Diesel Kiki: Can't find the primary fuel filter

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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karotto
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Joined:14 years ago
Location:Southern Australia
Diesel Kiki: Can't find the primary fuel filter

#1

Post by karotto » 13 years ago

Hi there,
I had another post regarding a problem I had (see below) and the guy recommended changing the primary fuel filter. THERE IS NOT PRIMARY FUEL FILTER. At least I can't find it. The fuel line goes directly from under the car to the fuel pump, then out of the fuel pump then into the main fuel filter and back into the fuel pump. I am stumper. Any suggestions are very much appreciated. Ken
Datsun SG720 2WD ute (pick up) with SD22 diesel engine

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asavage
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#2

Post by asavage » 13 years ago

I did not say "Primary filter". I said "filters". If you read the entire thread, down lower the thread talks about the Secondary filter as well. The primary filter rarely plugs, because it uses a very coarse screen that functions to keep large things out of the lift pump.

The secondary filter plugs easily, if you get a batch of dirty fuel, because it filters to a fine degree.

You may also want to take a look at a nicely colored schematic of the low pressure fuel system that Philip did.

You can easily diagnose fuel system delivery problems using a low pressure gauge and hose tee. Picture of one is here.


Read an amusing tale of a paper towel in the fuel tank.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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philip
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Re: Kiki: Can't find the primary fuel filter

#3

Post by philip » 13 years ago

karotto wrote:Hi there,
I had another post regarding a problem I had (see below) and the guy recommended changing the primary fuel filter. THERE IS NOT PRIMARY FUEL FILTER. _SNIP_ PS: not sure if it makes a difference but I am in Australia
You have a 1984 720 truck with SD22(?) in Australia. Your engine could be two completely different injection pumps. Also, the engine could be SD23 or SD25.

1) Bosch inline injection pump
Image
2) Bosch rotary injection pump
Image
Which system is on your engine?
Last edited by philip 13 years ago, edited 6 times in total.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

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asavage
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Re: Kiki: Can't find the primary fuel filter

#4

Post by asavage » 13 years ago

karotto wrote:The fuel line goes directly from under the car to the fuel pump, then out of the fuel pump then into the main fuel filter and back into the fuel pump.
@Philip: Sounds like an inline IP with external lift pump attached, just like ours.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

karotto
Posts:10
Joined:14 years ago
Location:Southern Australia

mine is the #1

#5

Post by karotto » 13 years ago

Mine is the #1 picture. The Bosch (kiki) inline pump. So there is no primary filter? I did change the main fuel filter only a few months ago so it seems odd that it should clog that quickly. I'll change it today, bleed the system and the hopefully be up and running again.
Thanks alot. Ken
Datsun SG720 2WD ute (pick up) with SD22 diesel engine

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asavage
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Re: mine is the #1

#6

Post by asavage » 13 years ago

karotto wrote:Mine is the #1 picture. The Bosch (kiki) inline pump. So there is no primary filter?
If your Ute follows the way Nissan did things with the 720 PUs we received in the States, then there is a Primary filter to protect the lift pump on the side of the IP. Perhaps somebody removed/bypassed it -- I would not be surprised, given what I have seen done to some of the 720s I've worked on!

Not having a FSM for you model, I guess you might ask either the Dealer or a parts house if they have a listing for fuel filters (plural) for your Ute. That would be a clue. The Primary filter is small, simple, and inexpensive. It also keeps the lift pump from dying at a remote, rural location where you might have to walk a long way to find spares.
I did change the main fuel filter only a few months ago . . .


I have had the filter clog in a single tank of contaminated fuel. Also, if there is any water in the fuel, bacteria will grow at the water/fuel interface, given the correct temperature conditions, and will quickly cling to your filter media, rendering it nearly impermeable (clogged).

Use a gauge. It's a cheap investment and will pinpoint your fuel delivery problem. Why guess?
. . . hopefully be up and running again.
But what about the poor starting performance? Have you investigated the Glow Plugs thread I linked above? You may have high connections resistance, holes in the end of one or more GPs, or a failing battery. All those scenarios have been outlined in the thread. Excessive cranking only serves to wear out your expensive starting motor.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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