Mass911

My 89 911 w/193K miles suddenly began behaving strangely.

Traveling along at about 70 mph, I suddenly noticed that it was acting like we were driving into gusty headwinds (we weren't). It was kind of like an intermittent power loss. Slowing down, I took it in and out of gear. Didn’t' seem like the drive train was causing the problem, no strange or unusual sounds. Just under power was this occurring.

When I arrived home (10 mins later) and listened up close the engine had a decidedly different sound... that "sewing machine" sound I have seen mentioned before.

I know this probably can't be good... Sucked a valve? Spun a bearing?
Were would you guys look first?

lally911

Could this be a worn clutch?

Wayne Williams

I've just solved a similar problem on my 82 SC and it may be worth a look before tearing the engine apart.

The power loss was due to bad fuel pressure at higher revs which was causing the engine note to change and lose power.

Changed the fuel pump (didn't realise how noisy it actually was until I changed it!!) and hey presto, high end power restored!!!!

However, I didn't have the sewing machine noises you mention.

Best of Luck

Wayne

imcarthur

Wayne might be on to something. Fuel delivery would be my first guess. DME relay, fuel pump . . .

Ian

Dan Cobb

I recently witnessed a loss of power under load due to a poor contact between the spark plug end and the ignition wire, it was aseembled crooked, thus adding additional resistance.
I'm not sure why it ran smoothly when parked and poorly in gear, but I saw it happen.
+++

fixnprsh

it sounds like a cheap fix, if it was something detrimental to the motor, it would smoke or make a **** load of noise with that much of a power loss, I agree with wayne, check you fuel pressure first, I've seen where the pump can put out enough pressure to sustain idle or slight cruise, but fall on their face under load. a pump is a couple hundred bucks and easy DIY (change the relay too)

Mass911

Thanks to all for the great info. A fuel pump going south could very well behave this way.
After reading your posts and getting over my initial depression, I went out and fired it up.

What I discovered is that at about 3500 rpm the engine begins to miss. There is no backfiring, knocking or excessive smoke.

The computer, distributor, plug wires, plugs?

Your thoughts?

fixnprsh

misfire and cutting out are two different things, In person they are easily distinguished, over the net is harder, does it ever just flat out die? have you checked your fuel pressure yet?

Ive seen pumps that will sustain an idle but not RPM untill they go out completely

bwell

Broken head stud? (I had a similar problem on my '89 and that was the unfortunate result.)

Wayne Williams

Sounds so much like a fuel problem to me, have you checked the DME relay, Frequency Valve Relay.

See my thread on Misfire 82SC, you are getting the same symptoms I had.

A new fuel pump will cost a lot less than a broken head stud!!!