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#1
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tapping fuel pump, it works!
I just got back home from helping my friend get his car running again. The car had good spark. Spraying starter fluid allowed the engine to catch for a second. next i went to the fuel pump and had my friend turn the ignition on and off. the pump made no noise and even with my hand on it i could not feel the pump running. I tapped the pump and presto the car started up fine but still no noise. Is the lack of noise odd?
Every time you try to start the car it requires some tapping on the pump to get the engine running. Then the engine runs fine untill..you try to start it again, But even when it does catches the pump makes no noticeable noise. I suspect the pump must be replaced (the wire connections to the pump are held down tight as they should). Any other tests should be performed before replacing the pump?
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1972 450SL 1982 300D Turbo |
#2
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Does it continue to run after you depress the gas pedal? When my fuel pump died, tapping it with a mallet got it to run, but the second I gave it some gas it died on me.
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#3
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It runs fine but once you turn off the car it requires tapping on the ppump to get it to start again (and then it runs fine). We did this cycling almost 10 times.
1. Car won't start 2. tap the pump 3. car starts (and runs fine) 4. turn off the car 5. back to #1 Is something indirectly related to the pump causing this? I would think the car could start again. Somehow turning off the car triggers something which is remedied by tapping on the pump..
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1972 450SL 1982 300D Turbo |
#4
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Flushing fuel pump(s)
I was able to "nurse" a few thousand miles out of a bad fuel pump by flushing it with kerosene (or diesel fuel). Remove the pump from the assembly. Place in a vice with inlet at the bottom - outlet at the top. Place a bucket under the inlet of the pump and pour diesel fuel or kerosene in the inlet. Use a power source ie: battery to connect to fuel pump - negative to positive, positive to negative. Do this several times until the pump flushes clean.
DO NOT USE GASOLINE!! ANY SPARK WILL CAUSE AN EXPLOSION/FIRE AND YOU WILL BE HURT!! My pumps spat out all kinds of crud. The tollerances of these pumps are so close that any amount of sediment will eventually cause the pumps to "lock up". Unless you are very sure of yourself and very cautious -PLEASE do not do this. If you are wary of the proceedure then, by all means, purchase a new or used fuel pump!! |
#5
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pumps
The car needs a new pump. At about $215 for a brand new Bosch pump, the same as the original, bought online here such as from FastLane (see the link above), for most people it won't possibly be worth it to take the risk of getting stuck somewhere. If you search under my threads you'll see some DIY hint I have for changing the pump on my car. It's a relatively easy job but it is dangerous (gasoline) and very messy. A shop who does it for you shouldn't charge much to do the job.
If you are going to go to the trouble of taking it out and trying to dump kerosene down it/etc, I would personally go ahead and change it. If you go back there too many times (taking it on/off) you increase the risk of damaging other hoses like the fuel line to the tank which if you aren't careful with will crack so don't clamp it anyway. Again, I'd just put a new one in there, you have every indication it needs to be replaced. They are a common maintenance item on these cars at 100K+ miles |
#6
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The reason I did this with mine was (1) it has two fuel pumps and only the lower one was going bad and (2) I didn't have the money to buy both new pumps at the time (no sense in replacing one when the other is the same age and has the same mileage). Yes, I agree - it is very dangerous and just as easy to replace but if you are in between paychecks and living on ramen noodles this will do in a pinch .
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#7
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definitely understand
I was just pointing it out in case someone didn't know what they cost. I agree, if you're on a very very tight budget, it's great to know tips like yours to keep things going.
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#8
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there is almost 10gallons in the tank. We also plan on replacing the old fuel lines, filter and maybe the tank strainer. I'll capture the fuel into clean containers. Is it too risky (contaminated) to reuse the fuel if you pour it back in avoiding any sediment from the bottom of the container? What do repair shops do, reuse the fuel or dispose of it at a haz mat site?
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1972 450SL 1982 300D Turbo |
#9
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Wear on the amature bushings causes it to get a little out of alignment, which increases starting torque above the amount that the windings can provide. The shock caused by tapping the pump will move the amature enough for the windings to overcome static friction and start the pump.
Consider the "tap to start" as a emergency procedure to get you home. If this happens more than once over a few starts, it's time for a new pump. Duke |
#10
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You might get by for a few weeks by whacking the pump, but the thing is on it's way out. Great trick for getting home to safety.
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1986 300E 5-Speed 240k mi. |
#11
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OK OK. We all now know that the pump is bad. Let's move on.
there is almost 10gallons in the tank. We also plan on replacing the old fuel lines, filter and maybe the tank strainer. I'll capture the fuel into clean containers. Is it too risky (contaminated) to reuse the fuel if you pour it back in avoiding any sediment from the bottom of the container? What do repair shops do, reuse the fuel or dispose of it at a haz mat site? do you recommend changing the strainer too?
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1972 450SL 1982 300D Turbo |
#12
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I reuse the fuel. Assuming you transfer fuel into 5 gallon portable tanks and it sits there for a while, pour just the last 1/2 gallon or so of each into a clear container to see if there is any water or debris at the bottom. If so, let it settle out, and slowly pour the good stuff off the top.
I'd replace the strainer at the bottom of the tank if it looks like it can be removed safely. Mine was way fused on there, and I gave up at risk of breaking it . Can't be using sparking grinding tools on tank fittings.
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1986 300E 5-Speed 240k mi. |
#13
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Thanks csnow,
I'll try to take the strainer out and clean it since the mesh screen is visible once the strainer is pulled from the tank. The strainer only traps macroscopic particles so cleaning it should suffice. I will get a spare Oring to reinstall. The socket size to remove the strainer is huge and it doesn't line up with the access hole so it will probably be tricky to remove and i may revert to what you did, just leaving it in place.
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1972 450SL 1982 300D Turbo |
#14
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right rear humming noise on 300e 1988....only happens at startup...
is this normal, or is it going? |
#15
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A Cro-Magnon man and possibly a Neanderthal would have decided after smacking the fuel pump a half dozen times that a new fuel pump was in order. I suggest you get rid of the car and buy a car you can afford.
peter
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