Weird sputtering at part-throttle

Joel · Post by **Joel** » Tue Jan 19, 2010 12:05 pm

My '81 528i has developed a particular sputter that I've never experienced before. It's an E12 so it has a rough idle--hasn't been a problem yet. It has also had a whistling sound for the past month or so; the sound comes from somewhere around the front of the engine and disappears under acceleration, then fades back in as I start to lift off the throttle. It's been annoying but also not a serious problem.

Both of these issues may or may not be related to the real problem it has now--a few times over the past month it has had a sudden short sputter. Felt like it was running out of gas but there was at least a quarter tank and it didn't repeat often enough to diagnose it. Last night I had to drive 120 miles or so, and for almost the whole trip there was a serious jerking sputter when I was at part throttle, i.e. maintaining speed. If I was accelerating it wasn't a problem, and completely off-throttle seemed ok too--it seemed like it was engine-braking a little stronger than usual, but that might've been in my mind; it at least wasn't stumbling like it was at part-throttle. Since I had to keep coasting and accelerating I was getting less than 15mpg, used about one tank of gas for the trip.

I've replaced my vacuum lines very recently, which didn't affect how it ran and/or idled at all, so it doesn't seem to be a vacuum leak. I have had issues with it running hot if I sit still for too long, but the temp has been a lot better lately and was fine for this entire trip, so I don't think it's related.

I'm planning a 3.5L long block swap in the near future so I don't want to spend a lot if I don't need to in the mean time, but I do need to be able to drive it. Anyone have any ideas??

Joel · Post by **Joel** » Tue Jan 19, 2010 12:14 pm

Forgot to mention, I have also recently replaced the out-of-tank fuel pump, fuel filter, and fuel lines running between those parts and the tank. When the sputter started I thought it might be a problem with the in-tank pump, but I would assume that would be more of an issue under acceleration. I've ruled out fuel pump issues in my mind, but feel free to let me know if I could be wrong.

grumpsjr · Post by **grumpsjr** » Tue Jan 19, 2010 12:29 pm

A couple of thoughts: you could have a bad fuel pressure regulator. Have you checked this?

Also, given that you hear a whistling noise, this sounds like a vacuum leak somewhere. Have you tested the system for vacuum, or inspected the lines?

Those might be good places to start.

Brian

On Tue, Jan 19, 2010 at 9:14 AM, Joel <joelness5@yahoo.com (joelness5@yahoo.com)> wrote:

Forgot to mention, I have also recently replaced the out-of-tank fuel pump, fuel filter, and fuel lines running between those parts and the tank. When the sputter started I thought it might be a problem with the in-tank pump, but I would assume that would be more of an issue under acceleration. I've ruled out fuel pump issues in my mind, but feel free to let me know if I could be wrong.

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Joel · Post by **Joel** » Tue Jan 19, 2010 1:12 pm

Haven't checked fuel pressure regulator. The symptom that I can't figure out is the fact that there is no sputter under acceleration. Does this fit FPR-related prolems?

I did replace vacuum lines with new ones before the problem became this bad; didn't change how it ran in any way--I expected that to smooth out the idle a little but it didn't.

Joel · Post by **Joel** » Tue Jan 19, 2010 4:10 pm

I've been doing research to see if anyone else has had the same problem to see how they fixed it... I've found someone who had a situation that sounds identical posted on Roadfly a few years ago, but unfortunately the only response they got was "Go to First Fives site instead." Here's the other person's explanation in case it's a little clearer than mine:

roadfly wrote:I have a 1981 528 that starts fine ,excellerate smoothly , but it runs down the road very rough and sounds like it cutting out , very erratically. If I step on the gas it runs smoothly but one can not always have one foot in it. If I declutch it seems to go back to a decent smooth running . It seems as it may be electric in nature .

Any ideas??//

YouTube · Post by **Peter Florance** » Tue Jan 19, 2010 4:34 pm

worn airflow meter track?

Joel · Post by **Joel** » Wed Jan 20, 2010 10:08 am

I'm suspicious of the AFM now--I checked it out and the cover appears to have been taken off by a previous owner so it's been part of someone else's troubleshooting.

I don't want to loosen or adjust anything that I should be avoiding; can I reposition the arm to be outside of the worn "track"? Is there a screw that will loosen it without having anything spring-loaded move out of adjustment?

alotawatts · Post by **alotawatts** » Wed Jan 20, 2010 10:38 pm

Joel wrote: It has also had a whistling sound for the past month or so; the sound comes from somewhere around the front of the engine and disappears under acceleration, then fades back in as I start to lift off the throttle.

Alternator or waterpump bearings ?
Check belts condition and alignments too.

Firstfives.org