Misfire cylinder 2(actually 1) only under load

**Scottydoggs** · 03-30-2015

well its time to take it apart now, but you knew that already.

**GTPpower** · 03-30-2015

Sounds like that valve may be burnt or bent. You are probably going to have to pull the head no matter what.

**2004l67** · 03-30-2015

Sounds like a bad valve for sure then.

I had a crazy intermittant misfire on a vortec 5.7 last year. Chased it forever, thats when I learned the importance of the leakdown. Turned out to be a bent exhaust valve. Can barely tell to the naked eye but when you roll it on a table or desk it's obvious.

**Reptile** · 03-31-2015

Did you give the crank another half turn to make sure the cylinder is at BDC on the compression stroke?

**sseilmnop** · 03-31-2015

I spun it to many different spots.

**2004l67** · 03-31-2015

Heads off yet?

Having been thru the same issue on a different motor, I'm very curious...

My bent valve...

**sseilmnop** · 03-31-2015

https://vimeo.com/123792173

Bent valve

Where do I get new valve.

**Jomamma** · 03-31-2015

Its funny, the same thing was happening to me. At first my aeroforce kept telling me it was cyl 2 missing when it was cyl 1.

I wish I would have found a bent valve... pretty sure its the cam ill find out for sure tomorrow.

**Booba5185** · 03-31-2015

Assuming you have a Series II:

http://www.oreillyauto.com/site/c/de...=exhaust+valve

I think that the Series III might have a different size...but it might just be the intake valve that's different.

**2004l67** · 04-01-2015

That sucker is really bent. Any evidince on the piston that it kissed it maybe?

Probably a local machine shop or engine rebuilder. I PM'ed ya the guy I use. Probably a bit of a drive for ya though.

**sseilmnop** · 04-01-2015

Going to looks at doing my self, ordered valve from summit would like to check the valve guide. As I understand it the only way to bend a valve is with the piston. Suspect the valve stuck.

What size reamer for valve guide hole?

**Reptile** · 04-01-2015

Any head work, I take it to a shop. The cost should be minimal for them to check and ream the guide. I think I usually pay like....$15 bucks to have it done.

**0069GTP** · 04-01-2015

^^^ I'm with Reptile on this one. I would take the head (myself both heads) and have them both checked over and go ahead and get a complete valve job.

**sseilmnop** · 04-03-2015

I'm just not right.

**sseilmnop** · 05-25-2015

I broke down and took the heads to a machine shop. Put them on and and now I'm getting a misfire on cylinder 4 only.

I pulled the heads put brand new head gasket on and same thing. Replaced the intercooler same thing. I rotated the coils plugs, wires, etc.. and misfire on 4 only during boost or load.

I stumped! It's not the following.
*plugs
*wires
*coils
*ICM
*injectors

Misfire only under load or boost #4
Swapped. Nothing under vacuum

Compression on 4 is 140isg
Compression on 2 is 155 (think the rest are 150-155)
Machine shop replaced or put in 2 new intake seats in. Not sure which heads or cylinders. This think runs better without a supercharger belt!!!!!!!

Is 140 low enough to cause sputtering on cylinder 4?

**0069GTP** · 05-28-2015

General rule of thumb is no more than 10% difference which you would be at with the highest at 155 and lowest at 140. I would think this would be worse on a forced induction engine than a NA engine. Have you done a leakdown on cylinder 4 yet?

**sseilmnop** · 06-20-2015

Still chasing this. Would does a clogged cat act like?

Should I get 163 psi on a compression gauge with a L67 block and 1.9 ratio Yellow terra rockers? Seems way to high!

I did a compression check on a top swap motor with with a VS cam and only got 155 psi with the same gauge?

**sseilmnop** · 06-21-2015

Somebody?

Could a plugged cat have caused the bent valve?

Couldn't see a mark in the piston so not sure the piston bent the valve.

Somebody had to have seen this before?

**Scottydoggs** · 06-21-2015

did you pull the lifter out and check that as well? if it wont pull out that could be the issue. if it does maybe the cam or roller on the lifter is bad?

all guesses.

**sseilmnop** · 06-21-2015

I'm getting misfires now on some different cylinders but always seems to come back to #4.

There is no ticking, valve train is quite. I didn't pull the lifters out.

Pulled ported heads twice. Put front on back and back in front.

Put on stock heads.

Runs pretty good (smooth) except under boost.

Boost I get misfires not KR
Vacuum I get no misfire or KR