Diagnostic codes.

[Acousticplayer]

Hi everybody. So I continue to chase down my misfiring problem. I've replaced the upstream oxygen sensor to bank one and replaced both parts of the air intake past the MAF. The first rubber boot had a nasty split but the second part was ok with no split. The latest scan now appears to confine the problem to cylinder one,whereas before it showed misfires on 1 2 and 3. Model is 1999 2.8 roadster. The check engine light is not showing nor has it ever lit up during the whole saga. The scanner now shows:-

Fuel trim control unit. Po170

Misfire cylinder 1. Po301

Does this show that this is basically the same problem IE the misfire is a fuel trim problem or am I looking for two faults.

Thanks.

 

[ChrisD]

I’d expect it to be the other way round i.e. the misfire being primary issue, fuel trim code possibly a secondary effect. I’d be checking the ignition path from plugs to coils, fuel delivery particularly injector #1. Presumably you’re confident you’ve addressed all of the air leaks?
Unfortunately the CE light was not mandated for UK in ‘99 - if it was you’d see it indicate when the misfire happens.

 

[Lee]

Get a smoke test done from the MAF back, sounds like you might have a vacuum leak still

Obviously check the the easy things like the plugs and swap coil packs to make sure it's not that.

 

[Acousticplayer]

Hi. Thanks for your replies. May I fill in the story a little in case it might stir any more thoughts. The problem started about a year ago. It was running fine ,I took it for it's MOT September last year and was told they could not do the emissions test as it was misfiring. It was ok when I took it in. I scanned it and showed a misfire on 1 2 and 3 but they shortly disappeared and it was running ok again. I returned for a retest and this time it passed but shortly after it was misfiring again.. Rightly or wrongly I suspected the oxygen sensor and replaced that and that seemed to solve the problem as the car ran fine for many months after although not used a great deal. Exactly the same thing has now happened. Car was running fine I took it for it's MOT this year and as soon as the garage took it in it started to misfire. This time bringing up the codes above. I found the split in the intake pipe and have replaced that and once again it passed the MOT. However just like last year the misfire has returned but now on cylinder 1 only. Of course last year's problem may be entirely separate to this time but I am finding it very odd.

 

[Lee]

The fact the misfire is moving about tells me un metered air is getting in, look at the rubber bungs on the back of the manifold as they perish and let air in, also check the other rubber components for splits.