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Discussion Starter · #1 ·
Hi All,

Hope this is the right forum/thread to post this, as there isn't really a great fit out there and this forum seems to be quite active with knowledgeable folk, so here it goes.

Its a Navara, in oz, 2008 Spanish build 4.0 V6 petrol auto...its been around, with a healthy 355,000 odd km on the clock. Its still strong, but it was alot crisper up until a few months back.

It all started with a cracked exhaust, since I had to replace it I (maybe stupidly) replaced the second cats to high flow, a new "sports" muffler over a nice 3" pipe all through with a resonator to tone it down.

Coincidence or not, a few weeks later I started getting o2 sensor errors on bank 2 sensor 1, resetting those made no difference and the fun started...

I've replaced both bank o2 sensors, new MAF, PCV valve, all vacuum hoses (thinking vac leak), had the exhaust checked for leaks, had intake plenum smoke tested for leaks, thorough throttle body clean...everything seems ok.

I reset the codes, and it appears that when warming up, when it switches from open loop to close loop it trips o2 sensor 1 in bank 2 every time. I also notice when warm and running the o2 sensor readings aren't even across both banks, ie, this is an snapshot of what I see every day;
Bank 1 Sensor 1 - 0.31v
Bank 2 Sensor 1 - 0.55v
Bank 1 Sensor 2 - 0.78v
Bank 2 Sensor 2 - 0.73v

Its not a great ODB2 tool but the wave patters on sensor 1's on both banks are quite different.

So why am I not just ignoring the codes? Mainly the fuel consumption has gone from about 450kms on a tank to about 350kms....it has a rough idle, and it lags more on acceleration than what it used to do.

My next steps is to pull the plenum and intake manifold, check for damage/cracks and give them a thorough clean. Just waiting on gaskets to arrive and a free weekend to do this....

So....I gather we have people here that have pulled the VQ40DE apart and done more than change plugs :) ...So I'm hoping this post will be able to give me two things;

1. Advice on these symptoms could be and how to check for issues that I may have missed.
2. Since I'm pulling the plenum and intake out for cleaning, what else can I "service" whilst the engine's top bits are bare?

Its been close to 20 years since I've done any major engine rebuilds, and it was on simple naturaly aspirated beasts...these engines require a little more know how.

Thank you in advance for all advice.
 

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Discussion Starter · #3 ·
Hey Therealkoop, thanks for the response....yes, i agree that its over compensating and adding more fuel hence why its got poor efficiency.

The main code is P1283, thats been happening since the problems started.

I have also been getting P1273 (air/fuel ratio sensor 1) recently, which I think its still related to whatever the problem is.

I did the MAF reset after adding the new MAF, but I went back to the original after no improvement, the MAF readings didn't change and I rather keep the OEM version in than an aftermarket copy.
 

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Discussion Starter · #8 ·
Hi All,

Thought I'd post a bit more about progress, or lack there of in finding a solution here. Hope it helps others with some troubleshooting ideas...

Still getting P1283 and P1273 codes, occasionally rough idle where RPM seems to drop to just sub 500rmp.

Plenum, intake manifold and throttle body thoroughly cleaned, inspected for cracks/warps - all good! new gaskets and back in. No change to errors.

Looking at fuel trims, at RPM of around 2500 and over, trims are good (not great) with long terms around the -5% and short terms around +5-10%.

At idle, stopped in gear with break on (automatic) they jump around wildly anywhere between -25% to +25% on the short terms...not so volatile on the long terms but it adjusts.

There are a few reports out there about an internally leaking break booster creating a vacuum leak thats tricky to identify. I notice when I apply the break it jumps around +5-10% it then settles and on release it jumps a good +15-20%, up to what looks like a 25% threashold...

I've checked for engine bay vac leaks, smoked tested it, checked one way operation of the check valve, pressure tested the booster with tester/gauge and it appears fine...still doesn't explain the trim jumps on application/release.

Internal leaks are hard to find, the check valve should prevent back flow....I can't afford a new booster and kits are near impossible to find.

QUESTION: Anyone seen this behavior with trims and brake booster? Ideas? Solutions?

Another thing I found when smoke testing was a small leak in the power valve bearing (if there is a bearing). As this is right out front of the plenum, if it sucks as much air as smoke flow I could see it may be a significant problem. Again, this part is difficult to source without buying the actuator and solenoid, which is overpriced and overkill.

I'll attach a photos of the part I'm talking about.

QUESTION: Anyone seen this leak? Thoughts? Can it be fixed or is it a part replacement?
317021
317022



PS: Hope all in the US are hanging in there, it looks like you've got quite a while to go. We seem to have cracked it here in Australia for the moment...
 
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