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Old 10-07-2013, 05:45 PM   #1
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Experts- need some serious help

Ok, my car is doing some wierd crap between 2500-4000 rpm when attempting to throttle through that powerband. It almost feels like im lossing ignition and will buck/stutter really hard. It reacts better if I just stab it when im in that range but still has a stutter. Its almost nonexistant on the dyno due to being wot at an earlier rpm range(2k) and it will just push through.

Tuner has looked at it 3 times and swears there is a mechanical issue as he has added fuel/removed fuel, advanced timing/removed timing etc. I have replaced plugs, plug wires, coils, throttle body(TPS sensor), checked fuel pressure. Im not sure where to go next... I thought maybe it was in the harness, but im throwing no codes. Help!?

attached is a snap shot of whats going on in the datalog. You can see fuel trims going super positive and Knock going through the roof while pulling 4-10 degrees of timing. We have checked everything physical and cant seem to locate anything causing the knock.

one common I noticed going through my log and reviewing every event is that it happens at the 38-41% TPS everytime no matter what gear

Car is on E85 & meth
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Old 10-07-2013, 06:15 PM   #2
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Have you checked anything in the fuel system yet? And have you filled up since the issue began?

When I was involved in the import game E85 was the fuel of choice for lots of STi owners, and a bad batch of corn can lead to symptoms very similar to this.
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Old 10-07-2013, 06:25 PM   #3
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Ive dropped the filter and it was clean, have also had my ID2000 injectors cleaned. I have been on about 6-7 full tanks of fuel from 3 different stations.
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Old 10-07-2013, 06:33 PM   #4
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Gotcha, I really thought I was on to something there. What plugs are in it?
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Old 10-07-2013, 06:39 PM   #5
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currently BR7ef gapped at .028, previously had TR7ix and did it with them only after head swap/retune.
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Old 10-07-2013, 07:20 PM   #6
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Little weird how the map spikes just before you got that big knock
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Old 10-07-2013, 07:32 PM   #7
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Have you tried replacing/cleaning the MAP/MAF sensors yet?
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Old 10-07-2013, 07:46 PM   #8
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Brand new maf sensor. Was gonna swap the map with a known good one tomorrow.
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Old 10-07-2013, 07:51 PM   #9
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Brand new maf sensor. Was gonna swap the map with a known good one tomorrow.
Solid plan. Like motion427 said, that little MAP spike just before the big KR kick-in is slightly iffy-looking. Let us know how that ends up going for you.
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Old 10-07-2013, 08:39 PM   #10
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You could also try a warmer plug, if you are mostly just driving the car, try the ZR1 plugs. I had random misfires, car breaking up, coughing, etc. and it went away with the plug change to ZR1s.
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Old 10-07-2013, 11:18 PM   #11
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The timing is probably being pulled due to the knock. I don't really get why your AFR stays the same while your going into boost. It looks like it just stays at 12.5 right through that log.
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Old 10-07-2013, 11:21 PM   #12
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It isn't hooked up is why. Warmer plug would not solve this. It isn't a slight misfire, it is breaking up pretty badly.
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Old 10-07-2013, 11:30 PM   #13
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It isn't hooked up is why. Warmer plug would not solve this. It isn't a slight misfire, it is breaking up pretty badly.
Why log and look for this issue with no wideband. If its lean it would show the symptoms described. Knock and breaking up.
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Old 10-08-2013, 02:08 AM   #14
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My car did something similar and it turned out to be a loose passenger head ground... It would just fall on it's face and then pick right back up and buck back and forth.

It doesn't sound like you have the exact symptoms I did but it is something to think about. I replaced plugs and wires in my quest... turned out they were fine.
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Old 10-08-2013, 09:11 AM   #15
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My car did something similar and it turned out to be a loose passenger head ground... It would just fall on it's face and then pick right back up and buck back and forth.

It doesn't sound like you have the exact symptoms I did but it is something to think about. I replaced plugs and wires in my quest... turned out they were fine.

I have seen that before several times too, some aftermarket heads do not have the holes drilled as deep, so you go and tighten the bolt but the ground is still loose.
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Old 10-08-2013, 10:01 AM   #16
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Canuk, he has a wideband just not hooked into hptuners.

Camper, if it isn't fixed by Sunday bring it over or I'm coming to you.
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Old 10-09-2013, 06:04 PM   #17
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So have you tried listening to the engine to hear what noises are being made when it thinks it is hearing some knock ?
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Old 10-09-2013, 06:17 PM   #18
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Camper, any update on that MAP sensor switchout? Make any difference at all?
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Old 10-09-2013, 07:04 PM   #19
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So have you tried listening to the engine to hear what noises are being made when it thinks it is hearing some knock ?
Dude, my blower sounds like a jet airplane. I can't hear my motor let alone something that sounds off..
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Old 10-09-2013, 07:27 PM   #20
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I had the same problem with my TT Camaro, the only way I was able to get rid of it was by disabling dynamic airflow prediction (DAP) in the tune. This essentially makes the tune MAF only throughout the entire RPM range. See the attached screen shot, setting the high RPM disable to a low value disables DAP. Your's is likely set at the 4K RPM range.

There are ways to modify the DAP coefficients such that the prediction algorithm will work for a boost application, which I can explain but in all honesty my car ran just fine in all MAF mode. Just make sure your tuner dials in the MAF curve accurately.

If this is the problem, you should find another tuner as that fellow is not familiar with the E38 and higher PCM's.
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Old 10-09-2013, 07:31 PM   #21
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Camper, have you considering going speed density?
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Old 10-09-2013, 07:37 PM   #22
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I had the same problem with my TT Camaro, the only way I was able to get rid of it was by disabling dynamic airflow prediction (DAP) in the tune. This essentially makes the tune MAF only throughout the entire RPM range. See the attached screen shot, setting the high RPM disable to a low value disables DAP. Your's is likely set at the 4K RPM range.

There are ways to modify the DAP coefficients such that the prediction algorithm will work for a boost application, which I can explain but in all honesty my car ran just fine in all MAF mode. Just make sure your tuner dials in the MAF curve accurately.

If this is the problem, you should find another tuner as that fellow is not familiar with the E38 and higher PCM's.
Steve, I believe it is already maf only.
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Old 10-09-2013, 07:41 PM   #23
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Camper, have you considering going speed density?
Yes but I was previously SD but the best tuner in the Phoenix market wanted me to swap to MAF. I don't have a great reason other than he wanted to...
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Old 10-09-2013, 07:42 PM   #24
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Camper, have you considering going speed density?

SD is likely his problem now; the E38 is a hybrid in that below 4K RPM it uses DAP to calculate airflow (rather than looking up the in an VE table). The DAP coefficients are a hassle to adjust in an SD tuning process, especially with HP tuners.

HPT does offer a 3 bar custom OS that can be used to do a traditional (old school) SD tune. I put it on our TT Camaro, but in all honesty it didn't perform any better than the OEM OS in MAF only mode. Also, it takes 4X the time to dial in the tune, it's not worth the hassle IMO.
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Old 10-09-2013, 07:48 PM   #25
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Steve, I believe it is already maf only.
Interesting...sure sounds like the exact issue I faced. Camper, if you have it send me your .hpt file and I can do a sanity check on it for you.

BTW, I would avoid going into boost until you get this resolved.
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