Rovergauge, R3652 EPROM, over fuelling and AFMs

[Dalamar]

I've been tackling an over fuelling issue for a while now that I've captured up to now in a previous post:

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

Since then I've got a spare 14CUX and Steve Sprint R3652 firmware installed to remove the doubt of my unknown EPROM chip. No significant changes except to say that my short term lambdas oscillate more around zero now and the acceleration is a little sharper higher up the revs. My long term lambdas still show over fuelling.




So, I went back to thinking about my AFM which is an original Lucas 5AM from 1993. It was filthy when I got the car and I gave it a good clean out including the filament with the proper AFM cleaner. Rovergauge AFM direct value was 32-33 at idle and I'd tested the voltages before but thinking back I checked the readings were about right but not the response of the sensor to get to those readings.

Armed with a multimeter I probed the back of the AFM plug and found:

Between red/black and blue/green - Ignition on only, shoots up to 0.8V and then falls to ~0.32V by around 8 secs then continues to fall to 0.29V by about 20 secs - this is bad I believe. On start, the voltage rises to 1.6V on idle which is OK.

Between red/black and Blue/Red (the CO signal) I got 1.75 which I think is OK.

So - I think my AFM might well be contributing to this over fuelling issue.

What are people's thoughts these days on where to get a replacement unit? Or should I look to get my original refurbished?

If I go for a new unit there only seems to be 3 options (Part no. ERR5198):
Britpart £80-ish
Allmakes £85-ish
TVR Parts £216 (wow that's a jump!) (P/N E2036)

Any other thoughts please?

[blitzracing]

Firstly the cheap ones are Chinese copies and you get what you pay for. I dont know what TVR parts are selling as Lucas ones have been out of production some time, unless they have old stock. You could get a referb unit try APT Electronics from memory, they where £150, but I dont see them listed currently, so worth a call. There are two types, the the early Hitachi 3AM and later Lucas 5AM, both plug compatible. There are dozens of part numbers for different units used on Range / Rover or discovery, but the differences seem to be the castings that bolt on, not the basic electronics, so you can mix and match with the TVR one if needed. As for the voltages- this is what the start up trace should look like- Its shows the initial spike as the element heats up and becomes stable within a second, not as you describe it.- the lift in output to 1.62 volts is when the engine starts and idles on my 3.9

[Dalamar]

Thanks - I'm in touch with ATP (Steve) and he's checking if they can still be refurbished. All depends on what spare components are still available he was saying. I also phoned Racetech and they don't sell new or refurbished anymore, they've left it to TVR Parts. I'll see what the story is with the units they are selling.

The impression I get is that you can get a secondhand or new aftermarket item that won't flag a fault on your car but the calibration of the unit will be way off and it just won't perform as it should do. Most secondhand sellers don't know about the direct electrical tests but say that it worked fine on the car or that the diagnostics equipment said it performed ok.

I'll keep looking...

[Dalamar]

Steve from ATP got back in touch and they can’t refurbish the Lucas 5am units anymore. I also spoke with TVR Parts and the units they sell are apparently made by Lucas in the UK.