I have a 91 Z28 350tpi with speed density and I just installed a new GM engine and have about 50 miles on it and just yesterday it stalled at a stop light. It wouldnt fire up again so i pushed it in a parking lot and then it started after a few minutes. I drove it home and it was falling on its face on the highway. it felt like i kept hitting the brakes. It also backfires when i decelerate in gear. I took a look at it today and it will only run a 1 minute or so then just shuts off. I have oil pressure and fuel pressure. i also have a brand new Holley fuel pump, MSD distributor, all new sensors and i checked the plugs and they look fine. I also checked my MSd coil and its not the problem. I put my stock one in and it does the same thing. there is no trouble codes except for a VSS since my speedo doesnt work after I swapped to a t56.I have a ED Wright chip in it and havent taken it out yet but I dont think it could be the chip. What do you guyd think.

 

no codes, the tune up is good ,i'd consider the chip, run compression test, make sure all the valve springs and push rods are ok and not broken. you have poly locks on it? might want to check them too.

 

The engine is brand new. I did change out the stock rockers for some 1.5 rollers but that was it. Could them not being set right cause the engine to miss. I kinda think it is elcetrical now since the tach is bouncing all over the place.sometimes is will peg all the way to 8000. the tach started doing that at the same time the engine started missing. the engine doesnt rev with the tach though the tach just bounces on its own. you ask if i have poly locks. i have the locks that come with all comp cams roller rocker kits. i dont want to pull the covers since its a PITA and its hot as hell out right now. Id hate to take it to a shop and them tell me it was something stupid but i just got my put back together and i want it for the long weekend. anybody have any other suggestions where to look. i noticed just a little while ago that if the engine stalls out, sometimes I cant get it started again unless i let it sit for a few minutes and then it does it again. here is what i have checked today
oil pressure is fine
fuel pressure at idle is 40psi
timing was set to 6 BTDC when engine was installed
volts are at 13
coil works

 

The next time it stalls, immediately have everything ready to test for spark. If you can determine whether or not there is spark, you can pursue the problem better.

 

Vader, there is spark. i checked it today. now i am looking into an electrical problem. I figured maybe it was running like crap was because my speedo wasnt hooked up. i have the SGI 5 box for my t56. I had it hooked up and it worked but about 2 monthes ago and then it just stopped working. I figured maybe a wire came loose under the car, I checked it all today and it checks out ok now my speedo is bouncing all over the place since i have hooked my SGI box back up and when its hooked up the miles are turning over while it idles. it will stop if i pull the fan fuse from the fuse block now i know this something elcetrical. thing is, is that this car was in a fresh water flood 2 years ago and i saved it from the scrap yard. everything worked perfect for the 2 years since. and now that its done and i go for my first city cruise, it goes and runs like **** on me. i dont know where else to look. i think im gonna have to break down and tow it to a garage.