UNDER PLENUM FUEL HOSE REPLACEMENT PROCEDURE
This write-up describes how to remove and replaces that “bastard” fuel hose which
connects the two halves of the fuel rail system and is located beneath the throttle control
linkage. With this procedure neither the plenum nor the throttle bodies needs to be
removed! I’ll admit, if my Z didn’t have coolant lines connected to the Throttle Bodies –
I might have tried removing the TB's (or just the right TB) to access this hose!
However to my surprise...
This job is a lot easier to do than you might think at first glance! It’s about as hard as
changing out the PCV valve and hose on the passenger side of the engine. A little bit of
work, some lower backaches from bending, but no big deal to accomplish. If you follow
these instructions, the project should take a little over 1 hour to complete (not including
Here’s a summary on how it’s done, detailed instructions and pictures are shown below:
- Follow safety procedures to release pressure in fuel system & disconnect battery
- Remove mid-engine plastic NISSAN throttle cable cover
- Use cord/wire to hold throttle linkage pulleys into full open position.
- Loosen and slide off fuel line clamps
- Use Exacto knife to slice hose ends and pull off “bastard” hose.
- Hose is removed via opening under throttle linkage pulleys
- Remove old clamps, slide new clamps on fuel rail ends
- Install new hose on fuel rail ends and re-clamp both sides
Remove the plastic NISSAN throttle linkage cover – there are 4 metric hex head bolts
that hold it in-place. You’ll need a 5mm hex key wrench to do this – be careful not to
drop the bolts in the engine bay! This cover must to come off in order to access the
area where the fuel hose is located!
THIS NEXT STEP IS MOST CRITICAL!!!! REALLY (really) inspect the fuel rail
hose clamps looking from all sides and angles. Can the hose clamp screws be accessed
with a long screwdriver? On my Z, both screw heads pointed straight up to the sky.
One screw could be undone with the screwdriver held on a 35 degree angle from behind
the pulley spring and the other by inserting the screwdriver down between the throttle
body (TB) rod and TB front support bracket --- all was good!!!!
If for some reason all you can access is the bottom of the hose clamp screws – all may
not be lost!!! (see step-by-step instructions for advice). If you believe the fuel clamps
can’t be removed, GO NO FURTHER – this replacement procedure can’t be used!!!
Gather the following materials:
Hose: 10 inches of 8mm metric sized fuel hose rated for fuel injection systems (order
from COZ Click Here ). You must use Fuel Injector Rated high-pressure hose!!! I
didn’t use 5/16 hose, since is has a slightly larger (outside) diameter than the 8mm type
and the installation area is already a tight fit!. Note: Later you’ll be cutting this hose
down to size, I found that the longer length helped greatly with the first part of the
A long (6-8 inch) screwdriver with a small flat head –runs about $7 in Home Depot.
Grind the sides of the head to a 45-degree angle. This made it very easy for me to undo
the OEM Phillips head hose clamps, even when going at them on an angle! You’ll need
the reach of the longer blade for few other things on this project too!
Exacto knife and #16 type blade. This blade made slicing the fuel hose in those tight
spots nice and sweet! I’m sure other blades will work fine too!
Long needle nosed pliers - regular or offset type if you have them
Clamps: Two (2) fuel hose type replacement clamps small enough to fit in this location.
My favorites are aircraft grade clamps that have embossed (not cut) clamp threads, rolled
band edges and are vibration resistant to loosening. You can find them at Wicks Aircraft
Supply , do a search for ABA Sure Seal type.
One foot of solid (not stranded) electrical wire (14 or 16 gauge is fine) – used as a job aid.
Three feet of thin cord or stiff wire - for tying back the throttle pulleys
Small quantity of petroleum jelly -good lubrication is your friend on this job!
Rags to clean up any gasoline still left in the fuel hose.
For those who don’t like to read much, here’s a picture with many of the prep items:
I’ll admit that a few (maybe many?) will think this write-up is “total overkill”. I’ve tried
to make these instructions detailed enough so that Z “wrenchers” of varied experience
levels would find them helpful.
OK, let’s get started…
1. SAFETY FIRST-- You’ll be in contact with gasoline and gasoline vapors. Very
dangerous stuff that requires proper safety precautions! Go access the TwinTurbo Z Fuel
Filter Replacement FAQ at www.ttzd.com/tech/fuelfiltertech.html ]">TTZ FAQ -- follow
the procedures for de-pressurizing the Z’s fuel line system (steps 1-3). This MUST be
done -- the fuel system is under high pressure (even with the car off) and must be
depressurized BEFORE you can start cutting or removing fuel line hoses!!! In
addition, make sure the car’s engine is COLD, disconnect the car’s battery and be sure to
have a proper fire safety equipment handy at all times.
2. By hand, open the passenger side throttle cable pulley (halfway) and slide out the
control cable - this pulley is the one used by the cruise control system. Insert a piece of
wire or cord into the cruise control pulley opening, then pull on it until the throttle rod
moves to its full open position and secure the tie-back cord. This gets BOTH throttle rod
pulleys up and out of the way, just be sure they are fully pulled back -- you’ll need the
room to work! Hint: I re-inserted the rear NISSAN plastic cover hold down bolt about
halfway and wrapped my tie-back wire around it.
3. Now it’s time to remove the hose clamps. Use the long bladed screwdriver to loosen-
up the old OEM clamps. Loosen them most of the way – but you don’t need to go as far
as letting the screws/nuts fall down onto the upper plenum.
If you can’t get the screwdriver on the screw head it still may be possible to loosen the
clamps, here’s some other clamp loosening procedures:
Alternate Method #1: Wrap some tape (or double backed tape) around the open jaw
ends of the needle nosed pliers and then use them to grip the screw threads and rotate
Alternate Method #2: If you have a direct shot at the bottom part of the clamp screw
thread , try epoxying a nut (taken from another clamp) onto the end of small diameter
(long but thin) plastic or wood dowel (don’t get glue into the nut threads ). Use the dowel
to screw the glued nut onto the screw end and then rotate the clamp screw open. – might
also want to spray everything with some WD-40 if the screw is a bit tight. Don’t forgot to
go back and replace the clamp where you “stole” the nut from !!!!
4. Use the long screwdriver to expand the clamps and then push them off the hose and
onto the fuel rail ends. Needle nosed pliers or another long screwdriver can help here too.
5. Grab your Exacto knife and use it to slice each of the old hose ends lengthwise
(towards center) about 1.5 inches. Once you start to see wet fuel – you’ve gone past the
fuel rail nipple ends. Use the screwdriver blade to pry on the hose incision and loosen the
hose ends more. If the hose ends are really “heat” fused to the rails – try prying on them
while spraying a little WD40 into the cuts.
6. Use the needle nosed pliers to reach down into throttle pulley “valley” and rotate the
hose 180 degrees (cuts will rotate to backside and away from you).
Pull on the passenger side hose end and tug it free from the fuel rail then carefully yank
the hose fully out (be careful – throttle pulleys have sharp edges, watch your fingers!)
GO TAKE A BREAK – HARD PART IS NOW DONE!!!!!!!
7. Use the needle nosed pliers to help remove the old hose clamp from the passenger side
fuel rail. The driver side clamp is just a little bit tougher, since space is tighter there. To
keep from losing it, I inserted the end of a piece of 1 foot long 14 gauge solid copper wire
into the fuel rail opening maybe 1 inch or so. I then used my screwdriver to slide/push the
clamp off the rail end and onto the guide wire for easy removal.
8. You’re almost ready to slide the new hose clamps onto the fuel rail ends, before doing
this there’s two things to consider:
VERY IMPORTANT #1 – make sure that the hose clamps are loosened up enough for
them to easily slip from the rail end and onto the new hose ends. Clamp should be
OPENED at least 20 % larger in diameter than the fuel hose – just eyeball it and run a
quick test by sliding them over the new fuel hose as a test.
VERY IMPORTANT #2 – make sure that you determine how the hose clamps screws
should be orientated so that they can be easily re-tightened on the hoses using tools. You
would hate to install both hose ends only to find that you couldn’t tighten one of the
clamps because it was positioned the wrong way!!!! On my Z, the passenger side
screw points at a 30 degree angle towards the back of the engine bay – socket gets to that
one by going in near the left side throttle pulley return spring. On the driver side – that
screw points out towards the front of the car. It is accessed through the opening that faces
the fan blade area.
Once you’ve figured these two things out – slide the new clamps onto the fuel rail ends.
If needed, use the 14-gauge helper wire to keep from dropping the driver side clamp into
the engine by mistake.
Hint: I’d also recommend marking (scribing) a reference line on the fuel rail ends –
basically MARKING where the fuel hose ends stops. It can sometimes be hard to know
where that is once the hose is partially in-place. If you look carefully you should be able
to see where the rail end starts to become dirty or less shiny – scratching a line at this
point makes the stop point easier to see. Since you’ll be cutting the hose after it’s
partially installed (in step #13) – getting it in the right position and then getting the right
final length for best fit is important.
9. Next, a little prep is needed on the new fuel hose. This hose needs to be cut down to
size after you’ve installed the driver side hose end. The old hose removed was probably 4
1/8 inches long. I made the replacement hose just a bit longer – around 4 1/4 inches. The
longer length allowed for possible “over-sliding” of the hose on the rail ends – once you
get them on, they sometimes can be hard to adjust back off. I was also glad the hose end
was a bit longer on the passenger side rail – it allowed me to position the clamp a bit
more in the direction of the rail end “bend” for better access by my 1/4 ratchet extension. .
I marked the hose cutting point using a Sharpie marker. Unfortunately, just handling the
hose while I installed it on the driver side rubbed that marking off. I think it’s better to
cut some “shallow” slits into the hose to mark the final cut point – the Exacto knife will
do this well!
10. Time to install the new hose – you’ll be doing the driver side first (it’s the harder of
the two). There are three things that will make the new hose fit easily over the fuel rail
- Lubricate the fuel rail nipples with a small dab of engine oil (hey- where’s the
dipstick?). Just make sure you get enough all around going from nipple end and onto the
rail about 1.5 inches.
- Hose end (1.5 inches) needs to be warm. Hose is very flexible this way – warm it in
your hand, next to a work light bulb, in the sun, etc. -- just get it good and warm (but do it
safely – no open flames please!).
- Lubricate the inside of hose end with a small amount of petroleum jelly. I used a
long toothpick to get the stuff on the walls at least 1 inch down inside the hose. Hint:
Keep grease OFF the hose side that you’ll be handling – makes it much easier to grip and
push it around for the install.
11. Guide the warmed and lubricated hose end straight down into the throttle pulley
valley (can’t believe I’m writing this!!!). You want the hose to bend at a 90-degree angle
and move towards the driver side fuel rail end.
Once it gets there – start to rotate the hose and use the screwdriver blade to get it to slip
over the rail nipple. Continue to twist the hose and push it all the way onto the rail end. –
your rail reference scribe mark (done in step 8) will also help here.
Note: It may be possible to install a shortened (already cut to size) hose by just slipping it
into place from the throttle pulley valley. I decided that keeping the hose long (and
trimming it later) was a better way to go in case the hose got stuck I needed to pull it back
12. Next, slide the driver side hose clamp from the fuel rail and onto the hose end and
firm it down as best you can. Might have to use another screwdriver to hold it from
rotating while you get it firm enough to keep from slipping. Once firm, rotate the clamp
into final installation position and tighten it all the way.
13. Time to install the second hose end. Find your hose cut marks and cut the hose to
final size. A sharp utility knife works better for this than the Exacto knife. Note: There is
plenty of room to pull this hose firmly upward and cleanly make the cut.
14. Lubricate the passenger side rail end with some motor oil, SAFELY warm the hose
end (real good) and apply the petroleum jelly to inside. Pull the hose end up vertically
and bend it back down so it starts to slip over the rail end. Give it a small push and it
should slide right into place. Thought this was going to be a hassle -- I was amazed how
easily this went – almost made it into final position all by itself!!!
15. Slide hose clamp into position and tighten as needed. This damp is easy to reach, so
you can hold it in place with your finger while tightening.
16. Once you’ve completed the hose install, release the throttle pulley, re-install the
cruise control cable and let the pulley return to it’s normally closed resting position.
Tighten your gas cap if it’s still loose and re-connect the car’s battery. Next, turn on the
ignition key (all dash lights on) for 3 seconds but don’t start the car – this will re-
pressurize the fuel system.
Inspect the new fuel hose for any leaks – smell around the area too. If everything checks
out OK, give the car a start and visually re-inspect again. YOU MUST INSPECT
COMPLETELY FOR LEAKS! -- BE CAREFUL OF THE SPINNING FAN
BLADE WHILE DOING THIS!!!
It is very important that you continue to check and re-tighten both hose clamps for
the next few days. Your new fuel hose may compress and these clamps will not be as
tight as when first done
I’d suggest leaving the NISSAN cover plate off until you are satisfied that the hose
clamps no longer need to be checked for hose compression. No harm will be done to the
car by driving with this plate removed – it’s just for engine bay “appearance”.
We’ll that’s about it – hope you’ve found this write-up useful? Now there’s no excuse for
not replacing that “bastard” rail end hose ASAP!
READ AND FOLLOW ALL SAFETY PROCEDURES RECOMMENDED IN THE
NISSAN SERVICE MANUAL FOR WORK ON THE 300ZX Z32 ENGINE AND
FUEL SYSTEM. . MAKE SURE CAR ENGINE IS COLD, RELIEVE PRESSURE
IN FUEL LINES AND DISCONNECT THE BATTERY BEFORE STARTING
ANY WORK. YOU ARE WORKING WITH FLAMMABLE MATERIALS--TAKE
PRECAUTIONS AND HAVE FIRE SAFETY EQUIPMENT HANDY.
YOU ARE RESPONSIBLE FOR YOUR OWN SAFETY WHEN WORKING
ON YOUR CAR. THIS WRITE-UP IS AN EXAMPLE OF ONE WAY TO
PERFORM THIS MAINTENANCE, IT MAY NOT BE THE SAFEST OR BEST
WAY TO DO IT. YOU ARE RESPONSIBLE FOR DETERMINING HOW THESE
REPAIRS SHOULD BE EXECUTED IN A SAFE AND CAUTIOUS MANNER --
AUTHOR IS NOT RESPONSIBLE FOR ANY HARM TO YOU, YOUR CAR,
FUTURE GENERATIONS, YOUR PROPERTY OR TO OTHERS WHILE OR
AFTER PEFORMING THIS OR ANY OTHER AUTOMOBILE SERVICING... .