Way Too Much Air, Not a Vac Leak?
09-27-2015, 04:07 PM
#1
Way Too Much Air, Not a Vac Leak? I'm finally done with my LS swap on my 2000 Isuzu Hombre, very excited! A little about the build, it's a 5.7L I pulled from a 2000 B4C that had an LS6 cam, 42# injectors, 1 7/8" LTs and a Fast 92/92. Since then, I've swapped the cam for a 210/215 .561/.557 at 115+4 and a FAST 102LSXRT with a 102 TB, same injectors. Also, it has the Stainless Works 1 7/8" LTs and a full exhaust.
Unfortunately, it doesn't run for more than 15-30 seconds and HPT logging it shows 80kPa! Alright, so it's got a vac leak, where could it be? Well, I remembered the intake was purchased from a guy on eBay and I relocated the MAP to the top of the intake, but didn't plug the back hole! LOL, alright, took the intake off and put a plug in the rear opening. I hopped back in the truck and cranked it up expecting glorious idle, but no, it behaved exactly the same. I threw the scanner on it and sure enough, still 80kPa in the intake. Except I noticed the incredibly loud intake noise at the intake tubing, making me believe all the air is coming through the filter like the IAC is actually commanding it!
The tune I threw in it is basically the same tune I had in the Camaro when it ran this very same motor, except that the Camaro was A4 and this is M6. So I had to grab certain components from a tune on my 383 Camaro for the trans, but it was minimal. Injector tables were copied directly from the Camaro tune that this motor was in, VE tables, etc.
I tried swapping the IAC out with my 383 Camaro, works great in the Camaro and the Camaro's IAC does the same damned 80kPa bull crap in the truck. So the IAC is good, but I'm suspecting somewhere in the tune that I'm commanding way too much air.
So where should I be looking to fix this? Let me know what I need to upload for help!
Unfortunately, it doesn't run for more than 15-30 seconds and HPT logging it shows 80kPa! Alright, so it's got a vac leak, where could it be? Well, I remembered the intake was purchased from a guy on eBay and I relocated the MAP to the top of the intake, but didn't plug the back hole! LOL, alright, took the intake off and put a plug in the rear opening. I hopped back in the truck and cranked it up expecting glorious idle, but no, it behaved exactly the same. I threw the scanner on it and sure enough, still 80kPa in the intake. Except I noticed the incredibly loud intake noise at the intake tubing, making me believe all the air is coming through the filter like the IAC is actually commanding it!
The tune I threw in it is basically the same tune I had in the Camaro when it ran this very same motor, except that the Camaro was A4 and this is M6. So I had to grab certain components from a tune on my 383 Camaro for the trans, but it was minimal. Injector tables were copied directly from the Camaro tune that this motor was in, VE tables, etc.
I tried swapping the IAC out with my 383 Camaro, works great in the Camaro and the Camaro's IAC does the same damned 80kPa bull crap in the truck. So the IAC is good, but I'm suspecting somewhere in the tune that I'm commanding way too much air.
So where should I be looking to fix this? Let me know what I need to upload for help!
09-28-2015, 12:04 AM
#3
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I would still guess vacuum leak. Your cam should make good vacuum. You're at 80kpa, which is like having the throttle open a fair amount. It would almost have to be something as large as the brake booster hose to leak that much air.
Reason I'm thinking vacuum is that if it were commanded air, you would also get commanded fuel, so it would run but run high and stay running. Vacuum is unmetered air, so not getting fueling.
One thought is the fast 102 requires oversized injector o rings. If your o rings are still stock sized, you would be leaking at all eight injectors. I don't know if the 92 also uses oversized rings
Reason I'm thinking vacuum is that if it were commanded air, you would also get commanded fuel, so it would run but run high and stay running. Vacuum is unmetered air, so not getting fueling.
One thought is the fast 102 requires oversized injector o rings. If your o rings are still stock sized, you would be leaking at all eight injectors. I don't know if the 92 also uses oversized rings
09-28-2015, 07:03 AM
#4
Thanks for the feedback, I may take the intake off again to look for additional holes. I've capped the rear brake booster port and I'm pulling on the brake booster at the side port on the intake. I did change the lower injector o-rings when I reused the LS1 injectors, I think the O-rings were 15mm OD and 7 or 7.5mm ID, I can't remember off the top of my head but I got the dimensions from FAST.
You don't think the IAC is just wide open during this period? The throttle is definitely not sticking, and the TPS confirms it with the 1% reading. I'd hate to hose this thing down with starter fluid, but it may come to that. I may be able to play with it after work today, but I was planning to play with the tune. A friend suggested if I truly believe it's the tune, adjust VE tables 10-15% to get it running and go from there.
A few other things, it showed 20 degrees of advance during this period of 300-400RPM, I presume to create torque. Why wouldn't it adjust with fuel, which is showing 0 LTFT and STFT on both banks?
You don't think the IAC is just wide open during this period? The throttle is definitely not sticking, and the TPS confirms it with the 1% reading. I'd hate to hose this thing down with starter fluid, but it may come to that. I may be able to play with it after work today, but I was planning to play with the tune. A friend suggested if I truly believe it's the tune, adjust VE tables 10-15% to get it running and go from there.
A few other things, it showed 20 degrees of advance during this period of 300-400RPM, I presume to create torque. Why wouldn't it adjust with fuel, which is showing 0 LTFT and STFT on both banks?
09-28-2015, 09:18 AM
#5
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I guess it could be the IAC sticking open, but if it is it would have to be two of them, and one is a known good unit on another engine, right?
I've seen larger cams than your start and run on a stock tune.
But I hear you, I wouldn't want to spray that crap all over my engine bay either if I could help it. There's a lower and upper shell on the FAST intakes. Hopefully, that seal isn't blown.
I have three LS vehicles, and all of them idle near 20 degrees of timing. I don't know the why of it, but it seems to work OK. one was professionally tuned, one is still basically a stock tune, and one is a work in progress.
Have you been able to log your idle air? there is a config file that is out there you can download that will log your base running air for you. If you become certain the issue is too much commanded air, you could try cutting some air from that table. Thing is, I don't like taking stabs at stuff like that, because it's sometimes very hard to get it back the way it was.
I've seen larger cams than your start and run on a stock tune.
But I hear you, I wouldn't want to spray that crap all over my engine bay either if I could help it. There's a lower and upper shell on the FAST intakes. Hopefully, that seal isn't blown.
I have three LS vehicles, and all of them idle near 20 degrees of timing. I don't know the why of it, but it seems to work OK. one was professionally tuned, one is still basically a stock tune, and one is a work in progress.
Have you been able to log your idle air? there is a config file that is out there you can download that will log your base running air for you. If you become certain the issue is too much commanded air, you could try cutting some air from that table. Thing is, I don't like taking stabs at stuff like that, because it's sometimes very hard to get it back the way it was.
09-29-2015, 04:21 PM
#6
I guess it could be the IAC sticking open, but if it is it would have to be two of them, and one is a known good unit on another engine, right?
I've seen larger cams than your start and run on a stock tune.
But I hear you, I wouldn't want to spray that crap all over my engine bay either if I could help it. There's a lower and upper shell on the FAST intakes. Hopefully, that seal isn't blown.
I have three LS vehicles, and all of them idle near 20 degrees of timing. I don't know the why of it, but it seems to work OK. one was professionally tuned, one is still basically a stock tune, and one is a work in progress.
Have you been able to log your idle air? there is a config file that is out there you can download that will log your base running air for you. If you become certain the issue is too much commanded air, you could try cutting some air from that table. Thing is, I don't like taking stabs at stuff like that, because it's sometimes very hard to get it back the way it was.
I've seen larger cams than your start and run on a stock tune.
But I hear you, I wouldn't want to spray that crap all over my engine bay either if I could help it. There's a lower and upper shell on the FAST intakes. Hopefully, that seal isn't blown.
I have three LS vehicles, and all of them idle near 20 degrees of timing. I don't know the why of it, but it seems to work OK. one was professionally tuned, one is still basically a stock tune, and one is a work in progress.
Have you been able to log your idle air? there is a config file that is out there you can download that will log your base running air for you. If you become certain the issue is too much commanded air, you could try cutting some air from that table. Thing is, I don't like taking stabs at stuff like that, because it's sometimes very hard to get it back the way it was.
Interesting on the 20*, didn't know that. I cracked open HPT yesterday to compare tunes of the previous car with that of this truck and noticed the timing curves... knowing is half the battle I guess!
And the revelation... I did not properly set it up for SD operation. I went back and set the frequency for the MAF fail at 0, multiplied the VE tables by 1.15, etc. I'll get to try throwing the tune in Wednesday after work, will report back.
10-01-2015, 07:44 AM
#7
Problem solved, I had not properly set up SD mode and the engine was apparently considering the unplugged MAF to be an actual signal, outside of range. I set the fail frequency to 0 and adjusted some other SD related components and it fired right up. I've now got 18 miles or so on it. Thanks for working it out with me, this is the second time, right Darth? LOL, might as well be part owner!
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10-01-2015, 11:14 PM
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I'll just take 10% of your winnings. 
