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Old 04-27-2013, 03:02 AM   #1
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Default High RPM Lean Spike MSPNP2

Data log is in post 5

Hello fellas. I have been having an issue that causes my car to spike suuuper lean and I can't find the cause. The car jerks and bucks as you would expect it to. It's almost as if I am hitting revlimit, but I'm not. It happens most of the time around 5800-6500 RPM. I have found others that have this issue online, but none of them are turbo and none have MS.

First I was having issues with my IAT, and I thought that was related. The DIY pigtail from MegaSquirt kept coming unseated. I replaced the sensor before I realized this. Eventually I bought a pre-made 6" pigtail from them and since I have had 0 issues with the IAT. That works fine now.

Recently my o2 died for my LC-1. I replaced that tonight and everything looks peachy from there.

SO...



Here is a screen shot of where the issue happens. I went through every single sensor there was to make sure nothing funky was going on. I couldn't find anything.

1. I have 100% fixed the Air Temperature Sensor. That is not causing the lean spike at high RPMs.
2. New o2 Sensor - so that isn't causing it either. Now my computer and gauge are a mere 0.2 - 0.4 off as far as I can tell.
3. The car is still jerking and spiking lean at very high RPMs. The previous two shifts before this one here generated no issues. Smooth sailing.

So, the wideband isn't the issue. The IAT isn't the issue. The tune can't be the issue.

Is it possible, that even though my injectors aren't even close to their limit (550ccs at only 7lbs of boost) they are giving up and not injecting fuel at all for a split second?

The problem is intermittent. I can go whole days without the issue, then it will suddenly crop up again. It is not related to the weather at all, or my driving style.

What am I doing wrong?!

And thanks in advance!


INFO about car:

95 Running MSPNP2
99 Swap
6 speed
BEGI S4 Turbo Kit (mostly) with GT2560
Innovate LC-1
Stock Coilpacks
Rather New NGK Wires
MSM Plugs with the stock gap (.040?)
550cc injectors - TLFPerformance - under warranty.
No MAF, only IAT.

Last edited by dhyde9; 04-27-2013 at 02:06 PM.
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Old 04-27-2013, 05:31 AM   #2
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Nm... That was a stupid idea.

And for clarification, in this example I never hit redline.

Last edited by dhyde9; 04-27-2013 at 07:55 AM.
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Old 04-27-2013, 10:18 AM   #3
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Next question would be:
- Is the MS reducing injected fuel?
- Are you losing fuel pressure?
- Are you adding waaaay too much air? (boost control failure)

For that plotting another graph showing PW and MAP would be helpful.
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Old 04-27-2013, 10:39 AM   #4
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dont post the log. whatever you do...
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Old 04-27-2013, 02:04 PM   #5
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Point taken. And my apologies, I wasn't aware I could attach a file to a post on this forum. Nifty.

The only time it occurred in this log is on the very very last shift but I suppose you can see the location in the screenshot.
Attached Files
File Type: msl 2013-04-27_01.00.44.msl (1.19 MB, 45 views)
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Old 04-27-2013, 02:24 PM   #6
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Quote:
Originally Posted by stefanst View Post
Next question would be:
- Is the MS reducing injected fuel?
- Are you losing fuel pressure?
- Are you adding waaaay too much air? (boost control failure)

For that plotting another graph showing PW and MAP would be helpful.
-My suspicion is that yes, MS is reducing the fuel. The PW for the lean spike is 0.

-I do not have a fuel pressure gauge, but the way this problem occurs makes me think that fuel pressure isn't the issue. I would think that the FP would slowly wane and taper off, then take a second to build back up.

-The highest boost in this log is indeed immediately before the lean spike, but it is only 149.7kpa. Could there be some correlation these even at that low boost?
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Old 04-27-2013, 02:32 PM   #7
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What is your boost cut value?
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Old 04-27-2013, 02:46 PM   #8
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Quote:
Originally Posted by Bax View Post
What is your boost cut value?
I have never initiated the boost control settings in MS. My wastegate hasn't had any overboosting issues, so I haven't used it.
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Old 04-27-2013, 02:48 PM   #9
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WAIT!.... Overboost protection is on at 150KPA... could it be intervening early, at the 149.7 mark? eh?

EDIT: And it is set on fuel cut. I just upped that to 170KPA, and I'll test it out. I don't know how on earth that got turned on... ugh.
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Old 04-27-2013, 02:49 PM   #10
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Τοo fast to log it...
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Old 04-27-2013, 02:53 PM   #11
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Quote:
Originally Posted by Bax View Post
Τοo fast to log it...
Thanks, man.

I guess it didn't occur to me because I've never messed with overboost protection in TS. I've been having this stupid issue for months... maybe the base tune from DIY sets overboost protection at 150kpa. hmmmm
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Old 04-27-2013, 09:22 PM   #12
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Confirmed that was it. Gracias everyone.
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