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I am trying to help a friend out with his car a 2006 G35 sedan 4 cylinder. His son had it and who knows what really happened. The car has a crank no start issue. First thing I notice is the fuel pump isn't priming or running when trying to start. I'm seeing only 8v to the pump when it's trying to prime and only 6v when actually cranking. Fresh new battery installed that tests good. So where does the fuel pump voltage come from? I believe it may becoming from the IPDM? I only saw a fuel pump fuse listed on the cover but not the fuel pump relay? I'm guessing the relay may be bad/corroded, or possibly the entire IPDM is bad. Any helpful pointers or direction I should go would be very much appreciated.
On a side note my Autel scanner was unable to even communicate with the ECU, but I know the ECU is sending a signal for the fuel pump so that may be an entirely separate issue.
Last edited by Grizzman; Jun 17, 2022 at 06:33 PM.
My guess is the fuel pump relay cooked, it's in the IPDM. Contacts probably got dirty, fried, and has high resistance now thus the lower supply voltage.
Here's the schematic for the fuel pump electrical.
My guess is the fuel pump relay cooked, it's in the IPDM. Contacts probably got dirty, fried, and has high resistance now thus the lower supply voltage.
Here's the schematic for the fuel pump electrical.
Thanks, needed that diagram to see I was testing the wrong pins. With the fuel pump connector disconnected I am in fact getting battery voltage when turning ignition to run position. But oddly the voltage comes down very fast 11v,10v,9v,8v,7v,6v all within about 2 to 3 seconds. But when I am cranking I get a solid 10v to the connector. No fuel came out of the hose when i disconnected it to check for any pressure. Hopefully the odd voltage thing is just some Nissan thing, I haven't seen that before testing other pumps. I'm going with a new pump tomorrow, hopefully I get some results.
Unless the car is actually running the fuel pump relay only turns on for 1 second to prime to the pump. Once the ECM get crank position sensor signal THEN it keeps the fuel pump relay closed. That's why you see the voltage bleed off, ECM opened up the relay again.
Thanks cleric670, makes sense. As I was taking apart the fuel pump assembly to replace the motor I noticed it was installed without the rubber grommet that goes from the actual pump to the housing, no wonder, the pump couldn't even build pressure like that. Was able to source a new grommet on ebay since the dealer didn't have it. Will update once pump is put back together correctly and installed.
Finally got the grommet in today, fuel pump put back together and installed. Now I have pressure all the way to the injectors, checked for fuel at the regulator in the engine bay. But the darn thing still wont turn over. My Autel scanner was able to communicate with the ECU but looking at the live data, nothing is sticking out to show what's wrong. Next I guess I should physically check for spark.
The engine cranks when you try to start, but it won't fire up right? If so then yes the next step is to check for spark.
Is your NATS/security indicator light on the dash SOLID RED when trying to start the engine?
Correct, crank/ no start. I have verified that the NATS light is not solid red while cranking. If I show no spark, is it safe to assume a faulty crank or cam sensor?
If you pull the plugs and they're dry then yes, if you pull the plugs and they're wet then no.
If you lose cam or crank signal it won't fire either the spark or the fuel.
Crank sensor is an easier one to diagnose since you can just watch to see if the tach moves a little while trying to start the engine. Cam sensors are more problematic since you need to backprobe the ECM harness and use an oscilloscope.
One of these days I need to just make a video on how to do that part, it's not difficult but you do need an oscilloscope which is a couple hundred bucks minimum.
If you pull the plugs and they're dry then yes, if you pull the plugs and they're wet then no.
If you lose cam or crank signal it won't fire either the spark or the fuel.
Crank sensor is an easier one to diagnose since you can just watch to see if the tach moves a little while trying to start the engine. Cam sensors are more problematic since you need to backprobe the ECM harness and use an oscilloscope.
One of these days I need to just make a video on how to do that part, it's not difficult but you do need an oscilloscope which is a couple hundred bucks minimum.
Should the tach be moving a little during cranking indicating a good Crank sensor? I have my friend take a video when I was checking for the security light, I can clearly see the tach not moving at all while the car is cranking
Yeah the tach should move, it's a small movement but it WILL move. If your battery is significantly discharged and it's cranking really sluggish it might not move though.
Normally though if you have a cam or crank sensor that's just flat out not sending a signal you'll usually have a hidden OBD2 code for that sensor. If you are confident you don't have ANY codes it's probably another issue.
I confirmed myself in person the tach wasn't moving, but no codes or shadow codes either. I order up a crank senor. Go to replace it and there is no bolt holding the sensor in, just sitting ever so slightly out of the hole, only millimeters but it was enough. Replaced with new Hitachi sensor. Good thing though the car is running great, apparently when it was running it ran like crap, no wonder since the fuel pressure was low. Thank you @cleric670 , I really appreciate you taking the time to provide the schematics and the helpful information!
