Hi folks,

New here, been observing the forums for a long time, good information to be found. I am looking for some advice and thoughts on a problem.
As for the car it's a Nissan Skyline V35 sedan swapped with a F50 VK45DE engine. Custom long runner 4-1 headers which did push the cat's a bit further away than stock and a 350Z modified intake duct.

I have a rich running engine which did show a P0175 Fuel injection system too rich bank 2. I can obviously smell that it is running too rich even when the engine warms up, pulled out all the spark plugs and there is soot/fouling on all of them. Also the MPG is a bit worse as well.

I did some data logging over Consult and found that both A/F Alpha B1 and B2 jump between 78-84% at idle and at around 2k rpm constantly 75%.
Am I correct that it is trimming down the fuel to 75% because it is too rich and the P0175 happens when it can't compensate for the over fueling anymore?
O2 sensors seem to be working as they switch lean/rich as expected. MAF at idle measures 1.34V and 2.1V at 2500 rpm, that seems to be correct according to the FSM.
Attached photo of the data log and also the actual log file that can be opened in nissan data scan. Attached a photo of the spark plug as well, all look the same.

Suspecting that the ecu is injecting too much fuel and the fuel trim can't compensate for that amount, would that be because of high fuel pressure?
I have used the fuel pump control module with the dropping resistor but the fuel pump is the original V35 unit, but the FSM specifies 51psi fuel pressure for both V35 and F50 at idle.

Can't find any vacuum leaks or exhaust leaks, that would indicate running lean and the A/F Alpha would go above 100% am I correct?

Any thoughts or suggestions please?
Thanks!

marekku wrote: ↑

Fri Feb 10, 2023 2:17 pm

I did some data logging over Consult and found that both A/F Alpha B1 and B2 jump between 78-84% at idle and at around 2k rpm constantly 75%.
Am I correct that it is trimming down the fuel to 75% because it is too rich and the P0175 happens when it can't compensate for the over fueling anymore?

That's correct. Nissan alphas run 75%~125%, once adjustment hits the rail for a period of time they throw a P0171/174 for lean and a P0172/175 for rich.

marekku wrote: ↑

Fri Feb 10, 2023 2:17 pm

O2 sensors seem to be working as they switch lean/rich as expected. MAF at idle measures 1.34V and 2.1V at 2500 rpm, that seems to be correct according to the FSM.
Attached photo of the data log and also the actual log file that can be opened in nissan data scan. Attached a photo of the spark plug as well, all look the same.

Those plugs are "just rich" and not "I'm gonna foul" rich. The swing rates on the front O2's look okay but maybe not the voltages. If I read your scale correctly they're going near the limit rich (1V) and below normal lean. Healthy swing is generally between 300~600mV, with codes getting thrown around 100mV. So your fronts may have a problem.

marekku wrote: ↑

Fri Feb 10, 2023 2:17 pm

Suspecting that the ecu is injecting too much fuel and the fuel trim can't compensate for that amount, would that be because of high fuel pressure?
I have used the fuel pump control module with the dropping resistor but the fuel pump is the original V35 unit, but the FSM specifies 51psi fuel pressure for both V35 and F50 at idle.

You're misunderstanding something here. The ECM determines fuel trim, it doesn't react to it. It calculates the injector "open" time according to the amount of air coming in, and modifies it in realtime according to whether the front O2's show complete combustion or not. That's what's meant by "closed loop" feedback. So the only way the wrong amount of fuel ever goes in is 1) one of the sensors is fooling it and causing it to miscalculate, or 2) some external factor it can't control directly (like fuel pressure) is overriding the largest adjustment it can make.

Thanks for the good information, appreciate a lot!

The swing does go between 0.05V to 0.96V, from the FSM they specify:
HO2S1 (B1)
HO2S1 (B2) Engine: After warming up Maintaining engine speed at 2,000 rpm 0 - 0.3V ←→ Approx. 0.6 - 1.0V

That would make me assume it's okay, but I do not get any up/down swing from the log I've done, keeping it at 2000 rpm I only get static 0.91V and 0.92V both banks meaning running rich and as if it was in open loop?

One thing to mention I have used the long wire o2's on the HO2S1 front side and HO2S2 short wire on the post-CAT side. I understand all four are the same o2 but just different p/n for different cable length. Normally the short cable ones would be on the front and long cable post-CAT. Reason I did this was that the 4-1 headers pushed the CAT's further away so was a quick and lazy way to get them connected. But o2's go to the correct connectors to the ECU in the correct bank and pre or post CAT, just didn't want to splice and extend the front o2 wiring.

Will have a fuel pressure gauge fitted to see what fuel pressure I am running. Also will have a look at the EVAP system as the V35 (G35) is a bit different from the F50 Cima.
Noticed all the Infiniti FSM have a fuel temperature sensor fitted but the JDM ones do not have any. Wonder if there are any more differences that I am not aware of.

Anyway thanks a lot for any input!

marekku wrote: ↑

Sun Feb 12, 2023 5:45 am

Will have a fuel pressure gauge fitted to see what fuel pressure I am running.

Good plan. This (high fuel pressure) needs to be ruled out as the cause, although one might argue that high fuel pressure would affect both banks (barring a pressure regulation/obstruction issue).
Check pressure both at idle, and with RPM, preferably under some load if possible.

You said all 4 plugs from bank 2 showed *some* soot fouling (not just the one you attached photo of)?

3Q Jay wrote: ↑

Sun Feb 12, 2023 8:18 am

marekku wrote: ↑

Sun Feb 12, 2023 5:45 am

Will have a fuel pressure gauge fitted to see what fuel pressure I am running.

Good plan. This (high fuel pressure) needs to be ruled out as the cause, although one might argue that high fuel pressure would affect both banks (barring a pressure regulation/obstruction issue).
Check pressure both at idle, and with RPM, preferably under some load if possible.

You said all 4 plugs from bank 2 showed *some* soot fouling (not just the one you attached photo of)?

Looking at the logs both banks are rich but only one came up with the P0175.
Just made some more logging when driving and at idle will upload in a moment.

All 8 spark plugs had same fouling no difference between banks.

Ordered a fuel pressure gauge so will see what it's running at, does the pump try to maintain 51psi even above idle?

Had a look at the logs and after warmup (short drive) I am still in the 75% at 2k rpm, idle 82-91% that seems alright.
Attached a screenshot and also included log zip file.

Just thinking out loud, my fuel pump is currently stock V35 (G35) which should run 51psi which both cars specify.
The slower speed (8V through a dropping resistor) still retains 51psi with the integrated PFR in the pump assembly, but at less flow rate?
Under acceleration (system voltage 14V) it maintains 51psi but higher flow rate to support the higher RPM, am I understanding this correctly?

I've measured 11.62V across the pump at idle and 13.66V when revving the engine, that seems a bit off and I need to check why is that but the only use for this system is to decrease fuel heating when the pump is running constantly at 14V and heating the fuel in the tank, isn't it?

Some more thoughts:
- EVAP is purged when throttle is in any position except closed, would the EVAP cause rich mixture to the extent of going over -25% on alpha, not likely I think
- vacuum leak after the MAF would lean out the mixture and would not try to trim down the fuel
- exhaust leak before the o2 would let more oxygen pass the sensor and require more fuel rather then less

Will do some more driving and logging to try to catch the event when it shows engine check.

Thanks a lot guys for the help and info!

to NICO marekku - This is the best first post (now thread) I've seen in a while!

Q451990 wrote: ↑

Sun Feb 12, 2023 2:58 pm

to NICO marekku - This is the best first post (now thread) I've seen in a while!

Thanks for the welcome!

Later I will post my build thread of the VK swapped Skyline in case anyone would like to attempt doing it.

Also I may have sent myself on a wild goose chase, I think I have the incorrect MAF housing (narrower diameter) than the VK stock one, at least when I compare photos the outside diameter seems different. That should explain why the engine is over fueling, cause the ECU is being told more air is entering (higher velocity through narrower housing).
Suppose all Infiniti/Nissan MAF's post 2002 use 22680-7S000 sensors, but the housings "calibrate" the air flow for each different engine capacity?

I did not receive any MAF with the VK engine so ordered one which was specified to be suitable for all sorts of Infiniti's like G35, M45 etc but they look very different!

Anyway, I've ordered the correct 22680-AT300 now.