Lucky#13

I donīt know if anybody has suffered the same, but here are two cars with an identical problem.

Both have 2000-2001 Ls1+T56 and the engines are untouched internally, just headers, no cats and cold type intake system. The problem is the following:

Everytime when you come to a stop sign, lights, crossroads etc. and you press the clutch and start to brake, the engine almost shuts down. Same thing happens when you are cruising on high speed and press the cluch and keep it down. Engine RPM drops rapidly and almost stalls, every now and then it actually shuts down. All this can be avoided with the gas pedal by keeping the rpm around 1000 for few second when the clutch is pressed. Both cars idle just fine when started and also after the mentioned quick "stalling point" has been passed. Both cars do not have any wiring coming from the tranny to the ECM, these have been deleted when the package has been installed on early cars (-68 camaros).

Is there something that we should "disable" from ECM (by HpTuners) because no speed information is preseted to it, or what?

Any ideas are much appriciated!

Pop N Wood

iTrader: (1)

Check for vacuum leaks or air leaks prior to the MAF. Check of proper PCV operation. Then check your TPS and IAC motor. Make sure the throttle body is clean and the MAF connection good.

chuckd71

iTrader: (23)

Is your VSS hooked up? NM - not sure if manuals have it. Sorry.

squee

iTrader: (16)

Yes, T56s have VSS. I'm almost positive its necessary for them to run right too...He said nothing going to the tranny though, so I'm guessing its not hooked up...

LS1MCSS

iTrader: (18)

Without the VSS hooked up, the pcm tuning(DFCO) doesn't know what to do for a couple of seconds after you push in the clutch to stop, or in the case of an automatic, come to a stop. You need to hook up the VSS and you will most likely fix the problem.

Lucky#13

Thanks for all replies.

First of all this problem is not connected to vacuum or TB on our case. Those have been checked and they fine.

I was suspecting that it might have something to do with the VSS. Yes, T-56 normally has the VSS connected, but as mentioned on both our cars the wiring harness has been modyfied to work with 1 gen. camaros. I have all new harness from Techrods (which is great) and on friends car there is a modyfied OEM harness. And like mentioned no wires to the tranny.

We can not hook the VSS up because they have been removed(TechRods did not have one), so I am sure that there is a feature on ECM which needs to disabled. Just do not know which one?

There are hundred of similar hybrids on the road, so somebody must know how to solve the problem. Please, share the wisdom

bjamick

iTrader: (31)

The LS1 PCM needs to see how fast your going. It's not hard to wire the VSS in.

jashell1562

iTrader: (2)

You are going to have issues till you hook up the VSS. I have swapped 5 different cars. The last one I did had a keisler 5 speed conversion. I had to get a pass thru signal generator from Dakota Digital so I would have a vss signal. The ecu needs to know when you are coming to a stop to compensate so the car will idle. Unless you go to a speed density tune you will have issues with this.

garys 68

iTrader: (1)

Definitely due to the missing VSS, I had the EXACT same issue. Just repin for the 2 wires to the ecu and get a plug for the trans.

LS1MCSS

iTrader: (18)

If TechRods doesn't have VSS plugs, they should stop harness production until they get some. You can order your own plug at http://currentperformance.com/Connectors/LS1_LS6.html

bczee

iTrader: (12)

I know that everyone is saying you need it.. and for better drivablility, you should have it.

Just to add to the fire...

I have not had any VSS connected on mine due to the Viper VSS sender being of a differenet signal. I have been operational for 6 years now.. I have have very little problems of the engine RPM dropping on stopping.. but I might be the exception.

It is not disabled in my Tune. Idle is set to 700 RPM's. Then again it could be my driving style.. I don't go racing around in the street, but do drive quickly.

(don't flame me guys, just adding my 2 cents).

Lucky#13

Thanks for the link! What I meant was that the wiring harness I got from TechRods did not contain any wires that should be connected to the tranny.

What about a situation when one is having a LS1/6 engine with one of the older trannies (TH350/TH400 or even M21). They should be suffering the same symptons, right?

Is it really so that there is not a feature on PCM which could be disabled and problem wuold be solved?

garys 68

iTrader: (1)

My issue was with a Richmond 6 speed and a Muncie, same sympyoms. Added the Dakota Digitall VSS, no problem.
Nothing to tune out. In fact one of mine had the vss turned off, still had the issue.

Lucky#13

After little research at internet

"VSS - If using a non electronic trans, You should KEEP a vehicle speed sensor regardless of what transmission type you use. The PCM needs to know if vehicle is moving. Without the speed sensor, you can suffer from reduced fuel economy, reduced power, and idle problems."

"The VSS has two primary functions for our ECM's. It has a basic idle control function where if the VSS says the vehicle is sitting still, and there is no throttle input it will tell the idle to go into closed loop (where the IACV is used to control engine RPM directly) Otherwise, Idle will be in an open loop mode known as Commanded airflow, and it will also use the throttle follower. Without the VSS, the computer won't know which mode to control the idle with. This induces stalling in some situations.

The other function for the VSS is transmission Control. You won't be able to do this at all without the VSS.

So, That being said, to run with no VSS, Just simply disable error code 24, And set the transmission type as a manual.

Now, if this were on a vehicle, you would have some stalling problems. It will always try to control the engine down to an idle when your throttle is closed. If your engine is being spun up by the transmission like when you let off without pressing the clutch, the idle valve will close. Then when you press the clutch the engine will stall almost instantly since there isn't enough time to open the idle valve and recover. So normally, a VSS is required."


This applies on LT so maybe it the same with LS, probably?

garys 68

iTrader: (1)

This wont work, I tried it, you'll still have stalling issues.

"So, That being said, to run with no VSS, Just simply disable error code 24, And set the transmission type as a manual."

Lucky#13

This must be the way to go! Thanks "garys 68"