90 Cutlass Engine Swap Questions (2.8 to 3.1)

[nnharris]

History: Cracked the block in my 1990 Olds Cutlass. I got a good deal on a 3.1 from a wrecked 1991 Lumina and swapped it for the cracked 2.8. Used all components from the 3.1 with exception of the intake, which is from the 2.8.

Problem: After driving 5 or so miles in the Cutlass with the swapped engine, it become completely unresponsive to acceleration and idles to a stop. If I put it in park, I can repeat the procedure for another mile or so before having to do the same. After checking the computer codes, I found that it reported the MAP sensor as being bad.

Questions: Is it possible that the 2.8 intake is causing the 3.1 to run lean? (I'm not sure that I can get enough miles on it in it's current condition to get telltail signs of it running lean on the plugs.) If it is running lean, any suggestions? Would injectors from a larger displacement 60 Degree V6 compensate? Or would the computer module need to be reprogrammed to acheive the correct Fuel-to-Air Ratio?

[Rhedalert]

the intakes are the same in terms of flow and all that. The engines themselves are identical except the stroke, PCV system, and supposedly the 3.1 injectors flow just a tiny bit more. Which lower intake manifold did you use? from the 2.8 or 3.1? Also maybe the vacuum line to the map sensor is cracked or crushed somewhere, that could cause a heavy driveability problem.

[robby1870]

Yeah, when the MAP vacuum line is broken the car wont hardly do anything.......tried it, lol

[nnharris]

Thanks for the input. The lower intake and injectors are from the 3.1. I'll definitely check the MAP line for vacuum leaks.

Regarding injectors, would the 3.1 injectors actually flow less when connected to the stock computer designed for the 2.8? I've read that the computer pulses from the 2.8 engine may cause the 3.1 injectors to actually run lean in the 3.1 engine and that using injectors from a 3.4 or 3.8 can help compensate. Any thoughts?

My only other worry is that the engine from the wrecked car has damage. It has needed small amounts of coolant after each driving session. I'm hoping that there was just some air pockets in the system because there is no coolant leaking under the car while parked. After checking the vacuum lines, my next step is going to be attaching an aftermarket temp gauge and verify that it isn't overheating when it's acting up.

[jmgtp]

Regarding injectors, would the 3.1 injectors actually flow less when connected to the stock computer designed for the 2.8? I've read that the computer pulses from the 2.8 engine may cause the 3.1 injectors to actually run lean in the 3.1 engine and that using injectors from a 3.4 or 3.8 can help compensate. Any thoughts?

Would be much easier to get a memcal from a 3.1 engine then to go through the hassle of injector swaps. One of the admins on this board (sappyse107 => Ben) may be able to help you out (and at a very reasonable price, likely much less than you would have to spend at a junkyard for one) if you cannot find a memcal to replace it with locally. However, I dont believe the fuel/spark differences between 2.8 and 3.1 programming would cause such a dramatic problem. Definetly look into the map sensor issue, as that will likely solve the problem.

FYI, you probably most definetly know this but in any case... the ecm in a W chassis is located underhood, by the passenger side strut tower. It is a weather proof unit, on the backside are 4 screws to remove a small plate in which access to the memcal is achieved.

[Rhedalert]

I should ask to verify, this is a 1990 Cutlass Supreme that had a 2.8???

GM stopped using 2.8's in the 1990 model year across the board for FWD cars. Possibly the engine was replaced once before? Also did you use the EGR valve that was in the car, or the one from the Lumina?