Knocking...but only between 2500 and 3500

[priapism]

My engine has an engine-speed related knock. It only occurs when the engine is warm and only between 2500 and 3500. It seems to be coming from right in front of the driver, the back of the motor.

I put a little 100 octane in there and it seemed to lessen, but didn't go away completely. These things are designed for 91 octane AKI, right? What could it be? I'm not much of a mechanic (yet).

(sorry, it's a 1991 2.5 "i")

[jlevie]

It would be a help to know what car you have, but all 325e, 325, 325i/is variants are designed for 87 octane. Serious carbon build up in the head could raise the compression ratio, but I doubt it could be enough to cause knocking that only 100 octane would fix. I'd be more suspicious of bad motor/transmission mounts, a flywheel/clutch problem, a rod bearing, or even a drive shaft problem.

[priapism]

It would be a help to know what car you have, but all 325e, 325, 325i/is variants are designed for 87 octane. Serious carbon build up in the head could raise the compression ratio, but I doubt it could be enough to cause knocking that only 100 octane would fix. I'd be more suspicious of bad motor/transmission mounts, a flywheel/clutch problem, a rod bearing, or even a drive shaft problem.

Sorry, it's a 1991 "i". Sounds like it could be anything. I've recently replaced every one of those parts as well as the head. Basket case car argh.

[xwill112x]

318i? or 325i?

[priapism]

325...I thought M20 designated the 2.5s?

[accident]

318i? or 325i?

dumbass

[xwill112x]

dumbass

jackass.^



I was just trying to help..jesus..

[accident]

you're in the fucking M20 subsection, obviously it's not a 318.

[xwill112x]

does it knock when under a load or just cruising? milage?

[priapism]

Now now kids, play nice. :)

does it knock when under a load or just cruising? milage?

Seems to only do it under light throttle, but when I'm on it it goes through those RPMs pretty quick so it's hard to say. Can't hear it at speed over the wind noise.

[xwill112x]

if under light throttle and coasting could be your rod(s) knocking.

how many miles are on the m20?

[priapism]

Odo shows 155k, it was working when I got it...

Guess this is a job for the shop.