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ECMlink Low Vacuum with High Airflowperrev - DSMlink v3

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406_Talon

Supporting Member
116
13
Jun 30, 2014
Kalispell, Montana
Hello,
This is a "crosspost" with my post on the ECMlink forums, I thought I'd ask here as well to maximize exposure.

I am having some issues with my car, it's a 1995 GSX with a basic 2.0 7 bolt, Wiseco 8.5:1 pistons/eagle rods and crank bottom end, (built by me - first engine I've ever built
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), GSC S2's & supporting valve train stuff, MLS HG, PTE 5862 and a FMIC running in SD with Mitsu MAP and GM IATwith Precision WG and GFB BOV. Stock Intake manifold and stock 2g TB. PCV system run correctly with 2 sealed catch cans. Passed a BLT with flying colors before I started the motor, but I could do another one. (All details in profile are up to date)

Attached is a log I took today while trying to get my car to idle with all parameters in line. I managed to get my ISC position to oscillate around 30, and my trims are pretty close, but my airflowperrev is way high at .4-.45 and my vacuum is consistently low, in the area of 10-12. Car idles fine and controls RPM, and it seems to run fine and drive well in closed loop (I've barely driven it - maybe 5 miles and 20 minutes just putting at varied rpm in closed loop to shake it down) I tried blocking the line to the aftermarket BOV as well, to see if it was leaking internally and affecting vacuum, it did not affect it at all.

Also attached is a second log, where I tried to dial things in further, I reduced VE in the Idle cells, then I dialed fuel back in to get Combined FT back in line. I got everything fairly close, but my Injector settings are way off from their calculated values... Can anyone offer any clarification on why this would be, if it is correct? Am I just compensating for low vacuum by pulling out fuel - it seems like that's not the right thing to do...?

Based on the low Vacuum, and some reading I've done here in a few threads, I'm concerned that I may have a mechanical issue. One suggestion I saw to a similar issue was that the exhaust cam out of time. I also saw suggestions that incorrect ignition timing (CAS adjustment) can cause this but I have a 95-96 style CAS, so I think I can eliminate that. I have three specific questions, but I would welcome any and all suggestions.

1. If the exhaust cam is to blame, would I likely need to retard or advance it? I have adjustable gears, but I installed the cams straight up as I was unable to find a degree wheel that would work. I can't really work out in my head which way would increase vacuum...
2. The motor has barely been run, I'm not totally confident that the rings are fully seated this point, could that be a contributing factor to my low vacuum? If that is the case should I run the engine more or drive more to seat the rings? I was told it would take 100 miles to get the rings fully seated, and wait that long to do a compression test to ensure accurate results...
3. Could my lower compression pistons and somewhat aggressive cams be causing this issue? Perhaps my VE is still a bit high in this area at .58ish?

Any help is appreciated, I'm really at my wit's end with this project haha.
 

Attachments

  • Log 1 - Idle tuning log clipped.elg
    22.2 KB · Views: 24
  • Log 2 - trying to get airflowperrev right.elg
    372 KB · Views: 20
I'm on my phone so I can't look at your logs rn but, I would double check your mechanical timing. Aside from a vacuum leak or leaky pistons rings, the only way to lower vacuum is by changing the mechanical timing. -10-12 I would imagine that the car cranks awhile before it starts? Also probably idles very poorly?

As for the airflowperrev, it's most likely off due to your vacuum being so low. Low vacuum isn't something that you can tune and change. It's something mechanical.
 
That's my thought. I'm gonna pull it in and double check everything again tonight. starts first or second turn every time and idles pretty well, though, actually. I'm kind of leaning toward the rings still aren't fully seated yet, but it can't hurt to re-check mechanical timing.
 
Your timing is all over the place with 5* in the first box. You can try these timing settings and see what the car does. If it "HATES" it, put your table back in (its the same as the TimingMinOct table). Don't be afraid to experiment. ;)
You can copy that to the TimingMinOct table also if it likes the change and you think it is needed. The 5* is what it should be "mechanically" timed at. :thumb:
 

Attachments

  • directaccess.2022.05.09-01.eda
    15.5 KB · Views: 26
Your timing is all over the place with 5* in the first box. You can try these timing settings and see what the car does. If it "HATES" it, put your table back in (its the same as the TimingMinOct table). Don't be afraid to experiment. ;)
You can copy that to the TimingMinOct table also if it likes the change and you think it is needed. The 5* is what it should be "mechanically" timed at. :thumb:
I used your timing and a slightly altered VE and fuel settings from my previous run, it was also cooler and more dense outside, I think, and here is the log I got. I'm beginning to think that this is within the realm of "normal" for the combo of GSC S2s and lowered compression, based on some reading - I've seen people report similar vacuum numbers with Kelford 272s. If anyone with a similar setup would care to look at the log and let me know if this looks like a relatively healthy motor I'd appreciate it. I feel like there aren't a lot of 9:1 builds on here, but Montana has really bad gas...
 

Attachments

  • timing and SD changes - Better.elg
    558.9 KB · Views: 18
And here's another log with more driving, it seems to drive pretty well, although it isn't making any power with the waste gate pinned open by my SCG-1's safeties LOL. The idle at the very end shows .31 gm/rev of air, the trims are way off though. Just thought more data may help.
 

Attachments

  • Longer drive.elg
    515.2 KB · Views: 19
I run Kelford 264s and 9:1s with my Holset and 2150s. My vacuum is around 13hg. I had those cams in a 10:1 motor and had the same readings.
I'm at work but will look at the logs later if I am not too busy.
 
I pulled up your long drive log. I think that it is Globally too rich by just a bit. Your short term fuel trims are still pulling 7% of fuel out of the mix. If it were my car, I would change my global from the current -45.3% to -46.3% and see if the STFT's come closer to zero. The log didn't look too bad, but I was just focusing on your trims and the WB. I hope she is running a bit better! With the GSC2s, your airflowperrev will be higher than normal so don't worry too much about it if the car is liking you. I'm sure others can find things I didn't. :thumb:
 
Well, I'm back. I ended up finding and having to battle a bunch of issues, finally have the car back together after chasing issues with exhaust leaks and fuel tank leaks and I ran it and it still really wants to sit at .43 gm/rev at idle, I think maybe that's juts what you get with 9:1 and GSC S2s. it seems to be running well at these numbers, I'll post a log when I can actually do a real drive and try to play with the tune.
 
Aftermarket cams and especially the larger lift/duration cams, will throw the airflowperrev off. If the car starts good, idles good, runs good.....for DSMgods sake, ENJOY IT ROFL. My airflowperrev is never right with my Kelfords. That doesnt make me worry about it one bit. Just my 2 cents.
 
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