| Author | Message | |||
     Thomas J. Bueld New User Username: thomas_j_bueld Post Number: 8 Registered: 04-2019 |
I have an 84 Spur, US - Config. K-Jetronic. So it has an Engine Running Sensor which controls the fuel pump. The fuel pump receives current from two sides : during cranking it receives 12V direct from the battery (not fuse protected, earthed by the lamp test). When the engine is running the respective relay (positioned R/H trunk) gives way to supply the pump through the logic of the Engine Running Sensor. One day the engine did not start. I assumed that it was due lack of fuel pressure. I bridged the relay to force the fuel pump to run what it did. The engine started immediately. But : the fuel pump was very noisy when bridged. Cutting the bridge after (while engine was running) the pump went smooth and silent while it was obviously receiving power through the Engine Running sensor - which I was able to confirm by a Multimeter. My question is : Does the Engine Running Sensor modulate Fuel Pump Output by Voltage depending on demand ? If not why this difference in noise ? | |||
| Robert J. Sprauer Grand Master Username: wraithman Post Number: 443 Registered: 11-2017 |
No. Fuel pump must deliver constant pressure and is not voltage regulated. There must be constant fuel pressure to the fuel distributor head and is released by a lever connected to the airflap in the airbox. | |||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2168 Registered: 09-2004 |
Ref noise could be a difference in supplied current or pump drag. Normal pump current 6.5-8.5 amps. | |||
| Thomas J. Bueld New User Username: thomas_j_bueld Post Number: 9 Registered: 04-2019 |
Thank you ! Yes it is my basic understanding that the fuel pump delivers constant pressure and the amount of fuel is controlled by a piston in the distributor head which opens the return pass. Also, the engine would stop without the pump running. It sucks 8.5 Amps in the "cranking" setup. Will need to find a way to measure Amps while in the "running" mode. However, the mystery remains that the pump's noise in the latter mode is almost zero. | |||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2169 Registered: 09-2004 |
One query, when the engine failed to start, was it from cold or hot? | |||
| Thomas J. Bueld New User Username: thomas_j_bueld Post Number: 10 Registered: 04-2019 |
Was cold, and some weeks not driven at all. - Now I found out that the pump is not supplied via the ERS- path once un-bridged from cranking mode (Volts=0). To Robert : That means that the engine will run even without the fuel pump running. Strange. No wonder that the pump is so quiet as described above..
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| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2170 Registered: 09-2004 |
IMO the pump will not run for so long ie until the accumulator maintaining the line pressure has dropped. If the pump has excessive generated noise when the pump is known to be serviceable, flow, pressure test and current draw etc then the accumulator should be changed. | |||
| Thomas J. Bueld New User Username: thomas_j_bueld Post Number: 11 Registered: 04-2019 |
I learned now that Crewe installed a fuel pressure damper downstream the pump output in the year 1985 to reduce cavitation noise. Mine is 1984 so I don't have that. I can live with it. Anyhow my pump is not running at all - only when bridging the Engine Running Sensor by means of the fuel pump relay as described. The problem now seems to be the Engine Running Sensor itself. I checked all cables and sensors involved, all ok. The market is asking for 300 to 900 € for this shabby piece. No way for me. Sure - bridging is not a good and lasting solution so I looked up alternates for this piece - and found (more than) one doing the same job for less than 30 €. It will let the pump run for 3 seconds (priming) after IGN on. If no running signal from ignition coil after this it will shut off the pump. If there is a running signal from the coil it will continue to operate. This will fulfill all safety requirements the Engine Running sensor was invented for. I will post further information about wiring and replacement relay for those who prefer a nice holiday weekend, candle light dinner with his/her beauty instead of buying mystery electric half size of a cigarette box for the same money :-) |
