Thread: 4BD1 Priming pump

Yes, it is an o'ring on the pump primer and they are prone to leaking past it when priming when they are in need of replacement. Hard starting sounds like your pump is sucking air somewhere and it is possibly the primer pump. If it is the screw in type, make sure that it is fully screwed down when pushed right in. New ones are relatively cheap to buy and it is hardly worth the effort of replacing the o'ring.

Originally Posted by fid-def

Any diagram woiuld be appreciated.

thanks Bearman - yep definitely screwed right down. I'll pull it out on the weekend an check it. Thanks for the quick response.

Throw it away and fit one of these:


I did years ago, no leaks, pumps better and doesn't need screwed down when not in use.

Hi Dougal - that looks pretty neat - where an I get one?

Any injection shop should be able to get them, otherwise google "bosch primer pump" to find sellers like this:
Primer Pump, New Style - BOSCH [0000908850] - $22.50 : Eurotruck Importers, Your source for Mercedes-Benz off-road vehicles and spare parts!

I bought mine off a guy who mail-ordered a pair, so I don't know exactly where it came from.

I just got one of those bosch primers due to leaky original one( it would prime but leaked fuel everywhere in the process) but the new bosch one i can't get to prime properly - pumped it many times but no fuel coming out of bleeder on top of filter. I assume you leave the plunger/spring in base of fuel pump before screwing it down. Perhaps the spring needs replacing? Any ideas?

Originally Posted by mattmac

I just got one of those bosch primers

Did you get the bosch part no 2 447 222 126? I got that one today, but it looks to be a smaller diameter than the original push/screw primer pump.

Edit: I found a reference to this part number in the Isuzu forum, so I'm hoping that it's just my eyes deceiving me.