One morning, my 1990 Infiniti Q45 (125K miles) wouldn’t start:
The 4.5 liter 8-cylinder engine cranked wonderfully, but would not catch.
It wasn’t the starter motor nor the battery (as it rotated perfectly).
As always, it had to be either gas, air, spark, compression, or timing.
Following is an idealized path others can follow to debug & repair.
Note: Re-assembly, in all cases, is the reverse of the dis-assembly
procedures described below.
1. I ran a quick visual/audible gas, air, spark, compression & timing check:
GAS: The gas tank was completely full (filled the night before).
The 15 amp fuel pump fuse was intact (replaced it anyway).
I could NOT hear the fuel pump humming (at any time).
AIR: The air intake & air filter were not clogged (left it open).
SPARK: I did not know how to run a quick test for spark.
COMPRESSION: The engine did sound like cylinder wash (no compression?).
TIMING: The camshaft rotated (looking in the oil-filler hole).
2. I soon realized no gasoline was being pumped INTO the fuel filter:
– I removed the 15 amp fuel pump fuse (by the driver-side right kneecap);
– I cranked the engine in order to release any residual fuel pressure;
– I removed the two 10mm bolts holding the fuel filter clamp to the body;
– I removed the two #2 phillips screws holding the fuel filter hoses on;
– I replaced the 15 amp fuel pump fuse and cranked the engine again.
– No gasoline spurted out of the open fuel line hose.
Note: One clue was that, after an overnight sitting, with the fuel filter
and activated carbon fuel canister still on the car, the engine
started for a split second. This happened for two mornings.
I suspect this momentary ignition was due to the burning of
fuel fumes collecting in the fuel system over long periods of time.
Note: I blew through my fuel filter and there was almost no resistance;
so, despite the fact almost everyone says that a clogged fuel filter
can cause the fuel pump to overwork and therefore heat up and
therefore melt the solder connections on the fuel pump control unit,
I suspect a clogged fuel filter was not my problem.
3. I studied the 1990 Q45 fuel system electrical & hydraulic circuits:
– Battery voltage goes to the fuel pump relay …
– to the fuel pump (in the gas tank) …
– to the fuel pump control unit (under the rear sundeck platform) …
– which provides three resistive paths (fuel pump speeds) to ground …
– based on input from the engine control unit (passenger side dash).
– Fuel is pumped out of the fuel tank …
– to the inlet of the fuel filter …
– to the fuel line & fuel plenum …
– to each of the 8 fuel injectors (which open at the same time) …
– with pressure regulated by the 43 psi fuel pressure regulator …
– which sends unspent fuel back to the fuel tank for recovery …
– and which allows fuel vapors to be trapped in the carbon cannister.
– The fuel tank is located in the center of the trunk room (between
the rear seat and the trunk).
– The fuel pump & fuel pump resistive gage & filter sock is located in
the top of the fuel tank.
– The fuel pump control unit is located on the underside of the rear
metal sundeck (near the rear passenger side speaker housing).
– The fuel pump relay (lime green) is located next to the antenna and
fuel tank gasoline inlet in the area between the rear passenger side
fender and the rear passenger side trunk fiberboard lining.
– The fuel filter is located on the passenger side of the engine
compartment bolted to the inside of the passenger side fender wall.
– Access the fuel pump, fuel pump relay, fuel pump control unit, & the
related fuel system harnesses for test from the rear trunk area.
– Access the fuel pump for removal & replacement either by removing the
rear seat & sundeck & storage binnacle or by dropping the fuel tank
(rear seat removal access is preferred over tank removal by most).
– The harness connector (white, female) to the fuel pump control unit
is called the fuel pump control unit harness connector.
– The harness connector (green) to the fuel pump relay is called the
fuel pump relay harness connector.
– The harness connector (blue, female) to the fuel pump is called the
fuel pump harness connector.
– The connector (white, male) on the fuel pump control unit
is called the fuel pump control unit connector.
– The connector (green) on the fuel pump relay is called the
fuel pump relay.
– The connector (blue, male) to the fuel pump is called the fuel pump
– Two #2 phillips screwdrivers (one six inch, & one two inch stubby).
– Two box wrenches (one 8 mm box & one 10mm) for bracket bolts.
– One 19 mm open-end wrench (for the gas tank fuel line lock nuts).
– One 16 AWG wire, about a foot long, with an alligator clip on each end.
– One volt-ohm-amp-meter (Fluke 77 or equivalent) with alligator clips.
– One needle-nose pliar or standard pliars (for spring-closed hose clamps).
– One paring knife (or similar) for removal of sound-proofing material.
4. The fuel pump relay checked out OK for proper operation under load:
FROM THE TRUNK:
– I removed the trunk room fiberboard bulkhead (between the rear seat
back & the trunk) by removing the 7 black #2 phillips screw-type
butterfly anchor clips holding the fiberboard bulkhead to the steel
– I removed the trunk passenger-side bulkhead (between the trunk and
the rear fender by the radio antenna & fuel filler opening) by removing
the 5 black #2 phillips screw-type butterfly anchor clips from their
– I removed the single 10mm bolt holding the two-pronged relay bracket
which held a blue relay (courtesy lamp relay) on one prong and a
lime-green (fuel pump relay) relay on the other.
– I pulled the lime-green fuel pump relay off the bracket tang.
– I jumped 12 volts DC across pins #1 and #2 (hearing a sharp click).
– The resistance fell (from infinity) as the actuator closed (to zero).
Note: I also checked power to the fuel pump relay, continuity from the
fuel pump relay to the fuel pump relay harness, continuity from
the fuel pump relay harness to the fuel pump harness, & continuity
from the fuel pump harness to the fuel pump control unit harness
(all asp per the factory shop manual EF & EC-169); but, not
surprisingly, I’m told the fuel pump relay and these fuel electrical
system wires almost never go bad; so consider this entire step an
ancillary case of over diagnosis.
5. The old fuel pump passed the basic factory shop manual test:
FROM THE TRUNK:
– I disconnected the fuel pump harness connector (blue, in the trunk room).
– As per the factory shop manual (EF & EC-185), I checked the resistance
between the top-left and the top-right (tab on top, facing terminal side)
of the six male terminals on this fuel pump connector.
– My resistance was 0.9 to 1.1 ohms which was inconclusive since the
factory shop manual merely states the resistance to be 0.5 ohms but
the factory shop manual does not supply a range value.
Note: It seems this factory shop manual test is almost useless.
When I tested the new fuel pump, it too tested about the same at
0.6 to 0.8 ohms. The online Infiniti mechanics noted the resistance
test merely checks one (of many) commutators. Online mechanics say
the clearest sign of a bad pump is HUMMING.
I must admit, the new pump barely made a sound, even when jumped
directly to ground providing it full battery voltage. I didn’t
realize it at the time, but, the old pump actually hummed loudly.
(There is so much soundproofing that I never heard the old fuel
pump motor hum until the rear trunk room lay bare & exposed.)
Basic recommendation: If the fuel pump has 100K miles on it; or
if the fuel pump is humming at all audibly; then replace it
(before it burns out the ground wire on the fuel pump control unit).
Note: The two most basic tests should have been (in hindsight):
– Did the 1990 Infiniti Q45 have more than 100K miles?
– Did the 1990 Infiniti Q45 fuel pump have an audible hum?
If either answer were yes, then replace the ’90 Q45 fuel pump.
6. The old fuel pump control unit failed the basic bypass test:
FROM THE ENGINE COMPARTMENT:
– I reconnected the fuel filter (passenger side of the engine compartment).
FROM THE TRUNK:
– I reconnected the fuel pump harness connector (blue, in the trunk room).
– I removed the fuel pump control unit harness connector (white, female)
from the fuel pump control unit connector (white, male) mounted directly
on the fuel pump control unit.
– Note: Nothing else was removed at this time; the fuel system was
otherwise completely intact.
– I filed an alligator clip’s teeth so that it fit into the small female
tab on the bottom left (terminal side, with the clip up) of the white
fuel pump control unit harness connector.
– I connected the other side of the alligator-clip one foot long 16 AWG
wire to a convenient ground (expecting from 7.5 amps to 15 amps based
– I turned the ignition to “ON” and listened for the fuel-pump humming.
– It hummed for about 10 seconds after turning the ignition to ON.
– I started the 1990 Infiniti Q45; it ran like a charm.
– The current draw was about 5.8 amps on the old humming fuel pump.
– The engine shut down approximately 2 seconds after disconnecting this
fuel pump control unit bypass jumper.
Note: I drove the car for more than a week (about 200 miles) with this
alligator clip shorting the fuel pump to ground bypassing the
three-position ([email protected] to 5.7 volts, [email protected] to 8.1 volts, &
[email protected] to 14 volts battery voltage) fuel pump control unit settings.
Note: Online mechanics estimate the old fuel pump might last a few weeks
(running full speed as it is when jumpered to ground); while a new
fuel pump may last a few months in this temporary full-power state.
Note: It is recommended the fuel tank be kept full whenever operating the
Infiniti Q45 in this state as the fuel pump is cooled by the
gasoline in the fuel tank.
Note: This is NOT the procedure in the factory shop manual (EF & EC-185).
This procedure is much simpler than that in the factory shop manual.
The procedure in the factory shop manual requires three test jigs,
of four, five, and then six wires between the white female fuel
pump control unit harness connector and the white male fuel pump
control unit connector. In most cases, this test is overkill.
7. Reconcile yourself to the fact you have a few hours of work to perform:
A: Because of these three basic facts.
FACT 1: The first fact is that the proper removal of the fuel pump
control unit is from the rear-seat direction & not from the
(otherwise more convenient) trunk-forward direction.
FACT 2: The second fact is that experienced Infiniti Q45 mechanics
have concluded most fuel pump control unit failures are due
to the fuel pump itself beginning to fail (and thereby to
draw excessive current, which melts the weak solder joints on
the ground wire printed circuit board connection on the fuel
pump control unit).
FACT 3: Therefore, if you merely replace or re-solder the broken fuel
pump control unit, you’ll eventually burn out the new or newly
repaired (and much more expensive) fuel pump control unit.
The good news is the Infiniti mechanics online have reported very few
(if any) failures of the repaired or replaced fuel pump control unit
once the fuel pump is replaced (for another 100K miles or so anyway).
8. Remove the rear seats, rear sundeck shelf, and rear package binnacle:
REMOVE REAR BENCH:
– Move the front seats forward as far as they will go and tilt the
front seat backs forward as far as they will go to obtain working room.
– Locate the two black clip extensions on the rear seat floor area and
pull out those two black clip extensions simultaneously pulling up on
the leading edge of the rear seat bench to lift it upward and out.
The rear seat bench removal requires no bolts to be removed.
There are only four clips in the leading edge; and two clips in the
trailing edge of the rear seat bench to take into account for removal.
– Scavenge the $1.35 (on average) in loose change under the rear bench
that the federal government suggests wreckers earn per car on wrecked
REMOVE REAR SEAT BACK:
– Pop out or pry out (with a thin flathead screwdriver) the four blue
solid butterfly anchor clips from the leading edge of the rear topside
sundeck where the sundeck overlaps with the rear seatback.
– Remove the two rear headrests by pressing the driver-side knob under
each & simultaneously lifting upward until the posts clear the seatback.
– Push down the rear seat armrest and pull back on the vertical backing
which is velcroed to the steel bulkhead behind rear seat back.
– Remove the two #2 phillips screws behind this velcroed rear armrest
– Remove the four #2 phillips screws holding the U-brackets at the
bottom of the rear seat back.
– Pull up the rear seat back vertically, to clear three reverse-u-shaped
wire brackets from their u-shaped metal brackets in the rear bulkhead
metal wall. This should remove the seat (except for the seat belts).
– Pull out the two side rear seat shoulder belts as far as they will go
and jam a pen or other object to eliminate the return tension.
The seat belts will be less of a nuisance if you perform this task.
– Flip the rear seat back (still attached by the seat belts) upside down
so that the foam side is facing the front & the leather side is facing
the rear and the headrest portion is on the floor of the automobile.
REMOVE REAR UPPER TAIL-LIGHT & REAR SUNDECK:
– After removing the three blue solid butterfly clips on the leading
edge of the rear sundeck …
– Pull toward the front and upward on the rear upper tail-lamp housing;
and disconnect the rear upper tail-lamp harness connector from the rear
upper tail-lamp connector. Remove the rear tail lamp housing.
– Pull up on the rear sundeck everywhere you can to unclip the 11 solid
white anchor clips (4 equally spaced in the rear, two in the middle
on each side of the package binnacle, and 5 near the front of the
sundeck shelf, three of which are closely spaced near the middle front
of the sundeck shelf and the other two nearer the outside edges).
– Collect all anchor clips in a zip-lock bag marked “rear shelf”.
REMOVE REAR SUNDECK PACKAGE BINNACLE:
– With the rear upper tail-lamp & rear sundeck removed, unscrew the
seven #2 phillips screws holding down the black plastic rear sundeck
package binnacle (aka storage compartment basin).
Note: This rear sundeck storage binnacle is the key to removing the
fuel pump since the fuel pump (with the attached fuel pump float,
fuel pump housing, fuel pump level gage, etc.), can only come out
undamaged through the rectangle left by the removal of this rear
sundeck storage binnacle (aka package binnacle).
Note: Almost none of this removal procedure is explained in the factory
9. Remove fuel pump assembly from the top of the fuel tank from the trunk:
FROM THE TRUNK:
– Disconnect the blue male fuel pump connector from the blue female
fuel pump harness connector.
– If you haven’t done so already, bleed pressure out of the fuel system
by cranking the engine with the fuel pump fuse (driver side dash, by
your kneecap) removed. Also remove the fuel tank inlet gas cap.
Have a large hotel towel handy because it’s inevitable that fuel
will leak as you remove the fuel pump assembly from the fuel tank.
– With a 19mm open-end wrench, remove the two 19 mm tubing nuts holding
the metal fuel pump outlet and vapor lines to the top of the fuel pump
assembly. Be careful not to break the three-line plastic separator
(as I did) when bending the rigid metal fuel lines out of the way.
– With an 8mm box-wrench or a three-inch stubby #2 phillips screwdriver,
remove the six 8mm bolts holding down the fuel tank assembly cover
plate to the fuel tank.
– Gently pull up on the fuel pump assembly taking care to prevent the
six-inch black rubber O-ring from falling into the fuel tank.
– From the trunk, twisting gently as needed through the rear sundeck
shelf package binnacle opening, remove the fuel pump assembly.
– From the rear seat area, look down into the opening left by the
removal of the rear sundeck package binnacle and inspect the fuel
tank for debris (mine was as clean as a galvanized chambered whistle).
10. Remove the fuel pump from the fuel pump assembly:
OUT OF THE CAR:
– Pull out the two one-inch brown plastic alignment clothes-pins
in the fuel pump wing bracket.
– Remove the two #2 phillips bolts bracing the fuel pump body to the
fuel pump assembly.
– Remove the one #2 phillips bolt holding the fuel filter sock to the
metal fuel assembly (and push out the alignment tab).
– Remove the #2 phillips bolt attaching the power wire and the #2
phillips bolt attaching the ground wire to the fuel pump itself.
– Gently force the fuel pump motor black rubber wings out of their
braces in the fuel pump assembly leaving just the fuel hose attached.
– Once the fuel pump wings are outside their slots, use pliars to
open the spring hose clamp on the plastic fuel pump outlet nipple.
– Remove the (now unattached) fuel pump from the fuel pump assembly.
– Compare the old fuel pump (in size & shape) to the new pump (the
two fuel pumps should match exactly).
– The replacement follows the reverse procedure.
Note: I purchased a new fuel pump from a parts store for $312.oo while
the Infiniti dealership listed the fuel pump for $320. The
Infiniti dealership sold me the six-inch fuel pump O-ring for
$13.oo (all numbers include tax). I noticed, afterward, that
online, I could get the same pump (including the six-inch O-ring)
for $235 plus shipping & tax. Go Internet, if you have the time.
11. Remove the fuel pump control unit for replacement or repair:
FROM THE TRUNK:
– From the trunk, on your left side with your head facing the driver
side rear fender, with your right arm through the opening left by the
removal of the rear sundeck package binnacle, place your index finger
on the topside location of the bolt head for the two bolts holding the
fuel pump control unit bracket to the underside of the rear sundeck.
– Have a partner mark the location of the two bolt heads (the actual bolt
heads are buried under 1/8th inch thick rubberized soundproofing material)
using whiteout or other suitable marking on the black gunky material.
FROM THE REAR SEAT AREA:
– With a small paring knife, cut out the rubberized gunky black sound-
proofing material on top of the two 10mm bolt heads.
– Use a 10mm box wrench to remove the two bolts holding the clamp on
the underside of the package shelf. Note that the clamp itself forms
a U, with one portion of the bracket above and one portion below the
metal horizontal sundeck shelf.
BACK IN THE TRUNK:
– Check that the fuel pump control unit (white, female) harness connector
is disconnected from the fuel pump control unit (white, male) connector.
– Remove the fuel pump control unit (with the bracket assembly attached)
by pulling it toward the rear of the car, and downward.
12. Inspect, repair, or replace the fuel pump control unit:
OUT OF THE CAR:
– Remove the four #2 phillips head screws holding the top plate
(with bracket assembly) of the fuel pump control unit.
– Remove the four #2 phillips head screws holding the bottom plate
of the fuel pump control unit.
– Inspect the wiring everywhere; notice any charred or burned areas
(my ground wire on the bottom right (terminal side, tab on top) of the
white male fuel pump control unit connector was charred a bit.
– Also, there was infinite resistance between that bottom-right male
terminal and the corresponding printed circuit board connection
(marked #4 on the PCB) on the underside of the printed circuit board.
– I used a 25-watt soldering iron & a blue solder sucker to vacuum up
the solder around that #4 pin and I re-soldered that ground pin.
– I also added a two-inch patch of 16AWG copper wire, soldered to that
#4 pin and to all the connections on the printed circuit board I could
identify as being that same ground connection.
– Test with a ohm meter that the resistance for that one ground lead
is near zero; and that accidental shorts to other traces did not occur.
– Replace the now-repaired fuel pump control unit in the reverse order
Note: Do not power-up the fuel pump control unit out of the car as the
holding bracket supplies the main ground for the fuel pump control
Note: The #4 terminal is the ONLY terminal on the male white fuel pump
control unit connector which is surrounded by EMPTY pins in the
white female fuel pump control unit harness connector.
THINGS I LEARNED THE HARD WAY:
– Basically, I should’ve replaced the fuel pump at 100K miles!
Apparently they all eventually go bad. I should have also listened
for the now tell-tale hum (I never even noticed it before).
– Also, once before, about six months ago, my car would not start for
about an hour; and then, all of a sudden, started. At the time, I
chalked it up to cylinder wash (loss of compression due to gasoline
washing the oil off the piston walls causing rings to temporarily not
seal); but now I realize it was probably the fuel pump control unit
#4 pin solder heated up and, when it cooled, it re-connected itself.
– It was recommended we should fill up when just about on one quarter
of a tank (or so). The (unsubstantiated) argument states that the fuel
pump heats up, causing more current draw (how?) which causes the solder
connection on the fuel pump control module ground circuit to heat up
which, if it melts, can cause the open circuit that I found in mine.
– The new six-inch fuel pump O-ring looked EXACTLY the same as the old
one (condition was imperceptably different). So much, I ended up mixing
the two accidentally, and I couldn’t tell them apart. Be advised.
– The new pump made almost NO SOUND. I didn’t even realize that until
I had replaced it. Even with the full-power jumper bypassing the
fuel pump control, the new fuel pump hummed vastly less than the old
fuel pump hummed.
– The current draw and resistance measurements of the old fuel pump
and the new fuel pump were almost the same; so do not rely on these
figures as a diagnosis test (listen for hum or check your odometer):
OLD FUEL PUMP: NEW FUEL PUMP:
0.9 to 1.1 ohms 0.6 to 0.8 ohms (from the blue male FP connector)
5.6 to 5.8 amps 5.8 to 6.7 amps (with the FPCU bypass to ground)
– The factory shop manual makes NO MENTION of the quick and easy test
jumpering the fuel pump control unit harness connector to ground.
Instead, the factory shop manual walks you through an apparently
unnecessary lengthy step-by-step debugging process requiring the use
of a three, four, and then a five wire jig to debug the fuel pump
control unit. Don’t overdiagnose. Just use the jumper and if the
fuel pump operates, then replace BOTH the fuel pump and the fuel
pump control unit (or repair the fuel pump control unit).
– For the longest time I was confused about the various debugging
procedures in the factory shop manual. What cleared it up was the
realization of all the proper connector names! I’ve made a sincere
attemp in this note to use the proper names at all times.
– Many folks say you can test the deliver of fuel past the fuel filter
(in the engine compartment) by squeezing the hole while the engine
is cranking to feel for fuel pressure. I can’t tell. I recommend
removal of the fuel filter. It provides proof positive.
– The factory shop manual goes into the engine control unit debugging.
It was not needed in my case so I’m glad I skipped that part.
– The hardest thing in the world was to find the locations of the
various units; and to find out how to remove some of them. In this
note, I take special care to describe both the name of the unit and
the precise location, for others to benefit.
– Most folks recommend disconnecting the battery & removing it from the
car when working on the fuel tank. I didn’t do this, but you should.