Frequent Lean condition RB25DET

Hi as title mentions I have an ongoing problem with my Skyline.

For a long time now my car has sporadically been running lean.

In the beginning it was noticeable at idle but seemed to be better when driving.

When it ran bad my AFR gauge was reading between 16-17 at idle and the car began to run rough but felt better when free-reving.

Sometimes I could drive for an hour or more without any problem and then all of sudden it would start to run lean again.

I have noticed that it seem to get better sometimes when i shut the engine off and restart it after some minutes.

As time have passed this problem has become much more frequent.

Now I can start the car up and it will be fine for a while, but almost as soon as I begin to drive, it will start to progressivly run lean and struggle.

as mentioned above it was just noticeable at idle first but now afr will drop to 16-17 when cruising too.

My gauge has been reading full lean sometimes at idle aswell.

my Afr gauge is not connected to my ECU it's just a standalone gauge.

im running an Apexi power fc. car was mapped 4 years ago and afr has been fine with this map before.

I don't run with closed loop activated.

The engine is mildly modified rb25det.

main things that is upgraded is turbo, injectors, fuelpump and airflowmeter and supporting mods.

recent things I have done and checked are.

* supplied the fuelpump with full battery voltage with a relay kit and fixed proper grounding points for it.

I have visually checked the connectors to the fuel pump assemlby.

* Filled up tank with new gasoline, the car had been standing in storage for 9 months until recently

* checked base fuel preasure. It was reading 38psi without vaccum. I also replaced the fuel preasure regulator soon after with a Nismo adjustable one and set that up to 40psi base preasure. one thing though everytime I have checked the fuel preasure the car has been running fine unfortunately so have not been able to verify the preasure when it runs poor.

* removed old sketchy alarm system that was in the car since I bought it. and mended all bad eletrical connentions there.

* replaced fuel filter with genuine nissan part.

* replaced CAS with new genuine Nissan part

what else.. spark plugs was replaced 2 years ago along with a PRP VR38 coil conversion kit. spark plugs are NGK BCPR7ES gapped at 0.7mm.

Injectors was replaced with Nismo 555cc 5 years ago at the same time the ECU went in.

Fuel pump was replaced 8 years ago with a Tomei 248/lph drop in asembly.

Im running on pump gas 98 octane. here we have 5% ethanol in the petrol. how much 5% would affect injector condition when storing for around 9 months im not sure about.

Any input or tips would be greatly appriciated!

Thanks!

Klas,

Based on all the info you have provided, I'm assuming you are still running on MAF? You have mentioned you have noticed the problem slowly getting worse? Have you cleaned MAF sensor? It is possible that you are getting a scewed reading. As the MAF uses a little heater element and as air passes by depending the intake air temp it determines air flow by how fast the heater cools down, so if you have a dirty MAF it may take longer for the heating element to cool, so the ECU will think that it is not getting as much air flow that you truly are, and it will start to pull fuel back.

You can 100% ignore all of that if you aren't running MAF sensors lol.

-Tobes from New Hampshire USA

Thanks for the tip!

Yes, I do run a Z32 MAF sensor that was replaced at the same time as the injectors and turbo, forgot to mention that.

But no I haven’t cleaned it so I will look in to it.

So I inspected the MAF and looked at the output signal while driving and couldn’t notice anything abnormal like an odd voltage drop or value jumping around etc.

I have noticed though that after replacing the fuel preasure regulator and setting it up at the same fuel preasure as the stock one (40psi) that the car seem to run leaner more often than before, even tough it did run lean with the stock unit as well. I notice it at light acceleration and when transitions occur.

It feels like the afr is jumping around a bit and is hard to dial in. It dosen’t seem to help much when giving it more fuel at those cells.

The car still ran into low 10’s at higher rpm when I did a full pull which i’ve reached previously.

How lean the car runs seem to variy a bit but I haven’t really done a full pull when the car is running at it’s worst so could affect high rpm as well.

Wideband O2 sensor drift perhaps.