Errant misfire

[Mr S]

First off, im booked into go see Matt and Ashley in a months time, but being a really stubborn fecker, I want to do all I can to see if I can get to the bottom of the issue to myself. Problem is with a GS, seems to be occasional, and basically it starts to misfire on Bank 1, especially when cruising at a steady speed, with cruise control also. It will then cough and splutter until you reset the codes, at which point they don't come back for ages. Error codes say its running rich and Bank 1+2 oxygen sensors are mixed, and iv swapped them over now, but was then given a code saying they had been swapped. Cant get to the rearward sensors at the moment.
Have changed all of the coil packs already
Now, what I have noticed on light throttle applications in the garage, so not under load, is that when I hold the pedal at a constant position, the revs can drop 500rpm, then go back up. Personally don't think this fluctuation is normal, but could be wrong. Could I have an iffy pedal or TB that is causing me grief, or maybe fuel pump? Appreciate Matt and co should be able to tell pretty sharpish when its plugged in, but want to try and at least get to the bottom of it, even if I cant fix it.
Any suggestions/pointers welcome

 

[Oneball]

If it’s just bank 1 it won’t be throttle pedal or throttle body or fuel pump as that’d affect all cylinders.

Without the codes being read how do you know it’s bank 1?

On most ECUs with a 2nd lambda after the cat it only acts as a check to see its functioning properly, it doesn’t feed back into the mixture settings.

Live data from the lambdas would be interesting as would TPS data when it does the 500rpm thing.

 

[Mr S]

MAF has also been replaced, as well as both rocker cover gaskets, purge valve and carbon canister, which seems to have fixed the hot start issues.

 

[Mr S]

If it’s just bank 1 it won’t be throttle pedal or throttle body or fuel pump as that’d affect all cylinders.

Without the codes being read how do you know it’s bank 1?

On most ECUs with a 2nd lambda after the cat it only acts as a check to see its functioning properly, it doesn’t feed back into the mixture settings.

Live data from the lambdas would be interesting as would TPS data when it does the 500rpm thing.

Cheers for info. The cheap and cheerful code reader i have reckons its bank one, multiple misfires. I was under the impression that each fuel pump fed each bank, hence the wondering.

 

[Oneball]

Cheers for info. The cheap and cheerful code reader i have reckons its bank one, multiple misfires. I was under the impression that each fuel pump fed each bank, hence the wondering.

Ooh they might do. My brain was thinking 3200 where both banks feed from the same t piece on the bulkhead.

If they are seperate, has the fuel filters been changed?

The one in my 3200 was still the factory one fitted 20 years ago.

 

[Mr S]

Dont understand why both banks would be running rich though if one of the pumps was iffy, but guess it could be doing anything, sticking etc

 

[Oneball]

have you checked for vacuum leaks?

 

[Mr S]

Wouldnt know where to start with that.

 

[Oneball]

Wouldnt know where to start with that.

Make sure all the hoses in the induction system are attached and clamps done up with no rips or holes there’s often little vacuum pipes that can become detached. Just have a thorough look and see if you can see any floating around.

 

[Mr S]

Ok cool thanks. Forgot to say, i have a slight stutter at 1500-2000rpm, which got better after changing the coils, but is still there, and seems to mildly get better when the engine is warm. On static rev’s apart from the fluctuations, all is well.

 

[tomoshea]

I had one that bugged the **** out of me for a long time... on the air inlet black Flexi pipe there is small connector under the pipe, there isn’t much length on it for a proper seal, if at any point the black flexi and associated small inlet pipe has been removed it is possible it doesnt get reconnected properly... and with passing glance / look / check it looks like it is connected properly...in my case it wasn’t, it was just touching the solid pipe but not sealed... resulted in a low grade misfire at idle and higher. Sorted once I reconnected it properly.. best bit...mine came back from main dealer like that after being “fixed”...

Have a look you might be lucky if it’s the same issue...

 

[Mr S]

I had one that bugged the **** out of me for a long time... on the air inlet black Flexi pipe there is small connector under the pipe, there isn’t much length on it for a proper seal, if at any point the black flexi and associated small inlet pipe has been removed it is possible it doesnt get reconnected properly... and with passing glance / look / check it looks like it is connected properly...in my case it wasn’t, it was just touching the solid pipe but not sealed... resulted in a low grade misfire at idle and higher. Sorted once I reconnected it properly.. best bit...mine came back from main dealer like that after being “fixed”...

Have a look you might be lucky if it’s the same issue...

Cheers for the heads up. I actually went searching the other day, and found the clamp around the pipes and connectors from the servo to the back of the inlet manifold were not the tightest, so i did them up as tight as i could, and it does seem to have helped somewhat. I also found a split in the end of the pipe that goes to the front of the inlet, so trimmed that off and reclamped it.