The V8 Owners Forum -

I have got my 3.9 with flapper (recon. engine on legacy efi) installed in the LR110. After a bit of troubleshooting, she now starts absolutely on the button and runs very smoothly but at around 2-3,000 rpm (cannot be precise on this as I only have half an exhaust and I bottle out very quickly!). It doesn't hunt, just holds highish revs - remarkably stable.

Before I go and investigate I would like to make sure I have all the bases covered for this fast idle. So can I run it by you:
1) Throttle potentiometer - to check correct voltage.
2) Would AFM send incorrect flap open signal? Are there any tests for this?
3) The guy who had it before me in his rangie had trouble running on petrol (it has lpg injection as well), which I am pretty sure was down to the loom which I have now rebuilt, and the top of the AFM had been removed at some stage. I seem to recall there being an idle screw setting in it. Could a garage have messed about with this when trying to fix the problem before and caused the problem - if so where is it and what does it look like?

Can't think of anything else, but suggestions welcome please.

Thanks.

The flapper was never fitted to the 3.9, so the fuel map might not be quite right.
The throttle pot just acts like an electronic accelerator pump. If it's not fitted, you'll just get a flat spot when you suddenly open the throttle. Very unlikely to be the problem.
Inside the AFM there is a carbon track which is 'wiped' by the flap turning. It turns against a big clockspring which sets the mixture in a crude kind of way.

I would try to borrow another AFM to see if that's the issue.

Alternatively find the diagnostics guide which tells you how to test the AFM. From memory, remove the rubber boot on the connector. Pins 6,8,9 are of interest. One is about 0V, one is +5V and the other is the wiper. Check that 0V and 5V are present, and that the wiper voltage changes smoothly as the flap opens. Also monitor it with the engine running (and misbehaving!) to see if it's a stable reading.

You might want to fit the exhausts!!

Chris.

Thanks Chris, I have been a wally.

Was testing the voltage on throttle and noticed 1600mv and had to turn it quite a way to reduce to 325mv. Turns out I had not quite got the cable assembly bracket on correctly and the buterfly was not closing fully.

Now reassembled correctly and runs like a dream.

I appreciate what you say about running lean, it is something I am aware of, although hopefully most of the time will be on LPG. I recall a post of badgers that said you need to up the pressure on the fuel regulator and then twiddle with the AFM to get 2% CO. Once I have put it all back together properly and serviced etc. I will look a bit closer into sorting this side out.

Cheers.

[quote="Coastcard"]I recall a post of badgers that said you need to up the pressure on the fuel regulator and then twiddle with the AFM to get 2% CO. Once I have put it all back together properly and serviced etc. I will look a bit closer into sorting this side out.
[quote]

If you decide to go inside the AFM this may be of interest:

http://www.vintagemodelairplane.com/pag ... ter01.html

What a great document - Thanks Ramon.

I had visited that site for some other useful diagnostic stuff, but missed this one.

Cheers.

Coastcard wrote:What a great document - Thanks Ramon.

I had visited that site for some other useful diagnostic stuff, but missed this one.

Cheers.

It's brand new in the last couple of weeks.