Well i thought i had it figured out but... wrong answer. Well here is whats going on, i just swapped out my TPI for a HSR on my 88 iroc with the comp 08-306-8 roller cam 30lbs SVO injectors, Brodix heads, MSD digital 6+ box, MSD coil, factory distributor with a pickup & mod only about 6 mouths old {ran fine with my TPI} Autometer tach and a custom eprom by LSRacing. With the car running at 1000rpm's and a scanner hooked up the computer is saying its running at 2500-2700rpm's, and with my tach at 2000rpm's the computor reads 5850rpm's. I checked the 4 wires running back to the ECM from the 4 pin on the mod and they are all ok and in the right spots, all the programing and sensors are checking good, jamy from LSRacing even got my BLM;s at 128 with out having the car so i dont see the problem in the new prom. A friend owns a dyno shop and told me to find out what wave length the signal from from the distributor to the ecm is Square or sign. He was wondering if we could take the signal from the tach drive off the MSD and pipe it into the ecm and what wire it is that carries that signal. Any help would be great cuz if i dont figure it out soon i will be converting to carb. I tried a different coil, mod, and running it without the MSD but no change. Thanks Chad.

 

Signal from distributor to ECM is a 5V square wave. Moving as it isn't diy_prom related.

RBob.

 

Just throwing this out there, Have you tried installing a tach filter?
The MSD multiple spark (3 per event at <3000 rpm, then 1 longer spark above that) may be indicating on your tach.
Might be worth a shot.

FWIW, my dash tach is now reading higher and bounces since I put the HSR on this winter (about 200-300 RPM more at idle)
Was matching the logs when I had TPI last year.
Coincidence ???

 

I didnt try a tach filter yet, my tach is reading right its just my ecm thinks the engine is running more then double my tach reading. I even unhooked the msd and scanned it this way but it was still the same. I wasnt sure which one of the 4 wires coming from the distributor mod to the ecm was the signal to tell the ecm the rpms either. I guess i wasnt to post this question here but thought since i was looking for the info the ecm reads i was in the right place. I reposted in electronics board, so hope i find something out soon there b4 i end up going carb thanks

 

Maybe the diagrams on this thread will help you to get a handle on it.
https://www.thirdgen.org/forums/alte...ht=distributor

 

If it's running right, you may have a problem with the scanner. Maybe the scanner isn't using the right vehicle information.

 

I wish that was the problem, i tried 2 different ones. And it isnt running very well, surging, popping, no power, i was told it is because the ecm is feeding the engine with the info from high up in the tables b/c it thinks its running at a high rpm. I dont understand why the iac isnt tring to back everything off since the tps is sitting on .54v yet it sees the rpms as almost 3000. I think i will be pulling the set up off this weekend and going to carb, iam just out of time to keep messing with it. If anyone is looking for a HSR setup let me know and if i go that way ill give you a price. It will include the HSR, rails, afpr, 30 svo injectors, bbk 58mm tb, some hoses, fittings, pretty much everything from the heads up with less then 50 miles and it will be fully assembled, just bolt it to your heads and go.