensors.

Thanks again - both

 

I think the unhooking the battery is in your head and unrelated. Unless you have an obd2 scanner plugged in that is not dropping communication when the engine is off keeping the ECU from unlatching the power relay. Most of the generic ones actually do this when speaking the rover's obd2 protocol (iso 9141), so there's that.

I still think its the crank sensor wiring. Remove the sensor and look at as much of the wiring as you can, clean it up, and put it back. The code is the symptom and not the fault. If the crank sensor stops feeding the ECU data but the cam sensor throws a signal as usual they will appear out of synch. Automated engine diagnostics were fairly new when this ECU was designed, it's trouble codes are far from fool proof.

 

"I think the unhooking the battery is in your head and unrelated. Unless you have an obd2 scanner plugged in that is not dropping communication when the engine is off keeping the ECU from unlatching the power relay. Most of the generic ones actually do this when speaking the rover's obd2 protocol (iso 9141), so there's that."

Robert you have hit something here... I do and it is a cheap scangauge so as you can imagine, I do not think the 4 (now 6) times it ran fine after the "shorting out" is just in my head. so ..

Can you expand on the unlatching of the power relay? To me it sounds like if I disconnected the ScanGauge it will run fine after i shut off the ignition and it sets overnight. I can confirm that is not the case.

After i confirm the wires again at the Crank Sensor and the VSS I am planning on running a group of 4 wires through the firewall and use paper clips to back probe at the ECM, using a multi-meter at the wheel to see what is dropping while under driving loads - the Crank or Cam sensor ... is that a safe idea? (assuming safe driving conditions)