2002 3800 no workie. Replaced plenum gasket, now won't run
 

Alright guys, here's the run down (and thank you for your help in advance). A friend of mine got an 02 Monte SS just to play around with. Full load, leather, but 160k miles. Was leaking coolant like a biatch, so we bought a thermostat and gasket kit and replaced them....replaced the plenum gasket too, as it was included. It was running a little erratically before (kinda lumpy, like it had a cam lol).

Anyway, we put them plenum / fuel rain back on, plugged in all the injectors etc, and now she won't run. First couple of starts, POP BANG! from under the hood... and now when she turns over she'll run rough for a couple seconds then just cough and die. I double checked everything, all the plug wires are back in order, everything seems right on. So what's up?? I'd say the timing was off, but we didn't touch anything besides the intake plenum.

haven't been on in a very long time, so this car will be a good excuse to get back on the boards. ;)

you need spark and fuel see which you dont have. listen for the pump(unless you have a pressure tester), pull a couple plugs and see

I'll have to go back to the basics with this one. It's getting fuel though, pump works...I actually smell a gas smell each time.

you shouldnt. my have a leak somewhere. orings or the quick connect on the fuel line

Everything looks dry on top.

Welcome back to the forums Jon.

Did you only replace the upper plenum gasket?
You should have replaced the lower intake manifold gasket as well, those fail typically anywhere around 60k miles, of course some fail sooner, some later.
If you did not replace the LIM gasket, it is possible coolant got into one of your cylinders, I have heard of connecting rods being thrown through the engine block, because the coolant does not compress, if that happened though I doubt it would run for even a second.
Not sure what that sounds like though, the only bang I have heard of is from a faulty fuel pressure regulator, they can cause the UIM to explode, you'd know if that was what happened though, see this video for what it looks like.


Back to the LIM, if that was never replaced with the aluminum framed gaskets, then that needs to be done ASAP, you want FEL-PRO Part # MS98014T

The fact that you are smelling gas makes me think it is possible the FPR could be bad, here is a video that will help you test it, see it at the 1:50 mark.

I am with Justin, you should not be smelling gas, if the injector o-rings are fine, then look at the quick connect for the fuel rail at the rear, those o-rings go bad and can cause intermittent leaks, I know because mine leaked, and I have seen others with the same problem.
I'm still trying to think of what could have made that bang, maybe it was a backfire, which could be due to a faulty FPR, it just dawned on me that you really won't be able to test it like you should, since it will not stay running, so I'd pull the EVAP hose from it, and smell it for gas, if the gas smell is strong then most likely the diaphragm in the FPR has failed.

If you can test the fuel pressure I'd do so, and then if you have good fuel pressure, check for spark at each plug/cylinder.

So coolant was leaking bad......did you ever find the source of the leak? Was it external? The car was running before you did this work?

When you removed the upper plenum to replace the upper plenum gasket, was the top of the lower intake manifold depressions, full of coolant? Did you check the upper plenum for degradation where the EGR tube passes through?

If you had an internal leak, did you replace the oil and filter?

As William suggested, check out the F/P regulator....normally, that doesn't cause a problem if it is leaking a little on a cold start...it causes a problem on a hot start(too rich)....

If leaking real bad like in the video, it can possibly blow off the vac line(or if the line is cracked) and that gas hitting a hot engine can cause that fire....

Recheck all your work.....injector o-rings not pinched, brake booster hose fully attached, etc.

Alright, so here's where we're at with this car.

It turned out there was a crack in the near the t.b. I also replaced the PCV valve as the old one was mickey moused together and I noticed oil inside the plenum. It's running now!. It's got no cat and an exhaust leak, so it still runs like crap, but it runs.

This car needs more work than thought. It was bought on a whim, and my friend didn't really look it over. The rad support is gone (wire holds up the rad), which is typical of Montes in the salt belt, it's missing one of the strut bars, zip ties hold everything in/up, from the PCM to lines underneath. And the ignition was punched out, so it starts with a screw driver lol

She's almost too much work, but it does have a solid body and is an SS/HS, so it has that going for it I guess.

Glad you are making some progress with it, sounds like you'll have enough to keep you busy for a while, if you need help fixing other issues feel free to make another thread, and ask for help.

Thanks for sharing the pic, it does not look bad!