Not sure if it's a fuel pump problem...

[74AlpinaTii]

I am hoping to get some different suggestions as to what the problem could be.

In late June of this year, I was driving from Lake Tahoe, CA and Las Vegas (470 miles) when the fuel pump started "groaning" and the car would cut out briefly quite a bit. I was barely able to make it back to Vegas before the car died. My mechanic, Chris Willet, determined that the problem was a fuel pump and installed a new fuel pump.

I got the car back the next day and drove it home about 25 miles without any problems. The car ended up sitting for the next 1 1/2 months because I had traveled out of the state for work. When I got back in mid-August, I put about 100 miles on the car and it started having similar problems (cutting out and also fuel pump was "groaning")

I let Chris know of the problems and he ordered a second fuel pump and installed it on Tuesday of this week just before I took the car on vacation back to Lake Tahoe. Directly after leaving his shop, I ended up sitting on the freeway in stop and go traffic in 110 degree heat and the car started acting up again (cutting out briefly under acceleration).

I drove the car up to the next town about 100 miles away and when I stopped the vehicle, I was able to hear a light "groaning" noise from the fuel pump. At this time, it was still about 105 degrees outside. I decided to continue driving. As soon as the temperature dropped as the sun went down and I was driving at a higher elevation, the problem completely went away. I did not have any further problems the remainder of the drive to Lake Tahoe, which was about 350 miles.

While driving the car here on vacation, I've put around 350 more miles on the car and have only had 1 incident where the problem re-occured. The problem occured when I drove to the southwest of Tahoe and dropped down to about 2500 feet in elevation and had a temperature change from 80 degrees to probably around 105 degrees. Also, I had been driving for about 80 miles when it the problem started again. As soon as the car cooled down, the problem again went away.

I was hoping to see if anyone had experienced a similar problem to this or had any suggestions as to what it could be. It seems that the car seems to start acting up in extreme heat conditions (above 100 degrees). I apologize for the lengthly story, but figured more details are better than less.

Thanks,

Brian

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[TobyB]

Is there a filter in front of the pump?

If not, junk in the tank might be plugging up the pump.

If so, junk in the tank might be plugging up the filter

and starving it for fuel, leading to a premature death.

Another thought- if it's getting air into itself, even just a bit,

that can kill 'em. They need the fuel to keep themselves

lubed and cool.

A final thought-

<>

it's easy to add a tiny 'bleed back'

to the tank for the pump so that it can circulate a bit of fuel.

It can be a small 1/32" restrictor with a tee after the pump output-

on my cars, they all have vapor returns on the tanks.

That way, any air gets bled out, and the pump can circulate some

relatively cool fuel to keep itself happy.

Best, of course, is to recirc it from the enging bay- but that's a lot

harder to do, and probably won't matter to your pump.

<>

hth

t

[74AlpinaTii]

I thought it could be something in the tank clogging the pump, but the problem only occurs when the temperature is extremely hot.

Couple other notes:

1. There is not any pressure inside of the tank when opening the gas cap

2. When it has acted up, there is more than 1/2 tank of fuel in the tank.

[markmac]

In the E-Book I am currently putting together on my 02 ALPINA Grp. 2 race car I have a small section on the custom fabricated VST (Vapor Separator Tank). While it could be an old fuel pump, junk in your fuel tank, filter or other, sounds to me like it has more to do with the weather (high heat). Back to the VST, ....."for the injection system to meter the fuel repeatabley, the mchanical pump must deliver a precise amount of fuel at any given RPM. In many installations, the pump delivers varying amounts of fuel, sometimes very erratically due to plumbing of the vehicle, or operation at high altitude and or hot conditions. The main problem is caused by pump inlet cavitation, a form of "vapor lock". Because gasoline almost boils at room temperature, if the temperature of the fuel is raised or a vacuum is pulled on it, it will start to boil....as the pump tries to draw fuel into its inlet, it pulls a slight vacuum on the fuel. The higher the pump speed the higher the vacuum. The vacuum combined with hot temperatures causes at least some of the fuel in the inlet hose to flash to vapor (boil) ..... pump cavitation........just a thought.

http://historicracingbmw.blogspot.com/

[BillWilliams]

dump any idea of replacing the original pump with a rebuilt pump or paying crazy money for a new old technology pump.

http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,viewtopic/t,298095/

[jgerock]

Here are some suggestions:

I recommend you connect a fuel pressure gauge to see what pressure you are getting from the pump.

When the fuel pump was replaced (twice!), did the mechanic inspect the expansion jar/canister for rust/leaks?

My rusty/leaking canister

When were the fuel lines last replaced on your car? If there is a leak on the vacuum-side of the tii system, then the pump will not pull enough fuel to satisfy the engine.

There is a check valve on the outlet of the fuel pump. I've been told replacement tii fuel pumps don't include this fitting (so you need to re-install your old one on the new pump).

There is a small cone-shaped filter on the inlet of the pump. Was this cleaned when the pumps were changed? IIRC, this filter is NLA.

Screen location on inlet of the pump

My dirty screen

Is the in-tank mesh screen clean?

Your problem may be the pressure maintenance valve on the back of the KF pump. This returns excessive fuel back to the pickup fitting on top of the fuel tank.

Good luck and keep us posted.

[dubois]

I don't think it has anything to do with your problem, but since a couple pumps have had the same problem, it may be worth checking the fuel pump ground, which is inside the trunk by the metal divider (under the trim panels). Any performance problems can be augmented if the pump is not getting the right juice - that is my thinking...

[Guest Anonymous]

front of the car as I believe it is a vapor lock problem. Make sure the rubber fuel lines and hard metal lines were not rerouted near a heat source.

shermanmartinez@hotmail.com

[jgerock]

front of the car as I believe it is a vapor lock problem. Make sure the rubber fuel lines and hard metal lines were not rerouted near a heat source.

shermanmartinez@hotmail.com

Good suggestion Sherman. Wonder if the car still has the original fuel filter bracket on the front bulkhead or if the filter is touching the radiator.