95 Grand Prix GTP engine Swap to 96 3.4L

[jeffglitman]

I have a 95 GTP with a factory 3.4L DOHC engine and 4T60E tranny. Motor is trashed but Found a NEW 1996 3.4L DOHC engine. Block Casting numbers are the same but the heads have been revised I was told from 95 to 96. They went from small oval ports to larger D exhaust ports. I also know the Intake is different as well as the throttle body. What I don't know is if the PCM / Computer will work. I am getting the intake and Throttle body and exhaust manifolds with the new engine so physical setup should be OK. Just worried about the PCM. I was told they changed the CAM RPM curve from 95 to 96. Didn't know if I just ordered a 96 flashed PCM from Auto Parts store for $85.00 would do the trick. Anyone out there know anything?

Thanks,
Jeff

[timg]

You have two options.
You can run the newer engine on your current ECU. I believe there are some articles on here describing how to do that. (you can either use your existing intake manifold or the new one)
The second option is to take the motor and use a 96 wiring harness and PCM. You could then upgrade to OBD2. This really isn't very much effort if you're already swapping in a new motor and is probably the better bet. It will likely cost you another $100-150 to get the harness and computer though.

The 96 computer will NOT fit on your existing wiring harness. It is completely different.

Tim

[jeffglitman]

Wiring Harness

Thanks, I figured the same but just wanted some one to confirm my crazy way of thinnking. Do you know other than junk yards, where I could find a wiring harness for a 96 PCM for the Grand Prix? Also, will I only need the engine harness or the harness that sends signals to the dash components. Thanks again for your help.


Jeff

[jeffglitman]

OBDII ?

Tim,
According to the tech manual, All 94 GTP's with 3.4L DOHC have OBDII already? I looked under the dash and found only the 12-pin connector. This is OBDI correct? I thought OBDII was 16 pins.

Thanks again,
Jeff

[bszopi]

I think its the same for the DOHCs, but I know 94-95 for the pushrods is a bastard year for PCMs. They are what we refer to as OBD1.5, whereas they have properties of both OBD1 and OBD2 systems.

[timg]

Yeah, 94-95 are still OBD1.

You need the engine harness only. You then re-pin a wire or two at the firewall connector and add a few wires. I have a wiring spreadsheet for the Monte Carlos (95 to 96 or 97) that should be close for the Grand Prix's). I've been told that it's a pretty simple swap, but haven't yet had the chance to finish my swap. RedZMonte has done his and there are also lots of details on this sort of swap over on motorswap.org (I used their materials plus my wiring schematics from the service manuals to make my spreadsheet).

Tim

[dohcfiend]

my opinion but depending on your time and patience, i would just use your existing ecm setup.

drop the engine in, hook it up to your stock computer and go.

There are few physical changes to get it going. going from memory you'll need to do the following:

i am assuming you want to use your 96 intake setup.

on the 96, the coolant is blocked off where there is a nipple on your old engine, switch them. done.

the coolant nipple on top of your tb, goes to the firewall coolant conection. done.

coolant nipple on the crossover tube, plug it. done.

remove all evap tubing, plug the holes. done.

ign wiring. 2 options here. 91-95 location or 96-97 location.

91-95, switch it over give it a try. i am not sure whether or not everything will fit ok but it should.

96 location, it takes a little work but worth the extra effort. it will take some patience but all you need to do is pull your wires out of the loom in your main harness and untangle the connectors that go to the coilpacks until you have enough to route them to the new location. no cutting.

downpipe, exact same length and everything. done.

old fuel lines plug into the new rail. done.

your oil pressure sensor, you can either stretch your wiring to plug into the new spot or plug that spot and switch over that aluminum plate off of your 95 that has the oil pressure sensor mounted in it. done.

i cannot recall 100% on the throttle cabling and bracketry but it will fit albeit a little tight. done.

EGR is a little tricky but it can be done. if you do not have emissions, plug the hole on your intake and on you manifold.done. There is 1 person i know of that can modify 94-95 memcals, he goes by darthfiero on pennocks fiero forum. ask him to delete your egr and maybe a speed limiter or whatever floats your boat. he only charged me $40 iirc. done.

if you do have emissions, you'll need your egr tubes off of both cars:

space will be tight but i have done it.

1. pick the most comfortable spot you can for your 91-95 egr valve.

2. attach the top half of the 91-95 tubing that connects to your egr valve to the rear half that connects to the manifold.

3. take an egr gasket to the machine shop, have them cut out a piece of steel to match it and punch a single hole in it to match the spot where the exhaust gas goes into the intake. make sure the hole is the same size as your egr tubing.

4. with the 1st half of your mockup in place, i used that 2-bolt flanged piece of tubing that was on the 96 intake. instead of being on the bottom flip it over to the top and with some subtle manipulation, the bracket will line up with the bolt holes.

5. with that in mind, run that rubing to that steel plate and take it back to have it welded together.

6. install it all. done.

note: when having the 2 pieces of tubing brazed together or however you go about it, be sure to test for leaks with water or something be4 leaving the machine shop.

i think that is all.

crank it up vroom vroom. done.

[jeffglitman]

thanks for the very detailed information. One Question though, I was told I could run my old 95 Intake and throttle body on the 96 Engine? Will it work ok with the larger exhaust ports? Didn't know if I would be starving the engine for air since I think the 96 is a larger intake? What do you think? Time and Patience I have so I want the best over all running solution.

Also, if I use the 95 Intake setup, then could I just use my 95 EGR as is?


Also, I'm confused by your comments on the Ignition wiring? If I keep my stock 95 wiring setup, why do I need to make changes?



Thanks again, I appreciate all the good advice!


Jeff

[timg]

You can use your current 95 intake on the 96-97 heads.

Tim

[dohcfiend]

okay if you plan on using your 95 intake, hook me up with a deal on your 96 intakes huh?

all you need to do in thjis situation if you plan on emissions is braze the top half of your 95 egr to the bottom half of the 96 egr tube b/c they way they plug into the manifold is different.

if you do not need emissions, plug them off and have a memcal burned.

your 96 heads will work fine on either intake setup.

on your ign wiring, what i was referring to is if you wanted to mover the coilpacks to the spot on the 96 setup. which is right beside the plenum.

if you choose to retain your stock location, it is your choice. i just do not like the spot gm chose for the 91-95 setup. it exposes them to alot of heat which makes them go bad more often and a PITA to service.

in lamens terms. if you want easy retain your stock spot and just switch over the bracket if it will work with 96 manifolds. if you want your coilpacks to last longer and be easier to service, try the 96 spot.

only curveball here is you'll need to modify your 96 coilpack bracket to mount somewhere else if you are using the 91-95 intake setup. id suggest that mounting bolt for the engine bracket that bolts to the top of the rear cam carrier.

[jeffglitman]

Thanks a bunch! I don't own the 96-97 Intake set-up, it belongs to a friend of mine but I'll see what he wants. I have know Idea what the intake and throttle body are worth but he was asking $200? Too high or just right? Let me know what you would offer and I'll ask him. As far as the Ignition coil pack goes, I'll move to the 96 position. I am pretty good with a MIG welder so I can fabricate what I need but I agree, less heat, longer life. As far as the EGR, will the 96-97 EGR tube and valve work with the 95 PCM? Is the connector different?

[dohcfiend]

$200 is high. $135 is what a complete kit goes for. i.e . intake, plenum, crossover tube, fuel rail, maybe the injectors, valve covers, egr tube and coilpack bracket.

just the intake, plenum, rail and maybe the injectors go for about $75.

id either be interested in a complete kit for $135 or the plenum, intake, rail, crossover tube and valve covers for $75.

the 96 egr connector is different and i think it will not work if you tried to splice the 91-95 wiring into the 96 connector.

[jeffglitman]

I'll ask him tomorrow and see what all he has and if he will do the prices you mentioned.
Thanks again for all your help.

[jeffglitman]

Ok, I got the 1996 Motor in today. I tried placing my 1995 Intake on it and it doesn't seem to fit properly. It is real close but the bolt holes don't line up perfectly. It seem like if I had a thicker intake gasket it would line up.

I am using the 1996 Intake gaskets that came with the new motor. Do I need 1995 gasket for the lower intake by chance? Any comments would be appreciated.

Due to the changes in vacumm lines and EGR valve, I would prefer to use my 1995 intake, plenum and throttle body if possible.


Thanks,
Jeff

[5speedz34]

To put the 95 intakes on you need the upper and lower manifolds. The 91-95 gaskets are also completely different.