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Old 07-14-2009, 10:59 PM   #1
keeneydj
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Car runs fine, but speedo is WAY wrong.

Ok, as complicated as this seems, I'm sure there is a simple explanation.

I have a '92 Achieva S that was a SOHC factory. When I got it, it was dead. The girl before me ran over something and shattered the oil pan. Still, 200 bucks for a basically new car that just needed a pan, crank, and one rod. ...so we thought. The oil jacket over the #2 cyl. had a crack on the outside wall. Yeh, the block cracked, and the head was fine. It's a shocker I know. Anyway, I got a different motor. The new one is a DOHC out of a '90 Calias. Aside from some bs I had to deal with on the wiring harness placement, it's in there. It runs pretty decent, and as expected. I lost a little low end on the tourque, but it gets up and hauls past about 3-4k or so.

Here's were we get to the problem. The '92 transmission is electronic, plus the '92 has ABS and sensors to match. Almost everything in this Achieva is electronic. The only program chip I had for this '90 DOHC motor was the one out of an '89 Calias which had a vacuum madulator style tranny. With the setup I have going on, I have no problems with anything (even ABS) except the speedometer is way off. It works smoothly and steadily, it doesn't fluctuate. It's acting like I have the wrong speedo gears in a TH350. At 5mph it's pretty much right, at 70mph it shows 40.

I have no idea where all the speedo gets it signals from in either car. The '89 and '90 were basically the same car. The '92 bridged a gap in design, mainly as far as ABS goes and wheel speed sensors. The thing that's stumping me on this one though is that the dash cluster and transmission haven't ever been removed or changed in this car. I figure if the speedo signal gets generated by the transmission, then everything should work as normal. (no chance of having "wrong gears" in the tranny to speak) Basically, I think the program in the PROM is not right for that dash cluster. (?has the wrong multiplier for the tranny speed signal?)

So, just to recap...
'92 achieva with everything except the motor and ECM program factory
'90 DOHC vin D motor complete (more than long block)
'89 DOHC vin D program chip in the ECM
= the speedometer (and prolly the odometer, therefore not inspectable) running slow.

Any thoughts? Anything that might fix this without breakin' me?

Thanks,
-Dan

Ps. I searched the threads for something like this, and only came up with broken/fluctuating speedos. I'm not having this problem, and I apologize if this has already been covered.
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Old 07-15-2009, 05:27 PM   #2
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Re: Car runs fine, but speedo is WAY wrong.

Welcome to AF !

Sounds like some wiring mught be out of place, or all that mix bag of parts isnt working well together to get the right signal.

The vehicle speed sensor-VSS (side of the trans) gives you the odometer signal.
Have you tried to use a scan tool to calibrate/reset the speedo?
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Old 07-15-2009, 07:51 PM   #3
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Re: Car runs fine, but speedo is WAY wrong.

Thanks zeroinfinity.

I do not have the equipment to reset or calibrate the speedo. So no, I haven't even begun to think that direction. This whole setup worked before, as the engine and prom were the only thing replaced. The transmission, all of it's sensors, and the dash are all factory. It is possible that the vss is bad however, just not likely. I did start it up for a few today, and ran it around the block a ways. Runs like a champ. I did notice that the speedo will rise and hover about 10mph at over 4.5k or so in park just revving. It will drop to zero again around 5.5-6k. The tach works woderfully. Does this sound like something that a bad vss would cause?
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Old 07-16-2009, 09:34 AM   #4
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Re: Car runs fine, but speedo is WAY wrong.

Well being a 92 its possible you vss is bad. Though their are also problems with the instrument clusters on these models going out.

Since the trans hasnt been changed I'd lean toward bad wires on the trans or the cluster is going out. So you might inspect these two thing.

Good Luck
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Old 07-16-2009, 10:32 PM   #5
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Re: Car runs fine, but speedo is WAY wrong.

Okie dokie...

well, I have had no change on the speedo, but I did get the ecm codes flashed (read). The SES light was on for code 62. Supposedly an electrcal fault in the transaxle gear range sensor. (neutral/safety switch) The SES light will start off, but come on a few seconds (about 15) later just idling. If you shift the car right after starting it, the light will come on. So, code 62 sounds about right for the light. Still doesn't pertain to the speedo though. And, the tranny shifts just fine. You can start it in park only like you are supposed to be able to. You can't start the car in neutral though. I don't remember if I could before or not.

I did notice that the timing chain cover was arcing to the crank pulley. Yeh, arcing. ...little spark about every second. It doesn't do this all the time, and seems so far to be completely random. Warm, cold, starting/stopping the motor, no changes seem to make it start or stop. Sometimes it's doing it, sometimes it's not, and nothing else in the car seems to change or act odd when this starts/stops. I checked wires and didn't see any bare/disconnected. This is just another thing that blows my mind. It's not arcing with the ignotion coils, or it would do it a lot more often and faster. ??? got me on that one. Nothing has blown up, and everything seems to work. The car runs great, and everything works like it supposed to, other than the speedo. ...and I guess this arcing.

I mean, it's not like I'm a complete idiot working on something I shouldn't be. I rebuilt this car once before. It ran as intended for 4k miles before we realized the block had a crack in it. I know how these things come apart, what all there is (sensors ect.) on the car. I know the general jist of why they are all there, and what they do. I'm a 3rd generation mechanic that's been in a shop most of my life. I mean, cars are getting more and more complex, but all the major components are there and working as far as I can tell. The ECM is only complaining about the gear selector switch. No other codes.

So, the VSS will run me $45, and the gear switch is $60, both "special order" from my parts shops. I haven't been able to track down a DOHC program chip for a '92 achieva yet. (anybody have an AUKX or AUKW chip?) I'm fairly certain replacing the gear switch will take care of the ECM code, but I'm not sure if that could be what is throwing off the speedo. I'm starting to lean towards the dash cluster being bad. As far as the TC cover arcing to the crank pulley... I'm completely stumped there. No ideas on that one at all. Boo. :P

Hey, also, sorry for misspelling your name xeroinfinity. The x and z are real close there, and I didn't even think about it. Also, thank you for your time, you have been very prompt about replies. I'm very gracious.

-Dan
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Old 07-18-2009, 05:23 PM   #6
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Re: Car runs fine, but speedo is WAY wrong.

Fix the code 62 trans axle gear sensor, bet that takes care of it.
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Old 07-18-2009, 07:36 PM   #7
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Re: Car runs fine, but speedo is WAY wrong.

Yeh, I'll get to the gear sensor when I need to. Turns out the speedo problem is just the PROM program. The SOHC chip runs everything just fine actually. I guess I just got lucky the two programs were close enough to run this dual cam decently. Just, the DOHC chip doesn't run the dash properly where the SOHC chip does. Anyway, I have a guy that can burn me a proper chip when I get around to that. With the SOHC chip, the only thing that doesn't run glass smooth is the low idle (about 700rmps parked for a few seconds) only when it's warm, lopes a little. ...hardly enough to tell. No backfire, no misfires, and I don't get any codes now.

Yay!, my dash isn't lit up like a christmas tree!

The electrical arc was an overload due to the old DOHC program, but since the code was being thrown from the gear sensor, I'll be replacing it asap. I'm not really looking forward to the adjustment of that thing, but a new one should only be half as hard.

Lesson here, it's best to try to make sure the ECM program is from the same year car with the same motor you are putting in. lolz Otherwise, much much research will have to be done first.

Thank you again xero, I think I got it from here!

-Dan
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