Running lean w/o boost HELP

[judasentinel]

If your coils are weak or if the spark is not strong enough, you would have sputter. But I am leaning more towards your fuel side. Glad you got the MAF ok. What is the situation with your fuel pump? Is it possible for you to flow test your injectors or replace them with different ones to see if anything changes?

I remember when I had my GTS last year and was running an RB26DETT in it, I had the exact same problem. I was idling at around 15-16 and cruising around 17, 18 or even off the charts on my AEM UEGO. Changed the injectors and the afrs came down a bit, but never to the ideal levels. Hell, I was running 13-14 at WOT, but there was neither any knock, nor was there a power loss. I then changed my fuel pump from Walbro 255 lph to stock GTR one and nothing changed.

Then it occurred to me that perhaps if I plugged/capped the vacuum line connected to the stock fpr, it would help. So I disconnected the vac line leading to the fpr and capped it. The afrs came down to safe levels. It seems that my fpr was causing the pressure drop and when I eliminated the vaccum on it so it wouldn't regulate the fuel pressure under boost, things improved. You may want to see to it that your fpr is working ok. Check the fuel pressure. If it is falling below 35 psi and your fuel pump is fine, then you have a bad fpr.

Our cars' engines can be so complicated when it comes to troubleshooting. One seemingly unrelated problem could end up causing all sorts of issues in the proper running of the car and the only way you find out the relation between the two is when you look at it in hindsight. Back in 2006, I had a severe power loss in my car. At the time, I was on my second RB20 in my GTS-T. Checked everything from coils to MAFs to injectors, etc.. Nothing seemed to be wrong. And then suddenly, I decided to check my timing belt. Took the cover off and guess what!! The timing belt had skipped two teeth on the intake came side and had retarded timing by 10-12 degrees. Needless to say that I had to change the timing belt and the rest is history.

So my vote would be for either an air leak somewhere, or it is fuel related. Also , while youre at it, can you PLEASE check your ignition timing? You just might have a winner.

Good luck and please keep us posted.

[Skym]

Disconnecting stock FPR vacuum hose raises fuel pressure roughly 7.1psi or so from factory 35.5psi at idle (same stock base fuelpressure for RB20DET, RB26DETT).

I think bigger lph fuelpump needs a adjustable FPR, as bigger lph fuelpump probably forces more fuel past the stock FPR and returns to fueltank

Or could be the voltage regulator to fuelpump. They are known to playup.

This device can replace stock voltage regulator (adjustable) and usually solves the problem -

http://www.kennebell.net/accessories/boostapump/boostapump.htm

It's good because it doesn't heat the fuel. Running full voltage to fuelpump, removing fuel damper and running say a Sard FPR can solve lean problem, but fuelpump can be noisey, puts more load on alternator when light's are on at idle, heats the fuel, etc.

[archenemy236]

I cannot find the stock voltage regulator on my GTR everyone has said to hard wire it but i cant find it...and there isnt a word of it in my service manual..

[M13]

I cannot find the stock voltage regulator on my GTR everyone has said to hard wire it but i cant find it...and there isnt a word of it in my service manual..

1. Open your trunk

2. Remove the right side inside liner

3. Reach in to the gap between the trunk and rear right side quarter panel through an opening above your ATTESSA fluid reservoir

4. You'll feel a rectangular box about 1" X 1" X 4" It has two 10mm holding on to it.

5. remove it, and bring the wiring loom out so you can see better.

6. There is a big WHITE cable about 12-14 gauge thick.

7. cut it, and attach a grounding end/fitting.

8. ground it to a good chassis ground.

9 Now your fuel pump runs on 12 V constantly.

[archenemy236]

Is this what you are talking about?
[YOUTUBE]
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http://www.youtube.com/watch?v=_cBvYC7O7JA

http://cgi.ebay.com.au/Nissan-Skyline-R32-GTR-Fuel-Pump-Control-Module-ECU-JDM_W0QQitemZ380221012007QQcmdZViewItemQQimsxZ20100403?IMSfp=TL1004031410001r12423

[M13]

No it's on the other side.

Between the fender and trunk inside. Reach in above the ATTESSA reservoir on the right side. You're digging left.

[archenemy236]

Just hooked up a fuel pressure gauge and at cruise its hitting 38 PSI and under WOT its maxing at 60 PSI is this normal? I also cannot find the Relay im pretty positive it doesnt exist on the GTR.

[judasentinel]

Dustin, the fuel pump relay is under the dash, as far as I know. Its like any other green relay that our cars have. If you take your ECU out, right behind it are a couple of relays tucked away in the crevice. I think one of them was a fuel pump relay.

But I dont think you need to do anything to it at all. If you're getting that kind of a pressure under WOT and at cruising, then you're fine. The fuel pump is ok, it seems.

Can you please check your ignition timing? See if it is at stock levels or a bit retarded. I know for a fact that if the timing is retarded a tad too much, your car will sputter and hesitate under normal conditions and if it is advanced too much, it will sputter and cut off under WOT (as the ECU will detect knock and will revert to knock maps and retard the timing, thereby reducing torque and power).

In addition to that, also check your CAS for any damage inside. Weirdest things have happened to me in my first Skyline. If the CAS has a broken half moon inside or for whatever reason it is not aligned properly at the right location, not only will your ignition timing be off, but your injectors would be firing at the wrong time, as well as you might be experiencing issues with camshaft. A friend of mine had this happen to him. He would lose all power at 5000 rpm. I suspected it was a fault of the CAS for some reason. And when he removed the CAS, he discovered that the half moon on the exhaust cam that lines up with the CAS had broken off. As a result, while his intake cam was perfectly timed, the exhaust camshaft had moved off. He had bent valves, and had lost all top end power. Hope it is not so in your case, but no harm in checking it out. Do the ignition timing check and that wil tell you a lot.

Andrew (kelaog) has a very detailed thread on fixing your car's hesitation. If you go through all the steps/checks that he has suggested in it, you may be able to find the culprit(s).

Another thing to check as I shared earlier is the injector flow. If getting them flow-tested is not a viable option right now, try swapping a different set and see if that helps in any way.

[Skym]

TPS or o2 sensors are the only other parts he hasn't tried / replaced that affect fueling. 02 sensor or sensors x2 for GTR can stop fluctuating enough and sit near lean, so could explain the lean condition. Unplugging o2 sensors can help to check for faulty o2 sensors, as ECU ignores them and uses fuel map only (ECU goes into open loop). TPS can cause hesitation, as it affects transient fuel enrichment when suddenly accelerating at lower rpm's. TPS usually needs to be replaced at same time / km as o2 sensors (every 40,000-60,000km or less if you do lots of short trips with o2 sensors). TPS could be earlier, as it depends on you driving style to when TPS fails.

[archenemy236]

I just disconnected the o2 sensors and it didn't change anything under boost, just made it run really rich at idle but still wasn't getting enough fuel under WOT i was getting a AFR of 15...I am going to be checking the timing this weekend..the car before it was running lean was backfiring quite a bit I dont know if it could have jumped the timing or what.

[archenemy236]

Problem solved was a crapped out MAFS and o2 sensor repairs done thanks for the help everyone!

[Skym]

Good to hear you have fixed the problem.

[archenemy236]

And look at all the maintenance I did! All is good!