My car is down about 80-90 hp on the top end (I have made many posts here trying to figure it out, you can search on it for more info). The rpm and map values pulse back and forth during hard acceleration.

I have attached a vacuum gauge to my intake manifold at idle.

The vacuum pulses about 2 inches from 12 to 10 in a rhythmic fashion about one drop per second to a second-and -a-half. You can see examples of it on both sites below.

Both of theses sites suggest that I have either a leaking valve or a mis-fire:
http://www.performanceprobe.com/inde...stics/imvt.php
I know it's for a Probe but the science is the same.

http://autospeed.com/cms/A_2393/article.html
Scroll down to leaky valve picture.

Anyways, the heads were ported and given a three angle valve job with new springs. I have replaced the following over the last year:
PCM, engine wiring harness, plugs, wires (twice), coil, stock opti, MSD billet opti. I have swapped out the MAP and coil module with a friends to no avail. The rockers have been adjusted and readjusted many times to 1/8 turn pe-load past 0 lash

I did a compression test on all cylinders except number 8. They were all at 185-190 after 3 seconds and 195-197 max. I performed a leakdown test on all cylinders except #1 and #8. All were at 8% leakdown except #2 at 6%. Cylinders were skipped due to access issues with headers.

What can I check next?

 

I know that accessibility sucks in our cars but a compression test and a leak-down test doesn't mean much unless you get all cylinders, am I wrong?

 

Another vote for completing the compression/leak down tests.

 

need to get all cylinders

 

The vacuum test could be one of these. A sticking valve, ignition miss or intake leak.

 

How can I test for the sticking valve? I'm assuming it's sticking open. Would that show up on the plugs in any way?

Could it be a weak spring? Maybe letting the valve bounce? but it's at idle speed - unlikely I think.


I don't think it's an ignition misfire due to everything being changed and all of the plugs are pretty much the same color (dark tan to tan). And I think an injector misfire would show up as either black (rich - stuck open) or white (lean). I've swapped the injectors bank-to-bank. And a non-firing or weak-firing plug would show up as dark (yes/no?)


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I yanked off the partial header and tested #1 - 185 compression and 8% leakdown. I may be able to yank the starter and get to #8. I will try today or tomorrow. 7 out of 8 are in the ballpark so far.


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I think this pretty much says it all:



11.58 : 1 AND NOS. Bad combination

Wouldn't 80 or 90 hp mean you have a dead cylinder? What about EG temps?

 

The new motor has only 1 -100 shot on it at the dyno to see if it made any difference ( it only increased tq by 63 ft-lbs , and the timing was retarded 5 degrees). It has 1100 miles on it, all NA. It has run a best of 11.87 @ 112 in speed density mode, while spending 3.1 seconds in 3rd gear from 5500-5900 rpm. With MAP and RPM readings pulsing up down, about 200 rpm after it hits 4000 (you can search for all the stinking posts I've put up trying tp explain the problem over the past summer)

The old stock bottom end ran with the spray. I haven't had time to update the site due to shear frustration with this thing. The heads were sent out to be ported, milled, and given a 3-angle valve job. There was nothing wrong with them.

I've compression and leakdown tested all of the cylinders as of last night.
All 8 were at 185-190 compression and 8% or less leakdown.


I think I've got it narrowed down some after some testing yesterday.

I am running a MSD Digital 6 through an MSD harness to an MSD blaster coil to a MSD billet opti. When I get over 6400 rpm it breaks up really bad, almost like a soft-touch rev limiter but way harder. It's not the fuel cut-off, that hits at 7149 rpm.

When I disconnect the MSD digital 6 I can pull all the way to 7000 rpm in 1st and 2nd gear. Even though it still feels like it has the same power output. (a little down).


Any thoughts on where to look for this ignition problem?