Continuing Stalling/idling Issue! Fuel Pressure Now!

[stimps]

Ok this problem just continues and its a long story now, hope you have time to read, but who knows we might all learn something! Hopefully me

When I drive, it seems to hesitate then go, then u slow down, return throttle to idle, it dies back, then u go a bit and it hesitates, then takes off ( and i dont mean boost im talkin about 1000 to 1500 rpm area of the map) its really annoying and actually a pain to drive. you cant go over speed bumps or drive slow without it really buggin the shit outa you.

and it stalls at idle, if allowed to settle for a while. Usually the air conditioner load causes this, when u turn it off it doesnt affect it so bad. So i did all the usual checks, Ive got a Oscilloscope and ive put it on the inputs and outputs on the ecu to check everything. Ive checked the AAC solenoid, its working properly, ive checked the battery voltage, its 13.7, and fuel pressue is 33 psi. is that a bit low? Ok so next I try raising the air input a bit by winding out the manual screw and it just takes away some of the work the AAC valve does (by the way i did clean the AAC) but that still doesnt change the problem much. anyway, i thought ok ill just put an extra air solenoid in to bypass the throttle - nope that didnt work! it just doenst want to put in the extra fuel.

so then i think "ok maybe its getting air but not registering the air and therefore not putting in extra fuel! "

so i put my cro on the air sensor and its seeing the air just fine!!!

I also noticed that when the throttle idle position contact switch is made, (idle position) the ecu retards the ignition and pulls back the fuel a bit and allows the engine to come back to a 600rpm idle. If you adjust the idle switch so it is NOT made, the ecu advances the ignition and puts a bit more fuel in and the revs rise. even tho you have not opeend the throttle. the car actually came into my posession like this and its a high idle, it wont idle low, no good!

so i dunno...THEN I thought ill check the injectors and i think they could possibly do with a clean and check. anyway have not done that yet, the car's economy on the highway is good, the cruise mixture cycles just fine (on the fuel mixture meter monitor) i have another set of second hand injectors waiting to go to the shop to get ultrasonically cleaned. So anyway I then observe the fuel pressure gauge

Its then i notice that when u gently rev the motor it goes up to 44psi, and as you would expect goes up and down as it should with boost/vacumn

THEN i notice that it waits 3 seconds at 44psi, then falls back to 33psi!! everytime after the throttle is returned to idle position (idle throttle position switch contact is made) it does this! is this normal?

and its identical to the wierd hesitation fault im experiencing when driving!!??

how does it do this? cant do it with the fuel pump! cant see any electrical thing connected to the ecu that would let the ecu take control of the fuel pressure like this! what the heck is goin on?

I can tell that this lowering of the fuel pressure is playing up with the mixtures at idle and making it stall, even tho its getting enough air, its not getting enough fuel coz the pressure is too low!

so can anyone else tell me what their normal idling pressure is? and if it does this wierd thing?

hope ive explained it well enough:)

[PUDZ 32R]

sounds pretty normal for the fuel pressure to do this. im not sure of the exact pressures but it does reduce pressure at idle as the vacuum is greater and opens up the fuel pressure regulator more. therefore when you rev a bit or under boost the regulator closes more hence increasing the pressure in the fuel rail. i am still leaning towards AFM or a boost leak in your intercooler piping or even a vac leak like an intake manifold gasket or a cracked hose.

take it to a good mechanic and get them to do an intake pressure test where they pressurise your intake tract with a harmless smoke that way you will see if there are any leaks that you need to fix.

if this doesnt turn up any leaks i would say your AFM or the wiring to the AFM are dodgy.

[stimps]

Ive just found that the RB20DET model has a "FPCM" function and an extra wire from the ecu that does something to the fuel pump. It cuts it back a little in voltage or something a few seconds after returning to idle position. This is definetly around the problem my car has. So it appears to be normal. So why is it making it run wierd is beyond me, and maybe this is why they dropped it on any other skyline models (you wont find it on any R33 or later)

its Terminal 104 on the ecu, goes to 0v while driving , at idle raises to 9volts. Wierd hey.

I will try the smoke in the intake tract idea, i still am not 100% sure that my intact tract is perfect, but i do notice that when i screws the idle up screw right in so it lets NO air thru, the engine will still idle and the aac valve takes over more letting more air in and if i unplug the electrical plug, boom, she stalls like it should. So no leaks after the throttle valve at least.

I am still leaning towards injectors dirty.

Starting to think this is just what happens to this system when everything gets old and tired! It just runs poorly.

It probably explains why the previous owner just had the throttle switch disabled, so it would never do this and just live with a high idle.

Found that at a fast idle (throttle open slightly) its supposed to have 3kg/cm2 fuel pressure and at idle, after 3 seconds, 2.5kg/cm2 which seems right coz that calculates to 35 and 43 psi exactly. which is what ive measured.

sucks when you find so many things in your car checks out hey, yet it runs like a dog

Think im going to get cracking on doing up a second set of injectors:)

thanks for your input PUDZ (lol)

Edited May 22, 2010 by stimps

[stimps]

ah and one more thing, sometimes the warning light starts flashing, but when you check the warning codes, 55 flashes up, which means all ok!!??

hey?

it starts flashing along with fuel mixture, goes off when rich, comes on when lean. yet i have not put it into mixture check mode!?

Ive got a spare ecu, tried that, same thing

ive swapped air flow meters, ecus, and TPS, *shrug*

HELP!

[stimps]

I am hoping to find anyone on here who knows how these crazy ecu's work in this model skyline, I'm at my wits end. I've disabled the idle control circuit, since it just won't properly do the job, and left the throttle open slightly to try to stop it stalling. Got a raised idle but it's better than stalling at the lights. But then it happened again, just slowed down to pop into a driveway then boom, stalls. Why would the ecu just shut down the engine like that?

No wonder most poeple turf out this horrible bit of shit ecu and put in programmable management!!

[QLDR31]

My auto RB25DET NEO Stagea is experiencing a stalling problem. About 50% of the time when I stop it stalls.

Pretty anoying, the mechanic said the battery was going down to 9V when starting.

So today I bought a new battery, but that didn't make any difference to the stalling problem.

It would be interesting to know what your problem is.

Maybe mine is just a simple idling too low problem. It just got serviced the other week maybe they stuffed it.

[stimps]

Ok ive done some testing/thinking, and i have found that the FCPM (fuel control power module) switches the fuel pump to a resister in series with the pump, which slows down the pump at idle. No one ive talked to has been able to work out or tell me why nissan did this and most people who have had experience with it, just short out the resistor and dont worry about it. If they install an aftermarket pump, they just wire it directly to the fuel relay. Makes any tuning easier. its just a pain to work with otherwise.

So im going to do this also and if that doesnt work, I nonticed also, that just openign the throttle slightly makes it idle fine, so why not just dupicate that.

What i mean is, let more air in and adjust the voltage on the input to the ECU from the throttle position sensor, up a bit.

Say, put some resistors into the wiring (with trail and error of course to get the right adjustment, probably put some variable resistors in) so even if the throttle closes off or the air flow goes to zero, the ECU will always put enough fuel in to keep a stable idle. Bit like a "no go" zone in the map.

I can put the TPS back to factory position, let the AAC work again and wire in a resistor to stop the fuel level getting too low.

I have also got my second set of injectors getting cleaned this afternoon and am waiting to see what results that brings along.

I could also using resistor networks, raise slightly the voltage of the AFM output too.

Eventually I will get this problem sorted, its just that its going to take more than just a part swap to fix it, like normal. Ill proabaly install a small box with two variable resistors (black box with knobs) on the dash temporary to play with to sort it.

Edited May 26, 2010 by stimps

[wlspn]

From what I have read, the idea of the fuel pump lowering voltage at idle is to minimise excess fuel being passed through the engine bay, heating up then returning to the tank.

[stimps]

From what I have read, the idea of the fuel pump lowering voltage at idle is to minimise excess fuel being passed through the engine bay, heating up then returning to the tank.

oh cool thanks for that

[QLDR31]

Your problem isn't something like the ECU needs reprogramming and tuning?

Sounds like it has a few mods.