My 2500 has failed to start after a couple of months of inactivity. Cranking with the outlet fuel hose in a jar revealed no fuel delivery. I can pull fuel from the tank with a vacuum pump so no issues from tank to pump. Pump removed, diaphragm looks ok so primed it with fuel and managed manually to get it pumping. Back on the engine and cranking it over it is delivering fuel but not what I'd expect. What would be the expected delivery volume after say ten seconds cranking ?. It could be wear on the pump lever or pushrod as I seem to achieve a healthier pump rate on the bench operating it manually. It appears to be the original Pierburg pump but on 60k miles I wouldn't expect excessive mechanical wear. I can only find the rate in gallons per hour so an idea of a realistic rate from turning it over would be a good start.
Mechanical Fuel Pump Testing
- Thread starter E3_UK
- Start date
a check valve in the fuel line may help
Even pulling gas with a vacuum pump doesn’t mean your fuel hoses are good. Even tiny air leaks from an old hose can not be overcome by the mechanical pump. Replace ALL fuel hoses, even ones in the trunk. Buy a check valve as Steve suggests and mount it before the pump. Your fuel in the carb bowls will evaporate in two months so you're starting with an empty carb which can take up to sixty seconds of cranking to refill.
After you do as Chris suggests...Disconnect the hose from the pump to the carbs. Hold it into a can/jar. Have a helper crank the engine (with the coil disconnected). You should see a pretty good squirt with every revolution of the cam (every other revolution of the engine).
It doesn't take much gas to run the engine even at full throttle and load. At 60 MPH and 15 MPG, you are using 4 gallons an hour or .06 gallons per minute. Or about 1/8 cup in 10 seconds. If a fuel pump puts our too much pressure, it will blow past the carb needle and seat and flood the engine.
It doesn't take much gas to run the engine even at full throttle and load. At 60 MPH and 15 MPG, you are using 4 gallons an hour or .06 gallons per minute. Or about 1/8 cup in 10 seconds. If a fuel pump puts our too much pressure, it will blow past the carb needle and seat and flood the engine.
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Thanks folks. I replaced the fuel lines last year so no issues there although i will check all connections. Operating the pump manually on the car gives a healthy squirt however cranking on the car much less so so it may be mechanical wear reducing pump stroke. However it hasn't just worn sitting in the garage and ran beautifully last year so perhaps once running it may be ok. I'll fill the carbs first then hook up the pump and get it running. The check valve is a good idea so I'll fit one as suggested.
The old trick for pump stroke wear is to sand down some of the bakelite insulator accordingly
Yes i had considered that Steve. If i can't achieve satisfactory delivery i may just replace the pump, assuming the wear isn't on the pushrod or camshaft. I guess modifying the spacer dials out the cumulative wear so might be a better option.
So the pump still wasn't delivering when cranking, so I removed it again and filled the carbs operating the pump manually. Pump back on and it fired up but very rough. Disconnected shut off valve on each carb proving it was running on both but very uneven. After about ten minutes it smoothed out to a nice idle, both chokes were fully open about five minutes before it smoothed out. Could it be that the pump is struggling to fill the carbs so runs weak but eventually it catches up allowing the correct mixture ?. I've yet to see a healthy delivery of fuel when cranking with the pump outlet into a jar. I'll try starting it again tomorrow after 24 hours to see if it's any different.
I had this same issue. It looked good when pumping manually, looked good when cranking and emptying into a jar. I punted and got a new pump and all is well. There is a Blog by someone called Leslie Wong, he did a nice job replacing the mechanical pump with an electric pump and has a decent write up on it if interested.
https://www.lesliewong.us/2007/09/07/bmw-bavaria-carter-4070-fuel-pump/
https://www.lesliewong.us/2007/09/07/bmw-bavaria-carter-4070-fuel-pump/
Thanks for this. It started after 24 hours but again very slow and uneven idle that slowly improved over a ten minute period then ran perfectly. I've ordered a new pump anyway. The evidence points to the pump not delivering sufficient fuel to maintain float chamber capacity but I'm not 100% certain as it does eventually run well after ten minutes. Both chokes are operating correctly.
Have you tried driving it (once the idle stabilizes)? I would think if it drives normally under all loads and conditions that the fuel pump is OK. If at some point driving it, it sounds like it is running out of gas then the fuel pump is suspect.
It's off the road for the winter so no chance to drive it. However the fact that the pump delivers next to nothing when cranking into a jar should be enough to suspect the pump. It hasn't just failed suddenly obviously, and it was driving perfectly last summer so perhaps it does drive fine once the pump manages to fill both carbs but some day it might not and leave me stranded so I'd prefer to just eliminate it from the equation.
You also need to ensure your choke is working OK. Go to the technical part of this site, look at the choke settings when cold, ensure they change with warm up. There is also a little aluminum covered samll box on the side of the carb, this is basically a cold start valve. I believe you can remove it and test it with warm water similar to a thermostat. This is all provided you have the original Zeniths. ...and put in a check valve. They are like 5 bucks and take about 2 min to put in.
Original Zeniths. Both chokes operate correctly as the engine warms, both flaps open at the,same rate. Even with both chokes fully open it still runs like a dog until gradually it starts to pick up to a smooth idle. I'm not sure mine have the cold start valves I'd need to check. Was this standard for all markets ?. This is a UK car. Noted about the nrv, I'll fit one soon as.
Thanks for all of the input, much appreciated. There may be another underlying fault but i need to eliminate the pump first.
Thanks for all of the input, much appreciated. There may be another underlying fault but i need to eliminate the pump first.
dj_efk
Well-Known Member
If I were you I'd get another pump as that will most likely solve your issue, I see them from time to time on ebay - Here's one I found without even trying (I would look up the part number and search for that, also translate to German and look on ebay.de etc. etc.)
PIERBURG Fuel Pump Mechanical 7.02242.19.0 - Discount Car Parts 4028977554780 | eBay
Outer/Inner Mirror. Outer Thread 2 [mm]. Outer Thread 1 [mm]. Outer Thread [mm]. Outer Length [mm]. Optical Impression. For cylinder. Opening Temperature [°C].
www.ebay.co.uk
The pumps are inexpensive enough that replacing it is probably a good idea. That doesn't eliminate cam lobe and push rod wear, but with only 60,000 miles on the car, that shouldn't be an issue,
Today I'm going to try to find time to do your experiment of cranking fuel pump volume on my good running carbed 3.0. Maybe someone else can do the same to give you a couple of other data points to compare yours to.
Today I'm going to try to find time to do your experiment of cranking fuel pump volume on my good running carbed 3.0. Maybe someone else can do the same to give you a couple of other data points to compare yours to.
may want to do a search here on the newer Pierburgs, reports are that some are junk
If I were you I'd get another pump as that will most likely solve your issue, I see them from time to time on ebay - Here's one I found without even trying (I would look up the part number and search for that, also translate to German and look on ebay.de etc. etc.)
PIERBURG Fuel Pump Mechanical 7.02242.19.0 - Discount Car Parts 4028977554780 | eBay
Outer/Inner Mirror. Outer Thread 2 [mm]. Outer Thread 1 [mm]. Outer Thread [mm]. Outer Length [mm]. Optical Impression. For cylinder. Opening Temperature [°C].www.ebay.co.uk
I have read that a while ago. I have a fuel pump that seems to be a bit leaky. Are there rebuild kits available? I was contemplating replacing it with an electric one, especially as I have an early M30 with the wide coolant passages and if the head is cracked, I'll put in the later head I have that doesn't have a mechanical pump fitting.
Some are rebuildable, depends on the model, I redid one once and yes a kit was available.
Here's a video of mine. 1972 Bavaria 3.0, original pump.
It delivered about 2 ounces (60 ML) in a little less than 10 seconds.
It delivered about 2 ounces (60 ML) in a little less than 10 seconds.