Dead spot in RPM range

[mrgraphics]

I think the winner is - #2, loose shroud.

When I went to remove the broken fan, I noticed that the shroud was not in the bottom tab on one side.

Bonus - my replacement fan is red, which matches the car :) I'm not sure why some cars had red fans, other's black. Seems to fit the same.

Thanks for the helpful advice jlevie.

[jlevie]

Broken fan blades will be from:

1) Worn water pump or clutch bearings that cause the blades to wobble.
2) The fan blades hitting the shroud because it is loose or not properly installed.
3) Bad motor mounts that allow the engine to shift and the blades hit the shroud.
4) A seized fan clutch.

[mrgraphics]

New CPS - car pulls strong throughout the RPM range. Problem solved. It still has a bit of a stutter from a stop (press gas, slight hesitation, then it goes), but that's probably a tiny vacuum leak I'd suspect.

On a bizarre note, driving the car my engine started to shake. Got it home only to find my fan blades spontaneously broke off, leaving only 4. I've never heard of this happening before.

E30 - always something to fix.

[mrgraphics]

Just ordered them. I took the car for a much longer ride on the highway and it actually was performing better at speed . . . so these sensors are definitely the issue. Just ordered from Pelican . . .

The existing sensors were Pick n Pull parts ($5 each) that I bought trying to diagnose why the car wouldn't continue to run. They served their purpose and showed that they were the problem, but 26 year old parts are probably not the best.

BTW - how critical is the speed sensor on an ETA? Obviously a bad CPS and it won't run, but what does the speed sensor do?

[jlevie]

So replace both timing sensors with new BMW parts.

[mrgraphics]

As a quick test (since I have two of the same sensor on the bell housing) I swapped the CPS and speed sensors. It ran, but idle was definitely worse. Engine seemed to shake. Same bucking action in the 2000-25000 RPM range.

Harmonic balancer looks good - no wobble.

[jlevie]

A jerking/bucking motion sounds like misfires. That could be from a bad CPS or bad harmonic balancer. Watch the balancer while you rev the engine. If there is any wobble, replace the part. If you don't see a problem there, replace the CPS with a new part.

[mrgraphics]

Spent the night rebuilding the AFM - moving it both north and south on clean sections of track. It didn't change a thing. I don't think it is the AFM.

The car almost feels like it doesn't know what to do with more gas under load. Just a jerking motion, as though the power isn't transferring to the wheels smoothly. And it won't rise in RPM on a steep hill with the pedal mashed - instead it just starts bucking.

[mrgraphics]

It was a pick n pull AFM, but on my old one I did crack it open and reset the dial on a non-worn area (making sure not to move it's correct trajectory). The fact that both are doing it in the exact same RPM range seems statistically improbable, although I do understand your logic.

And why would the amount of gas matter? That's what has me confused. After all, isn't the AFM at the same amount of "open" at 2500 RPM regardless of gas? Or is it that on hard acceleration more gas + more air is going into the engine, and therefore the AFM is actually more open than compared to a slow creeping acceleration?

I don't know anybody who has an e30 that I could test my AFM on, so I'm on my own.

[Gregs///M]

Was this AFM rebuilt or refurbished? Replacing a 20+ year old sensor with another 20+ year old sensor could lead to lots of wasted money on other troubleshooting. I would not rule out the AFM until you try it on another running and rolling e30.

I've refurbished many AFM's and find that is it very common to have wear or "drop out" of electrical signal from the AFM to the ECM in the 75% open range, which can easily correlate to the 2500 rpm range. Most common on the idle speed range.

[mrgraphics]

Well, the new AFM helped, but it is still doing it. After some playing, I noticed that it really depends on how much gas I'm giving for the symptom to expose itself. Take a look at the video and the description. What could this be? I'm stumped. I did clean the throttle body, so nothing is sticking.

There is a noticeable "click" when I move the throttle body through. It'll go 3/4 of the way smooth, then a hard push and it "clicks" all the way open.

http://youtu.be/MJ7pT8g0yhk

[Gregs///M]

i had a similar problem in my 325i 5spd. when getting on it it would hesitate at about 3500rpm then once i get to 4500rpm it would continue pulling. possible bad afm for me swell?

Without a doubt, bad AFM.

[mrgraphics]

tunethtmkII - that sounds just like mine. Mine's an ETA, so the RPM range is different, but 3500 is about equal to my 2000 RPM if you think about percent of revs until redline.

[tunethtmkII]

i had a similar problem in my 325i 5spd. when getting on it it would hesitate at about 3500rpm then once i get to 4500rpm it would continue pulling. possible bad afm for me swell?

[mrgraphics]

FLG - I had already tried that. I think it was more an electrical issue within the AFM.

I went to Pick n Pull, lucked out with a working AFM from an 85. No hesitation, no dead spots now. In fact it actually is running much better throughout all the RPM - and she even has a bit more power. The car has probably been running with the wrong air/fuel mixture for a long time.