Vss-ecm-stalling

Mike

New Member
#1
My car is street driven and was having the engine stall about 70% of the time when cruising in a mid to upper gear when pushing in the clutch. I also was having some slight bucking issues when creeping along at lower speeds – such as driving in traffic let’s say. I have the GM perf. LS376 (480hp) crate motor with the GM spec’d ECM and wiring harness for this engine.

After a bit of web research I found my answer, and hope this may provide others with a solution if encountered. There is a contingent of people that say it doesn’t matter and you can tune around it, but I believe they are mistaken. If you have a track car – this likely won’t matter. My Porsche 96.50 box does not have a VSS sender. There is/was a unused harness plug that is named “VEH SPEED”. The instructions that came with the GM ECM/Harness bluntly states that no VSS signal is necessary to run the engine. They are correct... the engine will run & drive without one – albeit with the above noted issues. Here’s a couple quotes from the WWW that nailed my issue:



The biggest problem I've seen on swaps with no VSS is idle instability and/or stalling after coasting to a stop.
Picture a car coasting down hill with no VSS. The PCM sees 0% TPS but high RPM. Since there is no VSS the PCM doesn't know the car is moving; it just thinks the idle speed is high and needs to be brought down, so it runs the IAC all the way in. Then when you finally stop, the IAC can't always recover quick enough causing a crazy speed fluctuation and sometimes a stall.

VSS - If using a non electronic trans, You should KEEP a vehicle speed sensor regardless of what transmission type you use. The ECM 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.

Now, if the ECM is not receiving a VSS pulse you would/may 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."



The VSS harness connection/ECM needs to see a sine wave pulse – I think any pulse will work. A good tuner can later check and see the VSS signal within their tuning program and adjust the PPM the ECM is seeing... if you need this signal to drive other systems like an automatic trans, cruise control or speedometer signals (which utilize square waves from what I understand).

A magnetic pulse generator is what I installed – it was Dakota Digital and appears the same unit is made by Rostra. SpeedHut also sells a VR sensor that has the magnetic pick-up within the bolt and one could use a metal tooth wheel or some metal pins/keys glued on the rotating axle shaft to interrupt the magnetic signal and the sender will generate the pulse to the ECM.


Here’s the DD unit: SEN-4165 - 2,000-8,000 PPM Pulse (Using 1-4 Magnets) Magnetic Pick-up coil for transmissions without a speed cable or VSS output.


Here’s the Speedhut: Magnetic Htz. Universal Speedometer Sender: G-SNDR-13 $38.00 Sender can be mounted anywhere that counts ferrous metal objects passing in front of sender. Sender works with all of our speedometer models. -Sine wave output. -connect directly to Speedometer to measure speed. -M18x1.5 sender body threads with jam nut. -Sender length 2.300" long threads -8 feet of sender wire.

DD also makes a GPS unit that can programmed to put out a sine wave but it’s pricy and does much more than I need:
Dakota Digital Speedometer GPS Interface Modules GPS-50-1



So the outcome of this all: my car didn’t stall once today, runs much smoother at small throttle openings and the exhaust “note” doesn’t burble away when off the gas.



Attached are several photos of the above noted pieces and my install to the G96.50 trans-axle.



Regards – M. Shark
 

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PeteB

Gold Supporter
#2
Do you have the "manual" or "automatic" ECM? I've noticed the auto version is cheaper than the manual version, but the only difference is the number of pulses per rotation the ECM expects to see from the VSS.

I've wondered if you could splice into the wire from the Koso speed sensor to send the signal to the ECM rather than have a separate speed sensor.
 

Alex

Active Member
#3
shark;425485[SIZE=2 said:
] with the GM spec’d ECM and wiring harness for this engine. [/SIZE]
Here's your real problem. The as provided tune in the ECM is horrible. Flat out horrible. It's like a 5yr old did it. Christ, a batch of them even came without the rev limiter set.

Throw it on the dyno, get a competent tuner to fix up all the issues (with the fuel trims and knock ..... from talking w/ people I've seen I'm not the only one who the ECU tries to pull like 15* of timing from becuase the settings are weaker than like an OEM camaro, lol...etc...) and you're golden.
 

Mike

New Member
#4
I do not believe they have different ECM's regarding an automatic or standard shift install:

Note the conflicting info in the quoted text below - ones from the included directions that came with my ecm and later info is from a revised instruction sheet dated June 28 2012:

Here's what I am using: 19258267 - GMPP LS376/480 Controller Kit - Contains Pre-Programmed ECU, Harness, Sensors


A vehicle speed output is included in the bulkhead connector
for use with auto-scaling speedometers. The vehicle speed
sensor connector in the harness must be attached to a
variable reluctance type speed sensor (typical of most late
model GM automatic transmissions) for this to function.
Attachment of a vehicle speed sensor is optional and not
required by the ECM.

Revised sheet:

Optional Connections (Not required for operation)
• Alternator Control Connector
• Engine Oil Pressure Sensor – 3 pin Connector
• Vehicle Speed Sensor – 2 pin Connector Only required for CPP
Connect & Cruise Transmission Controls
• Optional User Outputs Bulkhead – 12 pin Connector (12-way)
Vehicle Speed Input – optional

The ECM is programmed and looking for 40 pulses per revolution
typical for automatic transmissions. The LS Control System harness
is designed to plug into the output speed sensor of 4L60 & 4L80
Transmissions, which have a 40 pulse output. NOTE: If you are using
the CP Supermatic Connect and Cruise Transmission Control
System, the vehicle speed input must be plugged in.

NOTE: All Engines are shipped with an automatic transmission flex
plate. For manual applications, the clutch and flywheel used must be
purchased separately and is up to the end user.


Most my reading seems to indicate the VEH SPD plug/ecm needs a variable reluctance signal/pulse. The information off the KOSO wheel sender will be a square wave.

My dyno tuner is booked till mid November so planning on seeing him then. He did advise me that he likely could do a work around in the tune but strongly advised that the VSS should really be hooked up. I got the opinion that he wanted a signal (any signal for that matter) just so the computer knows the car is not sitting still and he would set the parameters internally.

I'm not a tuning guru so this is what I know -- and it solved my noted issues. BTW: it cost me all of $35.00 to do.
 
#5
Mike reluctor sensors are rare these day,I would guess its a hall effect .
If the wiring diagram shows 3 wires ,power ,ground ,signal its hall effect.
ECU can not read wave forms with out a module to convert it to a square signal, thats why they use hall effect as its one less part to make.
You #3 pic looks like 3 wire ,green ,black,white.

Im thinking you will need to match the oem output per rev of the wheel to give the correct speed input.
If its close it may not have to big effect but you would have to suck it and see.
You maybe able to use a drive shaft tone ring instead of the head off the bolts in pic 4.
I dont know what wheel bearing fran runs in these things but some have an ABS sensor.
If it has use the front as it wont see wheel spin and freak out

Hope info helps.
 
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Mike

New Member
#7
Jim - picture three is a two wire sender connection plug that would normally connect to the VSS signal off the trans; the wires have stripes so it might look like more than two. The DD sender in the last two photos is sensing four small magnets that I have glued and zip-tied to the rotating inner drive shaft ring. The Dakota Digital sender uses external rotating /passing magnets.

The Speedhut unit (which I did not utilize) has the magnet internal to the large bolt and will get it's interrupted signal by passing bolts, teeth or whatever else one decides to use.

The airgap on the DD unit is about 1/2" to 3/4"
The airgap on the speedhut is in small fractions of an inch.

My Koso gauge package does use a sensor installed on the front wheel - IIRC it does not offer a sine wave output pulse.

Thx for the input -
 

Ken Roberts

Active Member
#8
Great info Mike. I've read about these stalling problems from way back in the early days of converting to fuel injection.

The part number for the same Dakota Digital sensor sold by Rostra is 250-4165. Both are available at Summit Racing with the Rostra model being $12 cheaper @ $25.97.
 
#10
Pete, I recently got a GPS box from Dakota digital, so far, working better than the basic magnet setup. iPhone not conducive to responding, I'm an old guy :), I'll provide a better answer when at a regular ole computer
 
#11
Pete - he's the latest status and info I've gleaned:

From my reading the ECM needs to see a sine wave signal to the already factory existing wire harness plug tagged “VSS”. I tested my cheap magnet sensor with a meter set to low volts. It was reading the alternating 0 to 5 volts, but I’m likely getting dropouts or maybe it’s failed.... I do remember my tuner telling me he was catching a VSS signal sometimes and then on and off at other times. So, I saw that Summit was discounting a superseded model and just ordered it: http://www.summitracing.com/parts/dak-gps-50-1

It’s a GPS driven unit that does much more than I’ll ever need it to do and here’s the key for my VSS issues “Offering a user-selectable output of 4k, 8k, or 16k PPM signals and a selectable signal type of a Sine Wave or Square Wave, the flexibility is endless.”

I believe the ECM should be seeing a 4K PPM sine signal. My tuner said he can tune around just about any ”consistent” PPM signal. My code reader was showing a consistent P0507 code.... My G96.50 g-box does not has a VSS sender.


This is from the manual that came with the crate wiring: Note the manual is referencing pulses per revolution, not PPM.

The ECM is programmed and looking for 40 pulses per revolution
typical for automatic transmissions. The LS Control System harness
is designed to plug into the output speed sensor of 4L60 & 4L80


This is from a forum post somehow...:

The key to solving both the stalling when coming to a stop and code P0507, was providing VSS. In my application, there was not physical way to provide VSS from the transmission or transfer case. I stumbled upon a GPS based VSS signal generator from Dakota Digital, P/N GPS-50-1. The unit outputs various PPM ranging from 4K to 128K in 3 signal formats. My PCM used Output2 from the device and I used HPTuners to set the PCM to read 4K in and supply 4K out for the speedo. Both problems solved for a couple hundred bucks and an hour installing the DD unit and flashing the PCM.



Another LS tech forum post – this guy did get the GPS unit I just bought from summit and it worked:
Hey guys new member here working on a setup some of you may be interested in. It's not actually an LS1 swap, but rather a 6.6L Duramax in a boat built by PPE some years back. However the issue I'm attempting to solve would work great for any GM retro engine swap, if I can work it out..



Deal is, boats don't use an automotive style transmission, so no reluctor ring options to pick up a VSS signal from. Typically boats use a pressure sensor or small spinning pulse wheel on the haul to estimate speed. Newest fad is
GPS speedometers, but this still lacks an output for the ECM to read. That's where I'm at now, trying to adapt a GPS signal to the two wire GM VSS ECM input.


So bottom line so far: I've only taken the car out for a short ride and no stalling, idle drops etc. I have not had a chance to drive it over to my tuner so he can check the ECM and see what's happening, but I'd imagine as long as the ECM knows I'm moving - I'm good. --- Mike


 

PeteB

Gold Supporter
#12
Mike,

Thanks for all the info.

The speed sensor plug on the GM harness has two wires, Purple/White (VSS TOSS Hi Pos 2), and Lt Green/Black (VSS TOSS Lo Pos 1). The sensor has a grey wire and a blue wire. I guessed and connected the Purple/White to Grey and Lt Green/Black to Blue. Is that correct?
 
#13
I believe I read on LSTECH1 & HPTuners that it does not matter - as long as 1 wire see's the 5 volts, the other one needs to be grounded/see's ground. If you find out different let us know.
 

PeteB

Gold Supporter
#14
Did some investigating with the multi-meter. Both wires from the GM harness read 2.5V with ignition on. The sensor reads ~45omhs then drops to about 10omhs when a magnet passes by. So, I left the Grey sensor wire connected to the GM Purple/White, connected the Blue sensor wire to ground, and left the GM Lt Green/Black wire unconnected. Hope that works.

The Graziano has an unused bracket above the right side driveshaft. I don't know what it's for on a R8, but it was perfect for mounting the magnetic sensor.
 
#15
I just updated another forum post with this info and figured to keep it centralized in this thread:

The GM ECM VSS labeled plug in the wiring harness is expecting a 0-5 volt sine wave. If the Graz's sender unit does output this type of signal you may be okay.

I also tried the 4 magnet drive-shaft device but I'm afraid the resolution was too low. I have since gone to this : Dakota Digital Speedometer GPS Interface Modules GPS-50-1 - Free Shipping on Orders Over $99 at Summit Racing it was on sale but superseded by the "-2" version - more money (see attached user manual). It will do more than you'll ever need, but it worked. And is simple to hook up. No more off throttle, de-clutching, low speed idle stalls... among other low to mid throttle drive-ability issues .

My issue was the lack of a vss sender off a G96.50 trans (it doesn't exist on this Porsche model). The GMPP tune is set up for an auto trans- Quote: "The ECM is programmed and looking for 40 pulses per revolution typical for automatic transmissions". Let's read this again GM - regardless of what you later say in the same document.

The info from GM says you can run without a VSS. Yea maybe you can, but it'll run like crap for a street driven car. GM should be bitch slapped for this misleading information. GM's info sent me on a goose chase at first and then hours of investigation to the truth.

Basically -- my ECM was having time value issues related to VSS input... one of them was a timeout between pulses to declare zero speed --- excellent huh. This explaining why the 4 magnet drive-shaft system worked sometimes and most times not.

The lack of a VSS signal effects multiple tune parameters within the program - it's more than it appears on the surface.

Do I sound a little disappointed at GMPP.... understatement

Your results may vary -- my car now runs great.
 

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PeteB

Gold Supporter
#16
Mike,

Can you post details on how you connected and set up the GPS unit? What output from the unit did you connect to the GM harness? What pulse setting did you use?

Thanks
 
#17
Mike,

Can you post details on how you connected and set up the GPS unit? What output from the unit did you connect to the GM harness? What pulse setting did you use?

Thanks
I'll do a little write-up over the weekend with picture(s). The use of my code reader (that has a "live function") helped to see what the ECM was getting during the Dakota Digital's test function i.e. when you toggle between the GPS senders PPM settings, it then sends a 60mph test signal during each setting - you watch your live data off the reader and see the MPH jump from let's say 8mph, to 28 mph to 48 mph etc.. Keep toggling until you get to the PPM setting that gets you "close" to 60mph.

AC speedometer output - "speed 2" connection off the GPS unit.
 
#18
Pete, straight forward hookup. I mounted the unit to the driver side foot-box/left side "A" pillar area. I ran the GPS signal-out line down thru the driver rocker area back to the ECM wire harness plug labeled "VSS". There are two wires in this VSS plug. I hooked up to the striped wire on this VSS connection. The 2nd wire I just connected to the frame/as a ground.
 

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#20
I took my car for its first drive around the block and I suffered from bucking, but it accelerates fine. Sounds like this may resolve my issue ... Will try it out, thanks.
 
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