Fuel pressure question

[ricknismo]

Just trying to clarify something.

What is the relationship of the fuel pump and regulator to the injector duty cycle? By this I mean...if a pump starts to fail, does the injectors have more of a duty cycle because they have to open up more to compensate?

Same with the regulator..if pressures down..does that mean the injectors have to open up more?

[blind_elk]

The duty cycle of the injectors is controlled solely by the ECU, based on information it receives from the various sensors on the engine (temp, air flow, throttle position, etc). The ECU is relying on the pump and regulator to be working "as designed" - it doesn't have any sensor input from them.

The ECU computes the injector opening time based on the info from the sensors, including how much air it has computed is available, and directs the injector to open for a certain time.

This is why engines melt pistons when fuel pumps start to "go off" - the pump can't supply enough pressure, which is the sole determinant of how much fuel gets injected while the injector is open. So the fuel mixture is over-lean (not enough fuel).

[ricknismo]

So why is my car getting 48% duty cycle at 0.9 bar at 5000rpm then stays at 0.9 bar and goes to 97% as revs go up...which sensors should I be checking?

Should be 48% all the way

[Neo_R34]

So why is my car getting 48% duty cycle at 0.9 bar at 5000rpm then stays at 0.9 bar and goes to 97% as revs go up...which sensors should I be checking?  

Should be 48% all the way

no...as per blind_elk's answer...more revs equals more airflow hence more signal via AFM hence different part of ECU fuel map hence different % of injector duty cycle to provide correct air/fuel ratio. Constant boost pressure does not equate to constant airflow...hope that helps.

Cheers,

Michael

[ricknismo]

Not really, I have had 2 other cars exactly the same that didn't do it.

The other cars had 1.3 bar of boost at 96%...this one has 0.8-0.9 bar at 96% but only high up in the revs

[Neo_R34]

Not really, I have had 2 other cars exactly the same that didn't do it.

The other cars had 1.3 bar of boost at 96%...this one has 0.8-0.9 bar at 96% but only high up in the revs

ok....please try reading the following link

http://www.stealth316.com/2-calc-idc.htm

as for the 2 other cars and there duty cycles and different boosts there are too many variables and lack of information to tell you why they were running the duty cycles they were ie: aftermarket mods (fuel system,injectors, type of ECU and tune, obviusly not standard if running 1.3 bar....so Fuel map has been adjusted etc so comparison is illogical.

hope that helps more...

Cheers,

Michael

[ricknismo]

standard computers and everything on the others...just more boost

[pnblight]

standard computers and everything on the others...just more boost

your maps basically run the injectors (with small competations for temps etc factored in) and as your revs and load increase you move through the map so if you get high injector duty it's most likely the ecu maps are calling for it to do so .Have you put it on a dyno to see the a/f ratios as by the sounds of it ,it would be getting very rich high in the revs.

pete

[ricknismo]

very...black on the rear in one day.

how would you fix it?

sensor issue?

[Tommyk]

get it tuned - unless it has the stock computer

In that case buy an aftermarket ECU and get it tuned ?

[blind_elk]

1 step backwards - where is all this information / numbers coming from?

Back to your last question - if you are running stock ECU (which I'm guessing you aren't, because they don't give out this sort of info), they are programmed to run richer at the top end, to protect the engine.

[ricknismo]

I have a stock computer and the innfo comes from the nisdat I have and the display 34 GTR's have. And it is definetely wrong to be that duty cycle as I have a 32 GTR as well and had a 33 GTR. Never done this duty cycle wise.

[Beer Baron]

mate, it's not wrong. it's just the numbers that are in that fuel map. as to why it's accessing those parts of the map, it could be a number of reasons. get it on a dyno first and see what's happening. you could make your car have 98%duty at 4000rpm if you wanted to on stock boost with just a PFC and some editing of the fuel map. it is not shooting for a target AFR. it's just a number in the map that is causing the injectors to stay open that long.

[ricknismo]

Problems are that the closest 4wd dyno is 800k's away and like I said, I shouldn't have to tune anything.

[Sydneykid]

Problems are that the closest 4wd dyno is 800k's away and like I said, I shouldn't have to tune anything.

I need to clarify a few things......

1. This is an R34GTR?

2. Zero mods, just boost up to 0.9 bar?

3. How many K's?

4. Did this suddenly happen? Or was it always a problem from when it arrived?

It has been my experience that R34's have the most sophisticated of the RB ECU's, they have all sorts of comparison tables for determining problems and protecting the engine via the usual rich and retard mapping. It sounds to me like you have a dud sensor, the Consult interface should tell you which sensor is crook.

PS; you don't have to use a 4wd dyno, just drop the front tailshaft and use a 2wd dyno.

[ricknismo]

1.yep

2.yep

3.40000

4.Was like that when I got it.

Other 34 owners have confirmed that it should be about 50-60% all the way to 8000rpm

My consult thing says air flow meters ar working fine but I am yet to find out if it is compatable fully with the 34 as I bought it when I had a 33

[Sydneykid]

1.yep

2.yep

3.40000

4.Was like that when I got it.

Other 34 owners have confirmed that it should be about 50-60% all the way to 8000rpm

My consult thing says air flow meters ar working fine but I am yet to find out if it is compatable fully with the 34 as I bought it when I had a 33

AFM's would have been a good guess, easy to check with a multimeter. Just compare the voltages. Doesn't sound like it though. Some stuff I have seen, that causes problems but doesn't always result in an error code;

1. Loose knock sensors, rattle around, give false knock readings, ECU goes R&R to save the engine from non existent pre-ignition damage.

2. Faulty water temp sensor, ECU thinks engine is still cold and runs rich. Should show up on the Consult

3. Faulty Lambda sensor, unlikely to cause this problem but simple to check. Should show up on the Consult

4. Faulty throttle position sensor, ECU thinks throttle is open more than it is, so slips in too much fuel. Should show up on the Consult.

5. Camshaft timing not correct, won't show up on Consult, you have to remove the cam pulley cover and check it.

6. Ignition timing, won't show up on Consult, you have to check it with a timing light.

7. Faulty injector (holding open), won't show up on Consult, you have to remove the plugs and check them, look for one that is noticeably richer than the others.

8 The hardest one is air leaks, more air going in via the AFM's than is actually going into the engine. ECU adds too much fuel for too little air.

Hope that is of some use:cheers:

[ricknismo]

I got my missus to drive it today with me behind it...she only revved it to like 4000rpm and theres a lot of black smoke...overfuelling heaps. I don't think the timings out as I have done that before on other cars and it changes the whole power characteristics,it drives fine.

If it overfuels, I would be guessing in saying the pump and reg are ok and be looking at injectors and oxygen sensors....agree?????

[pnblight]

and like sk said i would check water sensor because if it thinks it is still cold it will add a lot of injector duty to run rich (like an automatic choke) i think this might be the first thing to have a look at.

pete

[ricknismo]

The mfd display reads the water temp from that sensor doesn't it?

It reads ok