G50 Q45 HARD START AFTER WARM

[branscoset]

I just recently did valve cover "gaskets", all hoses under intake, knock sensors, cleaned rails, tested and rebuilt injectors while replacing a few.. new plugs and power steering lines.

Car runs great, starts up quick cold and MAF quickly takes over setting idle to around 600 RPM according to tach.

After car is driven and reaches temp it is hard to start. It usually fires off fine, but seems like it can't hold its breath and stay running. I then have to feather the throttle to get it running and hold it at around 1500 or better steady for 20 seconds or more. I then let off slowly and make sure it catches, if it drops below 300 rpm I rinse and repeat until it stays running on its own.

I do not notice any black smoke or any smoke at all for that matter, so I don't think it is flooding.. but can't help but assume it is somehow fuel related...since hitting the gas pedal on a non-carb car should do nothing more than open the butterfly in throttle body correct? Meaning it needs more air to even out the AFR to start?

I should make note that my 2 solenoids on driver side valve cover are plugged in electrically, but not vacuum wise. I have direct vacuum to the EGR and the purge can from the throttle body.

[branscoset]

So I also have a inoperative tail light warning, so tails are not working, and neither are the dash lights when headlights are on. Except when braking? When I press the brake all my brake lights work fine, blinkers function also, and the dash lights come on, then off when brake is released?

What I am getting at is I popped the trunk to check tail bulbs were oem or sylvannia and I hear a sizzling... I track it down to what I believe is the fuel modulator? and unplug it, sizzling stops, car slowly dies. I took a picture of the part number and googled it NISSAN 1700160U00, MODULATOR-FUEL and nissan a63000220. I am going to remove the modulator from my parts car tomorrow. Thinking maybe this is my hot start issue possibly.

[3Q Jay]

the part number you posted is often referred to here as the FPCU.
i'd venture a guess that yours is on it's last legs. very common for the electrolytic cap and transistors to blow on them.
use the 'goody' jumper trick to see if that instantly cures the hot start issue.

[branscoset]

Should I replace the pump and the fuel control unit at same time? All the other threads I have read say yes, but my pump seems to be running fine and not making any noise like most bad pumps do.

[3Q Jay]

Assuming the jumper trick works--I'd replace the fuel filter (OEM--no FRAM crap)and find a good used FPCU. It is said old pumps stress the FPCU. maybe. personally i believe a restricted fuel filter will nuke the FPCU faster than an old pump will (although if the pump (sock) is clogged then that is another story....). you should also check the green relay by the power antenna and change it.

[branscoset]

The fuel filter is new, less than 200 miles on it

[branscoset]

OK so still having issues.

I replaced the FPCU with a known good one from parts car, still wont start hot.

Did the bypass trick, pump ran on high and still wont start when hot without feathering the gas pedal.

Thinking maybe a MAF issue or a coolant sensor? When I do get it started it never blows black smoke, so I assume it is not flooding?

I did however fix my tail light issue hopefully, replaced all bulbs with sylvania LL and swapped sockets with my parts car since my housings were corroded. I also replaced the purple sensor on rear body with one from my parts car. So far so good...now if I could just figure out this hard warm start issue.

[3Q Jay]

hard to know without measured data.
you could still have a bad fuel (rail) pressure regulator, but unlikely. measured fuel pressure at idle (warm crank)?
is the EGR opening at idle due to manifold vacuum (vs. ported vacuum)?
what does consult say (aac duty cycle, injector duty cycle when cranking, MAF voltage, tps voltage)?

[Q451990]

Your problem sounds a lot like one I had on my old Q. It started after I replaced my fuel injectors with remanufactured ones. I didn't know to lubricate the O-rings when I installed them, so I probably pinched a lower o-ring causing fuel to seep into the engine. I would notice a small amount of black smoke, but it probably wouldn't be visible from inside the car... I saw it using remote start. The car would start great first thing in the morning (after the fuel had time to seep past the rings), or if I restarted it within a couple of minutes after turning it off (not enough time to flood). But if I let it sit for 30-45 minutes, it would take 10 seconds of starter time before it would start running.

I should make note that my 2 solenoids on driver side valve cover are plugged in electrically, but not vacuum wise. I have direct vacuum to the EGR and the purge can from the throttle body.

Can you explain this a little more? How are you controlling the EGR and Purge functions?

[branscoset]

I had the rails cleaned and pressure tested, so I assume the regulator is ok also? I have not measured fuel pressure at idle for warm crank, but I will do that.

I should note that it didn't have this problem before the tear down and new parts.

Yes the EGR is opening at idle due to manifold vacuum, direct port vacuum instead of ported from the solenoid.

I am not sure what you are asking by consult say, I know what the duty cycle means and can check MAF voltage manually, but I don't know how to read real time data without a data port? I have a snap on solus? scanner that I use on 95 and newer obd2 compliant rigs to watch real time data, but as far as I know I can't plug into this system.

On the pinched o ring issue, I have done many injector jobs, and I made sure to lube well and carefully install the injectors into the seats to avoid pinching a ring. I have also watched the tail pipe when cranking hot to make sure no excessive black smoke is present and its not. I have also checked the oil for gas smells and I don't believe gas is making it to the pan.

Like I said above, it does start with very slight pressure on the throttle, then steady pressure holding at 1000 rpm for 20 seconds, then it idles fine and drives fine. As far as I know hitting the throttle when starting does nothing more than open the butterfly to the throttle body, therefor allowing more air to compensate for the higher fuel level? Like maybe it thinks it is cold and is giving to much fuel?

Does this have a coolant temp sensor for the ecu? if so where is it and how do I test? If the coolant sensor is telling the engine it is -30 degrees outside and dumping fuel to compensate, then there is my issue. Again hard to believe this is part went bad in the 6 months vehicle was stored in my heated garage, but anything is possible at this point.

Thanks for the help so far guys. I will get this thing figured out one way or another! So nice to drive my Q again, gobs of power for a heavy a** sedan.

[3Q Jay]

Yes the EGR is opening at idle due to manifold vacuum, direct port vacuum instead of ported from the solenoid.

this is not per design. could be related. remember EGR will dilute the A/F mix with waste products.
why it is s'posed to be fed in incrementally at 1200 -3000 rpm.

the ECU coolant sensor is the one in the very bottom of the valley on the y-pipe.

[branscoset]

So I rerouted the EGR and PURGE CAN? solenoids back to stock, instead of having them on direct intake vacuum. So all vacuum is stock setup. I also swapped to a known good MAF and CAS from my parts car, cleaned connections with file and spray. I also checked and cleaned the electrical connection to the TPS. Still wont start without help when warm. Runs like a raped ape otherwise.

I still need to test for fuel pressure. I keep hearing people talk about a "consult" type reader. I have a snap on SOLUS, but I don't think I can plug into this car since it it OBD1?

[GoadQ45T95]

You will need a consult cable. I got mine from Ecu talk and it plugs right into a laptop. Think it costs about 90$ . The consult cable will plug into the gray pin connector under the driver side dash fuse panel.

[3Q Jay]

consult like interface is the way to go. but that won't tell you measured fuel pressure. for that you need an old skool 5/16 fuel tee with a mechanical gauge 0-60 psi.