2G 7-bolt Lightweight flywheel stall?

[Connor Wilke]

I have been looking for a similar situation in the forums, but can’t find anything with similar build and conditions as mine.

I have a brand new rebuild (<300 miles)
Bc 280 cams with supertech dual valve springs, a big custom intake manifold (from my understanding). Fwd XACT 12lb flywheel with a XTD pressure plate and XTD six pick sprung clutch.

So the issue is when I clutch in, (release the clutch) the rpm’s drop so fast it dies out. And when in neutral and rev, it’s perfectly fine and keeps running. So I already understand how to adjust the BISS screw and since I have had the 280 cams in for over a year i already had idle set for 1100 rpm in EcmLink. I’m fully aware of crankwalk conditions and don’t believe it’s crankwalk. Not conventional way but I did a visual inspection and looks good because the crank pulley doesn’t move, I believe it has something to do with the big cams, big intake and lighter flywheel or even maybe something you can tune to help keep rpm’s up when you clutch in. Just can’t find anything like this if you know of thread that is specific to these conditions I’m more than willing to read but for the last thee hour I can’t pin an exact situation to this.

 

[twicks69]

Have you already tested your idle speed control motor? I know in AEM EMS I had to adjust decel throttle to remove the stumble to catch at 1500rpm then drop to normal idle.

I haven't touched DSMLink in years, but you could always ask on the ECMLink forums too.

 

[Connor Wilke]

Yes, it’s a new idle control motor and it is working correctly in ecmlink. Car full warmed up it sits around 30-40 for the isc position.

 

[pauleyman]

I have been looking for a similar situation in the forums, but can’t find anything with similar build and conditions as mine.

I have a brand new rebuild (<300 miles)
Bc 280 cams with supertech dual valve springs, a big custom intake manifold (from my understanding). Fwd XACT 12lb flywheel with a XTD pressure plate and XTD six pick sprung clutch.

So the issue is when I clutch in, (release the clutch) the rpm’s drop so fast it dies out. And when in neutral and rev, it’s perfectly fine and keeps running. So I already understand how to adjust the BISS screw and since I have had the 280 cams in for over a year i already had idle set for 1100 rpm in EcmLink. I’m fully aware of crankwalk conditions and don’t believe it’s crankwalk. Not conventional way but I did a visual inspection and looks good because the crank pulley doesn’t move, I believe it has something to do with the big cams, big intake and lighter flywheel or even maybe something you can tune to help keep rpm’s up when you clutch in. Just can’t find anything like this if you know of thread that is specific to these conditions I’m more than willing to read but for the last thee hour I can’t pin an exact situation to this.

If you can idle with no problem and all you did is push in the clutch how can this be a tuning or even idle control issue? Unless I'm not understanding what you're saying.
Also if I read correctly if you rev up at a standstill in neutral and revs fall to a normal idle then to me this solidified you don't have a tuning issue. It's something else. Hate to say this out loud but I would check your crank objectively with an indicator.

 

[Connor Wilke]

Okay, I’ll have to check end play of crank. But as far as everything else when I’m in neutral the cars perfectly fine. But one the clutch is released it seem like the loss of momentum drops the rpm’s extremely quick. I never had issues with rpm’s dropping so fast.
So to explain more….. yes when you release pressure from the clutch( clutch-in) it will drop from example 4,000rpm very fast and then below 800rpm for a second and then begin to sputter and then stalls out. If I just simply clutch-in at idle the rpm’s (1100rpm) drop 200 from set idle (~900Rpm). Then it will stay there the entire time, not continuously dropping like it would do with crankwalk

 

[pauleyman]

You shouldn't drop 200 from a clutch in at idle. Now from neutral rev dropping below set point with a lightened flywheel from higher revs. I could see that but at idle clutch in the only change in momentum is really the clutch disc. I don't know if I would consider the input shaft as the diameter is so small. I don't have cams but my car doesn't drop rev from idle with a competition clutch flywheel. Just my personal experiences. Cams may indeed change things?

 

[Connor Wilke]

I know the 280 are a bit excessive for a street build. And thats part my fault because I don’t really know anyone with 280s on a street car maybe 272 would be more appropriate

 

[Tyeler18]

Sounds like typical light weight driveline issues. My quarter master twin would do the same thing, just set your decel fuel enable higher so it returns to fueling before it can stumble out. I have lightweight flywheels or twins in every 4g car I own and they all dip below target idle like your describing without bumping up idle fueling.

 

[twicks69]

What does the ignition timing map look like? Is there a huge timing change when it is in decel that it is adding to the problem?

TPS range tested and within range?

 

[Connor Wilke]

fueling.

So I’m ecmlink, you are about the

fueling

So bump up the coasting fc offset?

What does the ignition timing map look like? Is there a huge timing change when it is in decel that it is adding to the problem?

TPS range tested and within range?

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My exhaust cam is about 1/4 to 1/2 a degree advanced. Could something that small cause an issue too? They are BC cam gears never adjusted them because I didn’t think I would need to.

The video is show the crank pulley not moving when I press clutch in. Not sure that help for the time being until I can actually measure the tolerance.

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[twicks69]

What size and impedance injectors and bat/voltage offsets are being used?

My exhaust cam is about 1/4 to 1/2 a degree advanced. Could something that small cause an issue too? They are BC cam gears never adjusted them because I didn’t think I would need to.

The video is show the crank pulley not moving when I press clutch in. Not sure that help for the time being until I can actually measure the tolerance.

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That is so darn little it wouldn't make this major of an issue unless you had a really poor overlap and the cams are no where near dialed in.

 

[Connor Wilke]

What size and impedance injectors and bat/voltage offsets are being used?

In profile, but they are 1600cc five-o motor sport high impedance. They are scaled to 60psi to flow around 1940cc on e85 with no ethanol sensor. So I will measure the e rating at pump and adjust tune as I go.

 

[DSMPT]

I know the 280 are a bit excessive for a street build. And thats part my fault because I don’t really know anyone with 280s on a street car maybe 272 would be more appropriate

Those cams are not super agressive and I guess it has nothing to do with your issue. If the valve timing was the issue, you should have the issue always, it shouldn't matter if you press in the clutch pedal or not.

 

[Connor Wilke]

That is so darn little it wouldn't make this major of an issue unless you had a really poor overlap and the cams are no where near dialed

That’s what I thought but I will try to provide as much information as I can to get help.

 

[Connor Wilke]

So…. Update. I dropped the oil pan to visually inspect everything and the crank has walked. So can an too much pressure from the pressure plate cause it to do something like this. But more than likely I installed things improperly. Trust me I know this is a dumb question but can you replace bearings with pulling motor? Haha

 

[We're on Boost]

So can an too much pressure from the pressure plate cause it to do something like this. But more than likely I installed things improperly.

I think most people in here would say yes those are 2 of the potential factors. Plus the block could have machining errors that cause the upper and lower halves of the #3 main bearing to sit with their thrust surfaces not perfectly flush to each other. Improper assembly might also cause them to not be flush to each other. In the Chilton manual for 1990 to 1998 they give a kind of sensible procedure for getting the upper and lower halves of the #3 main bearing lined up, the thrust surfaces lined up.
Plus if you are having to push in the clutch pedal to start the engine, that is bad and you should bypass that stupid switch that makes you do that. Then you can start the engine without your foot on the clutch pedal.

Make a read of post #76 in this build thread by 95REGF150. I think it's one of the better writeups about the 2g thrust bearings and crank walk. https://www.dsmtuners.com/threads/1995-eclipse-gsx-2-3-stroker-400whp.505261/page-4#post-153796119
He's got other good posts before and after #76 that are related.

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[Connor Wilke]

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Found out my crank bolt was loose. Would that cause crankwalk if it came loose after only 20 ft-lb