350TBI Vacuum Leak

[Phishin]

So my 1990 K1500 with the 350TBI started to develop an occassional high idle. I'm pretty sure it's got a leak in the base gasket between the throttle body and the intake (which is common). But I'm also gonna pull the IAC Valve and make sure it's not frozen or carboned up too bad. Maybe inspect the TPS as well.

But my question is, this TBI has all kinds of gaskets. For example, there is a ring that sits between the air filter and the TBI, and those gaskets are gone/shot as well on both sides of the ring. Is this important/critical? The rebuild gasket kit is like $50. The base gasket is like $5. I'm gonna replace that one.

Does anyone know which gaskets are critical or which ones aren't? Just trying to save myself $40 or so.

 

[Gotch]

Those gaskets keep unfiltered air from entering the throttle body and engine. The metal to metal fit is usually pretty good, however, fines will make their way though. I would change them.

 

[morepwr]

I would bet the IAC valve is dirty. Also check the little 90 degree rubber boots that the vacuum lines have going to the TBI if they are still the factory ones, they are probably cracked.

 

[morepwr]

I would bet the IAC valve is dirty. Also check the little 90 degree rubber boots that the vacuum lines have going to the TBI if they are still the factory ones, they are probably cracked.

 

[mechtech2]

Let's take a bit longer and get everything right.
Clean your throttle body manually as clean as you can get it. Same for the idle air valve.
Many gaskets can be sealed with additional RTV type sealers. Don't hog it on - a thin coat will work. This should provide an excellent seal, even for a compromised gasket, and at only a little cost.
Let it cure before starting.
And, let it cure before starting!

 

[Phishin]

Well, last night I took most of the TB apart. Cleaned it up pretty well. The IAC wasn't that dirty, but it got a good cleaning anyways. Put it back together and the TBI leaked like a screen door (never put in new gaskets). So, I got them today on my lunch break.

But, the fuel pressure regulator diaphragm area was TRASHED. When I got the truck, the PCV system was completely clogged...the valve, the hose, and the inlet on the intake. I just replaced the valve, cleaned out the hose, and squirted some carb cleaner through the vacuum nozzle at the base of the intake it worked great. But the lack of PCV pressure before I had the truck caused moisture to rust out the fuel pressure diaphragm and spring.

I got a complete TBI rebuild kit today on my lunch break. But I can't find the spring anywhere. My old one still works, just really rusty. I have to try to clean it up tonight. I found them on EBay, but $15 plus shipping kinda stinks for a spring. Hopefully I can clean it up sufficiently tonight.

So, when I get home, the complete TB is coming off and getting EVERYTHING cleaned really well. New gaskets everywhere.

I have a question tho....I noticed that my injectors both leak a little bit....both give a little drip of gas instead of all the fuel being atomized. I'm hoping with the TBI cleaned up, the fixed spring and new diaphragm, the fuel pressure might increase and the injectors will spray better.

Is there a way to clean these injectors? I sprayed the snot out of the tips with carb cleaner, but that didn't fix it.

Thanks in advance.

 

[Phishin]

Besides try to clean up my injectors......

I have another questions: Once I clean all the rest from my fuel pressure regulator spring, what can I coat it with to prevent rust in the future? I was going to put some steel wool on it and maybe soak the spring in some vinegar to get it clean....but since it's in the TB, what can I use to coat the spring with?

 

[Phishin]

Well, the throttle body is rebuilt now. Just need to re-install the IAC and TPS into the TB and install the whole assembly tomorrow.

I ended up not needing a new fuel pressure spring. It wasn't as bad as I thought. It cleaned up pretty well with steel wool and some Kroil (from Kano Labs, makers of Kreen). But then my OCD kicked in, and I took it to work (I am a chemist at a plating shop). I put a nickel flash onto the spring, and then zinc. She's better than new. LOL!!!

And another thing, I just left the injectors as is. Since my fuel pressure diaphragm was in such bad shape, I thought maybe just rebuilding the TBI might help fix some of the dripping. Probably not, I know. But it's pretty easy to pull these babies out later if I need to.

 

[mechtech2]

Nickle can crack as it flexes, and changes the spring rate.

 

[Phishin]

Originally Posted By: mechtech2
Nickle can crack as it flexes, and changes the spring rate.


The nickel was just a flash. Super thin, and the plating bath had additives in it that forces the crystal structure to be laminar, not columnar....which takes the stress out of the plate and allows it to flex without becoming brittle. How do you think they chrome plate Harley springs? LOL!!

I thought about the spring rate and simply saw how much the spring compressed with a large rock on top of it before plating. It compressed the same (or real close) after plating.

 

[Phishin]

Before.....

After.....

 

[mechtech2]

Wow!
You know your stuff about plating!

I was always confused about laminar vs columnar regarding this.

I do note the adjustment screw. This should be a great thing to have , if the pressures are off.

 

[Phishin]

Originally Posted By: mechtech2
Wow!
You know your stuff about plating!

I was always confused about laminar vs columnar regarding this.

I do note the adjustment screw. This should be a great thing to have , if the pressures are off.


You lost me mechtech2......what adjustment screw? If you are talking about the screw thread you see in the bottom of that bell housing.....it appears to be adjustable....but it is NOT. Kinda sucks. On the other end of that threaded shaft, is a ball that is pressed into the housing. It don't move. It's not supposed to move.

The springs are $20/each....so I doubt if I ever go the route of "tuning the spring" if pressure is off either.