Damage to hotwire AFM when engine (RV8) backfires?

[chassis 33]

Does anyone know whether it is possible to damage the hotwire AFM when a RV8 backfires?
What are the resistances and pins needed to check the AFM is still working?

Regards
Iain

[rev-erend]

I thought their usual trick was to let the car run very rich..
easiest would be to swap with someone else'sss who has the same airflow meter.

[pdV6]

Isn't a backfire petrol igniting in the exhaust, not the inlet?
The AFM is on the inlet side, so presumably can't be affected.

The lambda sensor, on the other hand, sits in the exhaust...

[leorest]

pdV6 said:

Isn't a backfire petrol igniting in the exhaust, not the inlet? The AFM is on the inlet side, so presumably can't be affected. The lambda sensor, on the other hand, sits in the exhaust...

You can get explosions in the inlet it's just less common than in the exhaust. LPG conversions on flapper RV8 systems have destroyed the AFM (Tallbloke beware) the flap acts as a one way valve which tries to contain the explosion, badly. The hotwire AFM doesn't provide the same reverse direction restriction it is obviously less susceptible to being blown up in such a spectacular way. As such it would probably survive the odd occurrence. The Rev said substitution, this is the acid test, but failing that try measuring for an open/short circuit across the transducer.

[chassis 33]

Cheers, yes, its from an LPG Discovery, that backfired a few weeks back.

I've just done some work on the NS exhaust manifold which meant I had to (carefully) move the AFM out of the way, put everything back together and now the bloody thing wont start, I'm just wondering if me moving the AFM was the final straw and its knackered itself up. There's fuel getting in (at the rail and in the cylinders; the plugs were wet from all the cranking), so I've replaced with new, the plugs are sparking when shorted to the rocker cover, and I'm at something of a loss to get the thing running, hence me wondering if the ECU knows the engine has an airflow.

I've try swapping the Chimaera AFM across to see if that helps.

Regards
Iain

[rev-erend]

Sounds like you forgot to connect the AFM cable

Seriously - if all you have done is to remove the exhaust : double check the obvious and don't look too hard for new problems.

[leorest]

chassis 33 said:

Cheers, yes, its from an LPG Discovery, that backfired a few weeks back. I've just done some work on the NS exhaust manifold which meant I had to (carefully) move the AFM out of the way, put everything back together and now the bloody thing wont start, I'm just wondering if me moving the AFM was the final straw and its knackered itself up. There's fuel getting in (at the rail and in the cylinders; the plugs were wet from all the cranking), so I've replaced with new, the plugs are sparking when shorted to the rocker cover, and I'm at something of a loss to get the thing running, hence me wondering if the ECU knows the engine has an airflow. I've try swapping the Chimaera AFM across to see if that helps. Regards Iain

A bit late now but I think a "trick" with LPG conversions is to leave an inlet connection slightly loose so that it becomes the weakest point to blow in the case of an inlet backfire. Before swapping I'd spend half an hour making some resistance comparisons between the suspect and the known working AFMs.

[chassis 33]

Yeah...thanks Rev...bastid I've done some really dumb stuff with engines in the past, but I've got that one covered ta! BTW tap me on the shoulder at Back Home, I'm sure I owe you a pint somewhere along the line.

I'm fairly certain it will be something simple and obvious once I've found it!!! Trouble is i'm running out of simple and obvious reasons why it wont run...

Regards
Iain

[Graham]

im sure it would run with the afm disconnected. I've had the odd non starting issue with v8 discos before...

if they dont start first kick then they flood very quickly. my usual trick is to pull the fuel pump fuse and crank it untill it fires...

G

[pdV6]

rev-erend said:

Sounds like you forgot to connect the AFM cable

Usually the engine runs better with the AFM disconnected if its knackered. Unless the ECU is programmed to detect this and shut up shop, I guess?

[GreenV8S]

I think it would be quite hard to physically damage it, but it's easy to contaminate the heated element so that it misreads. The 14CUX is capable of running with the AFM disconnected so this is well worth a try. (I get some pretty spectacular explosions in the inlet manifold too, but luckily (?) the blower stops these getting up as far as the AFM.

[chassis 33]

What's the best way to clean the AFM? The wires are quite delicate arent they? Should I just squirt brake cleaner down the bypass to the wire?

Regards
Iain

[GreenV8S]

I was told that they can't be cleaned like that, but some people have used carb cleaner and claimed that it worked.

[rev-erend]

My money is just on it being flooded - just put your foot flat to the floor and crank it over for about a min...

Perhaps you are just looking for problems..

[chassis 33]

Finally got it running...complimented the new plugs I'd already put in over the weekend with a new set of leads, also a new coil, and hey presto, job done. I've since reverted back to the original coil, and it still runs, so i can only hypothesise that there was some silliness going on with the leads, it decided not to play ball.

Ho hum best go buy some more £12 eBay specials to replace the leads that were due to go on the Chimaera.

Thanks for all your help...again!

Regards
Iain

[Graham]

SOunds like flooding to me, have you tried the old leads back on ?

G