Overfueling issue

[Sx-mad]

Hi from a newbie

Hey guys I'm currently having an issue.

My car run fine a couple of weeks ago and all of a sudden my alarm had stopped working meaning my car was permanently imobbilised.
So I get the snips out and bypass the immobiliser and get the car started but my new issue is the car is overfueling.
The only thing I have found so far is that my afm voltage on idle at 1000rpm is 1.6-1.7volts when warmed up.

Spec is

Power fc
Z32 afm
740 injectors
Apexi filter
Apexi gt spec exhaust
Nismo fpr

Any help would be much appreciated

Thanks mark

[Croustibat]

Boost leak, disconnected MAF, disconnected coolant sensor.

Most common issue leading to a sudden AFR gauge saying "rich" is the boost leak though.

[Sx-mad]

Thing is if I cause a leak by let say disconnecting a vacuum hose it runs better as it is now running leaner.

My maf voltage is high for some reason too

Ecu doesn't have limp mode so disconnecting it won't do anything

Power fc commander shows the coolant temp and it seams to be working fine.

Thanks for the reply

[Croustibat]

A boost leak will make your AFR gauge say "rich" . I dont know why, it just does that. On my car, i get around 2 points richer when there is a leak, any bigger leak and the car bogs down. Do you have a wideband AFR sensor and gauge ?

I dont think you MAF voltage is that high, it is not directly proportional to airflow, there is a conversion table in the ECU.

Maybe you mapped the car with a boost leak that has been corrected since ? That would explain why your MAF voltage is suddenly higher. Cold weather may affect that too.

[Sx-mad]

Don't have the wideband hooked up but it's struggling to idle and chucking black smoke.

I haven't drove it since last time I had it started so I don't understand why a boost leak would appear out of nowhere when there has been no boost in it to pop a hose etc

I did look for obvious signs of boost leaks but couldn't find anything, I think it would have to be a noticeable leak to cause black smoke on idle.

I have been advised that the voltage should be 1.1v on idle

[Sx-mad]

There is a conversion table on the ecu but it still reads what air flow voltage is regardless then gets converted through the vq. The vq table is standard on the power fc and nobody adjusts it. So everyone with a power fc and z32 afm will be using the same table to map.

[Sx-mad]

Also the map tracer on the commander used to idle at around load point 3 on the grid where as now its at like load point 10

[steve shadows]

Can you let us know what settings you have in the PFC for the injector settings and the lag time? Thanks

[Sx-mad]

45% 0.00ms

[Kingtal0n]

A boost leak will make your AFR gauge say "rich" . I dont know why, it just does that.

He is disconnecting a vacuum hose, which is behind the throttle body, which is not a boost leak during idle, that is a vacuum leak and it will cause the car to run leaner, not rich.

Since you have a power FC, why not just adjust the VE table during idle? Do you need help learning how to use the commander?

And looking at the injector setting you just posted, I am worried you have the original PFC map in there with just the injector correction dialed down, because whoever did that 45% 0.00ms does not care or does not know what lag time is.

[Sx-mad]

I am quite clued up when it comes to mapping lol

The problem is the car has been fine for 3 years and the reason the injectors are at 45% is cause that is where it got the best closed loop afr and 0.00ms is because they are deatchwerkz 740's which are just modified standard injectors.

It was mapped at 1.4bar and produced 340whp and 350lbft afr's where fine (11-12)

I did adjust the percentage of the maf at 1.9v down to 75% and the car then became stable and smooth.

I don't want to adjust anything as I think there is an issue that has caused this and want to get to the bottom of it.
The main problem is I think the afm voltage is to high for some reason causing the map tracing to be at load 10 instead of load 3.

I'm going out with a spare afm tomorrow to try

Also ill try

Ecu reset and load map back on
Check for 12v at the afm plug
Add some more earths to the engine bay
Check fuel pressure
Boost leak test although I think it's fine since when disconnect the vac hose it runs leaner and sorts it.

[Sx-mad]

I'm also wondering if whatever caused the alarm to break has caused this, ie voltage spike or something.

[Kingtal0n]

The main problem is I think the afm voltage is to high for some reason causing the map tracing to be at load 10 instead of load 3.


right there, 10 is usually full throttle for naturally aspirated engines. The maf is either seeing a massive boost leak or its bad. It could be wiring related but that is unlikely, it is possible the ecu went bad but thats even less likely.

[Sx-mad]

Will report back later lol

[Sx-mad]

So went out today got it started and it run rich as **** to start with but once it warmed up it sorted out and air flow voltage is back to 1.18v at 900-1000rpm.

Idling at load point 3-4 now :)

Also causing a leak from the same vac hose which helped before now makes it worse as it should.

Bit confused lol hopefully it's sorted.

[Croustibat]

And looking at the injector setting you just posted, I am worried you have the original PFC map in there with just the injector correction dialed down, because whoever did that 45% 0.00ms does not care or does not know what lag time is.


For once i do agree with him.

Every injector has latency; you cant just set it at 0 and hope it will work.

Latency affects mostly idle / low load, as injectors are open for short period of time, the latency time is high compared to the fully open time. On higher load though the fully open time is way bigger.

To get the latency right, set your whole fueling range to the same value (AFR 13 is ok), and check how your AFR varies when accelerating and when cruising. Then adjust K and latency until you can see around AFR 13 all the time (even blipping the throttle)

Note : just because they are modified standard injectors does not mean they have the same latency. It mostly means they have the same body, but the DW has been drilled out and all its internals replaced.
The latency is the time it takes to open and close the injector, the bigger it is the higher the latency (when the technology is similar, which is why bosch EV14 based injectors rocks. 1000+cc/min with 700cc/min inj latency is great).

[Sx-mad]

Well I get perfect afr's of 14.5 -15.2 afr when cruising. The car idles fine and my afr's are between 11&12 on 1.4bar of boost.

This is the latency that was recommended. I do find adjusting the latency to 0.20 makes it idle as smooth as a Mercedes but it affected full throttle afr's alot. I did a power run like this and lost 30-40hp.