hey ive got my 3400 swap started on my 97 cav . the donor car is a 2000 grand am se. i ve already scrapped the car and i have the full wiring harness taken out from front to rear. i was wondering if i should just swap the full harness and put digital gauges in the dash. but what should i do about the heaters and also what about manual transmission plugs, brakes and also should i use hptuners or some other program to get rid of the a/t codes. some opinions on this would be great as i am already started and will be rebuilding the 3400 this weekend..thanks.


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You're going to need to do at least some splicing to get the harness matched up to the car, but for the most part, you'll be using the entire harness.

Yes, you'll need to remove the plugs that are specific to the automatic, and you'll need to remove the tranny codes.

As for gauges, your option is aftermarket or to run your factory computer piggybacked with the 3400 computer. What you'd rather do is up to you. Talk to gtpsunfire about this, as I believe he's the only one who has done a 99 or older swap with a piggyback setup that works right. Most of the swaps so far have either converted to 00+ electronics (or started with an 00+ car), or run aftermarket gauges, or a standalone aftermarket ECM.

While you're collecting your parts, you should consider the GP on the 3400 upper mount I have going on right now. It requires no modifications to your car or your engine to bolt in.

I piggy backed the ECU's when I swapped a 3100 in my 1995 2.2, and as far as I can tell, the gauges work right. I only used two plugs from the 2.2 computer though, the temp and speedo. and my temp and speedo both work fine.


- Your not-so-local, untrained, uncertified, backyard mechanic. But my @!#$ runs

Quote:

but what should i do about the heaters

do you mean the heater/ac in the car
the a/c is pcm controlled-
piggybacking the 3400 pcm is not that hard, just get wiring diagams from both- been there done it

how to piggyback pcms from v6 and 2.2 how to make guages work off 2.2 pcm

first - buy both gm service manuals
second, get a good digital meter
third, have patience - relize you are dealing with 5v and 12v circuits


the 2.2 pcm is needed to run the guages, use the g/a stuff to run the engine
use either a 3 wire ect or run two seperate ones
wire the a/c to the g/a stuff or use a relay so v6 raise idle when needed

it been over 6 years since I did mine, and have since sold it- soo I can't offer to much more
changing the wiring to 2000 + does seem like the best way to do this swap as it "universalizes" this swap
everything else is just bolt in
using factory wiring also makes diagnostics a lot easier

I just recently got done doing a 3800SC swap into a U-body Olds Silhoute (chevy Venture)-- used all gm parts to do this (except exhaust)- looks factory - GM should have done this

Cleanest way is use a 2000 plus interior harness (J) and Bcm and cluster, then gauges will work.
I recommend DHP for the 3X engines as there is more flexibility there.



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not tryin to jack but as far as paggybacking does any1 know if the cav pcm recives tach signal from the 24x or the icm?

I piggy backed my PCM's the Fuel gauge works ,temp gauge works along with the Speedo. I put a 05 GAM in a 98 Sunfire and so far I have about 5000 miles, almost (trouble free) since the swap. I did have one problem with the VSS, I went with the 4T45-E tranny. I took apart my exsiting harness added and removed wires as needed. I never was able to get the tach to work, did'nt try too hard either after doing some searching on this forum. Sorry Ray cant help you , congrats on getting the 3.5 going.

The 3x00 ICM has a white wire which is dedicated as a tach output. I'm not 100% sure, but I believe the Cav ECM can use this as a tach feed. If not, you're going to have to splice into the feed dedicated for the ECM, which I believe is also white.

Everything wires into the 3x00 pcm temp,tach,fuel guage A/C and cruise. Read the wiring diagrams carefully. There's ways around everything. I got everything to work on my swap first try. No problems.

C:\Users\Phillip\Pictures

^^^^^^ u mean on a 2000+ rite? on a 1999- u need the cav pcm because the cav has no bcm.


Quick, r u sure the cav pcm reads rpm from the icm. i had no clue if it was that or the cps. jw if u knew that for 100% so wen i do my new harness i can just splice that in or if i need to try and split the 24X signal?

phil i c in another thread ur swaped in a 96. wat exactly r u running? u just ran the j uart into the 3400 pcm and it worked ur gauges? r u nunning a bcm? just curios always thought the signals were diffrent?

Im running 00+ engine harness to the 96 2.2 harness. I ran the vss to the pcm the to the speedo wires to the cluster. The fuel gauge was simple. There is 1 5v ref wire that goes into a 5v ref signal that comes out of the 3400 pcm. Works perfect. Then for the temp gauge i used a 3 prong temp sensor and spliced a connector for that gauge. No bcm. This is one of the main reasons I became a member to jbody because i've heard so much on piggybacking pcms on pre 00 jbodies with 3400 swaps. Reading all these threads i wanted to ease this swap for people with 95-99s. I think i'll have to make a sticky with a complete wire schematic for every1 to see im not bsn.

C:\Users\Phillip\Pictures

yeah but once again your no seeing what were talking about WHO gives a dick about you getting the gauges to work the reason people piggy back too is to shut off the idiot lights which your "wiring method" doesn't do

so your left with 3 options
1 autometer guages and have no idiot lights at all
2 piggy back the PCM
3 swap to 00+ wiring

i like method 3 i have method 1 on my car and i can do method 2 but i price option 3 low enough that people wont do 2. all you using the J PCM for is to send the data to the cluster it doesn't run the motor it gets infor from the sensors and relays to to you gauges theres nothing wrong with piggy back its just more wiring

for the record you don't have to change anything anything on the fuel or speedo side to make those 2 gauges work those to work even without the piggy back
VSS has a ppl and yellow wire to the PCM and a green out to the gauges and so far the VSS is the same signal on both 95-99 and 00+ trans and N and w bodys use the same signal

fuel nothing changes as long as you connect the wires to there proper spot from the C100 to the 3400 harness it works



JBO since July 30, 2001