Various running problems - what to try next?

[Dr Mike Oxgreen]

Cool, thanks Mark.

I'm planning to have another play when I get home this evening if it's not raining.

I'll repeat the static MAF test using RoverGauge's percentage display rather than dicking about with a multimeter, then I'll disconnect the ECU to reset the fuel trims, plug the laptop in and set it into logging mode and go for a drive to get it fully warmed up, then leave it idling for a while to see what the trims do. At some point I'll have a look at a plug as well to see if it's been running rich.

[Dr Mike Oxgreen]

Okay, this evening's results... Interesting!

I couldn't get a MAF reading using RoverGauge with just the ignition on - it simply said 0%. I only got a reading with the engine running.

I disconnected the ECU for a while, and sure enough the long term trims returned to zero. I then went for a drive to warm it up, at the end of which I let it idle for a good 5-10 minutes. The long term trims settled on -26% and -12% for a while, but then seemed to change their minds and gradually changed to +1% and +16%!! Slightly odd behaviour perhaps, but certainly not showing a tendency to head down to -100%.

When idling hot, the MAF hovers about 31%, which equates to 1.55V - a little on the low side for a 4.5 I'd have thought. Shouldn't it be more like 34 or 35%?

The short-term trims were lazily swinging back and forth between negative and positive, perhaps with a slight preference towards the negative, but definitely touching into the positive from time to time.

So now I'm not sure whether I've got a problem or not. With my multimeter, I definitely saw the MAF take 10-15 seconds to settle down to about 0.35V. The long term trims were both -100%, but it's almost like the ECU has now snapped out of that and they look a bit more sensible. The short term trims are now slowly oscillating both sides of zero, albeit with a slight preference for the negative.

I'm inclined to leave it be for a while, and keep observing to see if the long term trims end up back at -100%. Or should I splurge £200 on a new MAF on the basis of the evidence I've seen?

I did (hopefully) capture a log of my drive, so if I can be arsed I'll do a plot of the short term trims once Mrs Oxgreen has finished using her laptop to do the Waitrose shop - I think we'll see an asymmetric oscillation now, where previously I think they were always negative.

Edited to add: Based on Mark's comment below, I shouldn't splurge £200 on a MAF...

blitzracing said:

ist a bog standard Range Rover Classic part - a Lucas 5AM, so it would be worth checking Range Rover suppliers as well.

Edited by Dr Mike Oxgreen on Monday 5th October 18:33

[QBee]

eBay ref 181722363714 would seem to be it for £46

[Dr Mike Oxgreen]

QBee said:

eBay ref 181722363714 would seem to be it for £46

That says out of stock, unfortunately.

There is this one, though.

Are these eBay items just cheap crap that will fail within a week or two though?

[N7GTX]

It says it has a 12 month guarantee. Looks like a Chinese copy so very unlikely to be correctly calibrated but if it works then its a cheap part.

An old thread but may/may not be of use?

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Dr Mike Oxgreen]

Well, I've decided to go for a new MAF anyway because it's something I've considered doing as a long-term routine replacement. And I decided to order from a TVR specialist parts supplier to reduce the possible doubt over the quality and/or compatibility. It's £195 + vat, but at least I know it'll work.

So there just remains the question of whether to replace the throttle pot, which could be the cause of my "dead throttle syndrome", although it hasn't happened the last few times I've driven the car.


Edited to add: Oh, fk it, I'll order a throttle pot as well. But I will order it from the LandRover supplier that Mark linked to a while ago so it's "only" about £70.

Edited by Dr Mike Oxgreen on Tuesday 6th October 13:07

[blitzracing]

If the trims are reasonable, then the AFM voltage is OK at idle, so not much to worry about there. As for Chinese copies, Im far from convinced they are heat stable, so I would not trust one in a TVR engine bay.

[N7GTX]

This is a simple way of explaining fuel trims, both short and long term that might help understand what is happening with some suggestions as to what the problem may be.

http://www.easterncatalytic.com/education/tech-tip...