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Old 05-11-2005, 03:24 PM   #1
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Default OBD 1/2 idea...

My brain started working in a thread talking about 94/5 mutant PCM'*, could be trouble, so bear with me?

Know as we know, the 94/5 PCM'* are hybrids, are hard to get readers/scanners for, and have basically NO performance pcm'* for.

What are the main differences in a 94/5 SSEi PCM (for example) vs the 92/3 SSEi pcm. Granted the fuel tables are modifed for the differen't blower, but how hard would it be to convert one to say a 93 Full OBD 1 computer?

I know this isn't for everyone to attempt, and anything is possible, but what would have to be done?
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Old 05-11-2005, 03:28 PM   #2
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I believe the wiring is different, and there are more tranny sensors....er, have more features/duties than the 92/93'*. I know there'* more, but that'* what I'm thinking for now.
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Old 05-11-2005, 03:39 PM   #3
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I know OBD II has O2'* after the cat to read how well the cat works, but that can be spoofed. Tranny point is a good one...
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Old 05-11-2005, 03:55 PM   #4
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Swap/remove/add some sensors, modify the wiring harness where needed.
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Old 05-11-2005, 04:30 PM   #5
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First of all, the fuel tables are the same. The 94/95 M62 doesn't produce more boost, it just spins at a lower rpm to produce equal boost to the 92/93. It'* more efficient, but the output is 'pulleyed' to be the same. The TB is slightly larger in diameter to flow more efficiently, too.

The O2 sensor would have to be changed to the 93, and the trans is another big issue. 93 and 95 transmissions aren't compatible. The other things to check would be the ECC, and what communication it has with the PCM in 1995. There should be some, where, in 1993 there was little or no communication with the PCM, as it had it'* own onboard diagnostics. You may want to upgrade to that unit as well if you attempted this.

I do know that a 95 trans can be MADE to work with a 93 by altering some pinouts inside, but I don't know what'* involved in doing this.
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Old 05-11-2005, 04:45 PM   #6
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How does the 94/5 make more power if the fuel tables are the same? I don't think the change in */c pulley would release that much of a load on the engine...

Do people who swap a later blower onto their 92/3 need the AFC just because the MAF reading is different?
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Old 05-11-2005, 05:54 PM   #7
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Quote:
Originally Posted by BonneMeMN
Do people who swap a later blower onto their 92/3 need the AFC just because the MAF reading is different?
Yes.
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Old 05-11-2005, 06:30 PM   #8
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Quote:
Originally Posted by BonneMeMN
How does the 94/5 make more power if the fuel tables are the same? I don't think the change in */c pulley would release that much of a load on the engine...

Do people who swap a later blower onto their 92/3 need the AFC just because the MAF reading is different?
The faster it spins, the more hp it takes to simply drive it. VE (volumetric efficiency) is not a function of drive power (what you lose spinning it) but AE (adiabatic efficiency) is. The 94/95 has a slightly better VE and AE, simply because the rotors are a closer tolerance due to the teflon coating and the slightly larger TB supports this. Because of the increased VE, it produces the same boost PRESSURE, while operating at a lower blower RPM than the 92/93, thus requiring less hp to drive it.

The M90 takes more power to turn it than the 92-95 blowers, but because of it'* superior VE, in part due to the longer rotors (a direct improvement in the VE ratio), they spin it at a lower rpm, and don't lose as much hp to drive it as if it were spinning at the 94/95 revolutions.

Tolerance between rotors and case, as well as the length of the rotors have a direct impact on VE. This is why I'm transplanting 94/95 rotors into my 92/93. With my ported throttle body, I should be able to support the improved VE of the blower without having to use an AFC calibrator. I MAY have to increase my pulley diameter from it'* current 2.2".
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Old 05-11-2005, 06:36 PM   #9
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I didn't expect the drag difference to be that drastic.

Yeahi undestand why you're running rotors, but if you went to the full setup you could get a larger TB... Yes i know you modded yours, but still!
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Old 05-11-2005, 07:48 PM   #10
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I believe I've modified my TB to flow as well as a slightly larger 94/95 TB, and I suspect that the MAF passage is a different dimension on the later (larger) TB'*. I suspect that the larger MAF PASSAGE itself is the reason an AFC calibrator is needed, because (unless I'm mistaken) the MAF sensor part numbers are identical.....off to check that.....ok, they are different. Either way, what I'm up to should work without an AFC calibrator, and it should be within the abilities of my PCM to adapt to the increased flow.

Funny, 1993 lists two different part numbers for the L27 MAF sensor.

1993 and 1995 do indeed have different MAF sensors.
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