Bosch HP fuel pump mystery
Discussion
Suffered a "failure to proceed" a while ago and thought nothing of it until yesterday
It was a warm day and I'd just set off after a short visit to a motor factor. The traffic lights changed to green and I was aware of a lack of power so decided to pull onto the nice wide grass verge and investigate.
In the past I've experienced LP fuel pump failure so expected the same.
The bowl filter before the swirl pot was full and I could hear fuel returning to the tank so that part was OK. The missing bit was the HP pump pressurising the rail for a few seconds before cranking.
The pump relay was energising and it's fuse was OK.
I realised that the HP pump had died so replaced it with the spare I carry.
The engine started and ran normally.
I kept the "dead" Bosch pump to do a post-mortem on (I regret not doing this on the LP pump which failed).
A bit of spare time on Saturday I noticed the pump and decided to pop some power on it expecting nothing but it whirred into life.
Anyone else found this?
Any suggestions as to what I missed in my roadside diagnosis?
It was a warm day and I'd just set off after a short visit to a motor factor. The traffic lights changed to green and I was aware of a lack of power so decided to pull onto the nice wide grass verge and investigate.
In the past I've experienced LP fuel pump failure so expected the same.
The bowl filter before the swirl pot was full and I could hear fuel returning to the tank so that part was OK. The missing bit was the HP pump pressurising the rail for a few seconds before cranking.
The pump relay was energising and it's fuse was OK.
I realised that the HP pump had died so replaced it with the spare I carry.
The engine started and ran normally.
I kept the "dead" Bosch pump to do a post-mortem on (I regret not doing this on the LP pump which failed).
A bit of spare time on Saturday I noticed the pump and decided to pop some power on it expecting nothing but it whirred into life.
Anyone else found this?
Any suggestions as to what I missed in my roadside diagnosis?
GreenV8S said:
Maybe heat related, or perhaps it had simply jammed on some debris. If that was me I wouldn't be interested in putting a known unreliable pump back on the car so I'd just shrug and bin it.
I wonderered whether it was heat-related. I'll take it to pieces and see what's wrong.If you had an oscilloscope and current clamp you can diagnose it properly by looking for ‘dead sectors’ as the motor rotates.
The brilliant Eric O old South Main Auto shows this on a heater blower motor here
https://www.youtube.com/watch?v=PCArn6mm2HA
The brilliant Eric O old South Main Auto shows this on a heater blower motor here
https://www.youtube.com/watch?v=PCArn6mm2HA
100SRV said:
Suffered a "failure to proceed" a while ago and thought nothing of it until yesterday
It was a warm day and I'd just set off after a short visit to a motor factor. The traffic lights changed to green and I was aware of a lack of power so decided to pull onto the nice wide grass verge and investigate.
In the past I've experienced LP fuel pump failure so expected the same.
The bowl filter before the swirl pot was full and I could hear fuel returning to the tank so that part was OK. The missing bit was the HP pump pressurising the rail for a few seconds before cranking.
The pump relay was energising and it's fuse was OK.
I realised that the HP pump had died so replaced it with the spare I carry.
The engine started and ran normally.
I kept the "dead" Bosch pump to do a post-mortem on (I regret not doing this on the LP pump which failed).
A bit of spare time on Saturday I noticed the pump and decided to pop some power on it expecting nothing but it whirred into life.
Anyone else found this?
Any suggestions as to what I missed in my roadside diagnosis?
So you are 100% roadside the pump had good power and ground ? A current measurement at the time would have been good. Something jammed in the pump would likely show a high current, vs no current indicating some sort of open circuit.It was a warm day and I'd just set off after a short visit to a motor factor. The traffic lights changed to green and I was aware of a lack of power so decided to pull onto the nice wide grass verge and investigate.
In the past I've experienced LP fuel pump failure so expected the same.
The bowl filter before the swirl pot was full and I could hear fuel returning to the tank so that part was OK. The missing bit was the HP pump pressurising the rail for a few seconds before cranking.
The pump relay was energising and it's fuse was OK.
I realised that the HP pump had died so replaced it with the spare I carry.
The engine started and ran normally.
I kept the "dead" Bosch pump to do a post-mortem on (I regret not doing this on the LP pump which failed).
A bit of spare time on Saturday I noticed the pump and decided to pop some power on it expecting nothing but it whirred into life.
Anyone else found this?
Any suggestions as to what I missed in my roadside diagnosis?
You could break out a scope and do as suggested with a current clamp and voltage and start doing some testing....or you could cut it open to see what you find.
Only Bosch pump I ever killed was from a tiny piece of solder inside the tank, that found it's way into the entry roller cell section of the pump causing it to jam.
Entirely my own fault, and lack of suitable filtration for the pump.
Bosch pumps are generally very reliable, but due to that roller cell design, I would say very intolerant of dirt. Most of the more modern efi pumps are a turbo vane design, so would be a little more tolerant.
Either way, they should all have a good clean gravity fed uninterrupted supply of fuel at all times at a minimum.
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