Leaking intake gasket

[87Skier]

I have a 350 out of a 97 truck that uses coolant and misfires after warming up.

Could the intake gasket (see the picture) be the cause? I can't find anything else, and a compression test doesn't give much info.

Thanks

[Eddie H.]

Intake gasket leaks were a common problem on the L31 engines, so yes that is most likely your problem

[68gmsee]

^ Agree with above... I replaced intake gasket on my 96 Tahoe and colleague from work had to do the same on his 97. Common problem.

[sweetk30]

not sure of the felpro part# but they offer a better version over the stock oem style .

and missfire check the cap/rotor . huge moisture problems in them dist units . carfull of the plastic body with the tiny screws . the ear's snap off.

and the dist gear on them wears bad and causes timming to jump around . you will need a scanner to set timming on them tho . and not a cheepy scanner .

[B. W.]

The gasket in your pic has failed beyond a doubt. What sweetK30 said, Fel-Pro has a set of gaskets that won't fail, have used them for years. P/N MS98000T (comes with one valve cover gasket)

[Bigdav160]

Injector spider is prime candidate for the misfire. The coolant loss won't cause that.

[B. W.]

Not going against you Bigdav160, the spiders are a known issue as are the pressure regulators leaking. I've probably done 2 dozen intake gasket sets over the years. When the gaskets are in really bad shape coolant will get sucked into the intake runners & cause a miss. I found it is most noticeable when the throttle is chopped after accelerating. The engine will drop a cylinder or two then clear back out.

87skier, IMO, I'd replace the intake gaskets & run it. If the miss is still there & it's the injectors you can replace the spider without removing the lower intake.

[Killer Bee]

I concur with above..

the coolant passage in the picture has lost the gasket frame support around the seal bead and coolant pressure could easily push out..

I recommend replacing the whole gasket kit and troubleshoot remaining symptoms.. make sure to follow proper torque and sequence to ensure good mate..

if intake passages were also leaking, some other symptoms may also clear with new gasket..

leaking intake passages could cause lean condition and subsequent misfires..

but there is also a myriad of other non-related components that could be the source of your whoes..

I always recommend isolating symptoms and addressing known failures first..

sometimes sympathetic symptoms will just go away quietly..

please keep us posted and good luck!

[68gmsee]

Here's the symptoms I had on my 96 Tahoe in case someone else has problems with this or similar year motors.

In my case, leaking head gasket did not cause a miss but there was coolant loss and smell of coolant.

The spider assembly symptom I had was backfiring when starting after sitting for a period of time. Similar to a flooded engine. Once it was running there was no missing or backfiring.

It's wise to replace spider asm. and fuel regulator while the top is off. I wound up having to do the spider asm/reg a few months afterwards anyway. Regulator was the culprit but injectors were so bad they were brittle. After close to 300K I guess it's expected.

[87Skier]

This was on an engine I had sitting around that came out for a swap. It was a high mileage engine that I ran for a few years. The truck (1972 Jimmy), had enough problems that I was going to have to pull the engine, transmission, and bunch of other stuff to get everything fixed up.

The engine had a carb conversion and Edelbrock intake, with an 80's GM HEI (coil on cap).

I'm 99% sure that carb and distributor were in good working order and not the cause of the miss. The truck had dual exhaust and only the side with this gasket would smoke and miss. If you kept it above 30 mph, it would never smoke, but any amount of idling and it would start missing and smoking again.

I'm just diagnosing it now that I've got some time. I have been told by countless people that is either a blown head gasket or a cracked head, that it can't possibly be anything else. I pulled the heads just to check them out, and found no evidence of cracking or issues in cylinders 1 or 3, and the head gaskets looked good. I figure with over 250,000 miles it needs a rebuild and I've got something else I want to use the heads for anyway.

The lifter valley and bottom of the intake seemed to have kept all the moisture this let into the engine because there was no evidence on the dipstick of coolant contamination.