[Mk2] [Turbo] Fuel Pressure Regulators and Fuel Cut Defencers

[Mike]

Just got back from my rolling road session at Interpro, the car is indeed running lean above 5000rpm. AFM, Injectors, fuel pump were all ok, the issue seems to be that as the revs increase boost climbs north of 12psi and starts to nudge fuel cut. Fuel pressure was low but apparently within tolerance (just).

The mechanic advised me to install an FCD and to increase the fuel pressure with an adjustable regulator, so any suggestions?

p.s. Unfortunately due to the lean running, we couldn't do a power run but the mechanic did say it was making 250hp at 4800rpm so could be pretty good once I sort the fueling out.

[bobhatton]

Is this on a stock ecu and stock pump rail etc?

What was the fuel pressure and what are you calling lean?

[Mike]

Yep, ecu and fueling componants are standard.

CO figure was 4%, fuel pressure without vacuum at idle was 48psi.

[Peter Gidden]

CO figure was 4%, fuel pressure without vacuum at idle was 48psi.

What was the engine doing when the CO measurement was taken? Idling?

What were the measurements when the engine was reportedly running lean?

[Mike]

CO figure was 4%, fuel pressure without vacuum at idle was 48psi.

What was the engine doing when the CO measurement was taken? Idling?

What were the measurements when the engine was reportedly running lean?

The CO figure of 4% was taken at 4500rpm and 12psi boost which is where it's running most lean. At idle the figure was 0.2%.

[bobhatton]

What was the air to fuel ratio at max power? That is the important information.
Did they use a wide band sensor?
What is your base ign timing set to?
What fuel did you use?

[Mike]

What was the air to fuel ratio at max power? That is the important information.
Did they use a wide band sensor?
What is your base ign timing set to?
What fuel did you use?

The car wasn't run above 5000rpm due to detonation. The reading of 4% that was taken at 4500rpm translates to an AFR of 13.

I don't know if they used a wideband sensor.

Ignition timing was set by Rogue about 6 weeks ago so should be spot on

Fuel was (and always is) Shell V-Power.

[Mike]

BUMP

[bobhatton]

You need to check your fuel filter, fuel pump and fuel injectors for blockages, there are filters in the pump and injectors

[Mike]

You need to check your fuel filter, fuel pump and fuel injectors for blockages, there are filters in the pump and injectors

They did check the filter, which whilst old is apparently ok. He also said that the injectors and pump were fine too although the injectors are operating at the higher end of the scale duty wise. I assume he was just checking voltages?? Would that detect a blockage?

The thing thats confusing me is that even though the boost pressure is creeping, its only creeping to 12.5/13psi which should be well within the capabilities of the fuel system if the fuel pressure is indeed within tolerance....

[Peter Gidden]

They did check the filter, which whilst old is apparently ok.

If it's old. Replace it.

the injectors are operating at the higher end of the scale duty wise. I assume he was just checking voltages?

I assume he was checking duty cycles.

Would that detect a blockage?

Unlikely.

[Mike]

Hmmm, it appears that my MAP sensor (as in the turbo pressure sensor next to the diagnostics port) is disconnected. Would this mean that the ECU doesn't know how much boost is being generated and therefore isn't increasing the fueling to match?

[bobhatton]

Hmmm, it appears that my MAP sensor (as in the turbo pressure sensor next to the diagnostics port) is disconnected. Would this mean that the ECU doesn't know how much boost is being generated and therefore isn't increasing the fueling to match?

From what I can see you have a Rev 2 so the "map" sensor only works the boost gauge and does nothing for the ECU.
With it disconnected you will never have fuel cut

[Mike]

Hmmm, it appears that my MAP sensor (as in the turbo pressure sensor next to the diagnostics port) is disconnected. Would this mean that the ECU doesn't know how much boost is being generated and therefore isn't increasing the fueling to match?

From what I can see you have a Rev 2 so the "map" sensor only works the boost gauge and does nothing for the ECU.
With it disconnected you will never have fuel cut

Yeah, I guess the ECU looks to the throttle position sensor in order to determine how much fuel is needed rather than the map sensor.

It was worth a try.

[Peter Gidden]

Yeah, I guess the ECU looks to the throttle position sensor in order to determine how much fuel is needed rather than the map sensor.

And AFM.

[Mike]

So chaps, how do I check the injectors and fuel pump for blockages?

[Turbonoz]

RPM & load (AFM voltage in this case) dictate fueling firstly, TPS is used for enrichment if it's anything like the Nissan ECUs I work with.

48psi base fuel pressure? That's 10-12psi over what it should be. If the FPR is doing its job, and fuel pressure is rising at a rate of 1:1 with boost pressure, you should be running very rich. But you're not. Dodgy pump or FPR. Try the FPR first, it is cheaper. FYI, mine started to run lean at 1.2 bar (IIRC) and a 255lph pump cured the issue completely.

A dodgy injector may show up if you look at the plugs and if one cylinder has been running lean for some time. They can be flow tested and ultrasonically-cleaned.

It should have been run on the dyno with a wideband if you were having work done there, and not just a power run as you need an AFR plot. What was the fuel pressure on boost? There is no "nudging" of the fuel cut, it is akin to hitting a brick wall as all four injectors are cut instantaneously. Fitting an FCD is not required, as has been pointed out, you don't even have fuel cut enabled. Increasing fuel pressure on an old stock pump to mask an issue is stupid advice. If you must, take it to somewhere that knows what they're doing and will do a proper diagnosis for you

Why does everyone think 440cc injectors "max out" at the first sign of boost? 440cc injectors will not be anywhere near full duty on a CT26 at 12/13 psi whilst running at 13:1 AFR. Simply impossible. 1.4-1.5 bar with an uprated fuel pump at stock pressure with stock fuel rail/lines/FPR & stock ECU = Very Good Fueling

Check fuel pressure on boost, ensure it rises 1:1 with boost pressure
Replace fuel filter
Replace FPR
Replace fuel pump (access panel under the centre console )
Have the injectors flow tested

P.S. I have a stock FPR in mint working order