For all the gearheads out there

[gregzz4]

I've been having a bunch of problems with my engine lately
It passed AirCare in Sept, then started to act up
It's a GM Performance Parts ZZ4 (hence my username) 350HO crate motor with less than 50K miles on it that I bought brand new back in 2001
It's been idling rough, sputtering/missing on light acceleration, bogging down and sputtering big when the lockup converter activates, vacuum down to 15 inches and dropping to 10 sometimes for a brief bit, running-on on shutdown, and generally being a cow
It still had rolling power, but nothing to overcome the 10-bolt posi and was not 'all there'

I replaced the old ignition leads as their resistance was way up - 600 through 1100. The new leads are 78 - 123 depending on length
I replace the plugs, cap and rotor. No change
I replaced the pickup coil. Marginal change, but not fixed
I tested compression dry - 195-205 all around

I found #4 plug to be oily wet, so I remove it's lead from the dizzy and there was lots of spark. Same when removed from the plug end

This lead me to only one conclusion; a massive vacuum leak under the intake from the oil valley
Well, guess what I found today ....



I'm super happy I found the issue and it's all fixed now
Idle is back to normal, vacuum is back to 17-18 inches, and tons of power again. And I get to drive it to work tomorrow after leaving it parked 'till I had the time to fix it

I used the same Fel-pro gasket set this time, but I used some aviation form-a-gasket around the intake ports on the head side to stop them from slipping
I know, they look a 'tad' big for the ports, but I think they'll do otherwise I would have bought the expensive GM ones
If they do let go again you can be sure I'll be buying them from GM

[hillegom]

So how does that happen Greg, faulty install?
Yet it worked all this time, and fails now?

[gregzz4]

Can't for sure say why it failed
All I can think of is it slipped down a bit during the install, and the gasket ports are 'just' a bit big, allowing it to find an edge of the head
Then over time it failed

This last set of gaskets was on there for 2-1/2 years without issue 'till the middle of October, so go figure

I checked the intake with a straight edge and all is good
I checked the intake bolts before removing and all was torqued

No explanation here, but I'm just a hack with this stuff

As I stated earlier, I used some 'poop' this time to keep the gaskets centered over the ports and expect this to work

[sirruckus]

glad to hear you found the problem - at least its relatively easy fix

[gregzz4]

One other thing that comes to mind is while I was sitting in air care at the end of August and she got warm for about an hour maybe that allowed the intake manifold the warp just a slight bit and gave room for the gasket to crack
Then when I put the distributor back in last weekend I got it off by one cylinder and it backfired a couple times
This may have blown the gasket out when it was originally only cracked
As I said I can't say for sure

[hillegom]

Well, your troubleshooting skills rock!

[SanguinesDream]

Those are pressure cracks so it either was when she got hot (not likely) or over torqued. Although the original cast exhaust manifolds will bolt on and will work fine, the manifold openings should be ground on the top sides to match the ports on the heads, or this will just happen again regardless of the "poop" used, no?

But at least you isolated it. Way to go!

[gregzz4]

Thanks guys !!

The intake and heads are aluminum so the gaskets were torqued to 25lbs both last time and this time. I started at hand tight, then 15, 20 and finally 25 twice
The port openings on the head are less than an 1/8" taller than the manifold
I think it's the gaskets being a smidge too big for the application and not getting enough purchase on the inner of the ports

I hope it's the last time I have to do it but as I said if it's an issue again, I'll get the factory gaskets from GMPP

[mike31154]

Good stuff, relatively easy fix. I've been driving a Japanese import Toyota Surf (4-Runner) with a 2LTE diesel engine for a few years now. Should have done a bit more research on that engine prior to the purchase! The early production years had problems with heads cracking. Yep, I had to replace the head several years ago. More than a bit of a pain since I had just replaced the timing belt at 100,000 kms. Anyhow, new head, figured I should be good for a few more winters now. Not too likely. Early November there's a pool of diesel under the vehicle and it's leaking from the injector pump. Hard to see exactly where the leak is, but looks like on the side of the pump up against the engine block. No easy fix, have to pull the pump which means dismantling the front of the engine (again), radiator out, timing cover off etc...

Sure enough an o-ring under a plate that houses the timing piston in the injector pump comes out in pieces, totally dried out & flattened. Local diesel injection shop can overhaul it, but because it's the EFI model of pump, can't bench test it. A new pump from the place I purchased the vehicle is $1700. The overhaul would likely also cost about $1K, & without bench test, doesn't make much sense, since other than the seal, the pump was working great. No one local has a seal kit, it's too cold outside now to be working on the thing in an unheated car port, so I now have a new truck!

Older vehicles are a continual challenge & cold weather will often make bad things happen. If this had happened during the warm season, I probably wouldn't be driving a new truck now. On the plus side, it could have happened in the middle of winter on the highway between Golden & Kimberley or some other god forsaken road & I'd be stranded. Now that I have a new ride, I can take my time, replace the seals next spring & have a good winter beater for many years to come. New vehicles are pricey though, beans & wieners for a few years now for dinner.

Cover plate off


Knackered seal


Cover plate on other side of pump. This one could have been changed without pulling the pump. I should be so lucky, but judging by it's condition, I'll be changing as many seals as I can without getting into the guts of the pump, which is best left to a pro


The other seal. Wouldn't have lasted much longer either. All remaining seals I could easily check looked ok.