Hi All,

Originally I had a problem with my 4.9 conversion - no speedo. Thanks to several folks here on the forum I got it sorted out. Ultimately solved by have the VSS signals go to the ECM and added the special circuit to drive the speedo. Worked great. Car loves getting a vss signal, doesn't stall, accelerates well, good gas mileage.

Then, last week the speedo needle started jumping around. ECM was still seeing the VSS signal cause otherwise it just about stalls out. Now the speedo barely works...still spastic and sometimes not at all...and it looks like the ECM isn't consistently seeing the VSS signal (car almost stalls out coming to a stop). Definitely close to stalling when the speedo is not working at all.

So, here is what I have done.

confirmed gear is attached to VSS
checked continuity of the wires from the VSS to the ECM - good!
Swapped VSS from other Fiero (86SE) - no joy
plugged in other VSS into circuit and used a drill to spin it. Ran car, spun VSS, car was definitely seeing the signal

I am heading toward the dreaded thought that the gear inside the trans that drives the VSS gear is bad.

Looking for ideas.

Thanks

T

Continuity may not tell if the VSS correction circuit is good or bad.

I would bet that the correction circuit has a bad component.

Thanks olejoedad! Always nice to hear from you!

I was thinking about this last night and was also wondering if that correction circuit is bad, would it interfere with the VSS signal to the ECM? Right now both wires from the VSS go to the ECM (B9 & 10...if I remember correctly). In theory shouldn't I be able to disconnect the correction circuit (thus killing the speedo) yet the ECM would still see the VSS Signal?

I tried pulling the signal off both points of the ECM (11 and 12?) to the correction circuit. When I had the whole thing working it was on 11 and when I started trouble shooting I moved it to 12...worked for about 5 minutes. I am going to disconnect the correction circuit today and see what happens.

Thanks Again!!!

T

Do you have access to a signal generator? Remove the wires at the VSS and plug in the signal generator and use that to generate a signal to the ECM. I take it that this is a manual transmission? What part of Michigan are you in? I am near Jackson. If I can help let me know.

Jack

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If you can not run with the big dogs, stay on the porch!

quote Originally posted by michfiero: Thanks olejoedad! Always nice to hear from you! I was thinking about this last night and was also wondering if that correction circuit is bad, would it interfere with the VSS signal to the ECM? Right now both wires from the VSS go to the ECM (B9 & 10...if I remember correctly). In theory shouldn't I be able to disconnect the correction circuit (thus killing the speedo) yet the ECM would still see the VSS Signal? I tried pulling the signal off both points of the ECM (11 and 12?) to the correction circuit. When I had the whole thing working it was on 11 and when I started trouble shooting I moved it to 12...worked for about 5 minutes. I am going to disconnect the correction circuit today and see what happens. Thanks Again!!! T

You got it! B9 & B10 are for VSS input to the PCM. B11 or B12 for PCM output to speedo (both work but you only need one). The PCM to speedo circuit is seperate from the VSS to PCM circuit. You should still have a VSS signal going to the PCM even without the speedo hooked up. Sounds like an intermittant connection in one of 2 wires from the VSS to me. Depending on how your exhaust is setup and what trans you are using you might want to take a close look at the VSS connector itself. I used aluminum tape to shield my second connector from the heat since the first one melted. I found a replacment connector at a local Carquest.

EDIT: To add the VSS gear on the differential is much stronger plastic then the one on the VSS. More likely then not the VSS gear will strip out before the one in the trans. If its fine then I'd bet the one in the trans is also. They are simple to replace if needed but do require splitting the case to get to. If you want to check it you can jack up the car, remove the VSS, and stick a finger in the hole while rotating a wheel slowly to feel the gear. Be careful and don't lose a finger. Mine got me when I checked it since someone else was spinning the wheel. Hurt like hell and I lost part of that fingernail. It did finally grow back.

[This message has been edited by Fieroseverywhere (edited 03-10-2010).]

Thanks Everyone....problem solved...loose wire inside the connector at B9 connection. When I had checked the continuity earlier I checked it at the where the B9 wire was spliced to the wire that ran back to the VSS. Your guys comments made me rethink what I had done...or not done in this case...which was an end to end check. I pulled the connector to check the wires and that's when I got nothing on the B9. Took the opportunity at that point to check all the wires in that connector.

Thanks Again!

T

Sweet!

Glad it's fixed, now when the State Trooper pulls you over for 100 in a 30 you can confidently argue you were only going 96.

Joe

I'm not speeding! I'm just flying low


.....sorry stole that from someone here on the forum....love that quote!