To ALL engine swap guys and the VATS system S2 3800

[Trannyman95]

I finished up a custom engine swap in a car about a month ago and still had a few loose ends to finish up, but ran into some problems that until a few days ago was becoming a nightmare to be nice about it! The drivetrain is a Series 2 3800 L67 supercharged bottom end, 06 L26 NA heads, 97 Fbody intake, 99 4L60E trans, mild cam, ported heads,60 lb hr injectors, and TE60 turbo. The pcm I used was a 98 F-body pcm which would accomodate the 4L60E trans. I have always been told to switch the VATS option from PWM over to Serial in the tuner to get around not using the BCM's theft signal and I thought that it worked on grand prix's, but that was before I was aware that 97-01 Grand Prixs dont care if this wire is present or not so switching the option with the editor from PWM to Serial really wasnt doing anything at all. The F-body cars however use the resistor pellet in the key and the pcm does require the 40-60hz signal from the bcm for the VATS system. Here is what I ran into..... Initially after turning off a few base codes and getting fueling right the car would start but misfire terrible on every cylinder at any rpm. I custom built the wire harness for the car so and am very particular about wiring and checked every point at least twice before it went into the car but though maybe something was overlooked so I started tracing everything on car, keep in mind the vats wire was never hooked up to anything. I broke out my scope and check crank and cam signal waveform to and from the ignition module and was fine. Everything electrical seemed fine so I started swapping out a few things to see if there was any change such as the crank sensor, icm, coils, injectors, map, pcm. With each change there was no difference at all. Then my buddy stopped by with a Tech2 and realized that it would not display misfires on any cylinder and it would not go into closed loop no matter how long it ran. I found that by turning off code P0300 it would not display misfires... sort of odd we thought so I left the misfire code on for diag reasons and then noticed every cylinder misfiring terribly! My wideband would show 16:1 afr and I couldnt richen it up enough hardly to get it to move down, yet pulling out the plugs and looking at them they were all black! At this point since I ruled out electrical and moved on to mechanical. A compression test showed all cylinders the same and the numbers were good. A leakdown test seemed fine as well. I was really doubting a lot of things at this point and didnt know where to start so I ended up tearing the engine back down to block and heads and put a degree wheel on it to check cam timing and everything was fine, all valves moving in the correct order, rocker preload good after checking several times. I even put pressure to each lower intake runner to make sure I didnt have some sort of leak at the intake gasket and that was fine also. No vacuum port leaks, I checked the intake with a straight edge and carefully inspected the gasket crush apperance and it looked fine also. I was hoping I would find a problem mechanical but in the back of my head knew I wasnt going to, but that left me still with what is causing the car to run soo poorly and not go into closed loop? After everything was back together I tried stock files and some more tuning and nothing. Then after hashing things out with my friend who also does a good number of swaps and pcm tunes he remembered a customer a few years ago using an fbody pcm in a custom project and running into a very identical problem, except his car ran fine before flashing the pcm and switching the VATS PWM to Serial and he did have a bypass module hooked up. His car ran rough and couldnt sort it out and the only thing in the tune that changed was trans settings and the vats setting. So at this point there was really nothing left to try other than a different harness and pcm to rule out electrical. I hooked up a 99 GTP pcm to see if the car would run and guess what.... It started up and ran perfectly fine! Not only that but it would display misfire (larger than stock cam will show small mis at idle) AND go into closed loop! Knowing that the prix pcm doesnt care about the vats wire being hooked up we were on to something. Late friday night I built a vats bypass module and added the wire to the harness and hooked it up, switched the VATS mode from Serial back to the PWM that it had from the factory and the car started right up, no misfires, and closed loop turns on just fine!!! I went through near a month of pure hell and no answers over this so I hope this helps someone who opts to tackle a swap using a pcm that does in fact require the 40-60hz fuel enable signal from the bcm or vats module, it MUST be hooked up if the pcm originally required it!

[hcomplyr]

wierd, but i do remember reading that the GP PCMs give a little more room for errors when swapping

[Superdavesgarage]

I just wanted to bump this old thread to thank the OP. This is the exact issue I ran into with a '00 Camaro 3800 that we put into a '84 Regal.

I troubleshot every wire, sensor, cam timing, and lots more, car ran like garbage no matter what I did to the tune. I put in a new computer, paid for more credits and just happened to try and start it before I switched VATS from PWM to Serial. It started and ran great for a few seconds... Once I switched VATS over to Serial I was back to hot garbage. After some googling I found this thread, picked up a VATS bypass module on Amazon and we're good to go.

Both '00 Camaro 3800 computers I had did the same exact thing.

If this isn't in a sticky, it should be...