ECMlink Back to Link, back to dumb questions

[gofer]

Well, you said 27psi between 5k-5.5k so lets do the math together shall we?

((Actual Boost + 14.7 PSI) / (BoostEst + 14.7 PSI)) - 1

1. 5,000rpm @ 2600Hz=((27psi + 14.7psi) / (23.7 + 14.7)) - 1
   • (41.7 / 38.4) - 1
   • 1.085 - 1
   • = 0.085 or +8%
2. 5,500rpm @ 2900Hz=((27psi + 14.7psi) / (33.5psi + 14.7psi)) - 1
   • (41.7 / 48.2) - 1
   • 0.865 - 1
   • = -0.135 or -13%

Well Kris, I've determined you aren't a Elementary school math teacher for a living. I'd like to see how you've got your GM MAF plumbed into your IC piping, certain couplers can cause turbulence at the MAF creating weird airflow readings. Going from a +8% increase to a -13% decrease that quickly doesn't make sense, so I just increased everything from your 2600Hz slider +8% and smoothed out the ones behind it...

Set your MAFComp sliders to these points and do a WOT pull...

1700 : -10.2
1800 : -11.7
1900 : -10.9
2000 : -10.2
2100 : -8.6
2200 : -7.8
2300 : -6.2
2400 : -5.5
2500 : -3.9
2600 to 3100 : -3.1​

 

[snowborder714]

Dammit Corey. I was doing that, but got pulled away from my computer because of a work call.

 

[LandoAWD]

I'm missing something here, and I don't know what it is. I went back to the mini-getonthehighway pull in the recent log, and noted the data point at 5760rpm and did the work there, IIRC...but the boostest was 35psi or better. Do I need to adjust the resolution to be able to see a 5500rpm data point?

I'm familiar with the formula, but there is something I'm not following.

I'll snap a cell pic of the underhood at lunch. I won't use my nice cam as it's not a pretty bay.

 

[gofer]

You can't adjust the resolution, in that log the closest you can get is 5466rpm @ 32.8psi or 5556rpm @ 33.5psi. If you did the work at 5760 then thats a different story, its no wonder you came up with a different number then...

Kris, another possibility of the inflated airflow is a boost leak after the GM MAF. Its also important to note the temperature outside since the GM MAF assumes 80*, every 10* lower than that will increase BoostEst by 1psi, or vise versa. So if its 60* out and BoostEst is logging 32psi then you should calculate for 30psi, 20* colder than the assumed 80* = a 2psi inflation.

 

[LandoAWD]

Yeah, I've seen that as a possible culprit. I need to make friends with a compressor owner. Last BLT held through 25psi till the coupler blew off. Nothing IM side of the setup has changed since then , though the IC piping has been on and off.

The temp thing is interesting. I'll start noting ambient.

 

[gofer]

Like I mentioned too, its possible your IC pipe couplers are causing the strange airflow readings by creating turbulence in the pipe. The GM MAF couplers that I've seen create turbulence at the MAF look like these, its because there is no gradual increase/decrease going to or from the MAF. Some are even worse than this one, but the best ones to buy and prevent it from happening are sold at ExtremePSI.

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[DSMTyson]

Jeez, you guys are awesome . My car is running considerably better just from reading this thread and researching what I didn't understand, and then making adjustments. Thanks again

 

[LandoAWD]

...and I broke another re-man axle.

I hate, hate, HATE Autozone. 3 in 5 mos.

 

[gofer]

...and I broke another re-man axle.

I hate, hate, HATE Autozone. 3 in 5 mos.

AutoZone hates, hates, HATES you for returning busted axles, I get dirty looks every time I return alternators. What breaks on the axles and is it from launching or just normal wear and tear?

Your doing transmission fluid changes more often than engine oil changes!

 

[LandoAWD]

Well, it's not off, but I have a nasty vibration under acceleration (again), and there's some grease slinging around the outer boot on the driver's side.

I drive the car in a very spirited manner, despite it being my DD. I'm not sure what the culprit is, but I haven't launched the car on this pair of fronts. :/

 

[gofer]

I went through axle boots regularly when I was running my Sportline springs, the car was too low. I'm not sure if thats your problem but if you aren't tearing through neighborhoods and launching at stop lights I'd start considering suspension changes.

 

[LandoAWD]

Super-inflated BoostEST (still), but a quick 25 psi pull yielded a nice stutter/misfire as the RPMs climbed.

Little jaunt starts at 187s...spark blowout?

 

[delta448]

I see the misfire in the log.
Try gapping the plugs a shade tighter?

I think this may be related to your issues with the GM MAF readings.

 

[LandoAWD]

Will do. I have 7s and 8s somewhere around...just need to find them.

 

[snowborder714]

I would go with the 7's gapped at .024-.026".

 

[gofer]

...your MAFComp sliders are all wacked out, in that WOT pull at 187 BoostEst is hitting 43psi. Do some sanity checks (idle/cruise) after you replace your spark plugs or whatever it was you thought was going to fix the problem.

Basically, you're starting from the top again. Idle CombinedFT/AirflowPerRev then onto cruise, etc. etc.

 

[LandoAWD]

I hate tuning with the damned GM MAF.

Those sliders are untouched...hell, the whole "tune" is untouched, yet I'm back to square 1. :/

 

[LandoAWD]

Update: Replaced my UICP/BOV setup and went back to my 50mm Tial, only with the proper weight spring. I also slid some couplers around and refitted the t-bolts.

I immediately noticed idle problems. I really am starting from scratch as MAFComp was WAY off all through the range. Idle and cruise are doing well, CombFT is +/- 3 and I'm narrowing that down, but WOT is plain BORING now with zero'd out settings.

I'll get it "closer" and log will follow.

 

[gofer]

Look forward to seeing it then Kris. The GM MAF is a P.I.T.A. to tune since it doesn't take temp into account it seems somethings always off. I ran my GM MAF setup for about 2 months before I got fed up and went to SD, you might want to consider doing the same. It might seem like a stretch for cash but you can sell your GM MAF setup for what you spent to go SD, basically you come out even...

You can make good numbers on a GM MAF but its very temperamental and SD has a lot of resolution over a MAF setup, its SCHAWEET... just ask Nate.

 

[LandoAWD]

Yeah, our 80* to 29* swings here lately aren't making this easier as I just did it last weekend.

I also stopped venting my valve cover, dropped in a catch can, and re-circed the hose.

Once temp stabilizes and I can build a good basemap for the SD switchover, I'm doing it. A new UICP will likely be needed, but that's not bad.

 

[Calan]

Have you tried rotating the MAF 90*? They are pretty finicky about laminar vs. turbulent flow.

I agree that you may have a spark issue as well when you were seeing the misfires. Original stock coils?

 

[LandoAWD]

Coils are stock. Original? No clue.

I'll hold off on the 90* turn of the MAF for now as I don't want to add another variable, but rather address it as an issue if it ends up being part of the problem moving forward. Sorry, that's just the IT guy in me.

 

[LandoAWD]

Put plugs in yesterday, but didn't drive the car until this morning. The miss is gone, and I peed a little romping on it in second.

FWIW, the plugs (all but #3) were BLACK and WAY too firmly tightened in. Also, the gap was around .029. Never again will I assume my buddy (mechanic) is competent enough to do plugs while I work elsewhere on the car; never again.