Best Way to Diagnose a Vacuum Leak
07-31-2015, 06:39 PM
#1
Best Way to Diagnose a Vacuum Leak I think my FAST has developed a bit of a leak. I was driving the car last Friday and the check engine light came on. I put it on the scanner for HPT and the code was P0106 for MAP. The MAP is a new ACDelco part I bought back in November. I relocated to the front of the FAST and plugged the hole in the back with my old MAP (and screwed it in back there).
I had my hybrid OL MAF/SD tune going, so the car worked fine. I disabled the MAF and drove it that night and again everything seemed okay. I then went out of town for work and came back last night.
I fired it today on the OLSD tune and the car immediately jumped to 2K RPMs and held there (not good). Then it started swinging wildly, but I didn't have the scanner hooked up.
I went for a short drive and it drove okay, but the idle was not very stable. The idle is pretty stable in the car... even with the A/C on. So for it to just develop issues and hang with high idle when the VE table is tuned is weird. I'm guessing the P0106 was detecting an intermittent vacuum leak that showed up today.
What's the best way to diagnose it? I'm thinking the seam in the FAST may have a weak spot. Most of the hoses and things are new.
Thanks!
I had my hybrid OL MAF/SD tune going, so the car worked fine. I disabled the MAF and drove it that night and again everything seemed okay. I then went out of town for work and came back last night.
I fired it today on the OLSD tune and the car immediately jumped to 2K RPMs and held there (not good). Then it started swinging wildly, but I didn't have the scanner hooked up.
I went for a short drive and it drove okay, but the idle was not very stable. The idle is pretty stable in the car... even with the A/C on. So for it to just develop issues and hang with high idle when the VE table is tuned is weird. I'm guessing the P0106 was detecting an intermittent vacuum leak that showed up today.
What's the best way to diagnose it? I'm thinking the seam in the FAST may have a weak spot. Most of the hoses and things are new.
Thanks!
07-31-2015, 06:51 PM
#2
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I find wd40 in small targeted shots while engine running is best.
07-31-2015, 08:24 PM
#5
I'll be having some fun tomorrow. It's also possible the new MAP just went out. It's the exact same part number for the stock one. Not like an ACDelco part superceded. I got it from Amazon. Maybe it went bad? Hopefully it's just a small leak.
07-31-2015, 10:01 PM
#6
I doubt the MAP sensor went bad, but anything is possible.Just curious did you check the Intake manifold bolts? I had to tighten mine 3 times before they finally quit coming loose. Might check the PCV hoses while your at it...those have been known to crack with age.
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08-01-2015, 03:38 AM
#9
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If your engine is clean, i won't use wd40, i use a propane torch(not lit of course). The idle will climb when the propane gets pulled in. Won't make a mess on a clean engine. On a grimey DD, wd40 works good.
08-01-2015, 04:28 PM
#10
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I've used ether before (starting fluid). Only thing is I e read horror stories of engine fires. I never had one off it but heeded the warning
08-01-2015, 10:55 PM
#12
FAST bolts were loose in the back. Re-torqued. I put loctite on them... hrm.
Fixed the issue. Did a good data logging session trying to figure out where my timing needs to be to cure bucking. Ended up adding a ton of timing in the lower RPM/lower g/sec areas. Just need to play with the cracker some for off-throttle and the drivability will be as good as it can be with this cam.
Fixed the issue. Did a good data logging session trying to figure out where my timing needs to be to cure bucking. Ended up adding a ton of timing in the lower RPM/lower g/sec areas. Just need to play with the cracker some for off-throttle and the drivability will be as good as it can be with this cam.
08-02-2015, 09:06 AM
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08-02-2015, 09:27 AM
#16
FAST bolts were loose in the back. Re-torqued. I put loctite on them... hrm.
Fixed the issue. Did a good data logging session trying to figure out where my timing needs to be to cure bucking. Ended up adding a ton of timing in the lower RPM/lower g/sec areas. Just need to play with the cracker some for off-throttle and the drivability will be as good as it can be with this cam.
Fixed the issue. Did a good data logging session trying to figure out where my timing needs to be to cure bucking. Ended up adding a ton of timing in the lower RPM/lower g/sec areas. Just need to play with the cracker some for off-throttle and the drivability will be as good as it can be with this cam.
Far as the tune goes, sounds like you live fairly close to Geoff. I would take the car over there and let him tune it. Then you can go back through the tune and see what changes he made. Not saying you do not know what you are doing because you definitely have a good grasp on how the LS PCM's work, but even then Tuning big overlap cam cars definitely can still be tricky.
08-02-2015, 06:00 PM
#17
I plan to take it that way eventually. I've talked to him several times. The WOT part is actually pretty easy on the rollers. It's the part throttle drivability that's difficult with big overlap cams. I have mine pretty damn close. And that's using the 100mm MAF to boot. I run it both OLSD and OLMAF and prefer to run it blended, but have tuned both the VE table and the MAF table to be pretty spot on using my NTK wideband.
08-02-2015, 07:24 PM
#18
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Is 6.5 ftlb sufficient for squeezing the star washer enough to bite in...?
08-02-2015, 07:40 PM
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Yeah, 6.5 would partially flatten it. Plus it's biting into plastic on the bottom
