winnebagoman

I hope somebody can help figure this out, but i doubt it. toyota dealers haven't (spent an entire day testing everything and the only thing he could suggest was to change the injectors. he didn't charge me for his day of diagnosis because he had no definite answer), and i changed them, it's better, but that was 6 months ago and still lean. been going on for over a year.
91 toyota pickup 3vze. running lean. then running lean and rich. cel 25 and 26.
had a burnt valve last year. resolved that issue. engine has never run correctly since then, or before then.
new denso injectors. new injector holders. new denso o2 sensor. correct wires and plugs to spec, ngk and denso. no air leaks that i can find. tested TPS, tested VAFM, both check out to spec static and in motion, including the temperature sensor in the VAFM. the new o2 sensor checked out good when tested.
fuel pressure and compression are good. new coolant temp sensor.
checked for air leaks around every possible component with carb cleaner and propane, extensively. nothing.

no single spark plug shows signs of lean mixture. they're all the same. a little dark in color, no oil no residue, no white.
i'm not using up coolant at all.

sometimes a little rough at idle, and a shimmy while parked if i run it up through RPM's.

right after the valve job, the engine would randomly miss while cruising, but had no relation to RPM or load. that hasn't happened in months now, since new injectors and plugs and wires etc.

how would i know if the fuel pump is pumping the correct pressure but not pumping the right amount of volume. would it have died by now or gotten worse? it's running the best it's ran in two years right now. but still CEL with 25. and then if i let it run long enough 25 and 26 together.

when I unplug fuel regulator the idle smooths out a bit. same with when i unplug the TPS.
when i suck on the EGR, the motor stalls.
vacuum lines check out at idle and suck well at 3000 rpm.
i've done about everything i can to figure this out.
the toyota is a 20.5' winnebago and i'm getting 13 MPG that's with my 99cc two-stroke and all my belongings in the back. drives like a car and will hold speed at 70-75 no problem when there's not a headwind. i think i used to get closer to 17mpg, believe it or not.
I don't know what to do. totally stumped.
the only thing i can think of is to test the fuel pump volume, what should that be?
i'd be surprised if that were it though, because the problem has progressively gotten better with everything i've done.

any thoughts are welcomed. including if you know a good therapist, i should probably have my head examined.

scope103

It's not the fuel pump "volume." The injectors open and close, and if the pump isn't pushing out enough volume the pressure will fall -- it's just physics. There could, though, be a blockage (you don't mention a new fuel filter) or a weak pump (can't keep up with high flow, and so the pressure sags, leaning out). If you can hook up a fuel pressure gauge and drive with it (tape it to the windshield; pressurized fuel does not belong in the cabin), you might find it. I'm a little concerned about the idle smoothing when you remove the vacuum line to the FPR; that raises the pressure in the rail and should richen the mixture.

It's also pretty easy to watch your 02 sensor directly. With TE1 grounded (E1), VF is the "conditioned" O2 signal, varying between 0 and 5v. You can hook an LED and 1k resistor to it and watch it flash; it should switch 8 times in 10 seconds. http://personal.utulsa.edu/~nathan-b...42oxygense.pdf This will tell you directly when the ECU is detecting a lean condition -- that's what you're looking for.

winnebagoman

thanks scope103.
i just followed the directions on that link and the o2 sensor tests out fine again. i had done that before. never bad to check again.

the fuel pressure was checked out good a few months ago like you're mentioning.

also, if it were the fuel pump, wouldn't it have gotten worse in the last year? or would i see less power? i have to say, the engine seems to have great power. better than when i bought it a few years back. could just be the newer components.

yes, i put a new toyota part fuel filter on it last week. no difference. older filter wasn't noticeably dirty either.

is it possible for a VAFM to test OK but still be bad? i see online where a lot of people change the mixture via the VAFM. is that a bad idea?

i have 85,000 miles on this engine by the way.

scope103

If I understand your problem, it's the appearance of code 25, which means the ECU thinks the engine is running so lean it cannot compensate. How does the ECU know? Because the O2 sensor tells it. So if you watch the O2 sensor as you drive, at some point it will stop flashing, because the engine is lean (indicated by the O2 sensor) but the ECU cannot adjust the injector open-time far enough to bring it back momentarily to rich. So the code is thrown.

I'd like to know WHEN that happens, so I would hook up an LED and drive until I see it stop flashing -- what you just "did" is what caused it.

Another thing to check is the stored fuel trim. With TE1 open, VF1 has 5 voltage steps with the learned A/F value (<2.5volts means the ECU is decreasing fuel). If you're running regularly at >2.5 volts, it means the ECU is trying to increase fuel to overcome a lean condition.

I know you've checked for vacuum leaks (you've done much more than average by using both propane and carb cleaner), but that is a common cause of lean running. Could you have missed something?

IF your VAF had already been mis-adjusted, the ECU might miss the base fuel trim (because it is getting bad information from the VAF). If the VAF signal was "wrong enough," the ECU might figuratively "throw up its hands" because it is adding way more fuel than the (wrong) VAF indication says to, and yet the O2 sensor is still calling "too lean." But before you mess with the VAF, you ought to be pretty sure that the ECU is at least trying to compensate (hence the tests above).

I think most of the people who mess with the VAF are just trying to get the truck to run richer than the ECU wants, by trying to fool the ECU. I don't see how that would work anyway, because VAF only sets base mixture; the ECU will constantly adjust based on what the O2 sensor says. But wadda I know?

winnebagoman

it's >2.5 volts. definitely trying to enrichen the mixture.
i do get code 26 as well sometimes, which i assume if the result of the ECU trying to make the mix richer.
i adjusted the VAFM a few clicks rich and the engine shakes as i increase rpm the same. the vafm tests out good. i reset it to the factory setting.

it must be the fuel pump. it's the only component that hasn't been replaced. last time i had the fuel rails off everything is clear of debris.

i'll keep you posted. thank you for your input.

wyoming9

iTrader: (1)

It could be possible it is the ECU or something in the harness not allowing communication from the O2 sensor..

Which trips those codes .

Pretty easy to check the fuel pressure

just a idea off the top of my head

btu44

You could try checking the tightness of the intake air chamber bolts.

After I had my injectors serviced, I installed a new intake chamber gasket. It is a very thick gasket that takes a few heat cycles to stabilize. I had to re-torque the bolts 3 times before they would hold tight. Although my symptoms were different than yours in that a few of my plugs looked lean.

RJR

The fact that the O2 sensor is switching at the right rate tells you that, under certain conditions, the ECU is capable of keeping the mixture correct. The O2 sensor will only switch if the ECU is actively controlling the mixture properly. Or, another way of putting it is, when the O2 sensor is switching, the engine is not running lean (or rich). The O2 sensor should be switching any time the ECU is in closed loop mode, which is basically whenever the engine is warmed up, not idling, and not at near full throttle.

The diagnostic code 25 means that, at some point in the driving cycle, when it should have been switching, the O2 sensor was instead stuck high for over 90 seconds. This means there is a set of circumstances where the ECU is losing control of the mixture. Your job is to figure out what those circumstances are.

Scope's advice is right on. Run some wires from the diag port to an LED in the cabin. Connect the wires to the condtioned O2 sensor output (VF1) on the diag port, put the LED where you can see it, connect TE1 to E1, and start driving around. Once the engine warms up, the LED should be blinking at around once/second at all times except at idle and during heavy acceleration. If you can create and observe another set of conditions where it stops blinking, that may give you some idea of where the problem is.

bswarm

You said the O2 sensor was replaced, but check the outside of it to see if there's mud/dirt caked on it. Some O2 sensors give bad v signals when wet or caked with crap from the road.

Inu

In my research 2.5 v on the vf trim is no change at that load/rpm point. In my injector swap thread I have a few lunks with info on using a multi meter for cgecking fuel trim. After work ill post the links. Might not help but info is info.

Inu

http://pinoutsguide.com/CarElectroni...c_pinout.shtml

http://www.scirocco.org/tech/misc/afgauge/af.html

http://www.well.com/user/mosk/Vfsignal.htm

I keep a copy of those pages in my truck these days, hope it's of use to you and good luck.

superex87

All so check the condition of your cold start injector, if it has a slow leak it may be adding a little extra fuel. May help with the rich code. I would all so check out all the vsv switches and make sure they are functioning correctly, this includes the themo one on the back side of the intake manifold.

jimbyjimb

iTrader: (1)

A sticky EGR can cause issues at idle and under load. You'd also be surprised at the strange issues bad catalytic converters can cause.

Could be many things including what has already been suggested. Testing the EGR is easy if it's easy to access. Never worked on the V6 myself. If you've had problems running rich it doesn't necessarily take much to fry a cat either. Teeheehee, fry a cat...