I made the tbi to tpi swap in my signature, everything went fine except that my speedometer and odometer does not work. I have a 700R4 and the VSS that was with my TBI has an electronic speedometer. I was told that the pulses are different in a TBI VSS and a TPI VSS. Does anybody know what I need to do? GM shows one VSS for a 1990 camaro? has anybody else had this problem in their swap?I have driven the car and do not have any trouble codes. This problem is driving me crazy !!

 

As far as I know the VSS is the same. If the VSS is not working you should throw a code 24 (I think, at work no manual handy). However it will take a while to throw the code, it is not immediate. You will have to drive it for about 15 minutes over 25 mph for it to trigger code. If you get no code you can assume ther VSS is working and something happened to the feed to the speedo or some loss of voltage to the electronic part of the speedo. Look for a loose connector or something related to the work you did. If you need more help I will pull my manual. Drop me a message.

 

While on the topic of speedos, I just completed a manual swap in my '89 firebird and am loving every min of it. However, the speedo cable reached the speedo gear in the auto but unfortunately fails to reach the gear in the t5. Is there any way to elongate a speedo cable? or do I have to buy a longer one and deal w/ the super hassle that is replacing one? Or is it not a pain like it was in my 3000GT to replace?

-- Henry

 

Hey guys. I am having the same problem as sbrice18fan. I too just did the TBI to TPI swap and my speedo has not worked since. I am sure someone has run into this problem before but I have never seen a post about it and I have searched the archives and found nothing that helps. Any help would be greatly appreciated.

 

i just posted a post(redundant?) about my speedo not working too. I also did a TPI swap. I've gotta look into it because i'm gonna start driving the car as soon as i can. i've got the factory manual and i'll read until i figure it out. i'll keep you posted.

 

Let me know what electronic changes you made. My one manual shows 1990 TBI models having a mechanical speedo. In this case it has a VSS buffer module as opposed to a VSS sender. Mechanical types have a sender in the actual speedometer head and these pulses are amplified by the buffer module and sent to the ECM. If your speedo is electronic then it is going to be a wiring and possible programming change in the ECM. I will do more research later today and get back to you, but the way I am reading this it may turn out to be a real problem. Give me the particulars and I'll try to come up with an answer.

 

My TBI had the electronic VSS, every VSS that I look up for a 1990 camaro is mechanical. Anyway I have been driving my car, but still no trouble codes and no speedo.

 

I came up with essentially the same thing. I am using Chilton but the electrical info is just reprints of the GM service data. They show the 1990 TBI as being a cable driven speedo. With this setup the VSS Hall generator is in the speedo unit itself and they use a buffer module to feed the pulses to the ECM. If it were this way the speedo should still work as long as the cable is OK. MY 89 is wired this way. Do this if you can, jack up the car and look at the tailshaft area on the drivers side of the transmission and tell me what you see. With a fully elec speedo you will see two wires coming from a round fitting held in with a Y shaped bracket. If you have this then the info we have is inaccurate. If you have a heavy single black semi-rigid cable then it is a mechanical drive. I tend to think that it WILL be two wires. If this is the case then the problem will be with the input to the ECM(input ports not being recognized). This could simply be a programming change to the ECM E-Prom to get those ports to open up, or it could be they are being used for something else. Considering all the work you did it is VERY possible. At that case you should talk to the company who supplied the E-prom, chances are they will know what to do to solve your problem. Inputs B-9, and B-10 should be the VSS input from the trans mounted unit to the ECM. Get back to me on this one if you would. It could be that the chip supplier is laboring under the same misconception as we are. It could very well be that a certain number of 1990 cars came with a fully electronic speedometer and this may not be known to them.

 

Thanks for keeping up with this problem. I have the two wires going into the VSS, one yellow and one purple. I have pulled the VSS out and looked at it. The onlything on the other side is a plastic drive gear. I bought a VSS from painless for a speed density TPI, but it was mechanical, just like your description. I see what the difference is, why does everyone show a mechanical? This is very frustrating. Anyway , your opinon is that the chip needs to be changed to recognize the signal?

 

Ok, we are on a roll. My manuals SUCK(knew that). If you changed no wiring to the cluster than I totally believe it is something to do with the ECM and/or Prom programming. Did you change to a different ECM? If not then when you did all this work was the prom replaced at the same time? A short lesson on what the Prom does. Using different programming allows the manufacturer to use one or two ECM units in a given model year. By changing the Prom they can set up the vehicle personality e.g., throttle body or port inj., various different things from one model to the next. The Prom can be programmed to turn on or off input's and outputs. It is VERY possible if not highly probable that the new Prom is not programmed correctly or programmed to ignore these inputs because they are looking for a mechanically driven speedometer. My advise, contact the supplier of the prom and carefully explain this problem, and make sure you tell them you have a totally electronic speedometer. They may NOT know about this setup. If you find the answer you might help a lot of guy's.

 

with the change from TBI to TPI, I had to change computer and with all of my mods I got an ED Wright custom chip, so neither is the same. Since everything else seems to be working fine with the swap, I guess it would have to be the chip that is not receiving the signal. I am I right, the VSS sends a signal to the computer who then sends a signal to the speedo? I will call my chip maker Tuesday morning and I will let you know what they say. I wonder what the guys on the Prom board would say? Anyway thanks for the help, I just hope we have found the problem and this can help some others.

 

Danno, I talked to the people at Fastchip about my speedo not working and they guy I talked too said he did not think that they do anything with the speedo, when burning a chip. He asked If I had tried the stock TPI chip. I had not, so I thought that I would try it. If the speedo works with the stock chip I might finally be getting somewhere. Anyway, I just finished trying using the stock chip, I could hardly get the car to run, kept dying on me. I could not drive it, but from trying to back out of the driveway the speedo was not working. I put my custom chip back in and the car runs fine. So where do you suggest that I go from here? Is there some type of VSS buffer that takes into account the pulses on a electronic speedo, like the one you mentioned on the mechanical one?

 

Most likely at this point it is some sort of difference between the ECM units. Possibly a difference in wiring. I looked at both generic manuals I have and they are not specific enough to be much help. About the VSS buffer, as far as I know they are used only when a mechanical speedometer is used. The Chilton shows that the Electronic speedo VSS signal goes directly to the ECM on pin's B-9, B-10. At this point my suggestion is to put a post on the PROM section of the site. Some of the guys over there know the ECM units by memory. If you can, try to find out the P/N of the ECM you are currently using. I have a good friend at a Chevy dealer, I will ask him but generally I have found the guys on this site more knowledgeable than just about anywhere else.

 

Well I posted on the DFI & ECM board and have received no responses. I called Street & Performance and they told me that I needed a signal amp. it is made by Dakota Digital. They say that the VSS is different in the TBI and TPI. I need to change the pulse going to the ECM. Wouldn't a TPI VSS do the same thing? At this point I'll try about anything.

 

Something still puzzles me. If there are no VSS pulses going to the ECM it WILL throw a code. The VSS signal does more than just indicate speed. Without VSS input you will not get torque converter lock, EGR operation will default and driveability will suffer. If you are in doubt about there being two different VSS senders, go to a local dealer and ask the parts guy to look up the part numbers for the TPI and TBI models. Most parts guys will help if they are not too busy, my dealer will take a fax and get back when it is convienent. Did this outfit you talked to say why you needed a signal amp. That is basically a VSS buffer module, probably the same thing repackaged. It could be that there is an internal difference between the ECM units making this a requirement. I thought of a way to see if the VSS pulses are getting to the ECM on the right inputs. Do this, disconnect the VSS sender at the transmission and take the car for a drive. Let it warm up and drive for a least 10-15 min. at different speeds. You should throw a code 24, VSS signal missing. If you do, then at least we know the ECM is getting the signal at the proper place in the ECM. If this happens, then we work from the ECM back to the speedo. We'll dog it out.