VSS problem 1990 325i s52 obd1

[JohnyEndo]

This is my first post reguarding help with my swap, but i figured id post it up in case somebody can save me some time. And yes, searched it to death.

As far as i understand, late model e30s should wire up through the c101/x20 via pin 14 to 14. Well i've done that, and everything works in my swap. Even the speedo. Problem is im throwing a cel. Im reading it with my snap on modis and it gives me a code 42: vehicle speed circuit. When i read the data my road speed is stuck at 18mph.

Confusing. As far as i understand, if the guage reads then the dme should be getting a signal.

The other slight problem which i believe is related is, the engine wont idle once you unhook the battery and drain the memory. It will start every time and then promptly fall on its face. I have to keep it revved several times before it will even attempt to idle. After a couple days though it will adapt and idles rather well. It drives fantastic so no complaints there. But still very occasionally it wont catch idle and shut off. My initial thoughts were a tuning issue, and that still may be, but i would like to get a correct vss reading to the dme before i tackle that.

Also since break in, i started running it past 6k. There is a fuel cut, but i forgot to upgrade to a walbro 255. So one of those is on the way.


Should probably leave some more of the engine info:
S52, coated acl rod/crank bearings, forged rods, .40
Overbore pistons 10.5:1 cr, vac stage 2 race head, sunbelt stage 1 sport cams, arp headstuds/main caps, blueprinted, balanced rotating assembly,
Dr vanos stage 2, obd1 red 413 lable dme, 540i maf, long tube headers, stromung catback, custom midpipe with high flow cat, vac oil pan baffle, vac oil pump sprocket upgrade, 16lb flywheel, underdrive pullies,
TRM tune (not custom, going ms3x or similar soon)

[JohnyEndo]

Fwiw i was runing same everything except :had schricks, stock s50b30us bottom end, and it still threw code 42 but idle was perfect 100% of the time even when relearning, and revving to 7k never hiccuped with TRM software..

I know its a long post but all im basically asking is how to get roadspeed to my dme, i only listed the rest in case they were strangly related and it could be used as a clue. If fixing the roadspeed input does not alter my other symyoms then i will look into it, as this is my first course of action.

[JohnyEndo]

When looking up code descriptions it shows that knock sensor 2( the rear one) can also come up under dtc 42.

Anyone?

[JohnyEndo]

Update: took sunday to do a little diggin, so it was coffee and etm hell all morning. I took a vehicle speed sensor reading directly from the back of the cluster (blue/yellow) wire and hooked it directly to pin 42 (black/white) of the dme.

Now instead of my VS being stuck at 18 when i look in data its now stuck at 183, even with everything back the way it was. And after going through all the e30 and E36 diagrams (and through my own wiring) i have confirmed that everything is indeed correct.

Luckily for me i have a local friend with an obd1 s52 swap, so i bribbed him with some beer and he came by. Went to scan his car and wouldnt ya know it? Code 42 VSS circuit. Look in data, 18mph. His swap is and has been operational for a few years now. Idle is perfect, pulls past 7k no problem. So if i didnt get anything accomplished yesturday at least i know i have done everything right so far. Just more needs to be done, and i must figure out what.

So heres where im at, please correct me if im wrong:
-e30 & e36 dme get VSS reading from their cluster
-e30 uses the trigger wheel in the diff. Wired to the cluster which interprets the signal
-e36 uses wheel speed sensors, the abs module interprets the signal and sends that to the cluster

So if thats correct there is no way just 'hooking' some wires up will produce the correct signal to dme. Its something like a 43 tooth wheel to a 7 tooth wheel. There has to be some kind of way to convert the signal properly.

Gurus feel free to chime in any time...

[e30rapidic]

that is interesting.

is that a late model specific thing?! I have an early model with S50 and took my speed signal straight from the green plug on the cluster to the dme. No codes.

[nando]

OBD2 uses the 48 tooth wheel sensors.

OBD1 DMEs use a 9-tooth signal from the cluster just like the E30.

something's wrong with your wiring.

[JohnyEndo]

Late models should be plug and play via c101/x20

I can assure you the wiring is good, since i can take speed signal from the cluster and put it directly where it needs to go with the same result. Just like the early cars. And everything works including the speedo. If you could offer any other insight that may be a possible cause, other than simply the wiring is wrong , it would be greatly appreciated.

My eyes hurt from all the sifting thru etms, and ive checked everything more times than im proud of.


Its also the same conditions as my friends swap and he has a treehouse adaptor. His friend back up north (that did his swap) knew about the cel and told him there is a way to fix it but then never got around to it before he moved. Unfortunately we cant seem to track him down. I think his forum name is Bennett22. Apparently its kind of 'involved' to fix..

Either way, thats all hearsay till i speak with someone.


A little more info in case it helps anyone, obd1 harness from 95 m3, 09/89 325i. Didnt just steal splices, i looked them up myself and have since checked it at least 5 times.

[nando]

it's either the wiring or the aux "A" output from the speedometer is bad. it's a really uncomplicated system. the black/white wire coming from the cluster is the same as the "A" output on the green plug on the back of the speedometer, which comes straight from the UAF2115 chip that drives the speedo stepper motor.

ODB1 doesn't use a 48 tooth signal. it uses a 9 tooth signal just like the E30.

I don't know what other insights to give you..

[JohnyEndo]

Ive done all that, and yes the 9 tooth signal info was useful thanks.

Ive pulled speed from 4 different known outputs ( all three on green plug ) and also from the brown/red wire goin to the obc.. All results are the same. I will try pulling it right off the uaf chip on the black/white wire and bypass the green plug. Aside from that im out of ideas.

I think the simplicity is what is driving me nuts. Even tried a different known good cluster with same results.

The other thing that is bothering me is i hate asking for help.. Of all the years owning e30s this is the only time ive asked for help, im very good at figuring this stuff out. Did the entire swap myself, shaved engine bay and built the engine. Besides what had to be done at the machine shop. I guess i was hoping for some kind of cheat code, or sacred indian speedometer dance to get this damn thing 100%

[nando]

only one pin on the green plug is actually a VSS output. a couple of them go to nowhere and one is actually 12v.

you want the black/white wire at the C101. it might be worth doing a continuity check from the plug on the cluster to the C101 to see if there's a break.

does your OBC read the speed correctly?

could it be the DME itself? or even the connector at the DME? maybe the VSS wire is broken inside the harness.

[berlow94]

I have a very similar build!
Your poor idle problem after unplugging the battery is that you are running OBD 1 with a chip on a highly modified motor. Even with my build i only got about 245 to the ground. Im doing a Vipec standalone system over the winter and will easily be able to get another 20 hp to the ground just with tuning. Plus, ill never have to worry about losing my tune. (Vipec is also the only standalone ECU that plugs directly into the E36 harness, no wiring needed) OBD1 takes for ever to learn the motor.
Wish i could help with the VSS problem, i have an early model.
As for the studdering, what size injectors are you running? And what FPR?

[JohnyEndo]

I did check continuity but im going to double check everything again tomorrow. I just feel like there is something more to it

I just put in my walbro 255 today, it sorted idle out quite nicely and now there is a definitive rev limit at 6500 rpm with no fuel cut(besides what the dme does). I gotta call trm back to confirm my tune because i think its tuned for sunbelt stage 2 sports. I bought them from someone who got them new but never used them. Werent in the proper packaging but had sunbelt confirm that they were stage 1's after all. Its a new stock fpr 24lbers. I just hope the vs issue isnt imposing a rev limit.

[berlow94]

You'll probably want to consider an AFPR with the 24# injectors.
I know i was running super rich with my TRM chip, 24# injectors, and stock FPR. Got an AFPR and brought fuel pressure down to 39 PSI and i'm running an acceptable AFR now. (except for when vanos engages, but that's just the shitty TRM tune.)

[JohnyEndo]

Yea ill get one eventually, but after the walbro install its a non issue for now. I really want a standalone. Maybe after fixxfest. Just splurged and some wheels :P what do u have done with your build?

[berlow94]

Wiseco pistons, same bearing setup. Standard thickness MLS headgasket, all ARP hardware, oversized valves with supertech springs and Ti retainers, 5 angle valve grind, port matched, head and block decked of course, schrick 256/264 cams, Dr. vanos stage 2 kit, supersprint headers, 75mm VAC billet throttle body as well as the usual bolt on's: 540 MAF (for now) M50 intake manifold, 24# injectors, castro airbox, etc.