2000 With Unknown Issues, tried everything (that I know of)

[jpshoe]

Hey all,

So i've searched high and low on these forums for months now and done everything I can to try and solve my issues. Every step I have taken has not made a difference. Here's a rundown of what's going on, hopefully I can get some more guidance.

Bought the 4Runner in February with 103,000 on it. It's a cali-spec 4x4.

Shortly after I bought it I noticed I was only getting about 160 miles per tank. Did some investigating and did all of the normal stuff, spark plugs, wires, fuel filter, air filter. None improved gas mileage.

Also having some occasions randomly where I have no power and I get a backfire through the air box. It resolves itself within about 10 minutes and I have no issues.

About a month later I got a MAF code, so I replaced that. This is when all hell broke loose and my 4Runner began playing mind games with me. Had codes for front A/F sensor and rear O2. Replaced the front, rear was rusted in, I'll get to that in a moment. Then had codes for ECT sensor, replaced that...twice. None of this solved my issues either. ALL of the codes came back including:

P0171, P0172 (how I had a lean and rich code at the same time baffles me), P0125, P0141, P1130.

Took it to 3 mechanics, none have helped so far. Found a good one who told me I had to get that rear O2 sensor replaced since he couldn't think of anything else. So I bit the bullet and ended up having to buy the whole rear cat assembly because the rust was so bad (found one for 280 shipped). Today I replaced that, and the rear O2 sensor. 10 Minutes later after I cleared the codes, I have the following codes:

P0125, P0141, P1130, P0171P.

I'm at a loss, no mechanic seems to be able to help me out either, they all just want to replace every sensor, which I've done now twice on most. I'm a broke college student so that of course doesn't help me.

Yes I'm using Denso everything, doing all my research and everything I can in my power. Any help would be appreciated.

I'm torn as to what to do next, It's in great shape physically and just under 110k miles, I know if I can get this running I'll have a blast with it. Just sick of dumping money into what seems like a minor issue.

I included a picture, so you have sympathy for it like those ASPCA commercials... With your small donation of a little bit of advice, you could save this beautiful 4Runner.

Thanks all,

Joel

PS Here's the code legend to save you guys some time..

P1130 Air/Fuel Sensor Circuit Range/Performance. (Bank 1 Sensor 1)
P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0171 System too Lean (Bank 1)
P0172 System too Rich (Bank 1)


And a quick list of all the mechanical stuff I've done:
New battery, new plugs and wires, new thermostat, new front rotors and pads, new rear cat, replaced front A/F ratio sensor, rear 02 sensor, MAF, ECT, fuel filter, cleaned fuel injectors, new air filter, new starter, sway bar links, oil and filter (mobil 1 full syn at 5k interval)

 

[rcrick]

Too lean and too rich at the same time? I'm curious to see what this turns out to be? You mentioned you cleaned the injectors, could you have them flow tested? Has this truck been sitting for long periods of time?

 

[rcrick]

My train of thought is that if you are lean one minute and rich the next, all in the same bank, then could you have an injector that is sticking open and sticking closed as well.


Disclaimer: I'm not a mechanic but have been a few rounds with the 5vz.

 

[jpshoe]

Too lean and too rich at the same time? I'm curious to see what this turns out to be? You mentioned you cleaned the injectors, could you have them flow tested? Has this truck been sitting for long periods of time?

In regards to the too lean and too rich, only too lean is showing up now, and that has been the most common issue/

I didn't clean the injectors myself but the guy who did it said they were all functioning.

The truck hasn't sat more than a day since I've owned it, and the carfax showed regular maintenance with small mileage intervals, but seemed consistent throughout it's life. No huge gaps with low miles put on it or anything like that.

My train of thought is that if you are lean one minute and rich the next, all in the same bank, then could you have an injector that is sticking open and sticking closed as well.

Could that be causing my other codes as well though?

 

[gamefreakgc]

Two things to check:

1. Changing out the O2 sensor should not have caused more codes. Pull the EFI fuse out from the engine bay and see what codes are left. Unless of course, you put a front O2 sensor in the rear?

2. I once had a lean and rich code at the same time on my 91. After months of diagnosis (don't buy any more parts!) I found out it was an exhaust valve stuck open. It was allowing unburnt fuel to the front O2 sensor causing the rich code, then the ECU tried to cut back fuel so much that it threw a lean code on top of it. A compression test would reveal if your valves need adjusting.

 

[jpshoe]

So I pulled efi and replaced it. These are the codes I'm getting now:

P0125
P0141
P0141p
P0171p


Can't do compression until next week at earliest.

 

[97fourby]

Okay, So the p0125,p0171,p0172,p1130 are all related to the A/F ratio sensor. The P0141 is for the rear O2 Sensor. So, since you have replaced both with Denso stuff, Part #s- should be a/f #234-9002 and o2 sensor #234-4153. If that looks right my only other suggestion would be check the ground that bolts to the intake plenum is tight. I have seen those loose when someone replaced the valve cover gaskets. Hope that helps

 

[Pauly Walnuts]

Have you checked every single vacuum hose and air hose? I hidden hose that's cracked can cause some issues, maybe not this severe but it's a start.

 

[jpshoe]

So the ground cable on the intake plenum (seen below, I believe this is correct) was just a little loose but still making solid contact, tightened it down to be safe. All hoses seem in great shape, and follow the hose diagram perfectly.

Sorry for poor picture quality, didn't have the time for a better one.

 

[davidch]

Have you performed the 3-step test of the fuel pump as explained in the FSM:

1) fuel pressure while running
2) fuel pressure while running w/vacuum line to pressure regulator disconnected? (this test simulates what happens when you stomp on the accelerator)
3) fuel pressure bleed-off rate once engine is stopped

I purchased this item

Amazon.com: Actron CP7838 Professional Fuel Pressure Tester: Automotive

to do the test. The only other thing I needed was a 1/8" pipe elbow to make that kit work on Toyota's 5VZ-FE driver side fuel rail as explained in the FSM. I cut a small notch in the upper cam belt cover to facilitate using this tool.

The fuel pump itself has, I believe, 2 internal valves:

1) an anti-drain back valve (this is what test #3 above is for) and
2) a bypass valve (if the delivery line to the engine, or the return line from the pressure regulator, gets crimped, the pump's pressure is routed back to the tank)

I think others on this forum will back up my observation that if fuel pressure is all over the place, up or down, and outside the factory specs, you'll get lots of strange behaviors, and several different error codes thrown.

For under $50, you can prove or eliminate the fuel pump as the source of your problems.

 

[pluton]

At my level of mechanical declination(moderate), I'd find an independent garage with ex-Toyota tech(s) who learned this vehicle when it was current.
It's amazing how fast the experts can sort out crazy stuff....usually.
Diagnoses are cheap...it can't hurt.

 

[jpshoe]

Thanks for the input guys. Haven't really had too much time today to mess with it, lots of tornado warnings in the area so I thought it best to stay inside today. I reset the computer (by removing negative battery cable) and driven about 20 miles. So far no issues since I tightened that ground, normally the codes are up within a minute or two.

We'll see how that goes. Supposed to take it into a shop tomorrow, might just have them do the fuel pump while they're looking everything over if they don't find anything else. They're good on price and I can tell that my gas mileage is still suffering even after just 20 miles.

Fingers crossed it was just the ground, big face palm since I've gone through so much so far. They're running all of the wiring to check everything as well.

 

[gamefreakgc]

Well, at least there's no real harm in replacing the O2 sensor. The rear ones last a while, but not forever. The front ones only last about 90k miles and then will start to lower fuel economy.

Here's to hoping it was just a wiring issue!

 

[paddlenbike]

It does seem like you still have an oxygen sensor issue. First I would check is that the part number on the sensors you installed are correct. California 4runners use an air ratio sensor while federal emission models use a much simpler oxygen sensor. I would expect the pinouts to be completely different but I'm not sure...I would check part numbers.

 

[Red October]

In my experience sensor problems are "victims" of other problems. In other words sensors fail when they operate outside of their normal ranges due to other problems.

I would be checking things like fuel pressure (mentioned above), valve adjustments, and static (mechanical) timing. The fact that your truck backfires thru the intake would worry me, because that could mean the intake valves are open during a spark event. (This would also explain some of the lean/rich problems, having the valves open at the wrong time would let in the wrong amount of air)

I had a similar problem on a different (non toyota) motor, it ended up being that the crankshaft timing sprocket was loose and able to move back and forth, as a result the static timing was all over the place.