Mi16 Misfire

[savage16v 3 1 Cars]

Hi all,

 

Hoping for a bit of advice please.

 

My Mi16 is running on twin 45 webers, with Catcam inlet cam and a few other mods.
I had it set up on a dyno recently, and it has been running fine since, very happy.

 

Had it off the road for a couple of months and done quite a few bits to the car in general, although not much under the bonnet.

 

Rocker cover off for a repaint, fuel lines off for new DEI sleeves, and that's about it.

Got it back on the road on Saturday, went for a drive and noticed it was missing a bit......
Also the top end was tapping a bit, which was odd as I checked the oil and it seems fine.
Topped the oil up, top end went quiet!!

 

On the way home, the missing became a little more apparent, and the car died (felt like fuel starvation).

Got it going again, it seemed much better when driving quickly.

 

If you floor it and back off, its very apparent, around 4k rpm is when its worst.

 

Had a chance to look lastnight, it is cyl1 which is missing, on part throttle you can see it flaming through the carb and blowing back through a bit.
If you blip the throttle, its not so bad.

Swapped the plugs (all of which are fairly new and which looked like the cyl's were running perfectly)... Misfire stayed on cyl1.

 

Swapped leads, misfire stayed on cyl1.

 

Took the dizzy cap off, and it looks fine, as does the arm, but I know its not always possible to tell.

 

That's all the time I had on the car lastnight before I had to go out.

 

I am wondering, likely dizzy cap?

Might be a crazy idea, but maybe a lifter failing? Although the top end doesn't sound particularly tappy.

 

Any advice would be very much appreciated.
Thanks in advance.

Edited February 26, 2015 by savage16v

[savage16v 3 1 Cars]

I did also fit a smaller airfilter, but this is not the cause as its exactly the same without a filter.

[savage16v 3 1 Cars]

I have searched many forums as well, but cant see anybody has posted a similar problem....

[dcc 855]

compression test

[savage16v 3 1 Cars]

I have been round to my mates at dinner, borrowed his compression tester matey....

Will check it out tonight, hoping its all clear, really don't have the time to be stripping engines atm

Edited February 26, 2015 by savage16v

[savage16v 3 1 Cars]

Well I got home, free evening to work on the car, walked in the garage, realised I had left my tools at my mates and he is out so I can't go and get them!!

 

Closed garage, came inside!

 

That buggered my evening on the car

 

Will do the compression test tomorrow night!

[savage16v 3 1 Cars]

Finally got round to doing a compression test lastnight!!!

 

Cyl1 = 105

Cyl2 = 170
Cyl3 = 125
Cyl4 = 170

 

 

Think the engine is coming out

 

I don't have time atm, so its going in the corner of the unit, whilst I finish the GTE off to get up for sale, then will get the Pug back out and pull the engine........

[dcc 855]

Oh bad luck

 

If this is a 1.9 mi, I am sure the compression should be closer to 210-220psi.

 

The fact that 2 of those figures are so low, but not on neighboring cylinders leads me to think it could be more than just HG.

 

I am sure somebody will be along to correct me, but this could be valve seat damage, valve damage, worn piston rings or HG failure.

[savage16v 3 1 Cars]

Cheers mate, I thought 170 was about bang on for a performance N/A engine but I could be wrong.

 

I don't think its HG, as its misfiring through inlet & exhaust so I fear valve problem of some sort (cyl1).

 

However, I have no misfire or anything from cyl3, also no signs of water in the oil that I noticed, although I have not looked specifically yet.

[petert 586]

Depending on the inlet closing time (largish inlet cam), a figure of 170 psi could be feasable with standard CR. Values of 105 and 125 are bad however.