Manual gearbox Stall.
 

Okay so for as many years as I can remember we have all been trying to stop the car that have been converted to manul from stalling. Over the years many things have been tried and none seem to work.
What we do know,
- Mike says that there is no fuel map in the ECU under 700rpm so the engine shuts down if revs drop below that.
- Any adjustment of the idle control valve is corrected by the ECU learning ability.
- A million thinks have been tried and as yet I don't know of anything that works.

Here is what I think is the cause,
If you have a look at the idle control valve you will notice that the little baffel can fully close off the air to the engine.
During some of my trial a coupel of years back I noticed that when you lift off the fuel the valve fully closes to pull the engine revs back quickly.
I think that during this fully closed period the engine is staved for air so the revs drop to low (below 700).
Engine shuts down as a result.

My suggested fix is to drill a small hole through the body of the valve so as to bypass some air at all time. In this way even when the valve is fully closed the engine will be getting air flow to keep it running.
I have cut open a valve to investigate how best to do this. I will post images of it later and also when I get a chance I will install a modisified valve and report back.
Tony

My engine does not always shut down below 700. Mine drops all the way down to the bottom, dash flickers a bit, but stumbles back to life without throttle input on many, many occasions.

I have noticed what you have described, mostly during geared deceleration. Someone said they found idle fuel delivery is maintained up to 1250rpm. I tested this for weeks and for hundreds of miles.

When I decelerate, if I return to neutral over 1250rpms the stall situation probability is greatly increased, but at or below 1250 the rpms drop smoothly to idle.

My thinking was the fuel delivery simply was not able to anticipate a sudden drop in rpm.

I dunno, though, I'm no expert. I only excel at noticing patterns. Am interested to see the results of your experiment.

Re: Manual gearbox Stall.
 

No to sound like a jerk but, I have never had any of these problems. The closest I come is the fall to about 500 rpm and then back up like Nikfu described. I never have had it stall unless it was my fault (1st gear). The manual from what I remember stats the ideal speed to be 610+/- 100.

Re: Manual gearbox Stall.
 

The rpm Mike mentioned could be lower I can't remember.
Tony

Re: Manual gearbox Stall.
 

I have a great many thoughts on the subject, which I will share with you after I get some sleep. :/

Re: Manual gearbox Stall.
 

Ok, I have been having the exact same issue since I installed the swap. I switched to a 94 ECU, which seemed to help at first, but doesn't (I have a '92 engine and should be using the 92 ECU).

~700 RPM seems about right. If it dips under that, sometimes, randomly it will stall and die.

It happens a lot more often when clutching in from engine braking, and close calls happen a lot more often too. What NikFu said also very much sounds like my blue car.

Mine is probably a bit more sensitive due to the cams, but I'm not quite sure, since it will idle for hours and hours if you let it. Most of the time when I clutch in, I give the gas pedal a slight tap to prevent it from stalling. If I do that, it never stalls, regardless of how high the RPMs are when I do it. Falls perfectly down to idle speed and stays there.

I have thought of two ways of fixing this. Raise the target idle RPM speed in the software until it stops doing that. Basically have to get one of the ROM writer things that Mike uses and play with it until it's right. That would probably also help with driveability, since you could let the clutch out a bit more before giving it gas when starting off.

I was thinking instead to trick the ECU into always using the target idle RPM from when it's in A/C mode, since that's a bit higher. There's several pins on the ECU pinout that are related to the A/C - one must do that. I have been planning to try this for a while now, but I haven't had the time. My blue car has no A/C so I haven't been able to check whether it still does the same thing with the A/C on.

It does definitely seem to be more fuel related than air related. I'm not sure that bypassing the IACV alone would fix that.

Also, why not instead just run a small vac line from the plenum to the intake behind the MAF? You could put a valve along it to adjust how much air flows through it.

Re: Manual gearbox Stall.
 

I've had this issue occur when taking a turn with the clutch depressed and turning the wheel. Turning the wheel will generally lower the rpm and I have stalled. Since then I've generally always made sure i was turning while in gear and haven't encountered the problem.

Re: Manual gearbox Stall.
 

My IDE is all over the place .
Cold start almost 2,000 normal about 700 and when real hot , after driving all day as low as 600. I have played with the clutch on a hill and maintained 300( at least I think that last thick line before 0rpm. Looks like it should be )
I have a stacker ignition so it may be helping it a bit to idle so low.

Similar here. If I turn the wheel at just the right time it will cause a stall, more often when backing up and probably because I am not focused on the instruments.

Re: Manual gearbox Stall.
 

Turnung the wheel when the clutch is in will increase the load on the engine when its revs are low, so it pulls its bottom rev number even lower.



I agree that would be the simplest way to test the idea. I feel that a more comtroled method would have advatages as the amount of air is so small the tapes and hoses may vary in flow.

Go with me for a second,
Were my head is at was is to find a way to vary the air bypassed with some sort of screw adjuster.
Start car, increase airflow bypass in stages. With engine at temp and the right revs adjust a bit till revs increase then wait to see if the computer can lower the revs back. Keep repeating till the engine can nolonger adjust the revs back. At that point back it back to last setting.

My guess thats the flow that works.


I plan on working on this till it goes away.
Tony

Re: Manual gearbox Stall.
 

Yt answered ftw.

Re: Manual gearbox Stall.
 

The ECU is not capable of seeing sudden shifts in load. It was a massive issue with the stock ecu remapped for the supercharged engines... I know Mike has changed the firmware he was using to help with this... the results I have not paid any attention to in order to say one thing or another...

Simple fact is, when engine braking load is at 0. There is a fuel cut used to help the engine slow down thus slowing the vehicle down. when dropping RPM from anything greater than 1500 rpm into a neutral state the ecu has a difficult time reloading the injectors and adjusting the IACV to compensate and thus it will stall. These are all scenarios that an automatic transmission will not experience due to the torque converter so it was never calibrated for such.

I had done a SIAC bypass with a manual ball valve with some success in reducing in all cases the mt stall but some still had issues with it.

Someone with a SSM and a 5mt that has a common stalling issue, please note the timing advance, engine load, and injector pulse width while engine braking and clutching in to induce the "stall". These are where you will likely find the holes in the ECM's capability to handle the changes all at once

Tom

Re: Manual gearbox Stall.
 

and I still wish I had made the investment in the Hydra....no stall, more power!:cool:
YT - when are you getting back down to Maryland again?
-Bill

Re: Manual gearbox Stall.
 

Fuel gets cut because the ECU thinks the engine is not running when the revs drop.

I just made a simple adjustment and it appears to have fixed the problem. Given what I just read I think I will shut my mouth till I am sure that it is fixed.
The one thing that has bugged me is that Subaru would have designed the SVX so at some point in the future it could be fitted with a manual gearbox. When I accepted that as fact I realized were the adjustment had to be made. If I am right this mod takes 3 minute.
Will update you in the day or so.
Tony

Re: Manual gearbox Stall.
 

Okay did some more driving and I am going to go out on a limb with this one, as they say I am a big boy and prepared to take it on the chin if I am wrong.

You need 8mm ring spanner and 2.5mm allan key and you need to undo the lock nut on the throttle body then screw the screw in with the allan key, Do it when the engine is hot raise the revs to about 1400rpm (the ECu will pull it back over time). Lock the nut and thats it, if after driving for a day you can make further adjustment.
See photo.https://lh5.googleusercontent.com/-q...0/PICT0057.JPG

Why does this work, well base revs is now controled from the throttle body not for the valve, so when you lift the throttle and the valve cuts the air the throttle maintains a base air supply.

So there it is a 2min fix and so far it works perfect for me. As far as I am aware the SVX is the only car I have ever owned that has fully closed throttles every other one had it slighly open.


Good luck and I hope it works for you all. If it does we will all kick ourself for not figuring it out sooner.
Have a great day.
Tony