AFM / MAF

[Prizam]

I have a 400 with some idling issues. I have cleaned out the stepper motor and given everything a good going over. Including the trumpets etc...

I have also cleaned out the AFM with some electronic cleaner (Its good stuff, used it on lots of other MAF's before)

It seems to run a little rich and idels a bit too high, and also takes too long for the revs to reduce after a little blip on the throttle.

I figure the next thing to change is the AFM. The TVR part E2036 (i think) is a bit pricey and probably not that great.


Is there another part i can use with the standard lucas system?

[KateV8]

There will be people along who know far more than I do but the symptoms you descibe sound very much like an air leak around the plenum or trumpet base, especially when you said it takes too long for the revs to fall back to idle speed. Try spraying something like brake cleaner around the plenum base while the engine is idling and see if the revs increase. As I said, people on here like Blitz etc will be able to help with this one, idling issues are common enough.

[fausTVR]

Again no expert, but I wonder if the ECU is receiving the correct signal re coolant temp (ie low reading) and so is opening the stepper too far (raised revs) and over fuelling (making rich) to compensate. If you have the bible handy, it may detail what the output from the ECU temp sender should be.

[Sardonicus]

I would be inclined to check the Lambda probes are switching/behaviour before going any further but try to borrow/codge an ECU Mate(box of tricks) alternatively Mark/Blitzracing http://classifieds.pistonheads.com/classifieds/par... does the interface cable for the Rovergauge software and as far as I am aware the software is free to use if you want to do it with the Laptop/PC instead http://code.google.com/p/rovergauge/ Whatever you do don't just start throwing money at changing various sensors etc (spot diagnostics) as this can often be painful/costly and the chance of getting a quick fix is unlikely anyhow

Edited by Sardonicus on Thursday 27th December 09:38

[Prizam]

KateV8 said:

the symptoms you descibe sound very much like an air leak around the plenum or trumpet base

I did have all this apart and re-sealed it, will double check for leeks again today.

fausTVR said:

I wonder if the ECU is receiving the correct signal re coolant temp (ie low reading) and so is opening the stepper too far (raised revs) and over fuelling (making rich) to compensate. If you have the bible handy, it may detail what the output from the ECU temp sender should be.

I think the temp senders are correct, although when on the run on a motorway the coolant temperature goes down to just under 60.

I think this is a common issue with the sender for the gauge rather than the sender for the ecu?

Sardonicus said:

I would be inclined to check the Lambda probes are switching/behaviour before going any further

I did remove the pre cats recently...

[blitzracing]

It should never run rich unless the ECU has lost control of the mixture, and the ECU may have flagged an fault internally. The AFM can cause it to run rich if its output goes higher than it should (this does not always flag a fault however). You can do a basic DC voltage check on the AFM on a running engine, details here:

http://www.g33.co.uk/fuel_injection.htm

BTW the AFM is a bog standard Range Rover / Land Rover part- a lucas 5AM. You dont need to pay TVR prices. A new one from Lucas was about £200, second hand nearer £25. Watch out for nasty Chinese replicas on Ebay!

Edited by blitzracing on Thursday 27th December 12:23

[Prizam]

Interestingly, i went out today and disconnected the AFM and started the engine. It was a little slow to respond to throttle but seemed to run much the same. Suggests that the AFM is buggered?

Either way, i reconnected it, and still the same. Disconnected the plenum air supply hose and still the same.

I guessed the ECU had fallen in to some kind of "limp home / standard map" setting.

Any who.... an old school ECU reset seemed to fix everything.

Disconnect the battery for an hour, connect it again. let it idle without any intervention until the fans cut in. Turn it off for 15 mins then start up again and go for a drive.

Seems to have fixed most of the idling issues, though i still think it might be ~ 100 RPM too high. Need a proper RPM tester to be sure.

[blitzracing]

Running without the AFM will make the ECU run on the throttle pot reading for the required fuelling, and flag a fault code in the process. The ECU needs no more that 30 seconds disconnect to reset it- It takes around 2.5 mins at idle at at least 90'C to get the ecu to re-trim the fuel mix, so I guess your method with the fans would have been enough. Simply re plugging the AFM may have been enough to clear the basic issue as the connections are not that good. As for RPM, have a read through Steve Heaths ECU mate manual- it covers the idle control in depth.

http://ecumate.com/docs/Ecumate%20inst.pdf