Made some datalogger runs today...

[90 GSX]

Okay so basically ever since I got the car I have been trying to get it running in tip top shape before I do any large mods. Right now it has a Joe P mbc set to 10 psi, a k&n filter, and a bunch of brand new stock replacement/maintenance parts. I have not yet been able to do a successful boost leak test but I think that's the culprit. Tell me what you guys think...

On the datalogged runs that I reviewed I am getting anywhere from 10-30 knock counts above ~4500 rpm but it varies between runs. It usually doesn't get >10 until 5100 or 5200 rpm and then by 6500 it will be anywhere from around 18-28 counts. My timing has dropped as low as 12* at WOT and as high as 18* or 19*. When that much timing is pulled the car just falls on its face. I also notcied that my L,M, and H fuel trims are all at 140%. Another thing, the car only makes 15 in HG on the vacumn gauge... I have replaced the intake manifold, TB, and snorkel gaskets, along with the injector o-rings, etc. etc. Only thing I didn't do in that area is the throttle shaft seals.

What do those symptoms tell you? Could it be bad injectors? Boost leak? ECU caps (I did a 91 Eprom ECU swap along with the gauge cluster, coil pack, reisistor, etc. The guy said it had new caps)? Lifters (buying 3g lifters VERY soon)?

I have tried to do a boost leak test with the tester on the compressor inlet as per vfaq but I never got it pressurized for some reason (I didn't have a boost gauge hooked up either but from what I could tell it was not pressurizing). Could that tell you anything else? Could there be something more serious or something I'm overlooking? I'm not sure if I was doing it right but I will do another boost leak test tomorrow to see if it registers on the gauge.

If I have bent valves or bad rings or some crap like that I will part this motor out and buy another low-mile 6 bolt. Compression is around the 140's, low but not horrible. I have not been able to find a place with a leakdown tester yet. The car runs too good to have any serious problems like that but I will not rule that possiblity out. Any suggestions on that aspect?

 

[deusxmachina]

I'll lay out the bottom line: you need to do a proper boost-leak check or nothing else you do matters at all. The 15hg vaccum clearly says either the timing is off or there is a big boost leak. A DSM with more than minor boost leaks is a crap-ass-running DSM.

 

[Boosted93]

Are you getting the notorious lifter tick. If you are getting lifter tick that is making your knock sensor go crazy. When your knock sensor goes crazy, it retards your timing. Resulting in loss of power and if your @ 12 degrees timing @ WOT @ 5000+ RPMs your looking to blow that motor up. Careful. Replace those lifters, or clean them. Cleaning them is cost effective and not extremely hard. I use "Engine Restore" with every oil change, i get 1 count of knock tops. Used it for a while and saw no side effects from using this oil additive.

 

[ivanr4g63]

My opinion is replace your lifters as soon as you can, try to pintpoint any possible boost leaks even if you didnt had an aftermarket boost gauge your boost needle on the dash should give you and idea when you presurize the intake path...


Also I understand that your timing being pulled that much can cause low vacuum readings, but if your vacuum is low all the time thats a true sign that your catalytic conv may be clogged or getting there, my advice have that check, or simply slap a test pipe on and see if there's any difference.