Ok so I swapped engines, transmissions and ecm/harness. Engine runs, trans shifts but I get code 24. I know its vss. Makes engine like crap. I know my 89 has vss on back of speedo (brown and blk/wht wires) I connected these to the yellow and purple wires of ecm harness. Brown to yellow and blk/wht to purple. Still throws code 24. Further investigation reveals my 89 vss is 2000 pulse per mile and the 91 tpi vss is 4000 pulses. What do I do. Can I hook it up differently? Is it hooked up wrong? PLEASE HELP ME!!!!! Very frustrated ...

Thanks
Don

 

The '91 ECM is expecting a 4K PPM magnetic signal (AC). While the '89 VSS is a 2K PPM optical (DC or digital) signal.

There are a couple of ways to go:

The '91 trans should have the proper VSS in it as supplied. Use that and change the speedometer out for an electronic one.

Wire the current optical VSS buffer output to pin C6 of the ECM. Then change the option flag in the chip to use that input.

Use some caps, resistor, diodes to make a pseudo magnetic signal from the digital one and feed that to the yel & ppl wires of the ECM. Unless a freq doubler is included in the circuit the ECM will read half the speed.

RBob.

 

Would something like this work?

http://m.summitracing.com/parts/PRF-60116/media

 

According to the Painless website:

"4 pulse VSS for Late TPI and Early LT1 EFI systems"

It should work. Although you need to check the distance between the trans and floor board for clearance. Other wise a short piece of cable will be required.

RBob.

 

You are running a 91 730 ECM which is speed density and requires a 4K pulse. The VSS on the transmission is the one that supplies the 730 ECM with the 4K pulse it is looking for. Your VSS signal should come from the Trans mounted 4K VSS. The 2K VSS signal is useless to the 730 ECM. The 91 transmission that you swapped into the car should have this VSS already installed. My 85 El Camino had a 2K VSS built into the back of the cable driven speedometer. When I swapped it over to a 91 SD system, I had to add a 4K, Cable driven VSS to my car to give my ECM that VSS signal it was needing. My 2K VSS drives the cruise control only. That VSS that you show above is what you need, exact item that I used in my conversion. I think it will clear the floor pan.

P.S. want to wake that car up? Put a set of 3.42 gears in it! I do not see how a 700R4 equipped car performs very well such high gears! You must be turning 1200-1300 at 70 in high gear! I am running a 200-R4 and 3:42 gears and am pulling about 1900 rpm at 70. I am getting 24- 26 mpg on the road if I stay out of it. Those 2.73 gears MUST hurt the acceleration off the line!

 

This isn't true. The '7730 ECM has inputs for both a 2K PPM digital and a 4K PPM magnetic sensor. An option flag in the calibration tells the $8D code base which one to use.

So the 2K optical VSS will work with this set up. Just need to set the option flag in the calibration (chip) for it to work. If doing any tuning it is a better solution then adding in an external VSS sensor.

RBob.

 

Cheaper
http://tpiparts.net/inc/sdetail/10956/7587

 

Haha! Funny. I just ordered that today from them. Eventually I will get into chip burning but I have other projects to do and this external sensor will allow me to plug and go. I got lots of studying to do before I play with chips.

 

Well I actually just picked up a rear axle from a gta today with 3.42's in and its a posi! Plus it comes with brand new calipers, rotors, pads and shocks. Also master cylinder and proportioning valve included. Best part, 250 bucks for all of it! Ought to go nice with my new precision 2200 stall converter.

 

HOME RUN!!!

 

RBob,

Yes, I do not argue that point at all. I am sure you are correct and I had read that this was true. However, you cannot supply the 2K pulse to the 4K input. That will not work, the ECM will not recognize the signal. The 7730 was designed to run and DID operate from the factory with a 4K pulse VSS. So I believe that this is the best solution in this particular situation. If the chipset is stock (which is what it appears to be) then the 2K input is irrelevant here. Yes, you CAN have a chip burned (or burn one) and set the flag you are talking about. This guy is not really at that point right now and the 4K VSS is the cheapest solution that WILL operate with the equipment that he has on board. I was trying not to confuse the situation by bringing that fact out in this thread.

 

Yes ecm and chip are stock. I was assured by the company that this parts is for sure plug and go. We'll see come Wednesday when it arrives. "Fingers crossed"

 

I can tell you, that if it will clear the floor pan of your RS, it will work. My El Camino has the EXACT Same part installed with the 7730 ECM. I did have to change the connector to match the one supplied with the VSS. My harness had a different connector. Be sure to solder and heat shrink wrap all your connections, to assure the BEST connection. I found a lot of Crimp connectors cause problems down the road. This will give you a usable VSS Signal to the ECM. Good Luck.

 

Whatever, LOL. You give false info, I'm liable to correct it. For the benefit of the OP and others that know how to use search engines.

Was this part missed:?

"Wire the current optical VSS buffer output to pin C6 of the ECM. Then change the option flag in the chip to use that input."

RBob.

 

OK I give up! You are right!

However, for the record, I did not give "false information".

FIRST:All I told the guy was the SIMPLE WAY to fix his car quickly, without burning a chip, cutting into the wire harness or getting into building a "Science project" signal modifier.
SECOND: I did not say you were wrong, I did not say your solution would not work! Who pissed in your Post Toasties? At WORST, I am guilty of not discussing. in depth, every possible alternative to using the factory 4K VSS and the factory wire harness. Besides, you had already covered that subject Very Well. I did not feel it was necessary to expand on what you said.
THIRD: It was OBVIOUS to me that this guy did not want to burn chips and just wanted a simple answer to his problem. What I stated was not FALSE, In fact it was 100% correct! My statements just did not meet your obviously high standards for complete disclosure.

If you are liable to correct every statement on this message board that you deem "false", you have a full time job. Good luck with that one!

Sorry I said anything or tried to help the guy!

 

I appreciate all help and info given. My questions were answered and other options were also offered. That's exactly what I needed and why im part of this site. Thank you EVERYONE

 

Me to, that was all I was trying to do. Hope you get your car going! Good luck.

 

I had this same problem although i didn't have the option to use the optical VSS.


The best solution i found was to pick up a VSS for a 91 Caprice police interceptor. It's got both the cable and magnetic outputs. It was like $50 at autozone.

I just used a spare VSS plug from another harness and ran those leads right to the ECM, the speedo cable hooks up like stock and it all works great. The output is 4000ppm.