Down on power and running hot

[steve-V8s]

98 Griff 500, 224 cam, ACT trumpets, Bosch injectors, MA remap. Has been running fine but now seems down on top end power and is running (according to the gauge) about 5c hotter than normal.

It idles as normal (all lumpy and ragged) pulls about the same low down but runs out of steam at the top end. The fuel pump was making a lot of noise so changed that along with the filter and air filter. Have examined the plugs and plug leads, compression still seems OK and there are no unusual noises.

I hope to get a gas analyser on the car tomorrow to see if that gives any clues It still has pre cats so I am beginning to wonder if they are breaking up.

Any ideas anybody ? I am competing in the car on Sunday and need to be fairly swift to retain 2nd place.

[dnb]

fuel pressure regulator getting tired? The gas analyser should show this...

[steve-V8s]

I agree low fuel pressure fits the bill.

[Bastian]

If that fuel reg doesn't cure your issue check the airflow meter. Never had issues with my griff which has a new bosch airflow but had major issues with my BMW M5....no power above 4000 rpm .....turned out to be airflow meter issues in the end.

[350Matt]

could possibly be ignition timing as well, remember to check with the vacuum hose disconnected

Matt

[steve-V8s]

As suspected the analyser showed it was running very lean at both idle and fast idle also with fairly high Hydrocarbons. I have been meaning for some time to tidy the AFM leads where they get bent over by the bonnet so unplugged the lead and checked that each one went somewhere, which it did. Plugged it back in and tried again with much more normal results. Sadly wiggling the lead failed to reproduce the fault I will however remake the connector to be safe.

The only thing I did wonder is the initial test was with the bonnet closed and the later one with it open so the AFM was probably cooler. Anybody know what the AFM reports ? is it just mass air flow or does it also report air temperature ? My guess is two of the wires are supply and two are the output. I know it passes a fixed current down a heated wire and measures how much it is being cooled by the passing air, but I think (assume)it is a differential system so ambient should not change the reading.

[spend]

AFM's report volume flow & temp to adjust for mass of air I believe

Dave

[steve-V8s]

OK, so if it is reporting too hot will that make it Lean or Rich ?

[OscarT]

If it thinks it's running hotter than it actually is it will weaken the mixture IMO.