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Old 08-23-2015, 04:35 AM   #1
benz-tech
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Default P0500 (no VSS) Electrical experts' help needed.

edit:

Fixed thisI need to find out what wire from the DME goes to the obd2 connector under the dash so that i can plug in a generic scan tool).

I'm still having an issue with having a 5500rpm rev limit but figured checking codes (P0500) is a good plsce to start. For starters, I knoe the speed input(it is now), rear o2, fuel tank pressure sensor and DISA valve are not connected yet. Anyone know if any of these things could causea lowrev limit? It's not misfiring, just hitting an unusually low rev limit. The sound from my big cams is just getting warmed up at that rpm and want to keep going.

Last edited by benz-tech; 08-30-2015 at 01:36 AM. Reason: update
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Old 08-26-2015, 04:34 AM   #2
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It probably doesn't like not having a speed input...

dunno about the rest.

t
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Old 08-30-2015, 01:33 AM   #3
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update: I have successfully wired in OBDII and can read codes and watch data stream from the DME. Small victories...

I still have the P0500 VSS code, with no vehicle speed registered in the data stream. Soooo, after extensive testing, including running wires every to test, I am unable to get any type of signal to pin 83 of DME to make it happy enough to register a vehicle speed. This includes the E30 cluster output to its DME, the back of the OBC(where it should come from), and directly off the sensor in the differential. I've checked each signal with a scope and the two cluster outputs start at 5v and then have a small drop-down square spike. For the most part, they hang out at 5v but the 0v square spikes become more frequent with speed. The sensor in the diff puts out a pure square wave from 12v to 0v with increasing frequency. I even tried to ground pin 83 off and on by hand in an attempt to simulate a 12v-0v square signal. (im sure it wasn't anywhere near a real square wave) NONE of these inputs give me a VSS reading in the data stream.

My fear, and its a REAL BIG fear, is that the '96 ti w/o traction control still gets some form of speed signal from the E36 ABS module, which I don't and cant ever have.

2 questions, does anyone know if you were to unplug the ABS module on your '96Ti, would your engine speed be limited to 5,500 rpm? 2nd: anyone know what the signal on pin 83 should look like? There are several decent threads on Bimmerforums under P0500 but no one ever seems to reach a real conclusion.

Last edited by benz-tech; 08-30-2015 at 01:37 AM.
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Old 08-30-2015, 03:09 AM   #4
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Well, that's odd- the ETK shows pin 83, vss, coming from the 'board computer'.
I wonder if that's where the vss signal's distributed from...

Looking at the ABS diagrams, it doesn't show any links to the ECU.

The old (obd 1 and E30) way was to have the instrument cluster process the wheelspeed
sensor in the diff, and then present a 5v square wave to the ECU. I have a 9-90 E30, and if
you DON'T interrupt the vss to the ecu, it'll limit the engine at 128 mph.

Hell, I'd just try hitting it with a 5v square wave. the old vss in the diff usually had 9
vanes or so, so you can figure out the frequency- probably anything over 5 hz would do it.

hth,

t
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Old 08-30-2015, 06:06 AM   #5
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Unhappy

I have sent a 5v square straight from the sensor on the diff. Watched it with a scope to make sure it was a clean signal. I cleared the code also but DME is just not translating the message.

Pin 83 has 12v on it without any speed input.. that's why I tried tapping it to ground trying to fool it into thinking it was a 12v square.

I dont know if it should be 5v or12v signal and if it should be pure square or a pull down signal.
The ABS module does effectively connect through the Rxd line, pin 88 I believe, but I don't know if they share data on it.

My frustration level is escalating. Its pretty fabulous otherwise, if you can live with the lumpy idle. And I can!
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Old 08-30-2015, 10:08 AM   #6
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Could you give some particulars about the car, for example the month and year it was built, what engine is has and what market it was built for?

Is 'nor-cal' Northern California?
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Old 08-30-2015, 03:57 PM   #7
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Quote:
Originally Posted by John Firestone View Post
Could you give some particulars about the car, for example the month and year it was built, what engine is has and what market it was built for?

Is 'nor-cal' Northern California?
The car is a '91 (07-90) 318i E30 . The swap came from a '96 318ti manual car without traction control. I don't know the prod date of the ti but its early enough to lack air injection. Both are US market vehicles from California.

After hours and hours of searching, a few guys over at r3v have run into similar issues with obd2 m/s 52 swaps. Their issue seems to be that the E30 speedo output to DME is based on the diff sensor and it reads 5x slower than the 48t wheel sensor speed their DME expects to see. That tells me that at least their DME is getting some form of speed signal from ABS since even an E36 speedo gets its signal from the diff. I would be happy if it read too slow.

I'm down to a few possibilities. 1 the 12v sitting on pin 83 implies that the speed input is a 12v square wave. I kinda tried getting this straight from the diff sensor. 2 ABS sends a signal via Rxd line( I'm so screwed if so) 3 my DME is bad. Easy enough to fix.
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Old 08-30-2015, 05:42 PM   #8
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So it's an M44, right?

The air supply to the back of the injectors was present on my 12-94 M42...

t
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Old 08-30-2015, 07:31 PM   #9
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Thanks for the added information. I would not have guessed what you wrote. Is the engine indeed a U.S. market, early OBD-II M44?

If it is, its DME won't be happy without wheel speed pulses from the ABS unit. The signal is a 12V pulse train that is 48/9 (5 1/3) times faster than the speedometer speed pulses from the rear differential.

Last edited by John Firestone; 08-30-2015 at 07:34 PM.
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Old 08-30-2015, 08:17 PM   #10
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Quote:
Originally Posted by John Firestone View Post
Thanks for the added information. I would not have guessed what you wrote. Is the engine indeed a U.S. market, early OBD-II M44?

If it is, its DME won't be happy without wheel speed pulses from the ABS unit. The signal is a 12V pulse train that is 48/9 (5 1/3) times faster than the speedometer speed pulses from the rear differential.
Yes it is early M44 with a 5.2 DME.

I don't see anywhere on the wiring diagram for the cluster that abs connects to it, other than on the infernal Txd data line. So I dont see how, other than on that wire (in the form of a data message) that DME could get a processed 48t signal.
The VSS is a sqaure wave sensor, 9 pulse/rev. Wheels are 48t a/c.

What I don't, and really need to, know is this: The VSS output from the cluster is what on an E36? Square, 9t, 48t, data, 12v, 5v? If anyone can hook a scope up and see what it looks like I think that might be what I need to proceed. A lot of this is just thinking out loud.
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Old 08-30-2015, 08:49 PM   #11
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Quote:
Originally Posted by benz-tech View Post
I don't see anywhere on the wiring diagram for the cluster that abs connects to it, other than on the infernal Txd data line. So I dont see how, other than on that wire (in the form of a data message) that DME could get a processed 48t signal.
I found it on the first page I looked at, about 15 years ago, but I got a really good hint from Jim Conforti. I believe this is the signal in question:

I have a microcontroller driving it, so I am sure I have something written about it in my notes.

Quote:
What I don't, and really need to, know is this: The VSS output from the cluster is what on an E36?...
12V, active low, narrow but clean pulses. 4712 pulses per kilometer.

Last edited by John Firestone; 08-30-2015 at 08:51 PM.
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Old 08-31-2015, 12:34 AM   #12
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THANK YOU!!!!!!!!!!!!!!! The wiring diagram I have for the 318ti shows pin 79 is not used so I never gave it another thought. I just checked the connector and there's a pin there. This was the exact info I was looking for, nay, scrambling to find. I may still have an issue with the 5v VSS output from the cluster to 83 but I will def work on feeding somehing to pin 79. Is it 12v with neg pulse also?
I suppose I need to buy/build a micro controller to convert the wheel sensor signal to into something .this is way out of my league to build, though. Any info you have on that would

You have given me new hope since the only way I could see an additional signal was through data feed that I just couldn't have made work. Damn 20 year old diagrams
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Old 08-31-2015, 04:06 AM   #13
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Success, even if it reads very slow. I just hooked it to the vss signal and have a full rev range. Its amazing how the Ti diagram doesn't have pin 79. What a stressful week. Thanks for the help.
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Old 08-31-2015, 01:03 PM   #14
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You are quite welcome. I am glad you got things straightened out.

I am pretty sure both signals use 12V open collector logic – at least that's how I have been treating them for the last 15 years – with a resistor in the receiving module pulling a line up to 12V, and an open collector transistor at the driving module pulling it down to ground.

I am have been using a VNS14NV04 as the open collector driver. I have a receiving microcontroller present a ca. 20K input impedance with a 22K pullup resistor to 12V, with an on/off threshold at 5V. I RC-filter the ABS speed signal with a time-constant of ca. 8 µs. I sample with no electrical filtering, the vehicle speed signal from the cluster at 10 khz, but require it to be four times on more than off, or four times off more than on, to change the filtered input state.

Last edited by John Firestone; 08-31-2015 at 01:10 PM.
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Old 08-31-2015, 04:47 PM   #15
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I was thinking of using a late Mercedes wheel speed sensor, and magnetic wheel bearing ring. The sensor is digital like our diff sensor and I will count the teeth on the wheel but its got to be closer to 48t than 9t. I will see if I can mount it up somewhere on the rear axle. The air gap has to be pretty perfect so it would be a challenge to attempt.
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