FUEL PUMP CONTROL UNIT

[BOUDREAUX]

1992 Q45167, 000 mi

Can bad injectors create enough stress on fuel pressure to cause the fuel pump control unit or fuel pump to fail. I have been running three bad injectors (original 23+ ohm) for about 600 miles, perhaps longer.

Can the fuel pump control unit work but not as designed? In other words, will it function enough to allow the vehicle to run, but not contol the fuel pump as engineered hence decreased performance.

Thanks Boudreaux

[Q45tech]

Electric motors slow down with age and wear, as they slow down the draw more and more amperes......................when the amperes exceed the rating of the FPCU it fails.

There is no feedback loop the ecu just tells FPCU to supply a 3 step voltage based on rpm and load [tps voltage]................after the initial crank boost [time limited].

Fuel pumps need changing frequently [60-120k] to overcome the dirt in gasoline.

[BOUDREAUX]

Q45tech-

Thanks for the info. Is the tps the throttle position sensor? I removed my plenum, throttle body, etc. in order to replace the fuel injectors. Do I need to adjust the tps?

Kleofus

[Q45tech]

Only if you remove or changed its rotational position on throttle body.

Alway good to check what the Consult says the ecu is seeing at hot idle [0.44 volts]

[BOUDREAUX]

thanks for info

[silkysmoothyjud]

Can bad injectors cause a bad pump, or is it the other way around? Chicken or the egg. I believe Nissan fuel systems just go bad randomly. I had two injectors fail, one right after the other, then the fuel pump started to hum. Cause and effect? I thought so at first, but I still had cream colored injectors in my car. 5,6,7,8 were purple (I am one lucky used Q owner). I changed 1234, they are all purple now. Bad ignition coils cause a rough idle and non-OEM injecotrs will cause problems as well. The whole motor will noticeably vibrate and you will have a hard time finding which one is doing it without color. If your injectors do not have dots they might be botch (bosch are purple too). and they freakin suuuuuuuuuuuuuuuuuuuuuck!!!! botch will cause a rough idle when ac is on, hesitation when the car is cold, bogged down performance all together.....

[Q45tech]

A high resistance injector will flow less current and thus be slower to open.

At idle the 1.2 milliseconds of applied voltage is not enough for the injector to fully open and for the mass of gasoline to get to 100% flow rate, also the lower idle pressure 34 psi vs 43.4 psi reduces the flow by another 12%.

So the 1.2 milliseconds just puffs a tiny tiny tiny amount of gasoline about a single drop as the closed throttle restricts the air flow into cylinder by 90%..............instead of 562cc of air, probably 60 cc of air gets in the cylinder.

The idle air flow weighs 5-8 grams so the gasoline weighs 333- 500 MILLIGRAMS.

The point is that 10% less gasoline is a significant amount at idle. At WOT 10% would be meaningless since the ecu provides an extra 20% above ideal to cool cylinders. Same at 2000 rpm cruise as the ecu can add 20% via O2 feedback.

Smooth or rough idle tells you everything, worse with AC on reinforces the findings of a leaner than idle fuel mixture.

Everything must be perfect since idle is so critical

[maxnix]

Can bad injectors cause a bad pump, or is it the other way around? Chicken or the egg. I believe Nissan fuel systems just go bad randomly.

No, neither, not if they are maintained and not subject to additves for which they were not designed.

[Q45tech]

Even under the highest load/rpm conditions the return line is carrying much more gasoline back to the tank than is flowed out thru injectors.

[silkysmoothyjud]

I would say yes, in theory, since bad injectors cause acceleration problems and hard shifts. No disrespect, just a guess...the answer to the second paragraph. whatever, bud-wise-er

[Q45tech]

Assuming you don't damage injectors with the gasoline you purchase, they should last longer than 3 fuel pumps based on simple work load measurements alone, as the pump is transporting 3 x 8= 24 times more fuel volume than a single injector over the same time periods.

As long as you frequently change fuel pumps the control unit should last indefinitely.