3.4 DOHC Intake Gasket... GRRRRR!!!

[GnatGoSplat]

I finally got around to stopping by Wal-mart and buying some carb cleaner. I pulled off the cover on my 3.4 DOHC and sprayed at the gasket surfaces. Wow, no surprise, in 2 certain spots of the lower intake gasket by the head, the carb cleaner practically stalls the engine.

 

So it looks like I gotta replace the intake gaskets. Woo hoo! Can't wait! I noticed the oil pump drive O-ring is leaking a lot too! Oh happy day!

 

Questions:

1. Which is better, GM or Fel-Pro intake gaskets?

2. I have one of those little rubber rings that goes under the distributor plug. It came with my 2.8 head gasket kit that I used on my '89 Cutty, but I didn't need that rubber O-ring. Will it be enough to seal up the oil pump drive on the 3.4, or will I need to get a beefier O-ring?

3. Will it be ok to use some RTV on the intake gasket? I just feel like it'll seal a whole lot better with some RTV. I didn't use any RTV on my 2.8 lower intake gasket, and the thing slowly leaks motor oil into the coolant. I torqued it to spec and everything (using Fel-Pro gaskets) but it still leaks. I'd like to avoid that on this 3.4!

 

Can you believe there's a lower intake manifold bolt missing too? Some dummy has been in this engine before!

[Brian P]

Crappy! Anyway Ive always heard good things about felpro. I had good luck with the felpro lower and upper gaskets on mine. As for RTV, if it's good enough for the bottom "end seals" (between the lower intake and block) on the 2.8/3.1 then, hell, use it in conjunction with the fel pro's!

[Guest TurboSedan]

i got this one brand of plenum gaskets for my 3.1 once (i forgot the brand....red/white box), and all they were were cheap ass pieces of cut out paper gasket with plastic locator studs stuck in them. the fel-pro's i got later were steel with rubber 0-rings and acually placed the plenum 1/8" higher off the lower manifold. much nicer! i would 'stick' with fel-pro since they seem to be a specialty gasket company that knows what they are doing. Fel-Pro all the way IMO. i liked their oil pan gasket too...it even came with 'snap-ups', which made installation much easier.

joshua

[gpse3200]

2.8/3.1 Engines before '91 used the paper gaskets, the later cars use so composite design rubber/metal. What you got was the WRONG gasket kit, not the cheapest. FelPro and Victor Rienze(DANA Co.) are preobably the best aftermarket replacements out there. I'd get GM if I had no choice though.

[GnatGoSplat]

Hmmm, my 2.8 FelPro gasket set was that paper with plastic locator studs in it!

91-93 used composite metal/rubber gaskets? You say it's the wrong gasket set, why? Is there any reason why a 91-93 composite gasket set shouldn't be used on 88-90?

 

I'll probably get FelPro for the 3.4 since I can get it pretty cheap through my friend at O'Reillys.

[Brian P]

Well, lorenzo can tell you this from experience! LOL. THose metal gaskets will break a 88-90 plenum when torquing it down. They'll work fine on the 91-93 because of those different bolts and such.

[GnatGoSplat]

Well, lorenzo can tell you this from experience! LOL. THose metal gaskets will break a 88-90 plenum when torquing it down. They'll work fine on the 91-93 because of those different bolts and such.

 

Break the plenum, WHAAAA???? :yikes:

Different bolts???

I think I need pics to help me understand this one!!!

[Brian P]

I think you know what I'm talking about. The plenum bolts in 91+ are much thinner and have a rubber sleeve over it. This somehow allows the use of the metal gaskets without the chance of breaking the plenum.

[GnatGoSplat]

Hmmm, I'm vaguely remembering you mentioning this before.

Is the plenum itself different, or just the bolts? The plenum actually BREAKS?

[Brian P]

I am almost certain the plenum is the same, but the lower intake obviously has smaller holes for the rubber sleeved bolts.

 

When Lorenzo tried using those gaskets, the end piece of the plenum broke off, I think it was the one closest to the oil cap. I dont think he went past 10 lb/ft!

[Guest TurboSedan]

yeah that makes sense. i had a '90 3.1 in my car for a very short time and when i ordered the gaskets for that engine they gave me the paper gaskets. i was actually using my '91 plenum on that '90 3.1. about a month later my original '91 3.1 went back into the car, and i swapped the plenum back over (plenum just looked nicer). this time i got them for '91 and they sold me the steel/o-ring gaskets. i got the gaskets from different parts stores so i figured they just carried different brands. i got a '91 plenum to work on a '90 lower manifold, but yeah, there is no way you could use a '90 plenum on a '91 lower manifold since the bolts are WAY different. '90 has bigger bolts and NO rubber sleeve and the bolt holes in the plenum are smaller since there is no rubber sleeve, whereas the '91+ plenum has smaller bolts and bigger holes, and they use rubber sleeves.

joshua

[RedZMonte]

for the 3.4L DOHC get the Felpro. Somone said on efi Felpro made the OEM gaskets for the LQ1. Sence your doing your upper and lower intake gaskets you might as well do:

1. Injector Rings

2. Check plugs/wires1

 

as for the oil drive seal. you can eather pull the head and replace it (Pain in the ASS!) or spray it with brake clean and use some JB Weld to slop over it and fix it the easy way. I personally recomend the JB Weld route.

 

RedZ

[GnatGoSplat]

Are injector rings a common failure item too? I've never had to touch the injector rings on my 2.8. My 2.8 uses the brown silicone rings which are still nice & soft after almost 14-years.

[RedZMonte]

Are injector rings a common failure item too? I've never had to touch the injector rings on my 2.8. My 2.8 uses the brown silicone rings which are still nice & soft after almost 14-years.

 

one of mine was leaking, so i just changed them all. they are cheap and you allready have the fuel rail/injectors out so you might as well do them.

 

Shane

[brian89gp]

1. no clue, but i've had no problems with the felpro yet. Plus they are cheaper

 

2.may work if you feel like taking the rear head off

 

3.the upper gasket lookes like paper, the lower is quite different. it is a sheet of thick plastic with rubber run along it for the sealing. Hard to describe

 

Orielly has both lower, upper, and the tb o-ring for like $20.

[GnatGoSplat]

1. no clue, but i've had no problems with the felpro yet. Plus they are cheaper

 

2.may work if you feel like taking the rear head off

 

3.the upper gasket lookes like paper, the lower is quite different. it is a sheet of thick plastic with rubber run along it for the sealing. Hard to describe

 

Orielly has both lower, upper, and the tb o-ring for like $20.

 

Actually, the rubber gasket I'm talking about for the distributor plug is sort of flat shaped and is designed to fit underneath the distributor head. It doesn't replace the original O-ring.

 

So it sounds like the new lower gasket is designed not to use RTV?

When the original goes bad, what happens to it? Cracks in the plastic, or some of the rubber missing?

 

Also, what kind of fittings are these on the fuel lines, and how are they disconnected?

[ZXXXIV]

1.Use Fel-Pro

 

2.Grind a little of the lip of the plug to lift it higher and apply some silicone under the plug and let sit for 24 hours then put the clamp back on.I did mine this summer and have not had a single drip of oil.

 

3.DO NOT USE RTV ON ANY OF THE GASKETS UNLESS INSTRUCTIONS SAY SO. I did not use any on mine and have had no problems.

[Brian P]

um...pardon my ignorance, but is that luke's old car?

[Guest Anonymous]

um...pardon my ignorance, but is that luke's old car?

 

 

Lukes had no pinstriping and I believe the front bowtie was gone.

[ZXXXIV]

Nope.I've owned the car for 5 years.

[LukeZ34]

um...pardon my ignorance, but is that luke's old car?

 

What? What did I miss? lol

[Brian P]

Either way, I like the Z34 in that color! Thats probably the only color Id take if I bought a Z34, maybe silver also.

[timg]

Well, I had the GM and Felpro upper intake gaskets side by side and they're essentially identical. I'm not sure about the lowers. I believe the felpro were cheaper though.

 

Tim

[CPSMonteZ34]

If it will help, here's some images on the job when I did mine.

 

http://members.tripod.com/ShadowDog/intakepictures.htm

 

(Remember, if you can't click on it, cut-and-paste in the address bar)

 

There is some dispute on whether or not to use RTV sealant. I wouldn't bother. The most I did, in order to make a perfect placement, was to spray both sides of the upper gasket with sticky-spray due to how difficult it can be to re-install the upper-intake manifold.

 

Sealant on the bottom manifold should not be used. The gasket has triangular rubber moulded on both its surfaces, and is press-fit against each intake surface by tightening down from the top with two screws before inserting the angled intake bolts into the block. (Tip: Using two of the plenum bolts with a shit-load of washers will secure the lower-intake down so the lower-intake manifold bolts can be re-installed).

 

I'm not sure if failure of the gasket causes the majority of our intake leaks. In my case, the surface of the block had shown signs of scaring from the coolant. The deposits alone may have been enough to separate the gasket from the block to allow air through. Then again, there was also scaring along the plenum surface where the paper gasket went...so either one could have been the problem.

 

Don't confuse the rubber ring you'll receive in the gasket kit to have anything to do with the distributor plug. It's actually for the plenum-to-manifold coolant passage. You can see what I'm talking about in some of the images in the link above.

 

Get a couple of hose-clamps for the coolant passage hoses running to the plenum where the thermostat is. With how much a pain it can be to get the stock clamps off, due to the confines of their location, putting them back ON can be worse (unless you can simply tighten them with a screwdriver or ratchet as the hose clamps will allow)

 

Watch out for the vacuum lines under the plenum. If they're old, they'll break. Make sure you put them back where they're supposed to go before you put everything back together...nothing's worse than putting the LQ1 back together again and finding out you forgot to put a vacuum hose back in place. (Been there. Done that. Never gonna do it again!)

 

Make sure you clean those gasket surfaces well enough to eat off them. That's typically the reason people have to go back and do it all over again after figuring it's been fixed and the problem soon returns.

 

That's all I can think of right now.

[GnatGoSplat]

Thanks Chris, those are great pics!

I've already started the disassembly, but ran out of tools! Left 'em at the old house, oh well. We go back to work on it on Sunday so I'll bring over all my tools.

 

Don't confuse the rubber ring you'll receive in the gasket kit to have anything to do with the distributor plug. It's actually for the plenum-to-manifold coolant passage. You can see what I'm talking about in some of the images in the link above.

 

I don't think we're talking about the same ring, the one I'm talking about comes in the Felpro plenum and intake manifold gasket kits for the 2.8/3.1 engines.

 

The 3.4 DOHC definitely has a lot more to disassemble than the 2.8/3.1. I haven't even figured out how the fuel lines come off yet!