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Discussion Starter · #1 ·
Background: Car has catted Kook's headers and a cone filter, and was tuned for a cam by a remote tuner using EFILive scans. The cam at that time was a 226/230 600/600 112 +3. Recently, I discovered that I will need to have the ability to idle smoothly on the Stock factory tune in order to continue driving the car in California.
Therefore, the car now has a 223/230 615/607 115 +2 to get less overlap.

On the old custom tune under heavy acceleration I got some pretty bad detonation in the 3000-4500 RPM, which surprised me a bit because those cams aren't THAT different. So I thought hey, since I want to run on the stock tune anyway, maybe I can load the stock tune and make some tweaks to it for the cam based on the changes the tuner made for the other cam. Then I learned about how EFI live licenses work and that I couldn't do that without spending a bunch more (and then looked into HPTuners which sounds like it might be the best option in the long term). So in the short term, I still have my old SLP Predator, so I tried using that to tweak some fuel and spark values based on what I knew from the stock and custom tune. Went for a drive and everything seemed okay, only the power between 6500-7000 RPM dropped off significantly more than I expected, and then I got a P0068 and went into limp mode. After clearing the code everything was fine. My first though was that the MAF was reading too high because the cam was giving it more air than it expected, however after looking at the log, the air flow was reading barely over 200. After looking at logs from this car going above 300 g/s with the other cam both with the custom tune as well as the "SLP 455 Bobcat Tune", and my truck reaching 280-290 with a smaller cam, something seems off to me. I recalled seeing a ton of motor oil that had backed up into my intake tube and throttle body at a track day, and then inspected my MAF and it looks like I can see some residual motor oil on it. I sprayed it down with MAF cleaner, took some more logs (a little bit conservative on the rev limit), and that only improved it a bit to the 230 range which still seems low to me.

So... is that P0068 just because I exceeded the stock rev limit with a mildly tweaked stock tune, or is there something deeper that I'm missing here? And is that low MAF reading likely related?

My next attempt will likely be to take SLP's 455 bobcat tune and pull a bit of timing and PE AFR from the high rpm stuff because both of those look a little too high to me, and then add some low RPM timing because of the cam.

Thanks in advance. I already reached out to the tuner for a retune but haven't heard anything... and he also changed his policy that used to include retunes and now only does retunes within one year. The cost of another tune would likely be roughly what it would take me to grab an HPVI2, so not interested in another one-off if he won't tweak it as included with my purchase a couple years back.
 

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The p0068 has something to do with the ECM not seeing the manifold pressure it expects based on the airflow the MAF is seeing.

I would have thought it would happen at idle or close to it, because of the poor manifold vacuum due to intake reversion from the cam overlap. Your airflow could just be high enough to trip the code, as well.

You may be out of luck trying to get your car to pass. Maybe get a junkyard 5.3l, slap it in and reload the stock tune.
 

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Not sure about the low MAF reading. This is with the tweaked stock tune or your cammed tune?

Wondering if you might be getting some valve float at higher rpm and that is killing power and messing up your airflow readings.

Kept the same springs with the new cam?
 

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Discussion Starter · #4 ·
As I understand, the P0068 means MAF/MAP/Throttle position don’t agree. At WOT the map sensor reading was 14 psi, at idle it’s around 6.

As far as passing smog, flashing the stock tune and swapping manifolds should get me there, it just has to idle and not throw a code long enough to get it there. The p0068 happened after this (hope this is readable):

Slope Line Rectangle Font Pattern


So if I can avoid doing that, smog won't be an issue. You can see partway through third my revs just start dropping which is when limp mode was engaged, so definitely not at idle.

The MAF reading low is on the tweaked stock tune, but the MAF frequency conversion hasn't been altered from the SLP 455 tune with the first cam that gave me MAF reading almost 100 g/s higher. You can also see the MAP pressure is right about at atmosphere under WOT, and not shown here, but sits around 6.5 psi at idle. The cam has technically -2 degrees of overlap, vs the previous cam which had +2.

Valve springs are the same, Lunati Duals, and have about 14000 miles on them. I wouldn't expect float causing that issue, but even if they were floating, that wouldn't explain the lower MAF reading a 5-6k RPM.

Got all kinds of data, not sure what should be jumping out at me aside from that MAF reading.
 

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Discussion Starter · #5 ·
Also, isn't 18 degrees of timing at redline a little low?
 

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You need some way of logging the actual MAF frequency. The MAF calibration from your tuner and on whatever tune you are using now may be totally different.

You also need some way to actually see the spark tables, and log all the spark retard PID's, as there are several.

Also, that cam could still set off codes. MAP at idle is still kinda high, so despite the small overlap there is still some reversion going on. With a stock cam it might br around 4 psi of manifold pressure. I don't see how the ECM is going to be ok with that on the stock tune. You also might see some phantom misfire at certian rpm ranges.

That predator tuner isn't enough to tune for a cam.
 

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Discussion Starter · #7 ·
You need some way of logging the actual MAF frequency. The MAF calibration from your tuner and on whatever tune you are using now may be totally different.

You also need some way to actually see the spark tables, and log all the spark retard PID's, as there are several.

Also, that cam could still set off codes. MAP at idle is still kinda high, so despite the small overlap there is still some reversion going on. With a stock cam it might br around 4 psi of manifold pressure. I don't see how the ECM is going to be ok with that on the stock tune. You also might see some phantom misfire at certian rpm ranges.

That predator tuner isn't enough to tune for a cam.
MAF Frequency: The tuner did change the MAF frequencies. However, even when I compare to the SLP455 predator tune that was on the car when I got the first cam, the number is still coming in far too low. I verified through EFI live that the SLP455 tune has MAF frequencies identical to the stock table.

Also, turns out I was logging MAF frequency, and one other Knock retard PID:

Rectangle Font Screenshot Pattern Software


9500 Hz matches up with the MAF table at ~215, and would end up being about 250 on the tuner's MAF table, so still too low.
I can see all of the spark tables in EFI live after scanning the ECM, I just can't change them due to licensing. It looks like 18 degrees is very close to the Low Octane table for 7000 rpm and 0.7 g/cyl, so for some reason I'm getting more knocking than expected.

Maybe I jumped the gun on changing tunes. Swapping between those cams should have been relatively minor and I would have thought the ECM could adapt. My next course of action will probably be to return to the custom tune and take some logs with this cam to see what's going on in there. Maybe there is a leak that is throwing the MAF off, or the motor oil on the MAF ruined it...

The computer would have to pull timing if it was in a lean condition wouldn't it? That seems to track with MAF reading low, LTFTs at 13-15% at times, and low timing, doesn't it?

Yeah, predator definitely isn't enough I agree.
 

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Looks like you're getting a lot of burst knock retard, perhaps?

Computer will pull timing if it actually sees knock, or pull timing if it anticipates knock during a transient condition (burst knock). Burst knock is usually triggered by exceeding a delta cylinder air value, which might be measured as change in cylinder air between ECM clock ticks, iirc.

Yeah, I agree with the fubard maf sensor. If you switched back to a tune where your previously had higher readings and still have unusually low readings, given nothing mechanical is wrong, seems like the MAF is suspect.

Do you have a wideband? Any change in AFR during WOT?

Pretty big difference between 200/230 and 300 g/s of airflow. I would chill with the WOT runs for the moment.

I have had issues with bad MAF sensors in the past causing a fuel cut.
 

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Discussion Starter · #9 ·
Yeah, I just took another log but it got cut short and I didn't get data on the runs, but I'm going to have to chill on the WOT runs, got some bad detonation. Much worse that the other tune. Is it feasible that a minor cam profile change could make such a difference in detonation resistance? Seems odd to me.

Regarding the wideband, what's the procedure for that? I have one on my BMW but I happened to have extra bungs so it wasn't an issue, on the GTO I'd have to remove one of my front O2 sensors to avoid the effects of the cat, which throws off the whole control system. Is it standard to just add another bung? That's a little out of scope right now.
 

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You can buy a clamp that fits over your midpipe with a bung. They have a graphite gasket that seals against the exhaust pipe. You just need to drill a hole.

It definitely sounds like you have fueling issues. I mean we're talking around 30% less fueling at WOT. I don't think it has anything to do with the cam.

I would try swapping out your MAF and take it for a small spin, only light throttle, and see if your trims improve.

Don't blow up your stuff.
 

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Discussion Starter · #11 ·
Man, thanks for mentioning those, I guess I didn't look hard enough before.

Looks like there might be more room on the header than the midpipe but both are 3" so I'll get one and mock it up.

MAF: Genuine OEM vs Delphi... should be about the same quality right? (BMW guys make a huge deal about OEM/VDO MAF vs others, not sure if that's the same deal here)
 

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I think you should be ok with a delphi, but genuine OEM would be what i would go with if in doubt.

Honestly, even with either of the above, you might still want to get a retune. Could be slightly off from your current calibration.

Whatever you do, don't get a cheapo maf or a parts store brand maf. your junk will never run right.
 

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Discussion Starter · #13 ·
If inquiring minds wanted to know, my troubleshooting has led me to believe the motor oil in the intake is the primary problem. I started a thread about that specifically here:

 

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Discussion Starter · #14 ·
Update on this. Not seeing any more oil in the intake tube but the problem is remaining, so moving on to grabbing the new MAF. Couldn't source a Genuine GM MAF in a timely manner so got a Delphi unit. It looks exactly the same as the original.

The first log had the mass air flow pegged at 350 g/s probably by about 4000 rpm, and I heard/felt a backfire as I pushed the clutch in at redline (assuming rich/unburnt fuel) so I will send that to the tuner and hopefully we can get that frequency to air flow conversion sorted out, assuming the airflow isn't constant through that RPM range.
 

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Discussion Starter · #15 ·
Another update. Still not great. Tuner tried a couple of things but my brand new Delphi MAF is not outputting a frequency above 10500 Hz, so I'm getting a very flat MAF curve above about 4900 RPM. Don't suppose anyone else has seen something like this before?
 
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