Hi All.

Please forgive this slightly off topic post. I'm in the middle of swapping an '88 Suburban TBI 350 into my '82 CJ7.

I've got most of the swap done but I've come up against three issues that I haven't been able to get good answers on anywhere else.

VSS - I'm told I really don't need one. Several friends run TBI motors without them. What's the scoop? Does it make a difference to how the motor runs?

Grounding the Park/Neutral line - The ECM came out of a automatic equipped vehicle. In order to make it work in my manual equipped vehicle I need to gound the park/neutral line. Does this have any side effects? Will performance suffer? Am I better off getting a PROM from a manual equipped vehicle?

Auto vs Manual ECM/Prom - Assuming the answer to the last question was get a manual tranny PROM.... The tranny I'm using is a SM465 (or M20 as GM calls it). It's a truck 4psd that was used in '88 K5 Blazers. Is it worth the $$ my dealer wants to buy a factory PROM for an '88 TBI350/M20 equipped K5 blazer or is there a better factory solution?

Thanks in advance for your help!!! :hail: :hail:

 

The VSS won't terribly effect the performance in your Jeep. If it was still in a stock automatic GM vehicle, it wouldn't know when to lock up the torque converter, open the canister purge solonoid, and a couple other minor things. Since you're running a manual, and I doubt you're running a charcoal canister, I don't think you'll see any problems.

>Grounding the Park/Neutral line - The ECM came out of a automatic equipped vehicle.

It's better to drive around with the car fooled into thinking you're NOT in park/neutral, than it is for it to think it IS. Conversely, it won't hurt anything for it to think it's not in park/neutral while you're sitting there idling, especially since you have a manual transmission. The main reasons for wanting the correct PROM is <underline>idle issues.</underline>

>Is it worth the $$ my dealer wants to buy a factory PROM for an '88 TBI350/M20 equipped K5 blazer or is there a better factory solution?

One solution would be to check out the DIY PROM forum on this site and get into making your own PROMs. It costs about the same as buying a PROM in the first place, but then you can make as many changes as you want, and it'll be more specific to your driveline setup, driving preferences, and driving habits. Is the difference worth the money for a factory PROM? In my opinion, no.

 

Thanks for your help Jza. I appreciate it.

I'm running a charcol canister, just not a chevy canister

Do you know if the VSS plays a role in the operation of the EGR valve?

I had the same thoughts. I'd like to keep the ECM/Prom convinced it's in the original vehicle. I think it makes working on the motor easier.

I decided to pick up a factory PROM. It cost me about $60 US. The time it would take for me to figure out how to burn (it's been years since I burned chips) a new PROM is worth much more to me than $60US.

Now if I had a custom motor I'd be all over the DIY PROM burning.

 

Somewhere in the Tech/General Engine forum, Vader posted an excerpt from a hack of one ECM that listed all the functions that used a VSS reading. Try doing a search for that, and you can see every single thing that having/not having a VSS effects.