Apex High manifold vacuum ported head

[gvessey]

Hey Everyone

This is a little reverse for this section, but I figure I have the best shot of striking someone that has come across this before.

I am helping a friend with a 2011 apex that had a turbo and head shim in it and the head is ported. He is reverting this sled back to stock. Sled ran perfect with the turbo setup, put it in the shop and removed turbo, head shim, degreed cams back to stock and reset the valves, removed all power commanders. Now the sled has a rough idle, and it flares up to 4 grand on a hot start, and surges cold until it warms up. We checked the manifold vacuum and it’s double what spec is. The only way to settle the flare is to unplug the vacuum line from the map sensor and block it off, otherwise the isc valve will flare it up. Everything I have read is that head porting should not increase the vacuum.

Things tried:
-Map sensor and ISC tried in another sled and confirmed working perfect.
- Cam timing checked multiple times and is set correctly
- Checks all hoses and connections for vac leaks
- Cleaned the ISC
- All sensors checked for response in the diagnostic screen and verified changing as expected. Also compared to a known good running sled
- wiring checked to ecu
- throttle Bodies synchronized
- Adjusted throttle plates up and down a little to create less restriction(open) hoping to lower vacuum, and tried closing more to see if the isc could better control it, neither were lucrative.
- TPS is in spec and sweeps without bad spots
- Still has adjustable fuel pressure regulator tried dropping pressure, no improvement.
- New spark plugs
- Tried Power commander and playing with idle fuel with no improvement
- Fuel injectors
- New Cam gears that were not slotted to eliminate the possibility of some error in cam timing.


I realized some of the items would not affect vacuum but its been a long chase to try fix the flutter and came across the manifold vacuum as part of the process. I believe the issue is the vacuum being so high (measure from my techmate) because taking the map out of the stream seems to improve the flare and idle, but head porting really shouldn't be driving the vacuum up so at a bit of a loss and wanted to provide all the info.

Next Steps to see if improvements can be found
- Try a two bar map sensor thinking with the wider spread in voltage it might be enough to get the ecu back where its happy.
- Try a restrictor to lower the vacuum the map sensor sees.

Just wondering if anyone came across this with a ported head, or after a head shim removal.... Any ideas on something missed, love to hear ideas

Thanks in advance

 

[74Nitro]

You were using the tiny hole mark part way up the camshaft(s) to time them?

 

[gvessey]

You were using the tiny hole mark part way up the camshaft(s) to time them?

Yep

 

[gvessey]

I should add the sled has great power and works great off idle, just can’t get it to idle nice and without startup flare.

 

[kinger]

I would try to smoke test it, poor mans version is heat baby oil up, you have a leak for sure. I fought for years on a stumbling idle on my mod sled and just thought it was a mod sled and shrugged my shoulders. For a unrelated upgrade I bought all new manifold vacuum lines. Turns out I had a small pin hole under on the of the 90s that was impossible to see until you spread the 90 apart. Sled purred and still purrs to this day at idle.

A idle that high means you will have a severe leak and should be easy to see with smoke test.