Did an engine swap in this 02 sl2 ....had no code in donor car and now when i let off the gas pedal going down hill at 3000 rpm she starts flashing....flashes also at high rpm under no load in neutral....the engine temp runs at 1/2 on the gauge (usually they run at quarter) have changed almost everything in the car and still can't figure it out....crazy thing is the car runs perfect and smooth.

 

What was the donor car?

 

It's was a 2000 sl2 coupe....same engine

 

Are you using the OEM stock plugs (NGK) for the DOHC?

Are you using the same plugs that were in the donor engine when it was in its original vehicle? what plugs we're in the donor engine when it was in its original chassis?

What is the idle speed once warmed up? Also, automatic or manual trans? Mileage on donor engine?

Did you bring the PCM and BCM over with the engine?

 

Always use copper ngk plugs on my Saturn's and it's a manual.....didn't swap over the pcm but it seems at idle when I start it stays at 1200 rpm.....maybe a small intake vacuum leak? 🤔

 

Also mileage on the donor car was 117,250

 

Idle when warm, not at startup, please. 1200 is normal when starting from a cold soak.
Manual Trans DOHC should idle at 850 when fully warm. This takes a while if sitting in the driveway so drive it around and see where it is in neutral

 

Ok...I will check that...also when the car is warm and running the engine compartment is very hot...also this s series runs at 1/2 temperature setting...all my other s series run at a quarter...thanks

 

I did some reading and here's what I found:

1) older GM trucks seem to have an issue with the same exact phenomenon.
People have chalked it up to
a) bad CKP ---in the sense that it is not detecting the reluctor ring on the crank properly and the PCM is accepting the data but some of it is bogus, Thus the timing info going to the PCM is incorrect and this throws off the expected position (in time) of the cyl that is used for the resistance measurement to determine if a cylinder misfired or not.

I have never heard of this on a saturn S car. doesn't mean it can't be true. see 2)

2) the same chevy trucks and even the ecotecs require a crank position relearn procedure after any work done on the crank or after the CKP is changed.
I am not aware of the S series engines requiring a crank relearn procedure after CKP replacement. Someone confirm please.
Note that the crank relearn procedure involves holding the rpms at about 3K rpm until the PCM learns the new crank sensor output.

3) your crankshaft is actually shifting position when not under as heavy a load messing up the CKP data to the PCM. like #1, a phantom misfire.

4) a small exhaust leak

I've never heard of this on an S car engine -- but now I have

Hopefully the above will lead you towards the cause.

 

I actually tried the crank relearn by doing that but it wasn't a new sensor...didn't work...I also swapped the exhaust and put a new cat on her....still no luck