1998 Nissan Pathfinder 3.3L Intermittent No Start
Posted to Technical Tips Forum on 9/5/2011
19 Replies
Tip: Injectors do not operate while cranking, check
the EGI (main) Relay.
A shop I occasionally deal with called and asked for
direction on an intermittent no start on a Nissan
Pathfinder. The tech asked how I would start diagnosing the
problem. I told them that he should check scan data and make
sure that nothing is grossly out of spec, such as TPS,
Coolant Temps, RPM, or Injector Pulse Width. Just look for
something usual. Make sure there's nothing going on with the
security light. Check fuel pressure and volume. Check for
spark. The tech said the vehicle had fuel pressure and
spark, but no injector operation. I asked how they
determined that and they said that the injectors were not
clicking. He said he would check what I had suggested.
The tech drove the vehicle to my shop unannounced, and told
me to take my time diagnosing the problem. I asked the tech
if they checked scan data, and he said
"It has no codes."
I asked if he checked the TPS and Coolant Sensor values, and
he said
"They should be fine, we changed those parts".
I said, "We start with 1.5 hrs up front". "You can watch and
help if you want while you wait for your ride". I hooked up
my Solus Pro scanner and found none of the PIDs out of spec.
I tried cranking the vehicle over, but it wouldn't start. I
checked the #1 injector control circuit and I could see the
PCM pulling the circuit to ground, but there is no spike
when the driver turns off. I then dual traced the power and
control circuit at the injector with my Vantage Pro, and
this is what I saw.
[1998 Nissan Pathfinder LE, ECM/Inputs/Outputs
Waveform]
Looking at Alldata, it shows that the EGI relay powers both
the PCM and the Injectors. It's a 5 Pin relay, and
apparently there are 2 switches/circuits within the relay to
power the PCM and Injectors separately.
I took a #2 Phillips Dark Blue Snap On Screwdriver,
(There is a difference) and used
the handle to tap the top of the relay while the tech from
the other shop cranked the engine over, this is what
happened.
[1998 Nissan Pathfinder LE, ECM/Inputs/Outputs
Waveform]
I told the tech he probably could have used a DMM and a test
light to diagnose this problem. He said he used a "noid"
light and it did flash dimly. He thought that the PCM could
have been bad, but he didn't want to go there.
A hot test light on the control side would have resulted in
a bright flashing light while cranking. If he used a
grounded test light on the control side it would have
resulted with a very dim or no light. At that point he could
have monitored the "hot" side with either the test light or
DMM. KOEO with the multimeter would have shown battery
voltage, but connecting a test light to that circuit would
have brought the voltage down. Then he could have looked in
a wiring diagram as to where the power came from. Tapping
the relay would have resulted in a bright test light. He
said,
"Wouldn't be easier just to change the relay instead of
doing all that testing?"
Right, so I put up this tip.
Danny from California
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