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[Kevin Wood]

It is making a noise rather like a worn cam (clicking) when the misfire starts happening, then disappears when it starts running ok again

Could be spitting back through the intake due to a lean mixture. Have seen (heard) this before and it was the MAF in that case.

Kevin

[jonnycool]

It is making a noise rather like a worn cam (clicking) when the misfire starts happening, then disappears when it starts running ok again

Could be spitting back through the intake due to a lean mixture. Have seen (heard) this before and it was the MAF in that case.

Kevin

Yes, you might be right there, I think the new MAF can only be a good thing for my car..

[RossMk2]

Could be spitting back through the intake due to a lean mixture. Have seen (heard) this before and it was the MAF in that case.

Kevin

Jumping in on this thread.... i get seriously bad popping back down the exhaust (which the 4.0bar FPR seems to have calmed down a little) and have also had it spit back down the intake once or twice when testing which it may be doing while driving also just not as noticable as when your hands on the engine! hehe, and this is a good indication that this is the MAF? I've had tried 2 MAF's now and granted they are 2nd hand but still the same problem.

[Kevin Wood]

Spitting through the intakes can be an indication of a lean fuel mixture.

Whether that's due to the MAF or another problem requires more diagnosis.

A lean mixture burns very slowly or doesn't burn completely. This can leave some fuel in the cylinder in either an unburnt or "still burning" state after the exhaust stroke. When the inlet valve opens this can ignite the recently-injected fuel in the intake manifold, or, failing that, on a wasted spark engine, the "wasted" ignition event which occurs near TDC on the exhaust stroke can re-ignite fuel that previously hadn't fully burnt. The effect is the same. It flashes back into the inlet manifold.

Popping in the exhaust can be caused by a lean mixture but also by air leaking into the exhaust system, causing the engine to run rich (due to a false signal from the lambda sensor). Unburnt fuel then combines with the air that's leaking in and burns in the exhaust.

The fact that upping the fuel pressure makes a difference makes me think it's running lean and has run out of fuel trim to adjust it (normally changing the fuel pressure wouldn't make any difference because the ECU would trim the fuel back again).

It would need a look at the live data from the ECU to diagnose further IMHO. Has the ECU stored any fault codes?

Kevin

[valliant72]

Hi, i had trouble with what seemed to be pinking, if you check over my previous threads till someone suggested the auxillary belt tensioner. So i changed that with a new belt and the noise has gone and i had changed every sensor there is  . Just another thing u could look at.

[RossMk2]

Spitting through the intakes can be an indication of a lean fuel mixture.

Whether that's due to the MAF or another problem requires more diagnosis.

A lean mixture burns very slowly or doesn't burn completely. This can leave some fuel in the cylinder in either an unburnt or "still burning" state after the exhaust stroke. When the inlet valve opens this can ignite the recently-injected fuel in the intake manifold, or, failing that, on a wasted spark engine, the "wasted" ignition event which occurs near TDC on the exhaust stroke can re-ignite fuel that previously hadn't fully burnt. The effect is the same. It flashes back into the inlet manifold.

Popping in the exhaust can be caused by a lean mixture but also by air leaking into the exhaust system, causing the engine to run rich (due to a false signal from the lambda sensor). Unburnt fuel then combines with the air that's leaking in and burns in the exhaust.

The fact that upping the fuel pressure makes a difference makes me think it's running lean and has run out of fuel trim to adjust it (normally changing the fuel pressure wouldn't make any difference because the ECU would trim the fuel back again).

It would need a look at the live data from the ECU to diagnose further IMHO. Has the ECU stored any fault codes?

Kevin

Right, there is no leaks intake side of things, i have recently changed all the hoses to new stuff and a new filter. There may be a slight blowing in the exhaust but it is after the oxygen sensors would this still cause the problem with the sensors, even if the leak is after they take a reading?

There are no fault codes on the ECU since changing the CS to a GM version.

I did use a local dealer with Tech2, he wasnt very helpful tbh was like he was against my car from the start, said there was nothing he could see thats causing a problem! 

[jonnycool]

A friend suggested putting super unleaded in my car to see if it makes a difference ie upping the RON level of the petrol already in the tank. Hopefully this will make a difference for now

[RossMk2]

Thats all i have been using mate, made no difference to mine.

[jonnycool]

On a more general note, is supermarket petrol really that bad? I've used it for years, admittedly not on this particular car, which I've bought only recently. Never had any problems before!

Which brand petrols are the best in that case? Do Omegas run better on super unleaded?

[cem_devecioglu]

Spitting through the intakes can be an indication of a lean fuel mixture.

Whether that's due to the MAF or another problem requires more diagnosis.

A lean mixture burns very slowly or doesn't burn completely. This can leave some fuel in the cylinder in either an unburnt or "still burning" state after the exhaust stroke. When the inlet valve opens this can ignite the recently-injected fuel in the intake manifold, or, failing that, on a wasted spark engine, the "wasted" ignition event which occurs near TDC on the exhaust stroke can re-ignite fuel that previously hadn't fully burnt. The effect is the same. It flashes back into the inlet manifold.

Popping in the exhaust can be caused by a lean mixture but also by air leaking into the exhaust system, causing the engine to run rich (due to a false signal from the lambda sensor). Unburnt fuel then combines with the air that's leaking in and burns in the exhaust.

The fact that upping the fuel pressure makes a difference makes me think it's running lean and has run out of fuel trim to adjust it (normally changing the fuel pressure wouldn't make any difference because the ECU would trim the fuel back again).

It would need a look at the live data from the ECU to diagnose further IMHO. Has the ECU stored any fault codes?

Kevin

very good

[jonnycool]

Update on this, I fitted a cheap MAF sensor yesterday and after a little while the car became very quick and responsive, and the EML has gone out for the first time since I had the car - result! More importantly, no more pinking or misfiring

This car really is quite fast...

[Kevin Wood]

Sounds like it was running lean then. Glad it's sorted.

Kevin

[jonnycool]

Sounds like it was running lean then. Glad it's sorted.

Kevin

Thanks for all the advice Kevin, particularly about the cause of the noise I was experiencing - I thought something really bad had happened

[rustym95]

Hi there think this may help aswell, the timing belt may of come lose and ajusted out cheak that out did it to mine only 0.5mm out but made the diff, runs alot better even when going up hills.

[rustym95]

Hi have you checked the timing belt adjuster spring maybe worn out vauxhall mec told me they do that to engine when going,