GEMS Hesitation/misfire at 2000 rpm

Hi all - the rangie's ('98 4.2 Gems) been behaving itself for a while, but over the last few days its developed a reluctance to pull from about 1500 rpm.

While it's cold it's fine, pulls smoothly right up the rev range, but as it warms up, if I feed in the power gently while cruising between 1500rpm and just over 2000rpm, there's no acceleration - no deceleration either - but clog it, and the power comes back in, sometimes dropping a gear but not always.

Given that it's temp related I'm guessing that it's fuelling rather than ignition.

I've not had time to connect the Nanocom to check for fault codes, but is it likely to be the MAF? TPS? CTS?

Any pointers would be appreciated . . .

TIA Alastair

Update - plugged Nanocom in - no faults logged.

These were some of the readings with it idling and warm:-
Loop status - CL.USE O2 (both banks - not sure what this means)
Long term fuel trim is 20 on both banks.
Short term fuel trim is 11.25 on bank 1, -5 on bank 2, but again these fluctuate as it runs

Pre cat O2:- 2.12 on bank 1, 0.62 on bank 2 , but these fluctuate.

Adaptive FMFR 0.32 not sure what this means either . . .

Airflow rate is 4.898

I've reset the adaptive values and it seems to run OK but I've not been far enough to see if there's any change.

Any thoughts?

Thanks - Alastair

Anyone?

odyssey said:

Anyone?

Click to expand...

Shhh. The GEMS experts must still be in bed.

CL.USE O2 means the feedback system to monitor exhaust emmissions and fueling information is running CLosed loop and it is Using O2 sensors to make fuel adaptions....

I would start looking at the IACV and he bypass screw settings....an incorrectly set IACV will cause running and starting issues!

Think the IACV should be set around 15-30 steps at idle....

Read the attached information it is Morgan based but the control system and engine is the same!

http://www.gomog.com/allmorgan/GEMS/GEMSbyPoole.pdf