VERY Strange issue .. Definitely need some input! Lean condition @ WOT

[nelsonmxmarc]

Ok so for those of you who have me on FB know i've been running over this non stop..

But for those of you who don't have me on there, let me gladly explain my situation..

I took my rebuilt (completely rebuilt..) 32 GTS to the dyno the other day. Everything started off great besides my car being on knock maps (Knock sensors were faulty). This was tuned out. The Z32 maf was tuned in, and we were good to go.. A base run showed something in the numbers of 310whp / 280 ft lbs of tq.. This was with VERY safe AFR's (we're talking mid 11's..) and negligible timing. So there was definitely a lot more to take off this motor.. Anyways, as it progressed, we encountered a sudden lean condition. I noticed the FPR closest to the fire wall (since the RB20 has 2 on the fuel rail system for arbitrary reasons..) had lost its boost/vac signal from the plenum. Obviously this promotes the diaphragm inside to close, cutting fuel intake to vac conditions, so it was obvious why we were running into lean spots. I replaced the hose, and we continued, but to my dismay we were still running lean..

So to date, the car idles fantastic on cold start maps. Sees stoich regularly but then drifts into the 15's when the running maps enable.. Now it's not horrible, but the worst part is then whenever the gas pedal is depressed or we give it some degree of air, we run into a total lean condition. Tapping of the pedal goes - 12:1 directly to 16:1 and back. So there is definitely a lean situation involved and from what i can tell on nistune the AFR's should be safely in the 12:1 range with the foot down.

So far i have done this;

1. 150 compression across, cold
2. No exhaust leaks
3. No intake leaks (holds 20 psi steady with a pressure testing system i fabbed up)
4. Plugs are RICH (black but not terribly)
5. New Walbro 255 pump (Edit - pump runs 13.64 V at ALL times .. Is on a direct 12 v feed from battery with relay)
6. New vac lines to FPR's
7. Z32 is clean and runs proper voltage (checked with consult via nistune)
8. New plugs
9. Timing is 25 BTDC (this was tuned)
10. ... and cams are 15 degrees respectively and 5 BTDC
11. Wideband is not faulty - seeing the same readings on both the innovate and AEM respectively
12. New fuel filter
13. Working injectors (checked for pulse)

I bought a fuel pressure tester - this is my next move obviously, as it seems to be the only remaining factor in this mess.

The only thing i cant wrap around my mind is - HOW ON EARTH could my car gone from a perfect running condition, to massively lean on the dyno? And if it is low pressure, why?? What could possibly clog the lines.. I'm aiming at the FPR's being faulty. IF the vac line blew off the plenum then perhaps the diaphragm is cooked inside and is what lead to it blowing off in the first place..

I'm really stumped, this is by far the most confusing issue i've ever dealt with and for those of you following my build and helping me out along the way, you KNOW i've dealt with a lot of stupid, mind boggling problems..

Anything else you guys need, shoot it.. I have endless amounts of data logs sitting here that all lead to dead ends, but i'll gladly supply any essential info!

[derbeck]

Mad resolder time mine did the same

[nelsonmxmarc]

Mad resolder of what?

[cschepp]

Your maf.... I wouldn't mind seeing how do this.... Marc post up a diy to it.

[nelsonmxmarc]

I've done it already, same bs. And it's not the maf, because the car doesn't start without the maf plugged in for 2 reasons. 1. the O2 is on an open loop at all times as we tuned the car with the wideband so the O2 is irrelevant now. and 2. the car needs the maf to run and wont run without it plugged in.. Also i noted the MAF #'s on nistune and they correspond to a properly working maf..

[Zacho]

What fpr?
What injectors?
Were you able to monitor fuel pressure before/after the line came off?
Post up injector settings if you can. It almost sounds like the pw or dead time was changed by accident or something. It does this only when you transition maps it makes me wonder.

[BrianV8]

AHHH i think i might know what it is. Stock skylines have a fuel pump voltage regulator, meant to increase fuel pump output depending on throttle position i believe. Anyways these are notorious for failing and should be the first thing any skyline owner should do upon getting there car. Basically your giving your fuel pump 12v constant but instead of running a new 12v wire here is how to do it the easy way.

Go in your trunk pull the panels off on the drivers side. You will see a harness connector running in between your inner and outer fender. If you reach behind you will find a voltage regulator box. Two 10mm nuts will remove it. Once u pull it unplug it and throw the box away. On the harness you will see one big fat wire. Cut it from the connector and ground it. Bam you have a fuel pump with a 12v constant.

See what that does for you.

[nelsonmxmarc]

Did a pressure test on the system - 42 psi in IGN (not on) , 42 psi on, and 42 psi with or without the vac connected...
This was the same with 2 different FPRs.

Zach, stock FPR, and rb26 injectors.
Injection multiplier is 157
Latency is 760
Volt latency change is 184
Tps trigger is 5100 mv

I can gather more info from nistune if you like, unfortunately I don't have Internet here at the moment so the best I can do is relay via iPhone .

Let me know what you think!


Brian, I'm running on a 12v direct feed. So the fuel pump has it's own relay.. I'm only using the ecu 12v signal as an on/off.. All existing wires are out. Fuel pump runs 13.64 constant

[archaeic_bloke]

AHHH i think i might know what it is. Stock skylines have a fuel pump voltage regulator, meant to increase fuel pump output depending on throttle position i believe. Anyways these are notorious for failing and should be the first thing any skyline owner should do upon getting there car. Basically your giving your fuel pump 12v constant but instead of running a new 12v wire here is how to do it the easy way.

See what that does for you.

I think he has a constant 13.8 V alrdy!

5. New Walbro 255 pump (Edit - pump runs 13.64 V at ALL times .. Is on a direct 12 v feed from battery with relay)

what about the oxygen sensor?
What does the tuner say about the problem?

what happens if he adds more fuel to the map? nothing it continues to go leaner? so is it inverted then? what happens if he removes fuel from the map?... in some odd universe could the programming somehow have gotten messed up? something as simple as a blown diode on a circuit board could reverse polarities of circuits, but usually that has more harmful effects... but still in the realm of possibilities.

I think you need to get back to basics and start from square one and start ruling out entire systems.... thats what I do when ever I can't figure out a problem, and it usually at least helps to point me in the correct direction.

I'd start with the ECU, can you borrow one and see if that would make any difference? maybe someone who has a set up similar to yours alrdy M-A?

then borrow another Maf, see if that makes any change

etc.. and keep going and continue to cross things off the list, obviously something wont be worth the effort and cost to swap, but at this point its better than going in circles.

keep us updated man, good luck! and everyone chime in here, the more heads on this problem the quicker we can arrive at a solution!

[nelsonmxmarc]

Also.. Swapping fuel filter/FPR made no difference. I'm leaning towards injectors..

Oh btw Zach, pw runs off the charts at 2800 rpm - 47.8 ms.
It goes 34.5/34.5/21/19.5/19.5ms.... To 2800..values are 184@400rpm.. 184/111/104/104/104@2400 then spikes to 255@2800rpm
These are for max pw