3vz lean fuel problem - help!

[zlzgrom86]

I recently picked up this code:


The car seems to backfire whenever I shift or rapidly operate the throttle. Its a JDM engine too.
Engine is stock. Running 89 octane with 15* advanced timing (which was stock when I got the engine, assuming thats stock for JDM).

The fuel consumption is pretty high too.

Any ideas?

[zlzgrom86]

Here are the spark plugs

[Jason.MZW20]

Is there an air leak past the MAF sensor? Intake manifold gaskets/manifold leaks, vacuum hose disconnections, etc. I'm assuming you're running a JDM motor with a USDM ECU?

From your spark plugs, the rear bank is running a bit leaner than the front bank. The poor fuel consumption is likely from the ECU adjusting the fuel trims to deal with the lean code. The extra fuel can most noticably be seen on cylinder #2's spark plug. But other than that, your spark plugs look quite good (probably too good depending on how many miles are on them).

I'd check the fuel pressure going to the rear bank, since it seems to be affecting each cylinder. But first, I'd probably look for an air leak in or around the rear bank.

[zlzgrom86]

the hoses on the engine look new and are not hard/cracked. i have a boost guage in the car as well and i get good vaccum (20 inHg at idle).

i dont know why fuel pressure would effect the rear bank since if i follow the fuel lines, the fuel first goes to the rear bank and then to the front bank.

[Jason.MZW20]

Originally Posted by zlzgrom86

i dont know why fuel pressure would effect the rear bank since if i follow the fuel lines, the fuel first goes to the rear bank and then to the front bank.

It just seemed more likely than 3 clogged injectors. Fuel trim data would be useful here (but OBDI requires a special connector and reader), as would overall fuel pressure. Have your injectors been cleaned at all? Is the rear bank's O2 sensor new?

Something is happening in the rear bank that isn't occurring in the front bank that's causing an AFR differential between the two banks.

[zlzgrom86]

i tried doing the oxygen sensor test listed in the 3vz manual, here is the results:

with TE1 and E1 DISCONNECTED and engine @ 2500rpm:
I get a reading of about 2.2v on the front bank, and anywhere between 1.1v -2.2v on rear bank.

with TE1 and E1 DISCONNECTED and engine @2500rpm and PCV hose disconnected (but plugged to avoid stalling):

voltage rises.

with TE1 and E1 CONNECTED:
voltage is about 0 at idle and at 2500rpm. Im using a digital voltmeter so the voltage might be switching like it says in the manual, but it didnt look like it. it was pretty constant at .08 -.09 volts.

at first when i was doing the tests the rear bank had 1.1v while the front bank had like 2.2v but then when i was jiggling the probe the voltage keep swapping between 1.1v and 2.2v on the rear bank.


update:
with got my dad's needle voltmeter and doing the fluctuation test and the bank that had the semi-black spark plugs didnt show fluctuation at all. While the o2 sensor of the bank which had white spark plugs showed normal fluctuation.

Im confused.

[Jason.MZW20]

If the rear bank is the only sensor that is fluctuating in voltage, that means it's the only sensor that's actually working and detecting oxygen in the stream and the ECU is adjusting the fuel trims for that bank. Independent bank control requires two working O2 sensors. The front bank's O2 sensor shouldn't read constant voltage all the time because the O2 will vary in the exhaust stream. I think you need to worry about the front bank. I checked my spark plugs on my 1GR, and they look exactly like your rear bank plugs, so that's definitely the healthy bank with the working O2 sensor. Since the voltage is constant on the front bank, the ECU probably doesn't adjust the fuel trims as frequently (or at all, yikes!) as it does with the rear bank, leading to some AFR issues.

You might want to think about getting some universal Denso O2 sensors (since they're cheaper) and wire them up.

[zlzgrom86]

ok i agree that the front bank must be the problem now, its just confusing how the plugs look dark yet the code is for lean.

[zlzgrom86]

Fuel pressure right after the fuel pump, before fuel pressure regulator is a constant 40psi. After a few minutes after I shut the car down the pressure rose a bit to 45psi. Guess thats normal because there is no velocity.

So I guess the fuel pump is ok? What do I test next and how? There is no intake manifold leak I confirmed that too with carb cleaner method.

Im still guessing its the front bank oxygen sensor. There goes the cash.

[Jason.MZW20]

Sounds a good deal low to me. If 40psi is full pressure from the pump, then the pump is weak. The FPR is OEM set for 43-44psi, so you aren't even reaching the stock fuel pressure right after the pump. It can't keep up with the demand, nor can it keep the fuel pressure at a constant 43psi.

[zlzgrom86]

i know that if i just had the gauge as the dead end of the fuel line the pressure would be higher since there would be no velocity. But I did this test with the car running so there was velocity.

I am looking online and I dont see those high pressures you say, it I have the fuel line dead end into the gauge it will definitly be higher I know. Googling "fuel pump pressure" I see pages that have stats saying 35-45 psi range.

[Jason.MZW20]

Originally Posted by zlzgrom86

i know that if i just had the gauge as the dead end of the fuel line the pressure would be higher since there would be no velocity. But I did this test with the car running so there was velocity.

I am looking online and I dont see those high pressures you say, it I have the fuel line dead end into the gauge it will definitly be higher I know. Googling "fuel pump pressure" I see pages that have stats saying 35-45 psi range.

Well the 3VZ's range is 40-44psi at the fuel rails (not from the pump itself).

Remove the circuit opening relay and jumper the connection to run the pump with the engine off. Switch to IGN ON and test your fuel pressure that way. Although many fuel pumps can reach 80-90psi at full pressure, they can't run that pressure at the fuel rail because the pump would be at 100% of its limit all the time and flow would be restricted. Most stock Toyota fuel pumps for N/A applications should at least flow 50-60psi when new.

Do a pressure test at the rails to see how much the injectors are actually getting.

[zlzgrom86]

i can check the return fuel pressure, would that be the same thing?

i can also have the fuel line dead end into the gauge to get static pressure.



Even if i hold the lines between my hand I can feel some kind of difference between feed and return. I can actually feel the vibration of the fuel in the return line. dont know what that means though.


A failing fuel pump might also explain why when I had the 3sgte it was stuttering. But i dont know how it would cause one bank to run a bit rich and give a lean error code.

[V6'er]

With the gauge attached to the feed line with the fuel pump running, quickly (very quickly) and partially pinch off the fuel return, BUT BE CAREFUL. If you pinch too hard and the pump has capacity, you'll likely knock the return line off and gasoline will go everywhere. (Better yet, keep a fire extinguisher handy.)

All you need to see is that you can make at least 60 PSI or so from that pump.

Do this with a COLD engine and with somebody at the switch.

Hey, I'm not claiming this to be a safe method, but it will surely work.

[zlzgrom86]

with the fuel setup i have (where I had to use a brass barb to make the fuel send line longer) I could easily perform a volumetric flow test, i just need the specs.

[conor]

Did you get new O2 sensors yet?

If bank 1 is running lean and bank 2 isn't, then you don't have a fuel pressure problem. Bank 1 gets fuel first.


In any case:
- Check resistance spec on your O2s.
- Check voltage fluctuation (it's not supposed to stay constant)

Originally Posted by zlzgrom86

ok i agree that the front bank must be the problem now, its just confusing how the plugs look dark yet the code is for lean.

I would verify a failed O2 sensor first, but if your plugs are indicating a rich condition and your ECU is throwing a lean condition code, then I'd say we have a sensor problem of some sort.

Also, those plugs don't look particularly rich.

[Jason.MZW20]

Originally Posted by conor

Did you get new O2 sensors yet?

If bank 1 is running lean and bank 2 isn't, then you don't have a fuel pressure problem. Bank 1 gets fuel first.

Bank 1 is normal and has the working O2 sensor. Bank 2 is the one with a shot O2 sensor. The rear bank's spark plugs look really good. The front ones seem like they aren't getting to the same temperature as the rears, and cylinder 2 seems to be the worst of them. If it's soot on cylinder 2's spark plug, then it's overly rich.

I say replace both O2 sensors (you might as well), clear the code, and see if it returns. You should also swap the spark plugs between the banks to see if cylinder 2 still looks like that after both O2 sensors have been changed.

[zlzgrom86]

i just ordered 1 sensor an hour ago.. $100 damn (including shipping)

[Jason.MZW20]

Originally Posted by zlzgrom86

i just ordered 1 sensor an hour ago.. $100 damn (including shipping)

You could've bought 2 Denso universals and just reused your existing connectors.

[zlzgrom86]

the ones that i found that attach using a 2 bolt flange are more expensive.