I plan on checking the compression on my 02 3.4L Monte.

I've read that you can disable the fuel and spark by disconnecting all three of the Ignition Control Module electrical connectors. Is that accurate?

And I know you've got to rotate the engine forward to get to the back plugs. I'm assuming I'd have to rotate the engine back and bolt it back down to the upper mounts when checking the compression?

 

Disconnecting the harnesses from the ICM will disable spark, but I don't think it will disable fuel delivery. I would pull the fuel pump fuse and/or relay to make sure. You can get to the rear plugs without rotating the engine, but they are easier to access if you do. Since you are just turning the engine over and not starting it I don't think you'll need to rotate it back into place each time you check compression in a cylinder.

 

I'll get a ratchet tie down to keep the engine in place. I'm probably going to have to rotate the engine as it looks like the easiest.

One thing is I had read with the engine rotated is it puts a strain on the exhaust. Not sure if with the engine cranking would cause a problem with that. But I'll probably rotate the engine back just to be safe.

I'll probably look to see if there are any fuel injector fuses to pull as well. As I'd say with pressure in the system from recently starting the car would allow some fuel to spray till the pressure drops off from lack of pump.

 

Pull the fuel pump fuse/relay then start the car and allow it to run out of fuel before you do your prep for the compression test. That way the fuel system will be depressurized.

 

Thanks.

 

FYI - I don't know about doing a compression check, but just to change the rear spark plugs on a 3400 powered W-Body, I can do it with out having to move the engine OR moving the coil packs (something I commonly have to do on N-Bodies).

As for disabling fuel/spark, I am sure disconnecting the 3 plugs off the ICM will disable spark, not sure about fuel.

 

I'll look at it again, but it looked like you'd have to work blind. And/or try and use a mirror to see what you are doing.

Looks like the easiest is to get at them from the driver side of the car.

I've got compressed air I'll use to blow all the crud out of there before I pull the plugs.

Are you guys using antiseize on the platinum plugs? I know we do it on the older engines that use the copper plugs. I did read some tech bulletin about GM saying not to have the dealer perform a thread cleaning on the spark plugs. As it would wear away some anti-corrosion on the plug and allow corrosion. So, not sure if anti-seize is recommended on these plugs. I'm going with NGK 3403 platinum plugs.

 

I use anti-seize on ANY spark plug, ZERO problems (just a dab on the threads). Also on my lug nuts

As for the back plugs and "doing them blind", you are corrects. I've done plugs on the older kin of the 3400, which is a 3100 and YOU have to pull the coil pack assemblies (2 nuts, 2 bolts) and flop them forward out of your way when that engine is in an N-Body car (like a Grand Am, like my '94).

W-Bodies were designed for a BIGGER engine then the 3400, they have a LOT of space. Easy to reach my arm around to the back plugs. I'll admit, since I've worked on so many of the 3100/3400's for friends/family, I feel quite familiar to them that is an advantage to doing them "blind".

If you are uncomfortable with working on them blindly, the metal bracket holding the ICM and the coil packs is held on with 2 nuts and 2 bolts. You may have to remove some plugs that are held in place to it, but after that, lift them up from there mounted position and flop them forward. You should have all the room and visibility you need.

Certainly more then I got doing back plugs on the 305 V8 in my '84 Camaro

 

I'll try removing the ICM and coil packs first. I've also got a hand mirror I could try laying back there if needed.

Though, whats the danger in messing up the exhaust in rotating the engine forward? I believe there is some gasket or something that could get messed up? I noticed the exhaust is kinda loud at the back of the engine at the firewall when listening in the engine bay at idle. And when accelerating, the engine is kinda loud like having a muffler in the engine bay. By looking at the top mounts. I noticed they weren't straight, but kinda pointing at the passenger door like the front of the engine (Drive belt side) is leaning down compared to the back of the engine.

My older Camaro had a 305 V8 in it as well. I thought the plugs were easy once the AIR tubes were removed.

 

How old was your old Camaro? I know the 3rd gens suffered form lots of emissions "stuff" on them that made getting to the back plugs a pain....

As for your exhaust noise, take a look at the resonator (it's right after the cat). There is a flange joining the cat and the res, sometimes that goes bad OR the resonator itself rusted out. Just a thought.

As for the idea of rocking the engine, the exhaust has some flex points to allow it to move. Unless you went crazy, there should be no issue. But I'm certain you'll have the room you need getting the ICM and coils moved (worked plenty of times on the N-body cars, only way to reach one's arm down there on those cars).