Here's a fun one. 5000 RPM cut and misfires

[Watson]

Alright so here's the background:

 

After breaking in the engine in I proceed to make some third and fourth gear pulls to tune the top end of the VE table. It kept cutting out around 5K as if there was a fuel cut or something. Checked my variables and nothing was out of whack. That day, I ended up blowing the head gasket at cylinder one. I replace the head gasket with a Felpro, I still experience the 5k cut but the new gasket has held strong through a lot of trouble shooting.

 

A couple weeks later after trying many things e.g. plug gap decrease (with iridium plugs too), clean the fuel pickup, boost leak test, pull timing and dump fuel, I've got nothing. So I go to a shop I know...

 

As soon as I pull up he notices the intermittent misfire. He spray the intake manifold at each cylinder with carb clean and notices he can choke the engine when he sprays at cylinder one. We do a smoke test and no smoke pours out! He pulls a vacuum line on the intake manifold to verify there is smoke; it's billowing out. We do the same thing, start the car, choke it with carb cleaner, and then he gives it a steady stream to smooth out the idle to verify what is happening is no fluke.

 

We tried spraying in many areas around cylinder one to include the fuel injector. It only affects the engine where the gasket is. The manifold gasket did seem to look funny so I replaced it with a Felpro; a much better gasket than the JIS bullcrap gasket I had. Still the same issue. So....

 

How can there be a leak at cylinder one but a smoke test will not verify it?

Edited June 7, 2014 by Watson

[NewZed]

When the engine is running,throttle closed (idle) there's about an 8 psi differential between inside and and out.  Your smoke test probably has less than one psi differential, if any at all.  Pressurize the manifold with the smoke inside and see what happens.  

 

Just a guess.  You didn't give any details on what the "smoke test" is.

[Watson]

I would have to ask my guy how much pressure was applied. He did in fact pressurize the system and pump smoke into it but at what amount of pressure exactly, I can't remember.

 

I should also note that it revs freely up to 6500 with no issue while stationary, but of course there is no load on the engine at that point. Also, this is a turbo setup so "load" implies boost.

Edited June 8, 2014 by Watson

[Domzs]

Try to smoke test when the engine is cold , poss intake/exhaust manifold warpage . The smoke machines don't put out a whole lot of pressure . They're designed for EVAP leak detection but most people , including me , use them to find leaks .