wicked squeaks, possibly TPEFI related

[George M. Dailey]

I've got a weird one here. Every one I've asked so far has been stomped. I
drove my '89 5.7L TPI '58 chevy truck to Atlanta last weekend, 100mph
plus...420 miles one way from my home...so I'm perty sure it's not a
mechanical engine noise. The following is what I know. I think it's the EGR
valve or diaphragm resonating.

When the engine is hot (just after getting off the highway) I get this high
pitch squeaking sound. Sounds like a belt but much louder. I can hear it 100
yards off.  Changed the belt, operated the engine with the belt off, added
many cans of belt dressing, and the engine still squeaks. 

Swapped trannys and inspected the flywheel. Flywheel a-ok, still got the
squeaks.

Check this out, I can pull the engine oil dip stick when it's squeaking and
magicly, it stops. That's why I think it might be EGR related. The EGR valve
vacuume line is disconnected. The truck stumbles bad when it's connected. I
suspect the diaphram is leaking. I can't pull vacuume in it if the engine is
running. Pulls ok when the engine is off.

By now, I'm desperate to stop this damn squeaking so I connected a vacuume
gage to the engine dip stick tube to see why it would affect the engine
squeak. Here is what I found.

9.5"    engine idle, park, no squeak
11.5"   engine idle, Drive, light squeak
13.0"   engine idle, park, Loud squeak
9.5"    engine idle, park, no squeak, after pulling the engine dip stick to
'break vacuume'

9.5"    engine idle, park, no squeak
11.5"   engine idle, Drive, light squeak
13.0"   engine idle, park, Loud squeak
9.5"    engine idle, park, no squeak, after winging the throttle and reving
engine to ~3,000rpm quickly

Manifold vauume was 18" - 18.5" at idle and 17" in gear. 

What ever is causing the squeak is definitly vacumme related. I checked both
PVC vales, clean as a wistle and free.  The evidence suggest that there is a
ported vacuume leak from the manifold to the crankcase and that the vacuume
is held untill you pull the dip stick or kill the motor. I have all but
given up on finding the root cause of this irritating noise. If you guys
don't give a solution, I will be forced to treat the symptom rather than
solve the problem. I'll install a vacuume breaker that relieves crankcase
vacuume at 10"  If it turns out that this is not EFI related, feel free to
E-mail me personally...somebody somewhere has had this problem or is having it.

thanks in advance for any solution offered,
GMD

"Irritating sounds and actions can drive a man to do insane things"
George M. Dailey
gmd at tecinfo.com