Lumpy idle, mis fire heard through exhaust, lack of response when pulling away.

[em645]

It was nice to meet some of you at the Cotswold wildlife park - in particular Ajay.

My car seems to have developed the above symptoms. The plugs are new, as is oil, coolant etc so I'm confident that's all fine.

I've never checked my fuel pump so will start there and I know my maf would benefit from a clean so will do this too.

Had anyone else got any explanation for a low down mis fire? How does the 260 regulate its idle? Does it have a control valve?

Thanks

Ed

[WNJ516]

How does the 260 regulate its idle? Does it have a control valve?
A combination of ign/spark timing and IAC valve located on the air intake plenum.
You need a scanner to check the ign timing thro reading the live data usually around 12 to 16 deg @idle doubt if there is a problem there,
and your fuel pressure.
Clean your Maf with carb cleaner first and check for any obvious air leaks, plenty of how to on youtube if your unsure.
LUMPY MISFIRE HEARD THRO EXHAUST, mine does that and always has done without a misfire.!!!

[gignwah11]

mine does this when we have hot days and stuck in traffic for a while just evaporation in the fuel rail?

[Richb]

If it's lumpy at idle it's easy to check for a failed coil. Pull the electrical connector off one coil at a time with the engine running to listen for a change in the engine note. If one doesn't result in a change to the engine note, then that cylinder is misfiring (likely to be the coil but could also be the injector).

i had a misfire under light load recently and it turned out to be dampness on coil #8.

Rich

[em645]

How does the 260 regulate its idle? Does it have a control valve?
A combination of ign/spark timing and IAC valve located on the air intake plenum.
You need a scanner to check the ign timing thro reading the live data usually around 12 to 16 deg @idle doubt if there is a problem there,
and your fuel pressure.
Clean your Maf with carb cleaner first and check for any obvious air leaks, plenty of how to on youtube if your unsure.
LUMPY MISFIRE HEARD THRO EXHAUST, mine does that and always has done without a misfire.!!!

Ok great will check all of the above. Are there any daft vacuum pipes on the 260 inlet that can cause problems? I know my old V6 Vectra was a nightmare for this.

Where abouts is the IAC valve? This may need cleaning out... again an issue on the Vauxhall V6 that could cause an uneven idle.

mine does this when we have hot days and stuck in traffic for a while just evaporation in the fuel rail?

Yes it was a hot day when I mainly noticed it but I must admit, mine always seems to creep up from 0 revs to idle when you start the engine, regardless of temperature, the engine doesn't spring into action like every other car I've ever driven.

If it's lumpy at idle it's easy to check for a failed coil. Pull the electrical connector off one coil at a time with the engine running to listen for a change in the engine note. If one doesn't result in a change to the engine note, then that cylinder is misfiring (likely to be the coil but could also be the injector).

i had a misfire under light load recently and it turned out to be dampness on coil #8.

Rich

Cool Rich thanks for the advice. I did mention damp coils to Austin Garages but he seemed to think it was mainly down to people removing the sound deadening on the bonnet - which mine still has! Either way i'll check the coils next time it feels lumpy.

Strange really, on full throttle it's great - just starting, idling and slow manoeuvres it seems to struggle occasionally.

Not sure if mine has had the fuel pump clip done, does this solve many problems? I also have the Viton seal - whatever that means!!

[WNJ516]

W

here abouts is the IAC valve? This may need cleaning out

It's on the plenum chamber, held on by 2 allen headed screws, has a pipe and small black plastic resonator box which connects back to the intake air hose.
Or see it on page 36 of the 260 training manual, found under the index of the forum
Check all hoses that connect to the plenum chamber, Clean your Maf sensor

[Richb]

When mine was misfiring, it was fine at idle and on heavy throttle. I pulled the back coil and it had water tracks running down into the plug well. I've read the issue is due to leaking washer jets and the under bonnet sound proofing hides the issue, so that's why people remove them. No signs of leaks on mine though


The IAC is bolted onto the front side of the throttle body plenum, look for the valve with the diamond shaped mounting surface.

My car does spring into life with minimal cranking or fuss, then settles to a nice solid idle. Check all hoses that that connect to the air intake pipe as anything that's come adrift will cause an air leak downstream of your maf and effect all running apart from WOT.

I understand the orange clip (if that's what you mean by pump clip?) is purely to stop the fuel filter falling apart as they can do. It's on passenger side of tank under the rear seat. It won't cure any other problems... and you would know if you needed it as you'd be stuck at the side of the road.

Not sure where the viton seal goes, maybe this is the seal between the two halves of the filter. I'm still learning about these engines so others will probably have more definitive answers!

Rich.

[em645]

W
It's on the plenum chamber, held on by 2 allen headed screws, has a pipe and small black plastic resonator box which connects back to the intake air hose.
Or see it on page 36 of the 260 training manual, found under the index of the forum
Check all hoses that connect to the plenum chamber, Clean your Maf sensor

When mine was misfiring, it was fine at idle and on heavy throttle. I pulled the back coil and it had water tracks running down into the plug well. I've read the issue is due to leaking washer jets and the under bonnet sound proofing hides the issue, so that's why people remove them. No signs of leaks on mine though


The IAC is bolted onto the front side of the throttle body plenum, look for the valve with the diamond shaped mounting surface.

My car does spring into life with minimal cranking or fuss, then settles to a nice solid idle. Check all hoses that that connect to the air intake pipe as anything that's come adrift will cause an air leak downstream of your maf and effect all running apart from WOT.

I understand the orange clip (if that's what you mean by pump clip?) is purely to stop the fuel filter falling apart as they can do. It's on passenger side of tank under the rear seat. It won't cure any other problems... and you would know if you needed it as you'd be stuck at the side of the road.

Not sure where the viton seal goes, maybe this is the seal between the two halves of the filter. I'm still learning about these engines so others will probably have more definitive answers!

Rich.

Thanks again for the help guys.

Mine has always been a little slow at building up from engine off to engine switched on / idling. I assumed that the ten year old spark plugs were to blame for this and the low down mis fire. The mis fire had mostly stopped but seems to have reappeared. Also fitting a new battery helped the starter motor throw over more confidently but it's almost like the fuel pressure is weak to start with or indeed an air leak or similar?

My MAF has come away from the poorly designed U bend which leads to the filter housing. I've no doubt that cleaning that will help - plus I plan to reposition the MAF to where it sits on a mustang and get rid of the restrictive housing for a better filter.

[WNJ516]

My Maf broke away from the input section I glued it back with silicon sealer, I would seek advice on moving the MAF, if that's your intention. I don't why but in the early days there were some reason as not to move it, perhaps Herman, Nich or Brain could give you a reason not to. I have a K&N filter in the cars original housing and that's what is supplied with a S/C conversion so doubt if it creates a restriction. Perhaps other members could give you some advice.

[Herman]

My Maf broke away from the input section I glued it back with silicon sealer, I would seek advice on moving the MAF, if that's your intention. I don't why but in the early days there were some reason as not to move it, perhaps Herman, Nich or Brain could give you a reason not to. I have a K&N filter in the cars original housing and that's what is supplied with a S/C conversion so doubt if it creates a restriction. Perhaps other members could give you some advice.

The intake set-up on the 260 is not really a problem. Also the MAF is not in a U-bend but in a straight section, just after the elbow that come from the tube.
This set-up works well, even on S/C cars.

With mine I've cut away most of the filter housing and effectively created an open filter with K&N cone. The MAF is still in the same position.
I think the MAF position is not the problem. Anywhere before the throttle body is fine as long as it's not in turbulent air

When starting, just give it a second or 2 to let the fuel pressure build up. If the pump was at fault, you'd notice at full throttle.