Fuel Pump Wiring

[tmorgan4]

I'm hoping that one of the Q45 gurus can help me out with a problem I'm running into with my VH45 swap. Long story short, the fuel pump is not turning on as it should. I'm not sure whether this is just the start of other underlying electrical problems with the harness I made, or if it's just a minor problem I'm overlooking.

As per the FSM, the ECM terminal 18 should show .8 volts for five seconds after turning the ignition "ON". After 5 seconds with no engine rotation, it goes back to battery voltage.

I will not be using the fuel pump control that Q45s are equipped with as my Pathfinder didn't come with one from the factory and I don't see a need for it.

My main question lies in how the low voltage signal (.8V) signals the fuel pump relay to click on. I originally thought the ECU just supplied a ground to complete the circuit, but apparently this is not the case.

Any information is greatly appreciated. I'd like to get this thing running soon.

[maxnix]

I will not be using the fuel pump control that Q45s are equipped with as my Pathfinder didn't come with one from the factory and I don't see a need for it.

How do you expect the ECU for the VH45DE to function when it doesn't have the fuel pressure reserves for which it is programmed? The FPCU returns 3 different voltages depending on demand from the sensors to the ECU.

[T45]

I still haven't gotten mine up and running yet but when I grounded the FP relay in the Z it cut on so I was able to drain the tank of the old gas. A neg trigger to your pathy fp relay should do the trick as long as the rest of the fp harness is together.

Then if the pathy fp uses a fpcu just bypass it and throw your new pump in there. The ECU will easily compensate for the extra fuel pressure by simply shortening the injector pulse a few Ms.

[tmorgan4]

I did try just grounding the fuel pump relay itself with no luck....which terminal did you ground to kick on the pump?

Worst case I will hook up the fuel pump controller wires to 12V power and ground which is what it supplies to the pump under full throttle.

[Q45tech]

Study diagram on ef/ec-10 in fsm.Ecu grounds relay and 2 separate wires to tell fpcu what to do: 3 steps of quasi resistance from fuel pump to ground.

Necessary to extend fp life and to match the wide range of flows from idle to max while maintaining near perfection in pressure and pulses in rail.

Don't jury rigg something that works.

[T45]

He doesn't have the Q fpcu, just the pathy one. If it is anything like the Z fpcu then the voltages won't be accurate. The computer can compensate and adjust accordingly to obtain proper stoich.

But yes, the pump will probably last longer with it hooked up properly.

[Q45tech]

The problem is the rail shock wave and standing waves causing pressure differences from injector to injector when you suddenly downshift from a 2,000 rpm cruise at 1.8 msecs and 34 psi to 4,440 rpm and 43.4 psi and 10.0 millisecs..................you demand 27% [psi increase] + 2400% [ 2.3x rpm x open time].

This is a dramatic situation flowing a dribble to suddenly Niagra Falls out of the injectors. How many rpms does it take to stablize. How long in revolutions is the signal change from MAF until the injector responds?

Critical to get the rail input damper to function correctly [the pressure drop after MAF [vac port] goes from ZERO at cruise to -1/8 psi at 4k to -1/3 psi at redline..............this tiny change 1/3 psi [9" WC] is miniscule yet amplified by fuel damper controlls a significant fuel situation.

Unlike the fuel return line regulator which shifts cruise fuel 34 psi > WOT 43.4 psi from plenum rise in atmospheric pressure -18" HG [+8.8 psi] going to -0.5" HG [+14.2 psi] .... 10 psi fuel changed by 5.4 psi plenum pressure.

ECU/O2 do nothing to adjust AF during acceleration all what the MAF says to do and preprogrammed look up table in PROM.

Same thing with fuel pump how many revolutions of engine occurs before the pump revs up to new speed to provide all this fuel and not suck rail dry!

At 4400 rpm there are 74 revolutions in 1.0 seconds.

http://www.eng-tips.com/viewth...ge=79

[T45]

Sometimes people think on such a molecular level it becomes counter-intuitive.

If the fpcu is bypassed and the pump runs at 100.niner and the regulator controls the pressure at a balmy 43.4000000009 psi from detroit to los angeles at all rpm's then the damper that is controlled by vacuum and the regulator that is controlled by vacuum will both act accordingly to maintain said 43.4000000009 psi in the fuel rail regardless of the quantity of fuel consumed, revolutions in the engine and asteroids viewed on said trip.

If the regulator and damper fail to control said pressure the effect would be evident as well at 33psi. The microprocessor controlled engine control unit can react much faster to changes in stoich than the fuel pump and fpcu can.

At 4400 rpm there are 74 revolutions in 1 second. At 4400 rpm the ECU reads and adjusts the air/fuel ratio how many times in one second?

It doesn't matter anyways. Perfect stoich will never be obtained with the Q's technology. The manufacturing differences between parts such as tps, maf and O2 including set resistance values and physical adjustment will hardly ever be the same as intended in the original design of the system. Add dirty injectors into the mix and your EFI system is operating like a busload of Jerry's kids.

At the moment WOT is detected the system is in open loop anyways so you can throw perfect stoich out the window along with the trash in your car. At WOT your car doesn't care about the environment, why should you?

/rant

[Q45tech]

There are a BIG basket of other more complicated problems than just simple psi.One major one is the density changes of gasoline as the rail temperature changes and just one batch of gasoline to another. The viscosity changes and thus the mass flow vs open time............why obd2 measures fuel tank temperature to narrow the errors down some. Why coolant temperature is used during warm up to make sure the mixture is over rich even though it puddles in crevices.

In a high performance engine transient response is much more difficult than steady state cruise to maintain. The oem old Q systems offered a level of fine grandularity that is only now being mainstream.

A tenth of a second lost after gear shift while things adjust badly and acceleration slows is tenth lost forever.

[tmorgan4]

I need to go back and re-read your post Tech since I didn't necessarily understand everything, but T45 is right. My Pathfinder DOES NOT come with a fuel pump controller stock. It's simply 12V on (max flow mode for 300zx and Q45 fuel pump controller) or off.

I'm not trying to "jury rig" anything, but I'm not sure I see the need to put a controller in when one wasn't used stock. Why they got rid of them in the newer vehicles (mine is a 2000) I don't know.

Now let me try and understand what you said.

[tmorgan4]

Now Tech....from what I gather from your post above, you mentioned that fact that if it didn't respond quick enough, the fuel rail could be sucked dry resulting in an overly lean mixture -------> BOOM!!.

This shouldn't be a problem in this case (the way I'm thinking, anyway) if the pump is ALWAYS operating at full throttle. It will provide the maximum flow, most of which will just return to the tank via the return line when it isn't used at idle, cruising speed, or anything besides full WOT. I'll be using one of the Walbro 255 pumps which provides a large amount more flow than stock, and I'm not sure all the fuel will even be used at WOT.

Aside from a shortened pump life from running at 100% everytime it's pumping fuel, would you see an issue? The fuel damper and fuel pressure regulator should still regulate the pressure regardless of what the pump is putting out. I could put in a fuel pressure gauge to ensure that everything is operating properly, but I don't think it's necessary in this application.

[maxnix]

I My Pathfinder DOES NOT come with a fuel pump controller stock.

The point is, your Pathfinder came with a VG30?E, not a VH45DE.

You need to adapt the entire air fuel system to get it to run, or engineer a new one on a dynamometer bench.

Your choice.

[tmorgan4]

Study diagram on ef/ec-10 in fsm.Ecu grounds relay and 2 separate wires to tell fpcu what to do: 3 steps of quasi resistance from fuel pump to ground.

Necessary to extend fp life and to match the wide range of flows from idle to max while maintaining near perfection in pressure and pulses in rail.

Don't jury rigg something that works.

And one more...you mentioned the ECU does in fact ground the relay, which appears to be terminal 18 on the ECU.

Why does the voltage at terminal 18 on the ECU go from 12V (when the fuel pump should NOT be operating) to a mere .8V when the fuel pump IS operating???

[tmorgan4]

The point is, your Pathfinder came with a VG30?E, not a VH45DE.

You need to adapt the entire air fuel system to get it to run, or engineer a new one on a dynamometer bench.

Your choice.

Maxnix....I appreciate the response and I am not trying to come off as a idiot on this project. I have not skimped on the project one bit until now and I don't plan to. I'm simply trying to keep everything as simple as possible and avoid adding more electronics that aren't necessary and can fail. If I MUST put a Q fuel pump controller in for the pump to function properly, I will.

The way I see this argument and made mention of above, shouldn't the fuel pump damper and fuel pressure regulator provide the correct pressure inside the fuel rail (assuming enough fuel is being supplied) no matter what output of fuel the pump is supplying?

I look at it this way....My Walbro 255 pump has a higher out put than my stock VG33E pump, and what I believe is higher than the stock 300ZXTT/Q45 pumps. Even if I were to run a Q fuel pump controller with my new pump, at any given output voltage from the Q fuel pump controller the pump will be pushing MORE fuel than the factory setup would due to the new pump.

In this case, is a fuel pump controller necessary if I don't mind the shortened pump life?

[Q451990]

If you don't mind the shortened life I think you could run the pump in "high" mode by just installing it as the Pathfinder pump operated... on when the engine is running. I'm not sure what the disadvantages would be besides shortened pump life and more noise.

Heath

[T45]

In a high performance engine transient response is much more difficult than steady state cruise to maintain. The oem old Q systems offered a level of fine grandularity that is only now being mainstream.

A tenth of a second lost after gear shift while things adjust badly and acceleration slows is tenth lost forever.

This is a very true statement. Which is why it makes sense to me to have 43 psi in the fuel rail at all times. The fp and fpcu can't react fast enough to have 43 at the rail by the time the computer has already set everything else in motion for WOT. If the 43psi is there at all times then everyone is waiting on the ecu to hurry up and kick up the timing and inj pulse duration.

The only way a fuel rail can run "dry" is if air makes it into the system somewhere. Otherwise it's just a lean condition from lack of fuel which is basically impossible provided your fuel system is in good condition. The fpcu is just another weak link designed to enhance and fine tune stoich measurements at cruising speeds which is also not guaranteed due to mfg and physical sensor setting differences.

Having the fuel rail at full pressure and fuel pump run at full speed won't harm anything except fp life and even that is questionable. Some pumps last 100k some last 300k. You never know until you're stranded.

Tmorgan, I think you are confusing the output of the ECU in the fpcu wires with the output of the fpcu to the fp itself. The ECU sends varying - resistance to the fpcu to tell it to send varying + voltages to the fuel pump.

I don't know the resistance values of the - output of the ecu but the output voltages to the fp are the ones in the FSM on page 25 section ec.

Hope this helps.

[Q45tech]

The disavantage is pumping 255 lph continuously thru the fuel rail and excessively heating the gasoline as to much moves thru engine compartment................the entire tankful will move thru engine compartment 3.35 times per hour or every 18 minutes.

Each to his own set of problems........................plus the pump running wide open is like a 100 watt heater further heat gasoline.

If the engineers didn't have to do what they did do you think accounting would have allowed $350 more per car and $200,000 in development expense? They didn't do it for the fun of it! Just to be complicated.

[T45]

And one more...you mentioned the ECU does in fact ground the relay, which appears to be terminal 18 on the ECU.

Why does the voltage at terminal 18 on the ECU go from 12V (when the fuel pump should NOT be operating) to a mere .8V when the fuel pump IS operating???

Maybe I mis-read your post. I am having a hard time following the voltages as well. lol Either way if you use the pathy fp relay and it calls for ground to activate it then the ecu will handle it. You could always use a manual switch as well to activate the relay, kind of "race truckish". If it uses 12v to switch then you are in the same boat but add in a relay to change the - output of the ecu to a + one or put in a "race truckish" switch.

Not sure where you're getting the .8 from as I can't find it anywhere.

[T45]

The disavantage is pumping 255 lph continuously thru the fuel rail and excessively heating the gasoline as to much moves thru engine compartment................the entire tankful will move thru engine compartment 3.35 times per hour or every 18 minutes.

Very true. Which is why I am using the Q fp in my Z. It has a damper at the pump itself and running full speed is sending enough for wot but not enough to harm anything.

I am also using a NICO ecu so maybe even a little bit more fuel will be used during my excursions. I doubt it though, I think I recall Elwesso getting the best mileage ever in his Q on stage III of the nico.

[Q45tech]

All aftermarkets ecu get their extra torque from leaning the mixture from overly rich protective oem numbers..................everything works great unless you have cooling system problems or hold things wide more than 30 seconds or 15 depending on Summer heat.

Leaning WOT 20% can do wonders for a little while.

These things [aftermarket software] are not designed for continuous WOT like in a road race or at track where you are holding 160 mph....................wheras the oem programming can take it at Talledega for 15 laps at which time you'll change all tires anyway so it cools down.

[T45]

The sweet thing about the NICO tuned ECU is the 4 way map switching. Pick your poison and roll. Stock, stage II, III, valet, and even a boost setting if you desire.