General Misfire at idle but not under load.. Compression

[chrisb7777]

Drove to my local city tonight for late night shopping, before leaving car was running great, as I arrived I noticed the car was misfiring!

Parked it up and let it cool, came back and no change. Pulled the relays and turned over on the starter. Sounds like I have a dead cylinder!

Now this is were it gets strange, when I put the car under load it runs great! No loss of power and running like normal! Yet if I rev it in neutral it still misfires!

What am I looking at here? It's not overheating, am I looking at replacing valves?

Not having much luck this winter at all

Thanks

Chris

 

[rallycinq]

Drove to my local city tonight for late night shopping, before leaving car was running great, as I arrived I noticed the car was misfiring!

Parked it up and let it cool, came back and no change. Pulled the relays and turned over on the starter. Sounds like I have a dead cylinder!

Now this is were it gets strange, when I put the car under load it runs great! No loss of power and running like normal! Yet if I rev it in neutral it still misfires!

What am I looking at here? It's not overheating, am I looking at replacing valves?

Not having much luck this winter at all

Thanks

Chris

unlikely to be valves, but a compression test will reveal all.

Cheers

D

 

[chrisb7777]

Okay had a good look at it today...

Firstly compression test as requsted:

Dry Wet
1 165 165
2 70 75
3 160 170
4 120 170

So from that cylinder 2 is most likely the problem, although 4 is showing low..

Back in may i replaced the head gasket as it had gone on cylinder 2 on one of the coolant jackets

I took the throttle bob off and the tb has splashes of oil on it. Started it up with the bob still off and steam/smoke started coming out. Im not sure how much if any is normal...

Could this be head gasket again but on the oil side? Why is it running perfect whilst driving?

Im guessing this is going to get worse and im not prepared to repair the engine right now.

Thanks

Chris

 

[David C]

Could this be head gasket again but on the oil side? Why is it running perfect whilst driving?

Because with a closed throttle it is pulling a vacuum and sucking liquid in.
Under load the vacuum isn't there and the liquid stays where is should be.

 

[chrisb7777]

Because with a closed throttle it is pulling a vacuum and sucking liquid in.
Under load the vacuum isn't there and the liquid stays where is should be.

Surly this wouldn't be the cause? There is a higher vacuum during idle but there is still compression. Much higher compression during load. If it is able to leak into the cylinder it should also be able to leak out?

Chris

 

[sei16v]

Valves/stems on no2?

 

[chrisb7777]

Valve stems wouldn't cause low compression though

Chris

 

[sei16v]

I was going more along the lines of a possible leaky valve, but the stems with the oil prob, escaping into the inlet.

Poor compressions only going to be gasket, rings or valves..

 

[rallycinq]

There should be nothing coming out of the bob, there should be suction from the engine..would suggest that no 2 has an inlet valve/seat with a wee bit missing.

At higher gas speeds its not so obvious.

Cheers

D

 

[chrisb7777]

Sorry i think i made myself unclear as to where the steam/smoke was coming from. Its coming from the vent on the rocker cover which is then making its way to the bob. nothing coming out of the tb itself.

I took the bob off again yesturday and the top of the tb is covered in oil now. I have lost power throughout the rev range too. Look like the head gasket has gone on one of the oil passages.

I have a engine out of a x reg sei with 40k from my local scrappy for £100 to put in as i need to keep the car on the road, is it worth fixing these old pushrod engines?

Chris

 

[fingers99]

I have a engine out of a x reg sei with 40k from my local scrappy for £100 to put in as i need to keep the car on the road, is it worth fixing these old pushrod engines?

Yes and no. Morally, ethically and environmentally, yes. Financially, possibly not.

Assuming 899, it's a straight swap. If you're planning to keep the car (and the gearbag on the Sei is good) I'd get the gearbox, too.

 

[chrisb7777]

I feel bad killing a running engine thats all!

Whats the best way to lower the engine out of the car? I will grab the gearbox on my next pay check and keep it as a spare

Chris

 

[David C]

If it is just the head gasket it is an easy job to change on the 899 engine.

 

[rallycinq]

I feel bad killing a running engine thats all!

Whats the best way to lower the engine out of the car? I will grab the gearbox on my next pay check and keep it as a spare

Chris

Lower the whole car until the engine is resting on a couple of pallett then lift the shell off the engine

Cheers

d