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[Kevin Wood]

Sounds like a result to me.  

It would have built up a large fuel trim hence the chronic over fuelling when you started it with the correct signal from the MAF.

For future reference if you need to change a MAF that's built up a large fuel trim you can reset the trim by clearing the codes (e.g. with a cheapo Tech 2) or, warm up the car on the old MAF so the Lambda sensors are active and change the MAF while it's hot.

Hopefully we are near the end of a long, frustrating road.

Kevin

[Albatross]

I drove about 2 miles to the petrol station this morning, stopped, filled up, paid and then as I started her up again the EML light had cleared itself.

Result! Must have been the MAF sensor.

As this happened I have greater confidence in the root cause and have moved the secondary O₂ sensors back to behind the main cats again.

Still no EML light despite a 20-30 mile drive since.

Touch wood, this could be the end of this thread.

[Albatross]

Confirmed as another MAF sensor issue.

Replaced MAF and problem solved

Ironically enough, right at the outset my local garage said to me "check the MAF sensor, it's common"

Having asked on here the response was largely "Unlikely".

Recently I have noticed that there has been quite a little spate of these, so well worth getting it checked out. For £33.50 for a new one incl P&P & excellent service (see above for contact details) you can't argue really and my car is a different machine with no EML.


Thread finally dead and buried.

Thanks Kevin, Jaime and Chris for your help.

[feeutfo]

Excellent news. Glad its sorted. :-)

[kcl]

I had the same codes a year ago, local Opel shop could not find the fault but the mechanic said he had once searched for the reason on a vectra with 2,6 engine for several days and the result was MAF. However, when I changed mine, I had the same codes twice within two weeks from the change and since then have not had the codes.

[Kevin Wood]

It makes me wonder if the MAFs on DBW cars don't have the same legendary reliability. :-/

Kevin

[Albatross]

It makes me wonder if the MAFs on DBW cars don't have the same legendary reliability. :-/

Kevin

At 33.50 per MAF and at least I know what the problem is likely to be then I'll live with that though.

There is no sign of the 0420 & 0430 either so I think the moving back of the O2 sensors has worked.

Do you think I'd gain anything by putting standard 3.0 front sections on now and completely removing the pre-cats? There must be some resistance / back-pressure caused by them.

[Kevin Wood]

It makes me wonder if the MAFs on DBW cars don't have the same legendary reliability. :-/

Kevin

At 33.50 per MAF and at least I know what the problem is likely to be then I'll live with that though.

There is no sign of the 0420 & 0430 either so I think the moving back of the O2 sensors has worked.

Do you think I'd gain anything by putting standard 3.0 front sections on now and completely removing the pre-cats? There must be some resistance / back-pressure caused by them.

Not sure, TBH. :-/ There might be some benefit. On the other hand, the single cat on the 3.0 might be more dense to compensate.

Kevin

[Proz]

Mmmm i might invest in one of these to see if it clears my problem 0420 code too .

[Kevin Wood]

Mmmm i might invest in one of these to see if it clears my problem 0420 code too .

0420 is unlikely to be the MAF, I'd say. That's a cat efficiency code so relocation of the cat check Lambda sensor would be the best bet, IMHO.

Kevin

[Albatross]

Mmmm i might invest in one of these to see if it clears my problem 0420 code too .

Kev's bang on; read my last post on your "0420" post.

BTW, once you have fixed it by moving the O2 sensor back, I did notice that you're running an 11% long term fuel trim. For that reason only I might consider the MAF, but Kevin will know better than me. It is a lot less than mine was at 24% though. (EML code 0170 was coming up)

[Kevin Wood]

Mmmm i might invest in one of these to see if it clears my problem 0420 code too .

Kev's bang on; read my last post on your "0420" post.

BTW, once you have fixed it by moving the O2 sensor back, I did notice that you're running an 11% long term fuel trim. For that reason only I might consider the MAF, but Kevin will know better than me. It is a lot less than mine was at 24% though. (EML code 0170 was coming up)

A bit of diagnostics with a Tech 2 is required really. 11% fuel trim is on the high side, and 2.2s don't appear to suffer from 0420 codes generally. IIRC, a new cat has been fitted to this car to no avail so maybe something else is going on. :-/

Kevin

[Jay-C]

Hi all! I am new here and just found this thread. I have similar problems with my 3.2 engine (error codes P0170 & P0173).

I've checked for vacuum leaks but haven't found any, and I've just changed the plugs and the MAF. I've been logging the engine data, and it seems that when I lift the throttle pedal, the short term fuel trims shoots up to +25% (you can see that between 20 and 38 seconds on the graph). Otherwise it looks quite ok for me.

Can anyone advice what to check next? I think I will try to clean the throttle body and butterfly.

[Kevin Wood]

Lots of fuel trim on a closed or light throttle points to an air leak into the plenum after the throttle body - when vacuum is greatest on a light throttle. I'd check the breather pipes and plastic breather box on the plenum are air tight, the plenum-to-inlet manifold seals and also the vacuum pipe to the brake servo.

Kevin

[Kevin Wood]

Should have said... During the area where the problem occurs on that graph, was the throttle totally closed or just lightly applied?

It's showing a few percent throttle and a few percent load, that's all.  :-/

Will have to see what mine reports under similar conditions.

Kevin