Sloppy tach signal after adding VR circuit

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cscm094
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Sloppy tach signal after adding VR circuit

Post by cscm094 »

I'm using code 024s9, Megatune 2.25b514, pcb 2.2, with VR conditioner circuit. I have a 1989 BMW 325, with an M20 motor. It has a bosch motronic setup stock with a 60-2 wheel and VR sensor.

I believe my problem lies in the hookup of the VR sensor-- Stock is a 3 wire sensor from what I understand. Signal, ground, and shield. I simply cut the signal wire at the ecu, and extended it a foot or so and wired it into my VR conditioner circuit. Is this wrong?

The RPMs will jump all over the place with the engine not running but accessory power on, from 0 - 3500 or so and everywhere inbetween. See the data log below (this was with the engine not running).

Image

It will start, but run terribly and you have to feather the throttle. If you try holding it at say 1000 rpm, the spikes will bounce up to 3000 or back, but definately a much cleaner signal with the car running.

Any help is really appriciated. I just dont know how to get this VR sensor hooked up. I'm worried my conditioner circuit is wrong, but I dont think that would make a dirty tach signal. I'm really tempted to sell this and get a 3.0 pcb.

-Chris
renns
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Post by renns »

Chris,

How is the stock 3-wire set terminated now? Are the ground and shield connected together at the ecu, or at the sensor? Either way, you should pull all three wires back to the MS. Connect the ground to the MS signal ground pins on the DB37. If the shield was grounded at the stock ecu, then connect the shield as well to the DB37.

Roger.
1979 Mazda RX-7, running MSnSExtra hi-res 09c for fuel and spark control on a turbocharged, intercooled, and (of course!) injected 13B rotary.
cscm094
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Post by cscm094 »

Ahhh-- this makes sense. I believe everything is teminated at the factory ECU. I'll check it out. THANK YOU for your reply. I'm really clueless when it comes to this ignition timing stuff. I will try this tonight and repost my results!

-Chris
cscm094
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Post by cscm094 »

Hmm still no go. Right now I have three wires from the VR sensor--

- One wire goes to the "VR input" on the VR conditioning circuit, black in color.
- One wire goes to the ground at my MS, yellow in color.
- One wire (the shielding wire) also grounds at my MS, clear/silver in color.

If I can't figure this out by tomorrow, I'm just going to order a MS PCB v3.0

-Chris
mops
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Post by mops »

so let me get this right....

you get some rpm singnal even with the engine off ???

thats some wierd interference you are getting. that's not MS's fault...
it's really bizzare... if that's the case, dont try to run your car with this interference... it may cause spark at the wrong time which could even damaging the engine....

post back, i'm keen to help fellow e30'er :)
BMW, 1985, E30, 325i, 2-door, 5spd. Lots of custom work. Turbo build in progress: http://www.e30tech.com/forum/showthread.php?t=55733
cscm094
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Post by cscm094 »

Better--- But still no good.

I borrowed a friends V3 PCB. I did everything as described in the MSNS-Extra with the 330 ohm resistor and TSEL, and VROUTINV, etc....

No more erratic RPM with the engine not turning over which is good-- but its not detecting RPMs correctly. It will sit at 0 rpms when I'm cranking, and sometimes go to 60, 61, 62, 61, then jump to 262 rpm. Its very random, and I have tried grounding everything to everything, and just cannot get results.

Also -- I have no spark. At least with a few RPMs it should be sparking. I think its because my plugs are SOAKED from previous starting attempts. I'll try some new plugs, and maybe it will catch and turn over, who knows.

Would accidentally leaving wheel stim ON in the car for a few turnover attempts cause any damage to anything? I turned it off as soon as I noticed I had left it on.

Here are my wheel settings BTW:

Image

Image

Image


-Chris
cscm094
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Post by cscm094 »

Got it running for the record, had to adjust the pots :oops:
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