Proper numpty newbie question

[JMF894]

I have read several comments refering to certain wedges as 'flappers'. Is this something to do with the noise they make due to the type of ecu mapping/fuel injection they are running?

Is my 1989 450SE a 'flapper'? And what's the difference between a 'flapper' and 'hotwire'?

Jim

[mrzigazaga]

I think its someone who worries a lot...
I own a 280 so not 100% but i think the flapper is something to do with the air flow meter (Flap)..And i think it does create a different tone compared with a hotwire..Although im not too sure myself..

[350Wedge]

If it pops and bangs a lot on the over-run chances are its a flapper. I had an '89 450SE a couple of years back which was a flapper. That popped and banged a lot!!

My current 400 is a hotwire and doesnt pop and bang very much, unless you gently rest on the throttle while slowing down!!

[JMF894]

Hmmmmmmm. It defo pops and bangs a lot on the overrun. Noisier i think than my 92 400 was

Jim

[Aeroflop]

I think It's the MAF (Mass AirFlow) sensor - while it can be either mechanical or electrical, the terms would suite very well.

If it's mechanical, the incoming air turns a flap (therefore a flapper - the more air is coming in, the more the flap turns) and the injection system sees how much the flap is turned (how much air is coming in) and decides the amount of fuel by that (and possibly couple others - the engine temperature, throttle position etc) information. As an example, the Bosch K-Jetronic injection functions this way.

If it's electrical, there's a really thin wire, which is heated (therefore a hotwire) and it's resistance is measured. The incoming air cools down (more air = cooler wire) the wire and the injection system check how much the wire is cooled at the moment (how much air is coming in) and by that information (and couple other, of course) decides the amount of fuel to inject. As an example, the Bosch LH-Jetronic injection system functions this way.

[TOPTON]

Simplest way to tell>

Put ignition on to pre start, if you can hear the fuel pump prime for 3-4 seconds--It's a hotwire

Take air filter off, put ignition on to pre start and push the flap in the AFM, should hear fuel pump---It's a flapper

[jmorgan]

Hotwire also has the stepper screwed in the side of the plenum and not a flapper methinks?

[cello297]

And I thought it was simply a convertible. You're not the only numpty in the stable! Ho hum...

[pwd95]

looks like a flapper...

[JMF894]

pwd95 said:

looks like a flapper...

Thought I recognised that pic!!

[dixiebabes]

Have often wondered the same question but didnt dare say out. Heh he heeh hum

Mine is obviously a flapper as it bottled that 120MPH right turn on the A19 just like i did.

Dix