nonmechanicalguy90

I have a 91 Cutlass Supreme 2 dr with the 3.1 . HAD the 3.1 .. blew a rod and now have decided to replace with the down-graded 2.8(was given to me no charge). Fortunately was able to get the 3.1 engine out with no problems, everything bolted to the 2.8 without a hitch. But what I failed to do was take pictures of how all of the lines(fuel,throttle,vacuum) and electrical was ran under the hood ..so i was hoping someone with the 3.1 could post pictures of the under the hood with the throttle connections. fuel lines. Vacuum, and main electrical paths.. remind you i know this sounds silly but with me never have done this before i clearly should have taken all of the precautions while attempting to achieve this task. Any help would be greatly appreciated

joe_padavano

Welcome. Sorry, but unless you have the computer or PROM for a 2.8 motor, the EFI will not operate correctly with the different displacement. A stock replacement would have put you much further ahead, especially if you don't have the experience to deal with the affects of the different displacement on the EFI calibrations. "Free" isn't always the least expensive way to go.

nonmechanicalguy90

Thank You Joe Padavano for your response, for I do greatly appreciate your insight. I was hoping you could go more into depth on the problems i will/will not run into by switching/not switching the PROM? I have swapped EVERYTHING off of the 3.1 to the 2.8 excluding the intake manifold. I now have the engine set in place and everything SEEMS to line up perfectly. But as ive said i am not very knowledgeable in the department and any and all voices are always welcomed. Again thank you for your response, Chris

joe_padavano

The computer stores fuel and spark maps that control the injector timing and spark advance based on the specific engine, trans, and vehicle. Different size engines with different cam profiles have different fuel and spark needs. Unless the computer is programmed for this, it will be firing the injectors and adjusting the spark for the original engine, not the current one. At best, the car will run poorly and get awful gas mileage. At worst, it won't run at all. If you swapped the 3.1 intake onto the 2.8, that means you have the larger injectors for the larger engine. Even with the correct PROM for the 2.8 engine the PROM will be commanding the injectors ASSUMING that you have the correct flow rate injectors for the smaller engine. If you really have the larger flow rate injectors for the 3.1, and they are held open for durations that assume they are smaller, more gas will flow for each pulse than intended, resulting in an overly rich mixture.

nonmechanicalguy90

Thank you again for the response Joe and i will take this information in heavy consideration and do some digging on the matter. What your saying to me makes complete sense and i appreciate the info. I will repost on here when it all comes together and the install is complete. Thanks again

joe_padavano

You might be in luck. It appears that both the 2.8 and 3.1 motors use the same 16.7 lb/hr injectors. The PROMs will be different, however.

nonmechanicalguy90

From what other things ive heard it could run a little rich and with a good air filter it could help the problem a little.. worst case im hearing i could find a replacement computer or have it flashed? .. i will for sure let you know how it works out also let you know what i discover with keeping your info in mind. Again thanks for the info i really appreciate the help!

nonmechanicalguy90

Hey there. Finished the car Sunday. Things went great. Dry cranked it a few times and once i plugged the spark plugs back in it took off first try and runs smooth. The engine runs great but now im wondering if i should have gotten a new speed sensor thats on the back of the engine. Car is shifting really high (with correct amount of fluid) and speedometer is way off high also. (All digital light gauges on the inside) and all other gauges seem to be reading normally.. im hoping i can find out why its shifting so high? i believe it has the right amount of fluid in it but im trying not to drive it so much incase it is low.. (not a mechanics guy) but besides those two issues everything else seems OK at the moment. If you have and clue to whats going on with it ill be glad to hear it.

But for me never have even changed my own oil before..this is a huge accomplishment for me and hearing that puppy purrrr

nonmechanicalguy90

Found i had to adjust the tv cable. and speedometer works fine i was reading in KM.. LOL