Pushing clutch in results in bad vacuum drop

[DailyDSM]

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

 

For your sake I hope you find another solution than this but... usually when I see a car dropping revs when you press the clutch in, it ends up being a problem with the main thrust bearing.

 

[toybreaker]

Damn, Tim, that sucks. /ubbthreads/images/graemlins/frown.gif

Did this suddenly change?

Closed throttle switch working?

Does the iac increase it's count in response to the rpm drop?

Does the rpm imediately drop, or does it hunt around some?

I see you're running an act2600 with a light flywheel. It might be that the combination of a stiff pressure plate, minimal flywheel effect, and big cams makes just enough of a load that the ecu can't compensate quickly enough and the idle drops off.

The ecu will throw timing and fuel at it in addition to the increasing the iac count. What does the logger show for fuel and timing when it starts dropping off?


The vacuum will drop off as the rpm's drop, just because the engine isn't very efficient at very low rpm's. If the tune isn't right on, it'll feed on itself, with little flywheel inertia to keep things ticking along, a small tuning issue may be enough to cause some problems. (trying to be postive! /ubbthreads/images/graemlins/wink.gif )

The best way I've found to quickly check for thrust wear is to have someone push in and release the clutch while you pry back against A socket on the center bolt. (don't pry against the harmonic, it can seperate the bonding between the inner hub and outer ring)

Anything more than just a scosche of movement is bad news.

I've got a crank here with your name on it if you need it. /ubbthreads/images/graemlins/wink.gif

 

[Barnes]

Quoting RvlutionMtrsport:
For your sake I hope you find another solution than this but... usually when I see a car dropping revs when you press the clutch in, it ends up being a problem with the main thrust bearing.



That was my first thought. /ubbthreads/images/graemlins/frown.gif

 

[atc250r]

Me three.

 

[Rausch]

Me four. /ubbthreads/images/graemlins/frown.gif

Quote:
The best way I've found to quickly check for thrust wear is to have someone push in and release the clutch while you pry back against A socket on the center bolt.

Good advice here. Precisely the way I found mine. Although mine went so bad so quickly, the engine would die the second you stepped on the clutch. The above test only confirmed what we though.

For your sake I hope that's not it, but check it real quick to rule it out.

 

[DailyDSM]

Well I'll stay out of panic mode until I check my tuning as I know my tune is far from perfect. The motor is brand new and only has about 60 miles on it so I'll it so if it is the crank, I will be a little upset /ubbthreads/images/graemlins/banghead.gif

 

[Barnes]

IMO, check your end play first. It is actually really easy to do.

Just use your foot, breaker bar, piece of wood. Anything really to push the center of the crank pulley towards the engine. Then look down at the crank pulley from above or below. Below and really close if possible. Then have someone else step on the clutch as you are staring at it. Basically, if you can see it move (it will be towards the driver side), you have crank walk.

 

[DailyDSM]

I'll check end play tomorrow.

Here was Dave Mertz's (from ECMLink) response to one of my last logs posted on their forums regarding the RPM drop from higher RPMs when free reving. As I've stated, my tuning abilities leave much to be desired.

"It seems like it might be ignition timing related. The rather high idle rpm and the unusually high, even abnormally high, airflow reading at idle are pushing operation into an area of the timing table that has very high ignition timing. As rpm drops, operation falls into a more ignition-retarded part of the timing table which seems to be reducing rpm faster than anything else compensates.

Regarding the airflow readings, I can't explain how the airflow readings can be that high yet the AFRatioEst and LC1 match. It's acting like either there is a heavy load on the engine or perhaps base ignition timing is greatly retarded from where it should be."
-Dave Metz

Compensating for the extra load seems to be what is causing all of my problems but figuring out what is causing such a substantial load and/or why it isn't being compensated for is still unknown.

 

[DailyDSM]

Well it is the thrust bearing. I measured .035" of play using a dial caliper but I'm hoping a good portion of the bottom end is salvageable. Good news is my engine builder saw my thread on a local forum and contacted me about the problem. He had never seen any thrust bearing failures on 6 bolt engines he had built, especially after only 60 miles, so he's going to get me in sometime next week and pull the pan to see what can be done.

-Tim

 

[Rausch]

/ubbthreads/images/graemlins/applause.gif Good to hear he's getting involved.!

It sucks, but it's best you caught it early.

 

[Terry Posten]

Even with a 6 bolt, you must set the trust correctly or you will have this issue.

Hope things turn out OK. Looks like to caught it soon enough.

 

[DailyDSM]

Verdict: Spun thrust bearing.

Pictures to come. Hopefully the filter did its job and I only have a $3000 paper weight rather than a $6000 paper weight.

 

[DailyDSM]

Well I discovered something else today that may or may not have anything to do with the thrust bearing failure. When I removed my clutch, I noticed that each flywheel bolt had wear on the outer most edge meaning there were clearance issues between the clutch/PP and flywheel. On my old engine, using the same Fidenza flywheel, I noticed the previous owner hadn't used the spacer and slightly longer auto tranny bolts that are supposed to be used with aftermarket flywheels. When I installed the new clutch, I did use the spacer and new bolts. Given what I saw today, the spacer is obviously creating the clearance issues mentioned above. Any ideas as to why this would occur given that aftermarket flywheels require/strongly recommend the use of the spacer? I'll post pics of the bolts tomorrow.

 

[DailyDSM]

Flywheel Bolts:

 

[Rausch]

Quote:
Given what I saw today, the spacer is obviously creating the clearance issues mentioned above. Any ideas as to why this would occur given that aftermarket flywheels require/strongly recommend the use of the spacer? I'll post pics of the bolts tomorrow.

No idea. When I installed the Fidanza FW and ACT 2600 I used the OEM bolts, and no spacer. Bolts had plenty of depth to properly seat, and I never had any issues whatsoever..... /ubbthreads/images/graemlins/dunno.gif

 

I can definitely say that ACT 4G63 flywheels do not require or recommend longer bolts and in the past when I've used Fidanza flywheels their's didn't either.

Daryl

 

[DailyDSM]

This is the kit I bought orginially.

click

The argument for the longer bolts and plate make sense but it has obviously created clearance issues on my setup. I will be reinstalling the flywheel with stock length bolts and no plate just to avoid any issues.

 

The only problem with what I read in that link is that FP doesn't specify which aluminum flywheel/flywheels require the longer bolts which leaves it up to you the end user to determine if the longer bolts are necessary or not. As you've already discovered, in your case the longer bolts aren't needed.

Daryl

 

[CarRacer]

I bought that kit to use on my Fidanza aluminum flywheel as well. I didn't need the bolts as they bottomed out on the crank and ended up using the stock bolts with the plate. It was my impression that the plate was to prevent the bolts from digging into the flywheel.

Either way the bolts FP provided were too long for my setup and I ended up using the stockers.