P38A Adding D4 to early diesel fuse boxes to operate the lift pump while cranking.

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Datatek

Well-Known Member
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Location
Near Poitiers SW France
This is for RangeRoller dt and anyone else who thinks it may help with starting the diesel.

I had a spare hour yesterday while testing a bit of kit I repaired so I had a look at adding a diode to an early fuse box to operate the lift pump whilst cranking as is the case with later fuse boxes. Please bear in mind that there are several versions of the fuse box, so testing per #5 is important.

Items needed to do the mod, Philips screw driver, Solder, soldering iron, file and a 1N4005 diode. I can supply the diode if required FOC.

There are 7 photo's.
#1 Shows schematic with D4 as fitted on later fuse boxes.

#2 Shows schematic with D4 missing on the early fuse box.

#3 Shows the relays that need to be removed to access the fixing screws including Relay
16, the hardest part is getting the assembly out of the housing. I use 2 thin metal strips
pushed in on the long sides to hold the latches back, then the short sides can be held
back with fingers while the PCB's are eased out.

#4 Shows where a wire needs to be inserted in the Relay 16 socket for testing.

#5 With a meter on Ohms connect one lead to the test wire and with the other verify where
P1 C575 is. (Relay 16 pin 5). On this 1996 fuse box it is at the position marked by 2 red triangles.
Also shown are the 2 existing diodes D2 & D3.

#6 Shows where to file a small groove for the new diode wire, this provides support and
makes it easier to solder to the pin.

#7 Shows the new diode fitted. Make sure you get the diode the right way round, white
band end goes to the existing diode. A spot of silicone or super glue can be used to
ensure the diode is secure.
 

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I have to admit it’s good work. Things change but why? Is this a LR bodge on later models?

J
 
I have to admit it’s good work. Things change but why? Is this a LR bodge on later models?

J

When the engine has been stopped a while warm and the internal injection pump pressure has bled away, an attempt to provide a little internal pressure to aid fuel flow into the injection piston.
 
This is for RangeRoller dt and anyone else who thinks it may help with starting the diesel.

I had a spare hour yesterday while testing a bit of kit I repaired so I had a look at adding a diode to an early fuse box to operate the lift pump whilst cranking as is the case with later fuse boxes. Please bear in mind that there are several versions of the fuse box, so testing per #5 is important.

Items needed to do the mod, Philips screw driver, Solder, soldering iron, file and a 1N4005 diode. I can supply the diode if required FOC.

There are 7 photo's.
#1 Shows schematic with D4 as fitted on later fuse boxes.

#2 Shows schematic with D4 missing on the early fuse box.

#3 Shows the relays that need to be removed to access the fixing screws including Relay
16, the hardest part is getting the assembly out of the housing. I use 2 thin metal strips
pushed in on the long sides to hold the latches back, then the short sides can be held
back with fingers while the PCB's are eased out.

#4 Shows where a wire needs to be inserted in the Relay 16 socket for testing.

#5 With a meter on Ohms connect one lead to the test wire and with the other verify where
P1 C575 is. (Relay 16 pin 5). On this 1996 fuse box it is at the position marked by 2 red triangles.
Also shown are the 2 existing diodes D2 & D3.

#6 Shows where to file a small groove for the new diode wire, this provides support and
makes it easier to solder to the pin.

#7 Shows the new diode fitted. Make sure you get the diode the right way round, white
band end goes to the existing diode. A spot of silicone or super glue can be used to
ensure the diode is secure.
Would you really trust @RangeRoller dt with his fuse box and a soldering iron Keith?:eek::D:D
 
Sorry if this is a stupid question but can i do this on a P reg diesel p38 as mine seems to take quite a bit of cranking before it starts?

I know the pump works as i've been investigating this for a while but electrics isn’t my strong point

I assumed mine had a problem because i thought it should run the pump with the glow plugs or whilst cranking and it isn’t?
 
Your car runs lift pump with glows or when engine is running but not whilst cranking

It runs the pump when engine running but not with the glows so guess i have a problem?

Any ideas what it may be as i’ve checked relays and fuses etc?

Was going to wire in a switch to the dash so i can operate the pump when i turn the ignition on

Many thanks
 
It runs the pump when engine running but not with the glows so guess i have a problem?

Any ideas what it may be as i’ve checked relays and fuses etc?

Was going to wire in a switch to the dash so i can operate the pump when i turn the ignition on

Many thanks
It runs the pump when engine running but not with the glows so guess i have a problem?

Any ideas what it may be as i’ve checked relays and fuses etc?

Was going to wire in a switch to the dash so i can operate the pump when i turn the ignition on

Many thanks
Look at the glow relay in the ECU box lift pump is powered from glow number 6 so your glows may not be working either.
 
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