Hi there guys.

I've been experiencing a serious power down on the 4.2 for some time, she's running very flat. Everything demands more power and kick downs don't produce the power expected, but she runs through the revs as normal. Idle is lower than it should be even though base was set perfectly. It's a sports spec'd engine

I have changed all the usual culprits; Lambda's, MAF, stepper and checked wiring. I got her on a diagnostics and found that one of the Lambda's is over leaning bank 1. Under power it pulls full lean very quickly.

On overrun there is a negligible amount of engine braking and she pops. This suggests an air leak. But yesterday I checked the coolant and it's very low.

There is a very serious potential problem here that I've got a coolant leak into one of the cylinders, which would have wrecked the Lambda causing this over-leaning. Obviously I don't want there to be a coolant leak.

My question is this: Would an air leak cause this problem as well? Atm It's looking like I've got some serious engine works to do fitting a top hat, but am I being over pessimistic?

I'll fill up the coolant today and see if it moves, but seeing as it was filled up 3 months ago I guess things aren't looking to good.

Is it obvious that a trip to ACR/RPi is inevitable or is there hope?

Thanks guys.

sniff test over header tank with exhaust gas analyzer

Could it be a leaky membrane in the fuel pressure regulator? I had this recently. How is your idle?

pigfarmer said:

Hi there guys.

I've been experiencing a serious power down on the 4.2 for some time, she's running very flat. Everything demands more power and kick downs don't produce the power expected, but she runs through the revs as normal. Idle is lower than it should be even though base was set perfectly. It's a sports spec'd engine

I have changed all the usual culprits; Lambda's, MAF, stepper and checked wiring. I got her on a diagnostics and found that one of the Lambda's is over leaning bank 1. Under power it pulls full lean very quickly.

On overrun there is a negligible amount of engine braking and she pops. This suggests an air leak. But yesterday I checked the coolant and it's very low.

There is a very serious potential problem here that I've got a coolant leak into one of the cylinders, which would have wrecked the Lambda causing this over-leaning. Obviously I don't want there to be a coolant leak.

My question is this: Would an air leak cause this problem as well? Atm It's looking like I've got some serious engine works to do fitting a top hat, but am I being over pessimistic?

I'll fill up the coolant today and see if it moves, but seeing as it was filled up 3 months ago I guess things aren't looking to good.

Is it obvious that a trip to ACR/RPi is inevitable or is there hope?

Thanks guys.

Click to expand...

Pull the plugs and look for one that looks washed clean.

Compression test?

Thanks a lot for the responses guys. I've been busy as hell and haven't had the time to do anything with her atm.

The idle has been running roughish (not unbearable like a misfire) down from 800ish and is sitting on the 500 line, except that this afternoon she was struggling to hold any idle so I had to left foot brake keeping some throttle. So either the air leak is expanding () or the new MAF is ****ing me about, or..., or,...or,... You know how it goes!

I noticed this morning that there were a few drops of coolant sitting underneath the chassis below the expansion tank so it's possible (fingers crossed) that these two things are unrelated, certainly do need to get a dye test to find that air leak, but if I can place the origin of this coolant drip (likely expansion tank but will check), sort it and fill the coolant I may find it decides not to go down!

I'll get a compression test done as well.

Bit sad really. At first discovering this I was gutted and didn't want to loose the engine, then I remembered a pub chat a year ago discussing the possibility of chucking an LS1 engine inside. After a little research that doesn't sound like the most difficult conversion to do, and they're such cheap craters!

Shoppinit, if you did a thread could you link it? Not sure if I'm just overtired or overstressed but I'm unable to do a search without getting confused. I do have an issue with the fuel sensor not really working at all so perhaps that might be related.