1991 Grand Am 3800 Swap - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 12-18-2014, 02:48 PM   #21
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Originally Posted by jwfirebird View Post
he never said what year it actually was which would greatly help with the guessing, it could be anywhere from a complete PITA to not so bad.

being a 91 GA most all the hvac and sub systems are not likely spidered together like the newer cars and should be fairly easy to make work
What did you want to know the year of? The Grand Am is a '91, the Bonneville is a '98, the OBD1 (or OBD1.5, as Mike1995 corrected it) PCM that they use in Fieros (which I assume could be used in any other OBD1 car like the Grand Am) is a '95.
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Old 12-18-2014, 08:33 PM   #22
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Your going too far backwards with too much mixing.

Your best bet based on what I know is...take the 98 engine, convert all the sensors on it to 1995 OBD 1.5. Basically, just order sensors for a 95 Bonneville. Get a 1995 4T60-E-HD trans. Because anything beyond 96 and the sensors change to the point the PCM makes the trans work funky.

Now your also going to need the matching BCM for the OBD 1.5 PCM. Unless you can magically tell the PCM that the BCM is seeing the VATS ok, then your screwed. Last I knew, the 95 PCM'* disabled the starter if VATS didn't get a green light. 96ish disabled injectors and later years either disabled the pump or injectors.
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Old 12-18-2014, 08:37 PM   #23
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I still want to retain my gauge cluster, but if I went the OBD2 route, I don't know why a gauge swap from the Bonneville wouldn't work..? If all that need to communicate are the gauge cluster, engine, trans, and various sensors, why wouldn't a gauge cluster swap solve the problem?

Because everything is not plug-n-play.
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Old 12-18-2014, 10:01 PM   #24
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Alright, I'll take your word for it. I don't know that much about electronics. Are the Fiero'* just terribly different from any other GM? Because it seems to be no issue at all for them to run either OBD1 or OBD2 with a Series 2 and their factory gauges. What do they do to make it work? Nothing I've read about those swaps mentions anything about a BCM, it just says that you need an OBD1 PCM, and a trans controller if you use a 4T65E. I don't know enough about it to understand why the Fiero and Grand swap are so different from an electronic standpoint.
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Old 12-18-2014, 10:19 PM   #25
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Are you sure they are making them work correctly? Last I knew, the Fiero speedometer were shaft driven and the RPM gauge is analog which taps directly in the 3800 ICM. The fuel gauge is driven directly off the fuel tank usually with 5v, oil pressure is probably fed directly off the sensor itself. You should probably get Fiero out of your head, because that'* a whole different chassis. Concentrate on getting 1995 schematics and compare them to your 91 chassis schematics. Your going to need them anyway.
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Old 12-18-2014, 10:20 PM   #26
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I did a little more reading, found the answer to that question. Not sure if this would work the same in my car, because I don't know if my car does have a BCM or not, but Fiero'* do not, or so I've read. One guy said this, I think it kind of pertains.

"Its been my experience that you can simply have the PCM learned "key values" POT resister values deleted, so that when the time comes that your computer requests a value, there is none, then it will tell its self there is no security device (ie. BCM) to worry about."

If I'm being honest, I don't really understand what the BCM'* role is, but the Fiero'* lack of one may be why they don't have trouble with that engine in their OBD1 car and I would.
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Old 12-18-2014, 10:22 PM   #27
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Well, I really wanted to do the swap but I guess I'm in over my head. Maybe it'* best to just keep the Bonneville as is, and do a simple 3100 swap to the Grand Am to get rid of that Iron Duke.
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Old 12-19-2014, 08:28 AM   #28
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i dont think going with the 98 stuff would be all that hard if you get everything to do with the engine and trans, but you will have to get HPT to change the fuel disable from the vats and delete anything emissions wise you dont want to mess with. after 2000 it gets more complicated, and swapping to another computer is too complicated. hpt is not cheap though and you will be on your own to figure out the physical mounting, hvac, and stuff.

swapping to an optional engine would be way easier
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Old 12-19-2014, 08:48 AM   #29
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i dont think going with the 98 stuff would be all that hard if you get everything to do with the engine and trans, but you will have to get HPT to change the fuel disable from the vats and delete anything emissions wise you dont want to mess with. after 2000 it gets more complicated, and swapping to another computer is too complicated. hpt is not cheap though and you will be on your own to figure out the physical mounting, hvac, and stuff.

swapping to an optional engine would be way easier
I agree, a 98 PCM should be easy to program to fly on it'* own and a 98 should of came with the 4t65e. The only thing you might need to do is wire in your own fan relays and the HVAC should be fine as long as you make AC hoses to fit to the new compressor. But than again you would still have a 91 grand am in the end.
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Old 12-19-2014, 10:39 AM   #30
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I agree, a 98 PCM should be easy to program to fly on it'* own and a 98 should of came with the 4t65e. The only thing you might need to do is wire in your own fan relays and the HVAC should be fine as long as you make AC hoses to fit to the new compressor. But than again you would still have a 91 grand am in the end.
I hope you're right. And I know I'd still have a '91 Grand Am, but I like the '91 Grand Am. Don't ask me why, I didn't when I first got the car. lol

Also, I'm just trying to gather information at this point to figure out what it would take to handle this project. I need the money first, and another daily driver to take its place.

Another thing. If I do the project, I've decided the parts will come from a junkyard car.. the Bonneville seems kinda cool aside from the dented to hell fender and driver'* side doors, but I figure I can find that in a junkyard, it just likely won't match.
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