4.6 to 4.9 conversion

[serpentking]

I was recently given a 94 SLS that was litterally driven to the store and back by someones granny. The car is the cleanest 94 anything Ive ever seen. The problem is that the car overheats. Ive done all the other things to check the problem. Checked fans, new pump, new radiator and new thermostat. the only thing that Im left with is the head gaskets. I already own a 92 STS but its kinda beat up and I was wondering if its possible to drop the 4.9 where the N* is currently. The reason for this is that my 4.9 was rebuilt from the ground up about a year ago and I was given quotes of between 2900 to 3500 to rebuild the N*. Is ther anything I can do about this, because I dont think I can spend 3000 to fix a car that I can buy for the same price.

Any help would be greatfully appreciated. Thanks

PS. I have mechanics on standby that tell me that if it can be done without any major modification, then they will do it. They just need to be sure that it can be done.

[MAC]

The PCM needs to be replaced, etc. It's not simply a matter of yanking the Northstar out and dropping in the 4.9L. In my opinion, you would be better off sticking with the Northstar—Certainly, you should make sure whatever the problem is that’s causing overheating is not something that can be fixed with minimal effort. I remember this issue was raised in the past when one of the Northstar team members, a GM engineer, who was the most respected member of this forum and others he visited (Except Amsoil! LOL). Anyway, he said that you simply can't swap engines since the there are other considerations such as the PCM which is the brains of the operation. I'm certainly not an expert on this subject as I'm going by recollection, so I defer to other members of this forum.

[Ranger]

I doubt that you could do it easily. Not only the PCM would have to be changed but I would suspect the wiring harness, trans and you might have problems mating the exhaust.

Are you sure the head gaskets are gone on the '94? Have you run a cylinder pressure test? Are you using coolant? Have you checked to be sure that the purge line is clear? Have you checked the surge tank cap?

[Bruce Nunnally]

I would say that it is possible but it would be a real project. If you keep the PCM and dash from the 92, and the whole drive train, that would seem easier. You may find that the body module etc will only talk to the pcm in the 94 however, and end up with a real mess.

However, I'd say that repairing the northstar would be much much simpler technically than changing the powertrain.

[The Fred]

That is going to become a big unwanted mess.

You're going to spend three grand just sneezing towards a project like that one. That and time and frustration.

[serpentking]

I have both complete cars in my possesion so if the PCMs have to come out, then they are both there.

But asides from what I mentioned that I fixed, what are the other possible causes to cause the overheating?

[Bruce Nunnally]

Next you should test the coolant for exhaust gases to determine if the head gasket is leaking. Auto parts stores have kits.

Alternately, you can make up a fitting to blow air into a cylinder, then look for bubbles in the overflow.

[Astrak]

Not to mention drilling new holes to mount the motor and the transmission for the 4.9, basically pulling everything from the 92 and placing it in the 94 and making spots for it. How well will RSS respond to a PCM that is speed controlled ride, and the list goes on and on and on it would be cheaper to replace the Northstar then to fit the 4.9 in there.

[RichieR]

I doubt that you could do it easily. Not only the PCM would have to be changed but I would suspect the wiring harness, trans and you might have problems mating the exhaust.

Are you sure the head gaskets are gone on the '94? Have you run a cylinder pressure test? Are you using coolant? Have you checked to be sure that the purge line is clear? Have you checked the surge tank cap?

The transmission is different for the 4.9L and the Northstar. The 4.9 had the 4T60E transmission and the Northstar had the 4T80E transmission, so I would suspect there would definitely be compatabilitly issues there, not to mention all the other compatability issues that were mentioned already.

As others have mentioned, I would have the necessary tests run to rule out a head gasket problem. It is possible that it's a much simpler problem.

[serpentking]

You guys have convinced me. I will not even attempt to make that change. I will look around and see what I can do with the 94. If anything, I will try to find an engine and get that put in.

Thanks for all.

[msilva954]

Lemme ask you....just the last 4 days have been torture for me.....New radiator new waterpump new thermostat.........in the end the result was determined to be a pocket of air in the block which was pushed out when I had it flushed yesterday......get a flush if you have no already...mechanics everywhere thought it was headgasket...and tada a 69 dollar flush and im running cool!!