Bad compression/misfire

Technical Area Engine, Transmission, Exhaust etc
2

Hi all.

Got some time off work so I figured I’d stand in the cold and try a d track down my misfire.

I’ve replaced the coil pack, leads, plugs, maf (I broke it) still failed not on emissions I’m guessing from the slight misfire and fuel smell from exhaust.

I’ve just done a cold compression test and it dont look good

Dry

#1 105 psi

#2  90 psi

#3  105 psi

#4  55 psi

Wet

#1 75 psi

#2 90 psi

#3  115 psi

#4  60psi

 

Any ideas?

Valve clearances?

I’m using a cheap compression kit from euro so I guess the figures might be out due to that but #4 is way down

Any advice much appreciated.

Cheers,

Paul.

 

 

 

3

Hi Paul

Sorry to hear this - here is a good guide to low compression. 

Oil introduced into cylinders will confirm a bore issue.

A more sophisiticated leakdown test will need to be done to check valves.

If the engine proves not financially viable to repair you will need to find another from an auto. I don’t think this would be that hard as these 110bhp auto engines are not as sought after as the 115bhp Eunos/early MK1 manual.

4

Thanks for that, I’ll have another look and check the belt and cam timing before I set about taking the head off.

Seems weird as it starts no problem, only a slight misfire at idle and drives great, quite sprightly actually, but the emissions were very high.

It really was owned by an old lady I’ve k own for years and it was never driven with any sort of enthusiasm, maybe that’s the problem???

 

5

The ‘wet’ result from No1 looks to be an anomaly.  I’d recheck that.  However as No4 remains very low when ‘wet’, my thoughts would be valve leakage.  No. 2 doesn’t look that good either…

Going back many years an A series engined Minor I was gifted (by an elderly lady) was found to have a burned valve on one cylinder which showed as a definite misfire at idle, but seemed quite smooth when revved.  Started fine - the ‘good’ cylinders will get it away.

JS

6

Yes I think the cheap euro tester isn’t being completely honest with me, the car has been serviced regularly, I’ve just started stripping the head down today and it’s a lovely gold colour inside, the cams are like new, the oil looks like it’s only done a few thousand miles.

The engine has only done about 80k so I’m struggling to believe it’s the rings

There was no vapour coming from the oil filler, so I’m beginning to think that a lifetime of old lady abuse has covered the valves in a healthy covering of carbon causing them to not seal properly.

Started to get dark and raining now so will get the head off tomorrow and see what lurks beneath.