I've been noticing more and more on this car that it will hesitate a bit on acceleration. Usually it is just a quick "cough", but has gotten to be rather serious, to the point that I've had to pull the car off the road and let it "recover" by holding the accellerator at about 1500 rpms as it sputtered, then smoothed out after a few minutes. My first guess is that the car sat for quite a while before I got it and has water in the gas tank. I siphoned some out last weekend (from a full tank), and it seemes fine, although I might not have gotten a good sample from a full tank. It seems to do this more after filling the tank. I've run about four tanks through it since I got it. I would think that if it were water in the tank, it would have passed by now.

I'm wondering if there is something else that anyone has experienced that causes this hesitation? Maybe a sensor that is not functioning.

I've set the valves, although they seem to be making a bit more noise now, and replaced the spark plugs. It still has a bit of a rough idle, more so when it is warm, but runs well when it is on the road.

Any help would be appreciated. Thanks

mike,good to know you're getting to drive yours.i've only had mine out for 3 short runs so far,it's spent most of it's time on jack stands.on the last drive i noticed the main fuel pump buzzing,so i think the transfer(in tank)pump may have failed.haven't troubleshot it yet.a failed pump could cause the problem you're having.
i've got to do the front suspension and replace tires before i can start really testing,i cant believe someone was actually driving this car in it's present shape.the control arms are shot and the belt is showing on one tire.the whole car shakes when braking,but the engine and trans feel great.i'm really impressed by this 3.5 engine,it just keeps on pulling thru all gears. i've been able to sort quite a few problems with out having to drive it.

yeah, it's drivable. pretty amazing for a $600 car. So far I've lost the rear brakes (did a quick fix of new shoes on a bad rotor), which I'll have to do over again, in fact even though the front brakes are in good shape, I've noticed some vibration on hard braking in the steering wheel, so I'll most likely do all four wheels when the weather gets better (which around here should be sometime around February or March). This hesitation problem just doesn't seem to be going away, as I would expect water in the tank to do. Right now it is my daily driver, which i'm not complaining about, but it does have alot of work ahead. The spark plugs helped a great deal, car fires right up and idles relatively well, run out very well, except for the hesitation from time to time. I would really like to get that part figured out.

Only a lean mixture would cause a stumble.

Since it does recover, I would suspect the FPR, Fuel Pressure Regulator.

The only way to verify fuel pressure is to install a gauge.

http://www.bmwe30.net/pic/tech/motronic_s.gif

FUEL PRESSURE REGULATOR
The pressure regulator consists of a sealed, spring loaded
diaphragm with a connection for intake manifold vacuum. Fuel is
provided to fuel injectors under approximately 36 psi (2.5 kg/cm
Ò
)
pressure.
A connection for intake manifold vacuum provides a constant
pressure differential which ensures that the amount of fuel injected
is solely dependent upon injector "open" time. Excess fuel is
returned to fuel tank. See number 6.

http://www.unixnerd.demon.co.uk/m30_left.jpg

Later,

I'll have to see what I can do to check the regulator. I'm beginning to think there is something else going on other that water in the tank because it's been going on too long.

Ron, I'm gonna have to send you a bottle of wine, you've been a great help. Thanks.

i would also check for any type of vacuum leak.if all is well,simply pulling up the dipstick can cause it to stumble,there's 3 hose connections under the intake manifold(bottom center),i replaced all mine,they were bad..i just had to replace the intank pump on my wagon,the main started buzzing for about a week and i was starting to get a slight,intermittent stumble while stopped at traffic lights.
as for the the FPR you can also pull the vacuum line off(while running) and check that no fuel is coming out,the diaphram can leak causing a rich condition.on my volvo with a tube in the filler neck i could hear the fuel being returned to the tank(1/4 full),that told me the FPR was working.when i pulled the vacuum off the FPR the rpm's rised slightly.

If you haven't done so, you may want to check out your fuel filter too. Fairly easy job to do, and you may want to just go ahead and replace it.

Also, did you notice that the fuel tank has a drain plug?? It might come in handy if you want to elminate the potential "water in the fuel tank" issue from your list.

Thanks for the tips. I do have a new fuel filter, haven't installed it yet. I also took a look at the regulator, didn't replace it, but tightened up the lines leading to it, then took off on a 700 mile trip. It behaved much better, yes, still some hesitation, but not nearly as pronounced. I'm thinking that I need to replace the lines to it as most everything under the hood is showing some age. But I made the trip up and back without any real issues, even had to outrun a crazed semi. I now know that the car will do 110. In fact it really didn't even breath all that hard at that speed. I didn't stay there long, but long enough. I''ve got to admit, I am impressed with this beater BMW.

You need to consider a little faster speed.

http://members.roadfly.com/kcroncarter/Shark.GIF

Here in the plains, well on a trip in Oklahoma really, I saw a 165 mph on my 1985 Shark. Sunday morning and four lanes for 120 miles and no traffic or other cars.

This is a third gear run on my Dyno, kind of easy if you have one.
Hmm, that is 115 MPH on the speedo line referenced to the left scale.
I call it my Tow Mule since it tows the Dyno. I used it to tow the Dyno to Boston last summer.



http://members.roadfly.org/kcroncarter/towmule.jpg

http://kcrealtime.com/stang2.jpg

http://kcrealtime.com/images/e24onDyno3.JPG

http://kcrealtime.com/images/e24Tiedown.JPG


I also sell a fuel pressure indicator for $17.50 plus $3.00 sh.

http://i4.ebayimg.com/01/i/00/f8/ae/db_1.JPG

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7938562415&rd=1&sspagename=STRK%3AMESE%3AIT

BMW Fuel Pressure Indicator Mechanical, 0 to 100psi.
For under the hood and not normally removed.

But an allen headed plug with every order so the gauge can be removed.

I built three for my cars and can make a few extras, for the only REAL way to find out what the fuel pressure is.

All EFI BMWs have a flexable hose between the metal fuel lines and the fuel rail, on the engine side of the firewall.

That is the location for this indicator.

Also a good time to replace that hose if it is over 10 years since it was replaced.

Later,

When you replace the fuel filter, try to keep the feed side higher than the discharge side. That way you can pour out its contents (gasoline and fuel tank sediment) on to a piece of cardboard or something like that... this may give you an idea of how clogged the filter may have been. I guess you could try to open it up too to look at the element.

On speed, I've taken my car up to 130mph indicated at about 5k rpm. The only mod I have is a conforti chip and my diff is 3.64 limited slip. I only have H speed rated tires though, and that plus fear of state troopers on a two lane road at night kept me from "testing" any furhter. As a matter of fact, I passed a trooper, then decided to flog it, counting on that there was only one out there that night.

I think that with the conforti chip, that raises my potential redline to almost 7k rpm, but I never take her over 6k... I want to enjoy this thing for a while, you know.