Technical Tips > Post 84

1986 C4 MAF Sensor replacement?

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peterw:
My 86 (with 50,000 miles up) is throwing a MAF error code (34).

I have checked the connection and it is OK, can't find anything obviously wrong anywhere else so have been doing research on a replacement.

So far I have only found one place in US that has an original (new) MAF and it is $1200.

Many places offer rebuilt ones (as does a place in Victoria).

Most have non genuine replacements.  Has anyone used one of these and could recommend it or any other course of action?

I want the car to be reliable.  It is bone stock.

Thanks
Peter

Vettech:
Hello Pete.

R U referring to 6E3-A-44 and page 45. In the Service Manual ?

You need to follow the process, else very expensive.

I'm not SURE - but I would guess the MAF off other GM cars may he compatable.

There is not much in a MAF. Basically a small cct and a Hot Wire.

You have 2x Earths, 12 Volts power from the MAF Power Relay, 5 volts Signal from the ECM..
And a burn off signal from the Burn Off Relay.

The cct powers up and the wire is heated, as air flows into V engine it cools the wire, the 5volt signal is modulated from 0 ~ 5v.
At 5v it is high for high air flow and ECM applies more fuel. At idle it may be 0.6v so ECM sets enough fuel for idle.
Often a car with a faulty MAF has a rough or stumbling idle.

Any wiring with O/C or HR's - esp cct 998 Dk Green to Maf connector "C" will cause issues.

Vettech:
And just to finish.

The burn off is activated "JUST AFTER" the engine is switched off (if certain criteria met - run time/engine to temp)

The ECM applies via the burn off relay etc a full 12volts to the wire, lights it up, and burns any crap off the wire.

So - any openings, cracks in the duct from filter to MAF, will allow "muck" into the engine, which can cook onto the Wire causing incorrect sensing ergo 0~5v signal ergo incorrect fuel mix ergo dicky idle or running. (Mostly idle)

The two relays MAF Burn off and MAF power can after years (30yrs) of use develope dicky contacts, change both as a matter of course. Sorry I'm having internet issues which keeps dumping me off line.
What I'm getting at here is, if the burn-off does not or has not occured for some time then the Wire could be in a really crappy state, this will play havoc with the ECM's ability to metre the correct fuel to air ratios for efficient engine running

Do you get code 33 as well ? Let me know and if a cct diag required.

P.S In the past I've had 33,34 &36, all these relays after conversion are up on the LH side fire wall, covered in all manner of crap, but more importantly are very close to manifold heat, I've had relays cooked, plugs cooked, wiring hanging on by one minscule strand. Best of luck.
Regards. 

peterw:
Thanks for the detailed response.

Good tip about the relays.  I realise that any 35 year old electrics are likely to fail as the resin hardens and cracks in the components so would replace any that could be a potential failure.

Now, rebuilt MAF from Victoria (Injectronics or alternative?) or aftermarket one from USA?

I'm not 100% sure the MAF is faulty so I will youtube it and see if I can test it somehow.

Pete

peterw:
I just pulled the MAF, it's Bosch so is likely the original.

It looks pristine, no corrosion or muck anywhere.

Still could be faulty though.

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