Just curious if it has worked for anyone, or if there is anoter way. I changed my crystal to one that should have given me a 180 mph speedo according to the formula I found online. I drew up a new faceplate on autocad and printed it on permanent self adhesive paper(expensive paper). It works for about 10 minutes and the goes nuts, it spins goes foreward and backwards and all over the place. Then the next time I start the car it works again for about 10 minutes.

probubley fryed the crystal,From what Ive read,you heat the soder and not the leads on the crystal and you have to work fast.Probubley better off paying someone.Try a new crystal.

I played with swapping crystals in a 140KPH speedo trying to get it to work in MPH without much luck.

Here's the thread I had for the attempt.

https://www.fiero.nl/forum/A...020208-2-013619.html

Steve

Did the 8.000 keep working for the 165 mph ? If so, I think I have one in the garage. I bought a handfull of crystals, just gotta find em now.

i used a 7.1 MHz crystal for my 240KPH Speedo , works very well

------------------
1984 Fiero Sport
1987 Fiero
1984 Fiero SE
1999 Chrysler Grand Voyager 3.3 LX LPG

*** nuclear winter cures global warming ***

How did you add the digital ? thats sweet !!

quote Originally posted by Mike Gonzalez: Another thought or question. I will be running my speedo off a obd2 and 4t65e so I will need to get a signal converter anyway. Is there a way to change or make adjustable the speedo range with the converter?

...if you are running it off OBD2 ECM, wouldn't it just be easier to change the output signal from the ECM to the correct number of pulses to compensate when it is programmed for the passkey/etc ?

Wasnt planning on getting it reprogrammed, cant afford it right now. Also didnt realize that could be done. Who can do this ? Anyone in Colorado ?

quote Originally posted by Mike Gonzalez: How did you add the digital ? thats sweet !!

https://www.fiero.nl/forum/Forum2/HTML/081808.html

quote Originally posted by fierohoho: I played with swapping crystals in a 140KPH speedo trying to get it to work in MPH without much luck. Here's the thread I had for the attempt. https://www.fiero.nl/forum/A...020208-2-013619.html Steve

I've done this as well, and it worked great.
I didnt get the frequency exactly right with the crystal, but I adjusted the VSS gear to compensate - and its fine. I also recently got the odometer & trip odometer to tick off miles again, instead of kilomoeters.

anyways - to the thread starter - the crystal is pretty easy to access & replace with basic soldering skills.

and - can anyone present a table of some math or frequencies? I myself just found a frequency for the 140MpH to read in MpH thru searching. I am sure there is some math which can be done to work out ANY speed range

I know its easy to get to, done it once and it doesnt seem to work. The formula I found on line appears to be wrong and reading through some of the threads here it dosn't appear that there is a consistant formula that makes sense.

I have been running a 180 mph speedometer conversion in my Formula for more than two years without problems. Replacing the faceplate and crystal were all that was required. Replacing the crystal is easy if you have basic soldering skills and a small, low wattage soldering iron. It is good idea to "shock mount" the crystal with a dab of silicone rubber or a small piece of double-sided foam tape. This will keep the crystal from moving around and will minimize stress on the leads and solder joints.

Assuming that your speedo was good to start with, it seems likely that either 1) the crystal is the wrong value (e.g. 2x the desired frequency), 2) the other electrical specifications of the crystal are not compatible with the Fiero speedo (not likely, but possible), or 3) your installation is marginal (loose crystal, poor soldering, etc.).

For future reference, the speed crystal frequency is determined by the following simple formula (per Oliver Scholz, who is an authoritative source):

Crystal frequency (approx.) in MHz = 534 / max_speed (in mph).

(Example -- The crystal for a 180 mph speedo should be: 534/180 = 2.97 MHz.)

[This message has been edited by Marvin McInnis (edited 10-22-2008).]

I belive the value is wrong, and possibly cooked it by getting it too hot soldering. I have not yet figured out what value crystal to use. Do you remember what you used for a 180 ? does it matter what speedo you start with, 85 or 120 ? I noticed that some of the places that used to sell kits say it work for the 120 only or the 85 only.

Contact J. Brian Riley. He sells good quality, reasonably priced 180 mph conversion kits (new faceplate and crystal), which is what I have installed. He might even be willing to sell you just the crystal.

[This message has been edited by Marvin McInnis (edited 10-22-2008).]

quote Originally posted by Marvin McInnis: .... For future reference, the speed crystal frequency is determined by the following simple formula (per Oliver Scholz, who is an authoritative source): Crystal frequency (approx.) in MHz = 534 / max_speed (in mph). (Example -- The crystal for a 180 mph speedo should be: 534/180 = 2.97 MHz.)

that is - if it started out as a MpH speedo. for my 140 KpH converted to MpH - the crystal is 7.67 - which I expect is that same formula combined with the Kilo to Miles conversion.
lets see:
534 / 140 = 3.81
3.81 * 1.609 = 6.13
hmm....nope....but, 85 doesnt exactly hit 140 - so there maybe also be differences in the degree of the circle

That is the formula I used that I have found to be wrong. Just reading through this thread and the threads linked to it proves that. FieroHOHO got a 165 or so Mph using a 8.0 crystal. The other one with the indiglo gauges got 240 Kmh (around 150Mph) using a 7.1. When I did mine I think I went to a low frequency as the formula tells you, but it didnt work corectly.

quote Originally posted by Mike Gonzalez: That is the formula I used that I have found to be wrong.

Interesting ... I'll try to investigate further and report back.

What I definitely do know is that the crystal I received from J. Brian Riley does work correctly in a 120 mph Fiero speedometer.


Edit: I just checked the OEM crystal I had removed from my 87-88 (120 mph) Fiero speedometer, and it is clearly marked 4.430 MHz ... which would validate 534 as the correct conversion factor. (120 x 4.430 = 531.6)

Something else to think about: 4.43 MHz is a suspiciously common crystal frequency (used in TV sets and PCs, among other things), so it's at least possible that GM may have chosen it because it was cheap and they could force it to operate it in first-overtone (8.86 MHz) mode rather than in fundamental (4.43 MHz) mode. The only way to know for sure would be to check a functioning Fiero speedometer with a frequency counter.

[This message has been edited by Marvin McInnis (edited 10-23-2008).]

Just got an Email back from Oliver, He says there are several different formulas. He has Three different ones he just told me. I guess there are some design changes and the easiest way is to figure the formula by finding out what your stock crystal is and go from there.

It sounds like the 85 MPH speedo be converted to a 120 or greater, just by changing the crystal. Is that so?

If you want to know how fast you're going, you'll need to change out the speedo faceplate, too.

quote Originally posted by Marvin McInnis: The crystal frequency should be the same for Kph vs. Mph speedometers. The units conversion is accomplished by using different dials (i.e. different scales) on the face of the speedometer. On the other hand, the crystal is different between the 85 Mph and 120 Mph speedos.

yes - AND - then the crystal would have been the same between my 85 mph speedo and the 140 kph speedo

quote Originally posted by Pyrthian: that is - if it started out as a MpH speedo. for my 140 KpH converted to MpH - the crystal is 7.67 - which I expect is that same formula combined with the Kilo to Miles conversion. lets see: 534 / 140 = 3.81 3.81 * 1.609 = 6.13 hmm....nope....but, 85 doesnt exactly hit 140 - so there maybe also be differences in the degree of the circle

...there in lies your problem...why are you multiplying by 1.609?

There is no conversion factor - changing the crystal only changes how much the needle deflects given a certain speed. The needle does not care what the scale is (MPH or KPH) - that is to say when you make a higher top end, you move the 60 mph reference mark lower down on the scale (ie: the needle does not need to deflect as much to hit 60) - hence the reason for the new crystal.

If you want your scale to read in KPH you then multiply by the 1.609 to get the numbers for the scale - this does not enter the crystal calculation.

If you want the max speed of 140 MPH to be on your speedo - you install the 3.81 MHz crystal (as calculated) and mark the face plates max as 140 MPH (or do the multiplication and change the markings on the face plate to 225 KPH).

Oliver Scholz's formula is correct as Marvin McInnis posted.

[This message has been edited by Mickey_Moose (edited 10-23-2008).]

If that formula is correct, why does everyone who got it to work that posted here or on threads linked to this one have a crysta of 7.1 - 8.0 ?

Also why did Oliver E-mail me and tell me that the 534 formula only works on some speedos, and the ones he has the use 534, 1068, and 356 as the magic number on 3 different speedos ?

Looks like 534 is correct for 1/3rd or so of the speedos out there. Has not worked on two of mine, Mine were both 85's as were the two that worked with the higher Mhz crystals in this thread. I think 534 may be for the 120's and 1068 for the 85's dont know yet where Olivers one with the 356 ratio comes in yet.

Would you please ask Oliver's permission to post his e-mail here? It might help us all out to have his information, both now and for future reference.

[This message has been edited by Marvin McInnis (edited 10-23-2008).]

Just sent him a Email to ask.

After crunching numbers a while the formulas compared to the member results on this forum, the formulas are still not consistant. The trend of the formula goes the oppisitr of what the reported results have shown. The members here went to a larger Mhz crystal for higher speed reading and the formulas have you go smaller for higher.

The closest I can figure for a formula that follows the results is .048 x Desired top reading = Mhz

quote Originally posted by Mike Gonzalez: The closest I can figure for a formula that follows the results is .048 x Desired top reading = Mhz

Not seeking to argue with you, but that can't be right. We know that at least some 120 mph speedometers came from the factory with 4.430 MHz crystals. That is a fixed data point that we know to be correct, but it doesn't fit your formula ... which would yield 5.76 MHz, a 30% error. It seems more likely, as Oliver suggests, that there is more than one "correct" formula, depending on which specific speedometer revision you have.

The following is just my speculation, but since the quartz crystal was by far the most expensive single component on the Fiero speedometer circuit board, it seems possible that GM might have used several slightly different board designs depending upon whichever crystal was cheapest at any given time. Consider also that custom crystals are generally more expensive at lower frequencies (below about 5 MHz), although there are cheap "commodity" crystals widely available off the shelf at a few spot frequencies (e.g. 3.58 MHz, 4.43 MHz, etc.) below 5 MHz.

FWIW, an excellent source for custom quartz crystals at reasonable prices is International Crystal in Oklahoma City. They can manufacture a custom crystal for you at just about any frequency you specify (from 32.768 KHz to 200 MHz) for less than $20.

[This message has been edited by Marvin McInnis (edited 10-23-2008).]

Hmmmm, well guess that doesnt work either. Guess it is just best to know what the stock one is and figure out the specific formula for that speedo.

Anyway here is the response from Oliver,

as I said, there are different processor versions with different programs, so
changing the crystal frequency (hence the execution speed of the program
in the processor) has a different effect. I don't know which versions of the
processor were used in which year Fiero or which speedo. I only know
there is not one formula that works for all Fieros, there are more than one.
Two of those formulas that can be found on fiero.de (not my website) are

f = 1068 / mph, e.g. 150mph -> 7.12 MHz

the other is

f = 534 / mph, e.g. 150 mph -> 3.56 MHz

But I also have two speedos (one backlit, one not) here with a 4.19 MHz crystal and a max. of 85 mph.
In that case the formula would be:

f = 356 / mph

Hope this helps,

Oliver

Hi,

I have done some research a few years ago on that topic, but I can't find my findings anymore, so this is all from memory.

1) As mentioned by many in this thread, the speedo doesn't care if it's miles or kilometers, it's only in the dial (and the gears in the odometer are different, but that's a different story). The 85 mph speedo is practically a 140 km/h speedo, and the 120 mph speedo is a 190 km/h speedo. If you multiply 120 by 1.609 you don't get 190, but if you look at the dial, you'll see that the 190 mark and the 120 mark don't line up either.

2) there is a processor (a CPU) on the board that takes care of the deflection of the needle. That's the chip next to the crystal. The other equally large chip next to the coil contacts is the coil driver. The processor measures the frequency of the incoming 4000 ppm VSS pulses, and calculates the speed from the frequency and calculates this into a needle deflection and uses this to control the coil driver. This results in a deflection. By changing the crystal, you fool the CPU into measuring the wrong frequency.

3) GM used different processors and also different crystals on the Fiero. I imagine those parts were also used in other GM cars of the era. I know there were many different crystals used, 4.43 MHz, 1.79 MHz, 4.91 MHz and so on. I guess they used whichever crystal they could get their hands on for as little money as possible, and changed the code in the CPU accordingly. I don't know how many variations there are, but there are at least three. For instance, GM could make 85 mph and 120 mph variants by using the same CPU and different crystals or use the same crystal and different CPUs.

Why don't most people have this problem? Well, most people have a late model V6 (86-88) with backlit 120 mph speedo, so I guess GM always used the same CPU and crystal on those boards. I don't know of any L4 owner that would convert to a 200 mph speedo (no offense). But maybe it only concerns a certain type of speedo with a certain chipset/crystal combination.

Best regards,

Oliver

------------------
Visit my website: www.fieros.de for lots of technical and other Fiero related information

Oliver -- Thanks for chiming in with your uniquely knowledgeable perspective.

It appears that the long answer is: You need to examine your own particular speedometer before choosing the appropriate crystal for a new speed range. The good news is that at least some of the OEM crystals are clearly marked with their frequency.

I, like you, tend to think that GM probably bought the cheapest off-the-shelf crystals they could find and then programmed the processors to work with them. That might also explain the "strange" (non-binary) conversion constants ... 356, 534, 1068. If given a free choice, most engineers would probably have picked a crystal frequency that would have allowed them to use binary conversion constants (256, 512, 1024, etc.) ... or perhaps something more arcane (like prime numbers or Fibonacci numbers) if they had a well-developed sense of humor.

[This message has been edited by Marvin McInnis (edited 11-14-2009).]

Thanks for droppin by Oliver,

About those L4's that want to change to a 200 Mph....Mine was an L4 till I put in the 3800 L67, now 85 just doesn't do it.

Thanks for the Input

If my memory is correct a very long time ago Archie supplied a kit to alter the speedo. the kit contained a cyrstal that replaced the exsiting one and a new decal for the front of the speedo. I think it gave you a top speed of 200mph. I only rmember this becasue I purchased one for my lambo replica. You may want to ask him which cyrstal to use,

Mike

Hi,

a long time ago a company here in Germany did the same thing, but that kit didn't work with all speedos either.
I wonder if Archie has any insights into the matter, since he should have gotten some feedback from some of his customers.
Or he asks a few specific questions before mailing the proper kit. If that's the case, I'd like to know these questions ;-)

Best regards,

Oliver

Just an FYI on the whole speedo upgrade thing, first things first, most of my fellow fiero fanatics here, are slightly more intelligent and more innovative than I am. I usually learn by breaking things. (Unless you are Russ from GP, the engineering fiero god, then none of this applies, the man is a genius.)

At any rate, I bought a 180 speedo, spent many man hours trying to get it to work with no success; I bought several different crystals from DIGI. I began to think I fried the unit, however the trip and the odometer would work but the dial would not move.

Shortly thereafter I had an original 120 and 85 tested in my car, rigged up a radar and tested both, they both worked great.

So there I sat, with a bottle of the captain, (closed parking lot, no kids, no animals) frustrated as &!~#**, trying to figure out why the 180 would not work, had all three gauges in the car, plugged them in at different times, the other two would work but not the 180, THEN I notice something.

When you start the car the needle "pegs" to Zero, as all needles do for all gauges and dials at least on my fieros they do.

Someone (the frickin seller of this speedo or the nice infamous Ferrari parts dude) "pegged" the needle past the needle peg support.

So guess what? I pulled the peg and low and behold the needle started moving with acceleration, (I must have looked like an idiot driving in circles at the parking lot that day, screaming with glee with my head poking out the window like some rabid dog.)

I ended up using a 6.5536 crystal with the 180 face plate and I am right on give or take 1-2 mph tested by two different radar stations and trailing behind my wife (the empress) in her stock Pontiac vibe.

Just in case, some of you out there receive a "modified" speedo, make sure some idiot did not "peg" the needle past the original placement.

Peace.

As for the soldering, you could try to do it yourself.

Try with like about a 30 W iron, and make it quick.

Personally, my soldering skills are amateur-ish, so when it comes time to solder delicate components, I clip an alligator clip onto the lead of the part I'm soldering.

The alligator clip acts as a heat sink to keep the part cool.

Hot-gluing the crystal's body to the board is a good idea, to avoid fatiguing the leads.

[This message has been edited by pmbrunelle (edited 11-14-2009).]

This is what mine look like. Sounds like you have a cold solder or bad connection. Try using a heat sink the next time you solder, a allegater clip between your solder and component. I had a similar problem and ordered a new face (s) and crystal (capacitor). Found the problem and resoldered it , been working for almost ten years now and still have a spare. And on the crystal it has a 7.3728 ECS, can't tell on the capacitor. Hope this helps. Rick

------------------

85 GT 3.4
14.9 @ 90 1.9 60' Old TH125/3.06
Unknown New 4T60/3.42