: Pushing clutch in at idle results in bad vacuum drop

[95eclipseGST008]

Well I'm still trying to figure out my idle issues. I just finished installing a 160A Saturn alternator which did nothing to fix my idle/stalling issues. I currently have the common problem of stalling when come to a stop with the clutch pushed in or anytime the revs drop from 2k-3k or above. Yesterday, I noticed at idle, out of gear, that when the clutch is pushed in, vacuum drops from 15inHg to ~ 5inHg, and revs drop from a steady 1100 rpms (current idle setting) down to 5-600 rpms where the car stumbles or stalls while trying to bring the engine back up to idle.

Now what I'm trying to figure out is how the clutch being pushed in could cause such a substantial change in vacuum? Does it have to do with engine load? I know BC280 cams can cause idle issues with lower vacuum (which is why my idle is set higher than stock) but I don't see how the hydraulic clutch system can change vacuum pressure.

Mods:
1992 Galant VR4: G4CS Block, Eagle/Wiseco Pistons, FIC 1000cc, FP3052, Tial 44mm External Wastegate, Griffin FMIC, Walbro 255 HiFlow Fuel Pump -6AN Fuel Lines, BC 280/280, Mild Port/Polish Head, BC Valvetrain, 2G MAS, HKS SSQV BOV (recirculated), Mildly ported stock intake/throttle body, FIAV eliminated, Aeromotive AFPR, Innovate LC1Wideband, EVO3 Exhaust Manifold, FP 2.5" O2 Housing, CM 3" Turboback Exhaust, ECMLink (Upgraded from DSMLink V2), ACT 2600, Fidenza Aluminum Flywheel, etc

Thanks,
Tim

 

[TOONAH]

Could you be a little more specific with the conditions of your problem. I assume you are saying that while in neutral and clutch pedal up, your engine idles at 1100 rpm's. Then, just by pushing the clutch pedal down, (releasing friction disk) you engine rpm's drop to 600 and the engine stumbles. I believe your 4g63 uses a CAS for ignition timing so we can rule out the effects of excessively worn thrust bearings in the crankshaft. Mechanically, I can see no way clutch operation while in neutral can have any influence on engine speed.
There is a clutch pedal safety switch that lets the ecm know the clutch pedal is depressed.
Supposing that had a partial/near short to ground, I suppose the loading effect on the alternator and battery could deprive the ignition of enough current for the spark plugs to fire properly. How can the hydraulic system interact with rpms. The vacuum drops because the rpms drop.
I believe you are missing something in your observation and that is why I ask you to be more specific.

 

[95eclipseGST008]

Could you be a little more specific with the conditions of your problem. I assume you are saying that while in neutral and clutch pedal up, your engine idles at 1100 rpm's. Then, just by pushing the clutch pedal down, (releasing friction disk) you engine rpm's drop to 600 and the engine stumbles. I believe your 4g63 uses a CAS for ignition timing so we can rule out the effects of excessively worn thrust bearings in the crankshaft. Mechanically, I can see no way clutch operation while in neutral can have any influence on engine speed.
There is a clutch pedal safety switch that lets the ecm know the clutch pedal is depressed.
Supposing that had a partial/near short to ground, I suppose the loading effect on the alternator and battery could deprive the ignition of enough current for the spark plugs to fire properly. How can the hydraulic system interact with rpms. The vacuum drops because the rpms drop.
I believe you are missing something in your observation and that is why I ask you to be more specific.

Your assumption is correct about pushing the clutch pedal in. The GVR4s do use a 6 bolt engine and a CAS but that doesn't necessarily rule out a bad thrust bearing. The function of the clutch pedal being pushed in seems to put enough load on the engine to cause a substantial rpm drop. I'm hoping its tuning issue rather than mechanical considering my tuning abilities with DSMLink are still very basic.

The following is my reply to questions regarding this issue on another forum. It should provide more background information on the problem.

To start, the engine has 60 miles on it since a complete build with a new bottom end from MM so while I can't rule out a thrust bearing, I would be unpleasantly surprised. I am new to DSMLink and tuning in general and have had idle issues from the beginning. This problem has pretty much existed since getting it back on the road. Free reving with the clutch pedal in and allowing the revs to drop would result in a stutter at about 500 rpms and the engine would stall about 90% of the time. At this point, pushing the clutch in would always have an effect on the idle but wouldn't necessarily drop the RPMs by such a large margin. About a month ago, after changing my throttle body to a N/T throttle body for better I/C piping angle, I thought I had the tune fairly ironed out. I was able to take a 30 minute drive to work, had absolutely no stalling issues, had no problems with the car stuttering, A/F ratio across the RPM band was a little rich but acceptable, causing no driveability issues. On the way home on the same day, I was in the middle of driving and went for a 3-4 gear change under normal acceleration and the RPMs dropped like a rock, causing the car to stall, and continued to do so between each shift, and would stall anytime I came to a stop with the clutch pushed, just as before. I got home and found the ISC to be bad from testing resistance. I replaced the ISC with one from my old throttle body with little to no improvement.

The car has not consistently had such a dramatic RPM drop by simply pushing in the clutch but there has always been some form of drop or stutter when pushing the clutch in.

Currently, as soon as I start to push in the pedal, the rpms drop.

With the V.3 of DSMLink (unless they changed it in the latest update), the car will not run with the MAF unplugged so I cannot test it. I can say that it does it with both a GM and 2G MAF since I have been switching back and forth. In the past, the car seems to have run better with the GM unit which is located about 8 inches from the throttle body.

As far as boost leaks are concerned, I haven't tested yet but the problem exists with both the 2G in standard location and GM MAF near the throttle body which would likely mean that any boost leaks would be at the throttle body or the intake manifold. This could be the case but I'm still not sure how it would effect the vacuum drop only as a function of clutch position.

Pretty positive clutch switch is still hooked up but I'll double check (car won't start without the clutch pushed in and I've never unplugged it but given the number of owners this car has had, I'll take another look).

 

[95eclipseGST008]

Crank play is at most .035 inches or .899 mm measured at the crank pulley. Crank was pushed all the way in (toward engine) for the first measurement, second measurement was taken with clutch all the way to the floor. Probably closer to .02 inches but I took an average of the inner and outer pencil markings.