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I just yesterday started hearing a very hi-pitched whirring (almost a squealing sound) at idle (about 800-1000rpm) and at between 2500-3000rpm.

If stand over the motor and manually open the throttle slowly from idle, the sound slows and disappears by 1500rpm. As it is just about to disappear The frequency of the squeeling slows enough that I can hear that it is a series of discreet hi-pitched "clicks" tat I am thinking may be an the injector struggling and dying? I'm totally speculating on this.

I just installed a Jacobs electronic ignition box and started noticing this annoying noise just after that, BUT... I disconnected it and put my ignition system back to its original set-up and restarted and the noise is still there, so either the ignition box has nothing to do with it, or it caused some issue that is now ever-present. I reconnected the Jacobs box and drove the car last night and it seems ok, just this annoying squeal as described avove.

Any ideas? Is this an entirely unrelated issue?

Is my engine about to blow?

Thanks for your input

Have you lubed your distributor, lately? (addmittedly, the wick only lubes the advance shaft)
Seriously, I've had noisy ones that sound a LOT like you describe.
Could also be a vacuum leak.

Replace the injector seals with CIS ones FIRST.
(That's a good idea in any case, and will run you ~$6)

That is also the sound an L-jet fuel pump makes when its dying. It could go for 3 more years...or die in a week. Ray

raygreenwood wrote:That is also the sound an L-jet fuel pump makes when its dying. It could go for 3 more years...or die in a week. Ray

Have you noticed all the early 90s GMC products with high pitch sounding fuel pumps lately? In traffic it sounds like they are all taking a dump at the same time.

raygreenwood wrote:That is also the sound an L-jet fuel pump makes when its dying. It could go for 3 more years...or die in a week. Ray

I don't think so. The sound is most certainly coming from the engine area and the fuel pump on my '75 is in the front.

I also have a clarification on the nature of the sound and when it happens... it's not only in the rpm range I stated before... It happens whenever I apply the gas, like it has something to do with the throttle or the amount of gas being injected...something...

Also in the last few days it has stranded me several times. I'll drive it, park it and when I come back...it won't start.. It cranks until I drain the battery... but won't fire. If I leave it sitting for a couple hours and go back, it'll crank several times, very slowly, then fire up... And in the past 24hrs it has started sputtering and will almost stall out when I press down hard on the gas in 1st... It'll rev up at first then almost stall out before picking back up... and sometimes in between gears, it seems like the throttle gets stuck and the engine revs really high until i catch it by punching the gas to "loosen" whatever was making it stick...

Is this MULTIPLE problems or one problem with multiple SYMPTOMS?

Thanks again guys for the replies

I'll beat Ray to it for once...

Hook up a fuel pressure gauge and stop guessing.
(Try to buy a LARGE 0-60 PSI one so you can see small changes)

Ah...almost forgot. This sound can also be caused by a fuel pressure regulator. It is teh equivalent to the sound you normally get when the car has been sitting for a few days...and then you blip the key...and hear a high piteched rattleingsqueel from the back. It is air in the lines venting past the pressure plate in the regulator.

You can get this sound constantly from a fuel pressure regulator, for three reasons:
(1) Your fuel pump may be putting out incorrect volume or pressure causing a constant oscillation of that pressure plate and diaphram.
(2) The pressure plate may be pitted with rust...causing a wide variation in venting pressure...which also can cause an oscillation.
The fuel pressure gauge will tell all.

(3) the vacuum portion of the regulator may be leaking slightly causing an oscillation of the pressure plate. If you disconnect the vacuum l;ine while running and the noise stops..that generally confirms that it is at least the regulator. Ray

Also check for vacuum leaks. The 1.8's L-jet really hates vacuum leaks!

--DD

it could be the jacobs if it is like the msd they make noise and it will vary with rpm

You missed an important fact.

I DISCONNECTED the Jacobs unit and the noise remained.

Can't make noise if it's not connected and working.

Dave_Darling wrote:Also check for vacuum leaks. The 1.8's L-jet really hates vacuum leaks!

--DD

Thats what I would suggest too. I've noticed on an occasion that once the engine revs up enough, sometimes it can pull closed leaks and stop a sqeeal of a loose / cracked hose from leaking .... Quick and easy test ..... and perhaps a stethescope to really hear where that squeal area is coming from, just don't blow your ear drums listening ....