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Discussion Starter #1
2000 Grand Prix, L36, Cam, small turbo turned down to 5 lbs. Was running great, now it is dying off when we first hit boost. It goes way lean and timing turns way back, as low as 5 degrees total!

I got the HP Tuner setup, thinking it was a torque management issue, but I have turned all of that off and it is no better. The MAF appears to be reading okay through the range, but it's almost like the PCM is calculating in speed density and hits the wall when the 1bar MAP sensor tops out. (I understand that I cannot use a 2 bar with this PCM)...

Any ideas?
 

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1st step is to hunt down any boost leaks. They love to develop at various pipe clamps that have some flexing during operation. My initial turbo setup did this a lot when I first installed it with some shorter TB/MAF connections to clamp onto. Also double-check any couplers on the bottom-side, and make sure they haven't gotten hit/dislodged/cut/loose.

Also, look over your vacuum lines for cracks or being loose on the ports.

I would say you missed a setting to get the L36 PCM happy with boost (there's not too much that needs changing), but if it was already running fine, the above items tend to be a big factor.
 

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Discussion Starter #3
1st step is to hunt down any boost leaks. They love to develop at various pipe clamps that have some flexing during operation. My initial turbo setup did this a lot when I first installed it with some shorter TB/MAF connections to clamp onto. Also double-check any couplers on the bottom-side, and make sure they haven't gotten hit/dislodged/cut/loose.

Also, look over your vacuum lines for cracks or being loose on the ports.

I would say you missed a setting to get the L36 PCM happy with boost (there's not too much that needs changing), but if it was already running fine, the above items tend to be a big factor.
 

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Well I figured it out. The MAF was becoming dirty because it was after the turbo (maybe oil from the turbo), and the PCM was switching over to speed density. Even with the HP tuners, I do not know how to see that is switched to speed density, (I am very new to this tuning software). With the single bar MAP sensor the PCM could not process the boost condition. I have since re-located to MAP so it is in front of the turbo and am now in the process of re-calibrating the MAP. The MAP reading changed dramatically when relocating it, maybe due to tube size and/or the lack of honeycomb.
Should be in good shape now.
Joe
 

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You can monitor Open/Closed Loop (should display as a 1/0 condition, unless they have something fancier). I noticed you started saying "MAP" instead of MAF as you discussed relocating it. You'll want to be careful to catch that when typing it out, since it can be misleading as we follow along.

I'd check over what may be causing the oil to try getting the MAF back where it was (turbo seals need replacing, possibly, or improved PCV setup... I'm building an elaborate boost-triggered electric pump and catch-can setup).

Also, you can convert to the 2-bar MAP, there's just a couple settings you have to tweak, or overwrite and run a GTP file (not sure if HPT permits this as easy as DHP does).
 

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Discussion Starter #6
Dave - Thanks for the help. You're right about the "MAP-MAF" switch, sorry.

The oil fouling may have been from the crankcase vent (to intake) that I had tried, switched to simple catch can for now.

My PCM is from a 2000 Monte Carlo L36, I was told that it can't handle a 2 bar MAP although I've never tried it. If I could go to that, I would prefer to run speed density.
 

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The PCM hardware can run just about any file from the 98-03 W-bodies, it's just a matter of overwriting it. Speed density isn't a necessary conversion on these cars. It's more popular in LS cars due to being predominantly N/A and some other PCM differences. MAF tuning is much easier for us to deal with for accurate fueling, even with boost. I love only having to deal with a single chart when making adjustments.

I can hunt thru my archives to recall the minor tweaks an L36 file requires for boost, but it's much easier to use the compatible L67 file and adjust to that (transmission/fuel injector settings, etc.). With a Grand Prix, there's no reason not to take this path, rather than introduce many extra variables and stay blind to boost pressure from 0-14.5 psi.
 

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Discussion Starter #8
Okay, I am not clear on the closed loop comment. I know what closed loop is, but why does this designate speed density on this PCM? Can't it be in closed loop using the MAF to determine fueling and the O2 sensor to correct? If not, how to I force open loop (or force it to use MAF)? If I disable the O2 sensor, I can't check fuel trims to calibrate the MAF.

This car seems to be in closed loop always, once it warms up (I know I can set the min temp). But even though I am getting the LTFTs coming down, I still can't make boost. It just dies when I get to boost. It seems like it is using the MAP and not the MAF to determine fueling. I must be missing something.

I appreciate your help.
Joe
 

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Open loop ignores the MAF, and runs off the raw tables during start-up and when that sensor has a problem. I'm rusty on more of the details (not gonna be fun as I'm about to start tuning my 11-sec car with a ton of extra power added).

Feel free to share scans and a .bin file of the tune using Google Drive or something similar. It may help me or someone else see things clearer.
 

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Discussion Starter #10
I am struggling :(
I decided the MAF calibration was not my issue as the calibration and LTFT improved, but performance did not. Based on your closed loop comments, I don't feel speed density is my issue. The ignition timing is dropping dramatically as I near boost (like down to 5 degrees). I don't see where any abuse setting are kicking in. I did have a low octane timing table that I thought was the issue, but I copied the high octane table over it with no improvement. The timing is dropping in correlation with the MAP going up (very little from KR).

I raised the allowable torque per RPM, based on measured torque so this should not be a factor.

I am also struggling with the fueling - I cannot get it to run rich at all. It appears to always be targeting 14.7. I have tried increasing the RPM Adder in power enrich, and the TPS Adder, but my wideband gauge seems to always be too lean for the power and the VCM scanner ALWAYS shows 14.7 as the "Air-Fuel Ration Commanded (low res)" .

I have been making way too many changes, trying to get something to move the needle.

My other project uses MegaSquirt with Tuner Studio (supercharged V8, speed density setup) and I have no issues working with that, but I don't know this PCM or the HP Tuners software.

The funny thing is, I had a tune from Sinister Performance and the car ran great when we first fired it up with the turbo. The AFRs were great throughout the range. After a few weeks we started having issues, and thought we had tracked it to the MAF fouling, but now I am stumped. I have checked the cylinder compression several times, as I thought I had damaged it, but it looks fine....

Any thoughts?


Thanks,
Joe
 

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Ya, you played with too many things in a non-trackable way, and screwed yourself up. If you have that original file, I'd load that, and slowly make tweaks from there. Do it in a way you can scan and undo if it doesn't work.
 

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Discussion Starter #13
Finally solved!
I went back to the last known good tune from Sinister Performance, added my new MAF calibration numbers, and started to log to better understand the issues.

1. I did not know about the 'advanced view' in HP Tuners, this opened up a lot more information.
2. I didn't understand the the power enrich and it's enablers....

The logging showed me that the PCM was commanding 14.7 AFR under all conditions.
All my previous changes had no affect on fueling, because I could not see the Enable Cylair settings!

I changed the Cylair and Throttle PE enable settings and now I am back on track!

Still running a little bumpy under boost, I need to adjust fueling better to my low boost conditions. I only want to run 6lbs on this engine (it's my sons daily driver).

I appreciate your responses and help.

Joe
 

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Good deal. Ya, PE Enable is typically a throttle % (usually 30-40) where it'll start dropping from 14.7 to 11-12 where you have it set. Acceleration Enrichment (AE) also helps, but it's not as critical to tweak for this.

Keep learning what it likes and make yourself a Change Log document to help keep track.
 
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