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DrEntropy
04-09-2014, 02:26 PM
Learning more than I EVER wanted to know about GM V-6 3.1L engines. A pal has somehow convinced me that I should fix his 1991 car after it cooked off all the coolant. Intake manifolds are apparently the biggest issue with these things. Hoping it ain't a head warp situation. We'll see.

A Ferrari V-12 has less carp hung on it than this lump! Plumbing EVERYWHERE. And it ALL needs to come off.

And what's with the HV ignition on these things? Two plugs firing from the same coil simultaneously?!? Just silly.

Gliderman8
04-09-2014, 02:31 PM
My old Nissan Stanza wagon had two plugs and two coils... they both fired to reduce emissions... what a PITA.

Mickey Richaud
04-09-2014, 02:41 PM
One more reason I chose to go with a Holley 4-barrell and standard distributor for my GM 3.4 crate engine in the BGT conversion I'm doing.

GregW
04-09-2014, 04:10 PM
Two plugs firing from the same coil simultaneously?!? Just silly.
My 4 cylinder Ranger has 8 coils and 8 plugs.

DrEntropy
04-09-2014, 04:47 PM
Greg, this goofy thing has three coils, each firing two plugs on opposite ends of the cycle.

DNK
04-09-2014, 04:49 PM
Not sure , but I think my Safari is the same doc

TOC
04-09-2014, 05:10 PM
Those three-coil sixes are odd in another way.
If I recall, they are paired coils...sometimes we'd see on end fire positive, one negative. Freaks you out the first time you see it on a scope.
The intake issue is not limited to 3.1L. All started with the 2.8.
GM wrench twisters called those "milkshake motors", as that's what the oil looked like.
It's caused by the angle of the V. Expansion and contraction is a killer...eats the gaskets right out.
Lots of luck.
If you're lucky, and drained/flushed the crankcase (at least two full oil and filter changes), and the anti-freeze didn't kill the bearing babbit, you can do intakes and be done with it.

Cooked it hard (as in drove it 10 miles home with no coolant), well, heads, maybe rings.

Wait until you work on one with the EFI lines and regulator UNDER the intake.
POS General Misunderstandings.

Dave

Guest
04-09-2014, 08:14 PM
Doc, you'r probably looking at heads/gaskets too. It's 2014...1991?!?!?!?! How long does he plan to keep it.... Do the humane thing and shoot it...

DrEntropy
04-09-2014, 10:07 PM
Hoping the thing is just the intake, the oil is surprisingly not coolant contaminated. I expected chocolate mousse on the dipstick. When it got here on the flatbed and was on its feet I immediately pulled the stick... just oil. On removing the intake boot found plenty of water in there, though.

Back before Christmas I replaced three of the injectors, O2 sensor and a whole bunch of other bits in the fuel management "chain." Beast ran well for a while. :smirk:

This event may be its death rattle. We shall see.

Funny that the counter guy at the parts house said about the same thing as Billy. But he suggested explosives. He's a former squid, we've been pals for decades.

Guest
04-09-2014, 10:20 PM
Funny that the counter guy at the parts house said about the same thing as Billy. But he suggested explosives. He's a former squid, we've been pals for decades.

That's because I'm a former counter guy. The use of explosives is due to his military carrer. I'm not opposed to it but you're in city limits.

Choot 'em !!!!! :eagerness:

Banjo
04-10-2014, 04:48 PM
Been there, done that. GM V6 intake gaskets can be a money maker for the guy who's done a few, and doesn't mind doing them. The gaskets you get now are an improved design, but still not bullet-proof. Like has already been said, it's in the design of the engine. They often just leak externally. still worries me how long he ran it hot.
The 2-plugs per coil design is called "Waste spark" Like TOC said, one fires negative, the other positive. If you pull both plugs you will see one worn on the center electrode, the other on the tab. It's not a new concept. My 1932 Maytag twin cylinder uses the same setup, just as a magneto. Same with my 1941 Evinrude Sportwin.
The twin plug system is a different monster. Nissan and Ford both tried that as an emissions thing. Good luck getting the exhaust side plugs out on those Nissans!!!

GregW
04-10-2014, 08:05 PM
For me, one side is cake. The other side requires a different combination of extensions and U-joints to get each plug out. Gerrard.