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As some have probably noticed I have been on a mad search for answers concerning using an OBD2 controlled engine, with a RWD non-computer controlled 5-speed T5. The only real problem with this set-up is the loss of a VSS signal to the PCM, since the T5 doesn't have a VSS.
I have learned from exhaustive research of others' trial and error, that if at all possible, you need that VSS input for proper engine performance, especially for manual trannys. Reason being, when coming to a stop, and you let off the accelerator, and clutch pushed, the PCM sees no movement of the vehicle. it lets the idle drop too quickly and may stall out. Other uses by the PCM for the input are for air/fuel ratios at highway speeds. Not something I would choose to fudge around with. Make no mistake, you can run a vehicle with a swapped OBD2 engine and computer system without it....it just won't be optimal.
My setup is a 3400sfi engine from a 1999 GrandAm se, complete with it's PCM, Wiring harness, and ALL engine sensors intact. This swap is into a 1960's british car, so everything is foreign to the engine/tranny control system. The entire swap is flawless, the engine needs only those sensors already attached to it........except one,.....theVSS. It's in the tranny, a 4T45E, to be exact. Since I'm not using it, I've got to re-create those VSS pulses to the PCM using my T5.
First a little background on a VSS.....short for Vehicle Speed Sensor. The FWD cars have a reluctor ring on the final driveshaft of the transaxle that has a pre-determined amount of teeth on it. The sensor sends pulse to the PCM each time a tooth goes by. Some sensors create more voltage as teeth pass by faster and faster, the PCM knows the speed of the vehicle by how fast the pulses come, or by the voltage sensed. The # of teeth are matched to the tire size so that the PCM sees so many pulses in one mile of travel.
In my case I called the dealer to see what the available tire sizes were for a GrandAm that year...a 215/60r15, which turn 801.67 revs per mile. Next I had to find out how many teeth were on the reluctor ring of the original tranny. This is where it got fun. I called several dealerships and tranny shops over a months' time....no luck. There just isn't any info on such stuff for cars this new. Finally...I got in touch with three tranny re-build companies out west who were willing to pull the parts off the shelf and physically count the teeth on the ring. 30 teeth.. from all three companies. So...801.67 revs X 30 teeth= 24050.1 pulses per mile, that my PCM needs to see.
Now, to re-create that #, I have to formulate my own tire size, AND, because I'm RWD now, I have to take into consideration the Rear-End gear ratio. My new tire size is 205/40r16 which turn 898.1 revs per mile....97 revs per mile more than the original tires. So, if I divide the 898.1 revs into the 24050.1 pulses needed, I get 26.8 teeth needed. That is if I want to mount a reluctor on the rear axle near the tire hub. But I want to mount my reluctor onto the Driveshaft yoke that goes into the tranny, so I have to divide my 26.8 teeth into my gear ratio of 3.27....which is 8.19. Rounded out, it will mean I have to fabricate an 8-tooth reluctor gear to mount on my driveshaft to make the PCM see the same input as if it were still in the pontiac.
There is a company, Stealth Conversions, at www.jagsthatrun.com . that makes many VSS conversion parts. They make a 40-tooth ring that I intend to buy, then mill 4-out of every-5 teeth off, to give me an 8-tooth ring. I will then bore it out to the size of my driveshaft yoke, slip it on and tack it in place. Then I can fab a mount for the original sensor the GrandAm had, so I can keep everything the same across the board.
I wrote this up to try and simplify someone else's hybrid swap, if they should need the info. If anyone sees any holes in my method here, please post it. This is meant to help, I don't want to give bad facts. I have been helped invaluably by the guys here, just tryin' to do something for someone else.
I have learned from exhaustive research of others' trial and error, that if at all possible, you need that VSS input for proper engine performance, especially for manual trannys. Reason being, when coming to a stop, and you let off the accelerator, and clutch pushed, the PCM sees no movement of the vehicle. it lets the idle drop too quickly and may stall out. Other uses by the PCM for the input are for air/fuel ratios at highway speeds. Not something I would choose to fudge around with. Make no mistake, you can run a vehicle with a swapped OBD2 engine and computer system without it....it just won't be optimal.
My setup is a 3400sfi engine from a 1999 GrandAm se, complete with it's PCM, Wiring harness, and ALL engine sensors intact. This swap is into a 1960's british car, so everything is foreign to the engine/tranny control system. The entire swap is flawless, the engine needs only those sensors already attached to it........except one,.....theVSS. It's in the tranny, a 4T45E, to be exact. Since I'm not using it, I've got to re-create those VSS pulses to the PCM using my T5.
First a little background on a VSS.....short for Vehicle Speed Sensor. The FWD cars have a reluctor ring on the final driveshaft of the transaxle that has a pre-determined amount of teeth on it. The sensor sends pulse to the PCM each time a tooth goes by. Some sensors create more voltage as teeth pass by faster and faster, the PCM knows the speed of the vehicle by how fast the pulses come, or by the voltage sensed. The # of teeth are matched to the tire size so that the PCM sees so many pulses in one mile of travel.
In my case I called the dealer to see what the available tire sizes were for a GrandAm that year...a 215/60r15, which turn 801.67 revs per mile. Next I had to find out how many teeth were on the reluctor ring of the original tranny. This is where it got fun. I called several dealerships and tranny shops over a months' time....no luck. There just isn't any info on such stuff for cars this new. Finally...I got in touch with three tranny re-build companies out west who were willing to pull the parts off the shelf and physically count the teeth on the ring. 30 teeth.. from all three companies. So...801.67 revs X 30 teeth= 24050.1 pulses per mile, that my PCM needs to see.
Now, to re-create that #, I have to formulate my own tire size, AND, because I'm RWD now, I have to take into consideration the Rear-End gear ratio. My new tire size is 205/40r16 which turn 898.1 revs per mile....97 revs per mile more than the original tires. So, if I divide the 898.1 revs into the 24050.1 pulses needed, I get 26.8 teeth needed. That is if I want to mount a reluctor on the rear axle near the tire hub. But I want to mount my reluctor onto the Driveshaft yoke that goes into the tranny, so I have to divide my 26.8 teeth into my gear ratio of 3.27....which is 8.19. Rounded out, it will mean I have to fabricate an 8-tooth reluctor gear to mount on my driveshaft to make the PCM see the same input as if it were still in the pontiac.
There is a company, Stealth Conversions, at www.jagsthatrun.com . that makes many VSS conversion parts. They make a 40-tooth ring that I intend to buy, then mill 4-out of every-5 teeth off, to give me an 8-tooth ring. I will then bore it out to the size of my driveshaft yoke, slip it on and tack it in place. Then I can fab a mount for the original sensor the GrandAm had, so I can keep everything the same across the board.
I wrote this up to try and simplify someone else's hybrid swap, if they should need the info. If anyone sees any holes in my method here, please post it. This is meant to help, I don't want to give bad facts. I have been helped invaluably by the guys here, just tryin' to do something for someone else.
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