Hi all,

Me and Riceburner have encountered a problem with his HUD unit and 85 year cars.

86-88 year cars have a Green/White wire on the C1 connector on the bottom of the dash unit. This is the 2000 pulses per mile output from the internal converter in the dash unit.

I connected the YELLOW wire in Riceburners kit to the YELLOW wire on my C1 connector. But this YELLOW wire is the 4000 pulses per signal from the gearbox sensor. Using this wire gives me very high speed readings.

So...............
Does anyone have a 85 Pontiac manual they can look at for me ???
Its the signal wire that comes out of the dash speedo module and goes to the ECM and Cruise Control Unit.

Many thanks in advance.......

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Regards,

Paul Taylor, England.
85 GT Notchback, 2.8 V6, 4 speed manual. Custom made Tubular branch exhaust manifolds with true twin 3in exhaust system. No CAT, No EGR. No Crossover pipe. ADS Road Race SuperChip & 160 deg stat. Poly bushes all round. Lowered 2 inches. 16" alloys with 225/45 rubber. 0-60mph in 5.5 sec.

www.fieroforum.co.uk/Paul85gt.htm

Bump to the top.............

Hope someone can help........

Paul Taylor.

Paul,
I have an 85 manual here. I'll be happy to help, if I can figure out exatly what you're looking for?
Kevin

quote Originally posted by GT40 3.8 SC: Paul, I have an 85 manual here. I'll be happy to help, if I can figure out exatly what you're looking for? Kevin

Great !!!.
Look for the picture diagram of the instrument cluster. In the top left of the picture you should see the Speed pickup from the gearbox. In the middle of the diagram will be 2000 pulses per min control module. This then has an output which goes to the engine ECU and the Cruise Control if fitted.
What colour is this wire ?????

Many Thanks,
Paul Taylor.

Paul,
The wire out of the Dash unit is term. U in C204 to term. C in C245 and is BROWN. From C245 to term. D in C246 (the Cruise control Module) it is Brown/White.
Hope it helps,
Kevin

Well it would appear that the Speedo output wire on 84 - 85 model Fieros is the BROWN wire on the C1 Connector. This wire feeds the ECU and the Cruise Control with a 2000 pulses per mile signal.

But for some reason RiceBurners HUD kit will not work of this wire on 84 - 85 models. But it does work off this wire (Pin U C1) on 86 to 88 models.

Q. Does anyone "TK ?" have any ideas why this would be ??? Perhaps the output signal is in a different format ??

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Regards,

Paul Taylor, England.
85 GT Notchback, 2.8 V6, 4 speed manual. Custom made Tubular branch exhaust manifolds with true twin 3in exhaust system. No CAT, No EGR. No Crossover pipe. ADS Road Race SuperChip & 160 deg stat. Poly bushes all round. Lowered 2 inches. 16" alloys with 225/45 rubber. 0-60mph in 5.5 sec.

www.fieroforum.co.uk/Paul85gt.htm

I just ran into this myself, installing the HUD on my 85 SE w/85 mph speedo. The 2 power connectors were the same colors, but then couldnt find the green/white. checked the pinout, everything looked right, except the U was brown, not green/white. OK, got the service manual, and sure enough, that was the right wire, just different color. hooked it up. no reading. just get a 0 on the display. I've seen it change everyso often, i've a 1 on it sometimes, and a 27 popped on once. so, I belive the unit works, but I'm not getting a proper signal to it.

Ack, that's not good!!! As far as I know, the stock speedometers can be swapped between all the different years, right?? Anyone know why one would be different than the next? Are the ones that it's not working on the "steel" speedos, or the backlit plastic ones?? Unfortunately all I have is an '87 (which doesn't even run at the moment...), so I can't even hook up an ocilloscope to the output to see what it's doing.. I had one hooked up (years ago) to an '88 coupe, so I'm pretty sure it will work with that, but never had one connected to an earlier car.. This blows!! Does anyone have the ability to hook up an ocilloscope and check out that signal wire? Of course, that will be difficult considering the trans. has to be turning in order to get a readout on the speedo.. I honestly have no idea what could be causing this to happen.. Oliver, are you out there? Any thoughts?? I'll look into it further on my end, but that'll pretty much only be internet research, without an actual car to work on.... Worst case, we'll have to get the 4,000 pulse per mile version working (currently has a speed cutoff somewhere in the 70's), and tap it into the 4000ppm signal.. Hope to have this figured out soon! Thanks for letting me know!!!

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Bob Williams
Multi-colored '87 Mutt, a work in progress! (Got my 3800SC, installation in super-slow-motion progress. Only a Miracle will get me to the 20th in my Fiero now. Or a time machine...)

yes, I thought all Fiero speedos could be swapped between other Fiero speedos. I dont believe GM made the speedo's plug-n-play with autodetect. That isnt their style.

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1985 Fiero SE
Plain Red V6 Coupe

quote Originally posted by Paul Taylor: I connected the YELLOW wire in Riceburners kit to the YELLOW wire on my C1 connector. But this YELLOW wire is the 4000 pulses per signal from the gearbox sensor. Using this wire gives me very high speed readings.

I've been looking thru the service manual looking for a clue, and noticed what you posted there -
The yellow wire, as you said is the output straight from the VSS - called VSS Hi. Theres a second output from the VSS, called VSS Lo, its the purple wire, next to the yellow. being when you did this it read high, maybe if hooked to the purple, it would read right. But anyways, still confuesed, because the HUD unit is supposed to read the CLEANED signal that goes FROM the speedo TO the ECM & Cruise Control unit. And being Speedos, cruise control & ECM's are basicly swappable between Fieros, I cant understand why the speed signal from the speedo to the ecm is different. but then again, the ecm doesnt care about speed, does it? and the cruise control doesnt really care either, it just knows it wants to hold "X" speed.

The Purple/White wire is basically the ground for the gearbox speed sensor. Connecting the Yellow from the HUD kit to this wire has no effect.

Paul T.

so how many pulses does the stock fiero tranny VSS put out?

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85 LT4 GT
Custom Everything
in progress

I was under the impression that the stock fiero tranny sensor put out a 2k ppm signal, and that trannies from other cars used a 4k ppm signal. Hence the need for conversions on some engine swaps.

Do you know if the signal put out from the speedo is a square wave or a sine wave? I would think that the ecm would be able to handle both since some sensors put out one and some the other, depending on which car/year, whereas the GM ecms are all pretty similar.

On a slightly unrelated note, does anyone know of any problems with sending a converted 2k ppm signal to a 4k ppm ecm from a quad 4 car? I was going to try to do this to get rid of the speed limiter.

quote Originally posted by GT-X: so how many pulses does the stock fiero tranny VSS put out?

The Fiero gearbox speed sensor puts out 4000 pulses per mile. There is a converter in the speedo that reduces it to 2000 pulses per mile.

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Regards,

Paul Taylor, England.
85 GT Notchback, 2.8 V6, 4 speed manual. Custom made Tubular branch exhaust manifolds with true twin 3in exhaust system. No CAT, No EGR. No Crossover pipe. ADS Road Race SuperChip & 160 deg stat. Poly bushes all round. Lowered 2 inches. 16" alloys with 225/45 rubber. 0-60mph in 5.5 sec.

www.fieroforum.co.uk/Paul85gt.htm

so, from the sounds of it, we need the controller from a newer speedo, and wire it parallel with the existing controller, and use that output for the HUD.

Well thats easy for you guys in America.....but there are only about 11 Fieros in the UK !!

Paul T.

I just wish someone could post the actual difference in the speedo's. Maybe there isnt one, and our HUDs just dont work? and coincidently, we both have 85's. because everything I've seen, the speedos are 100% interchangable between the years. It is odd that GM changed the wire color tho. GM is pretty damn consistant with its wire colors. Which would make me believe that there is a difference in the signal type. Maybe some of you ECM guys can answer this? this is the signal that goes to the ECM. is there a differnce in the VSS signal on a 85 ECM and a 87 ECM?

There's *got* to be some little tiny difference between the earlier and later speedos that's just enough to screw up the HUD, but the ECM doesn't care... I got back from class too late today to hit a junkyard, but I'm going to try tomorrow to find an '85 or '84 speedo to test. (get out at 3pm tomorrow.. Gives me 2 hours) For what it's worth, the HUD works on the bench with either a square or Sin wave, and varying voltages... You can always test out the HUD with a LOW voltage (6v or less, preferrably like 3v) AC transformer... Well, in the US anyway. (Does UK use 60HZ wall voltage??) Hook up the low voltage 60HZ signal from the AC transformer to the input (of course the HUD has to be powered up first) and it should read something like 105mph. Hopefully good news tomorrow if I can find a speedo! Or at least some news...

quote Originally posted by Pyrthian: I just wish someone could post the actual difference in the speedo's. Maybe there isnt one, and our HUDs just dont work?

Well i believe mu HUD works, because if i connect it to the Yellow wire (the 4000 PPM from the Gearbox sensor) i get a speed Reading on the HUD that is actually double the real speed that i am doing. I have verified this with Riceburner.
I'm no Electronics expert, but this has to be a signal format thing......

Paul Taylor. UK

Hey Rice,

Any progress yet ???

Paul T
UK

Unfortunately no... Anyone have a spare '85 speedo they want to donate to the cause? I'm still looking for one.. A few years ago, there were Fieros everywhre in the junkyards around here.. What's going on?? They've all disappeared. Maybe they're crushing them as soon as they get 'em. That would suck... On a positive note, I picked up an '86SE yesterday, so now when I *do* find an '85 speedo, I can actually test it in a car. A REAL one.. LOL Not on the "bench". I drove it up to Boston, and man, I MISS driving a Fiero!! Now to install a HUD in it.. LOL And an '85 speedo as soon as I can find one....

PM sent.

Hi rice,

So any progress ????
I really really wish my HUD would work. Especially after paying for it...

------------------
Regards,

Paul Taylor, England.
85 GT Notchback, 2.8 V6, 4 speed manual. Custom made Tubular branch exhaust manifolds with true twin 3in exhaust system. No CAT, No EGR. No Crossover pipe. ADS Road Race SuperChip & 160 deg stat. Poly bushes all round. Lowered 2 inches. 16" alloys with 225/45 rubber. 0-60mph in 5.5 sec.

www.fieroforum.co.uk/Paul85gt.htm

Bump !!!.................

Doh!! I've been updating the other thread that this problem came up in, I lost the link to this one and it got buried in the 2,000 posts... The other post is: https://www.fiero.nl/forum/Forum1/HTML/032993.html ... I updated it the other day with what I found out. So far I've been running the resistor combination on my '86 and haven't had any computer problems, or the resistors heating up or anything. It might be easier to pick up the 2 resistors locally and install them (if possible), or if not then I'll definitely send them out to you.. Such a simple solution too.. Probably the '85 computers just have the internal pullup resistors isolated from the "outside world" so to speak, where the '86+ ones are pulled up externally.. Or something like that.. Anyway, if you'd like me to send you out the 2 resistors and where to connect them, let me know and I'll be happy to ASAP! - Bob

quote Originally posted by Riceburner98: Doh!! I've been updating the other thread that this problem came up in, I lost the link to this one and it got buried in the 2,000 posts... The other post is: https://www.fiero.nl/forum/Forum1/HTML/032993.html ... I updated it the other day with what I found out. So far I've been running the resistor combination on my '86 and haven't had any computer problems, or the resistors heating up or anything. It might be easier to pick up the 2 resistors locally and install them (if possible), or if not then I'll definitely send them out to you.. Such a simple solution too.. Probably the '85 computers just have the internal pullup resistors isolated from the "outside world" so to speak, where the '86+ ones are pulled up externally.. Or something like that.. Anyway, if you'd like me to send you out the 2 resistors and where to connect them, let me know and I'll be happy to ASAP! - Bob

It's not uncommon for the pullup to be in the load circuit and not the source circuit. I ran into that on the TR when I was playing with the Fiero speedo circuit for it. It took me a bit to realize there wasn't a pullup for the output.