My never ending problem engine that does not run above certain rpms has taken another odd turn.

History is is that this 98 d1 with 178xxx will run good and has run good for me but most of the time it stalls, misfires and will backfire and die if you try forcing it to run above the engines's determined limit. that ranges from 1300 rpm to 2500 rpm. Cold or warm, all usual suspected causes and all advice from this forum has been addressed. Even an ECU swap. Cats are 6 months old and I baby her to avoid damage to them. (city driving only and never forcing it past the first few misfires. This is a hobby car not a daily)

The only codes are the expected multiple misfires, catalyst damage from the misfires and an occasional p0340 indicating a sensor circuit failure.

Both the cam and crank position sensors have been replaced and the wires show no signs of damage or being compromised to the eye...

Only things left for me to get to are fuel pressure test (tomorrow) and coil test that I have not researched yet.

Here is my question....

While listening to the engine at around 1900 rpm and watching the ultragauge for any reveling info I noticed that while the tac on the dash was showing correct, my ultragauge was showing in the 800's.
I let off the gas and it recovered and read correct until i revved it up to the stalling rpms again and recreated the same odd reading.

This seemed to be a symptom of the running issue as it will not happen all the times as it stalls on me but ...... Considering the Camshaft Position Sensor Circuit Malfunction

Do you guys with deep knowledge on these things think that the odd behavior is indicating I should concentrate on that p0340 and start hunting for wire harness issues or do you think there are more basic issues like fuel or spark preventing high revs?

The p0340 had popped up at times while it ran good and it seems on these forums that hard misfires and revving issues are not normal symptoms when that code appears.

Thanks all

 

Will the engine run smoothly above 2500 rpm while parked? I'm trying to eliminate the VSS.

 

nope it does not. wish it was that simple but thanks

 

Update..
Fuel pressure test was 50/50
stayed steady and normal at idle and under load with no spikes or drops when "goosed"
BUT the pressure drops to 10 in less than 5 min when car is not running but key is in the run position..

I thought this might lead to a leaky o-ring on some injectors thus causing the engine to try adjusting but my long term fuel trim in showing the opposite. It is in the high positives..

Any ideas will be appreciated, my next challenge is to find a vacuum leak even tho a quick spray of starter fluid resulted in no change to the rpms at idle.

anything?

 

Fuel Pressure Regulator, it's at the end of the fuel rail, drivers side. It's a candidate for that loss of pressure while parked. It's not a cheap part. The issue with the RPM threshold is probably the Throttle Position Sensor. May have a "flat spot" on the segments. That is a cheap part. You can test that with a DVOM across two leads of the sensor, put on Ohms and watch the meter, should climb or fall (can't remember) with a smooth sweep. If it falls off suddenly and then picks up again then it's a chunked part.

 

Great info.. 2 quick follow ups

1)Wouldn't that throw a code?
2)can that be variable as well as intermittent?

Thanks

 

It's a Rover first and foremost. Yes a faulty TPS should toss a CEL according to the Rave but that's book and not real world. One member was having issues with his truck not starting and thought it was the TPS but found out that the TPS and the Fuel Tank Pressure Sensor are wired in series together.... it was the tank pressure sensor which is located on top of the pump housing. It's a 98 AES like yours. Easy to check the physical condition of sensor/wiring by removing the cargo space cover in middle of floor. His was obvious, the wires to the sensor had corroded off. That too should throw a code but it didn't on his truck. Rovers are right up there with the Enigma Machine as far as troubleshooting especially when well aged and climate worn. Electrical skills give you an edge. I found many faults through gut instinct and a ton of military and civilian electrical/electronics training. I'm a pipe fitter, welder, electrician, ammonia refrigeration, boiler, waste water technician in my current job...... I don't get paid enough...... Certs in boilers, welding, refrigeration and possibly in waste water plant. Know anybody who needs my talents or a husband?

 

wish I could help you with that last part but ... between a rover and a Japanese wife (both having their issues) i am treading in the deep end myself.

I am going to put a meter on that TPS tho, cant hurt

Thanks again