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Old 03-03-2009, 11:34 AM   #1 (permalink)
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How to clean mass air flow meter on 3.0 V6?

Hello,

I've been having problems with a check engine light sending codes 25 and 26 for years now, and recently did a tune up and replaced the o2 sensor and fuel filter. This didn't solve the problem so a mechanic friend recommended cleaning the mass airflow sensor. My question is how do you do this on a 3VZE? How do you take it apart, what parts do you clean, and can I use Gunk brand intake cleaner or is electrical cleaner necessary?

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Old 03-03-2009, 01:08 PM   #2 (permalink)
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First, did you clear your codes and reset the computer after installing the O2 sensor? If not, those codes would probably still be in the computer. You clear them by pulling the EFI fuse (with ignition OFF) for 10 seconds or so. The fuse is in the black fuse box on passenger inner fender. The computer can be cleared also by pulling the EFI relay or one of the battery clamps, but the fuse is easier and it won't reset your clock, radio etc.

Assuming you did reset the ecu and you're still getting mixture codes, cleaning the mass air flow sensor would be a good suggestion if your motor HAD a mass air flow sensor. It doesn't. It has a volume air flow meter, also called a vane air flow meter, which is a different animal.

A mass air sensor has a heated wire, and the incoming air cools it. The more air that comes in, the greater the cooling, and that is converted into a variable voltage sent to the computer. The wire can get dirty, and that has an insulating effect, so it will start to read low, and cleaning the wire fixes that problem.

The vafm has no wire but instead a trap door (the "vane") which is pushed open by the incoming air. The door is connected to a potentiometer and it sends varying voltage back to the computer to tell of the vane position. Stupid idea - the vane obstructs the intake of air - but that's what we have. The vafm usually does not get very dirty - I have 281,000 miles on my 20-year-old vafm, and I've never cleaned it and it still works fine. Even if the trap door gets a little dirty, it probably won't make any difference. If you spray any solvents in there, you are much more likely to f*ck it up than help it. If you want, you can gently clean the door and surrounding areas with a clean tee shirt and some isopropyl alcohol, but it won't make much if any difference.

That's not to say the vafm isn't causing your problem - it is possible. But the thing to do is to check the resistance readings of the various circuits in the meter with an ohmmeter. That will tell you if the meter has a problem with any of its circuits, which do sometimes go bad. Specs and instructions are in the factory service manual in the ENGINE - MFI SYSTEM - VAF METER section. If you don't have one, google 1993 toyota pickup service manual.

You'll need access to the vane which you get by removing the top of the air cleaner. Make sure the resistance between terminals E2 and VS changes smoothly "in a wave pattern" as you slowly push the vane open. There should be no spikes or dropouts of resistance. Check the intake air temperature sensor by measuring resistance between terminals THA and E2. Specs for the proper resistance for given temperatures are in the manual.

There is another sensor important for the computer's ability to control mixture, and that's the throttle position sensor. That's on the side of the throttle body, and it too can be checked with your ohmmeter. Specs and instructions are in the manual in the ENGINE - MFI SYSTEM - THROTTLE BODY section. For fine tuning the position of the sensor you need a feeler gauge, but to check it for proper operation you don't need the gauge - just an ohmmeter. Make sure terminals IDL and E2 have continuity (2.3k ohms or less) when the throttle is closed (idle position). Make sure those terminals DON'T have continuity when the throttle is opened about a mm, and that they don't have continuity when the throttle is in any other position (except closed). Check that the resistance between VTA and E2 changes smoothly as the throttle is moved from closed to open. You didn't give your year, so I can't tell you whether the specs in the 93 manual I referenced are correct. In fact, I believe there is a typo in the throttle closed specs for VTA and E2. It says resistance should be between 0.47k 6.1k ohms - I'm pretty sure that 6.1k is supposed to be .61k, since for other years the spec for the top end does not exceed 1k ohms. Also it makes no sense that the closed reading could be more than the open reading. The specs for 89-91 3VZEs are a bit different. Post back if you need them and I'll dig them out, or you can search this forum - I've posted those specs before.

You said you did a tune up - I'm assuming you now have new plugs, distr. cap, rotor, air filter, your plug wires are clean, soft and flexible and have no cracks, and your base timing has been properly set to 10 deg btdc with a jumper installed between te1 and e1 in the check connector.

When's the last time you cleaned your injectors? Most so-called injector cleaners don't do anything. About the only effective cleaners have a chemical called Polyether Amine (PEA). The only one I know available in Canada is Red Line's SI-1 Complete Fuel System Cleaner. Many Canadian Tire stores carry it - check for stock online. Run a bottle of that through your tank and your injectors will be in good shape.

The other problem that could make it impossible for your computer to regulate mixture is bad fuel pressure control. For that you'll need to have a good, thorough fuel pressure test according to the specs and instructions in the manual (in the ENGINE - MFI SYSTEM - FUEL PUMP section). It's possible your fuel pressure regulator or perhaps your fuel pressure damper is bad. That test requires a fuel pressure meter with the appropriate-sized banjo connector - something you'll probably have to have a shop do for you, unless you want to buy the meter and banjo connector yourself. If you take it to a shop, print out the manual section and give it to the mechanic and ask that in addition to their regular fuel pressure test that they do the pressure tests with vacuum tube connected to the fuel pressure regulator AND with the tube disconnected, as shown in the manual.

If all that checks out and you're still getting codes, post back and we may come up with other fun things you can try. Good luck, and let us know how you make out.
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Old 03-03-2009, 06:00 PM   #3 (permalink)
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Thanks, I'll work my way down the list! it's a 1990 by the way, approximately 225,000 miles, 360,000 km's. Also running a K&N filter, otherwise stock.

When I did the tune up I didn't touch the distributor or the timing, though I had a new timing belt installed less than a year ago, as the water pump went along with a few pulley bearings. I just did plugs and plug wires along with the o2 sensor. Recently it has also been starting like crap in the cold weather, it fires but runs at about 500 RPM and sounds like it's not firing on all cylinders, sounds like an old VW beetle. Not sure what to attribute this to, but I will try that fuel system cleaner you recommend. I assume I should use it in a full tank of gas?
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Old 03-03-2009, 08:31 PM   #4 (permalink)
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Yes, Red Line says to use one bottle per tank, so I would use it with 3/4 to a full tank of gas, and not fill up again until you had burned most of it. Once the injectors are clean, PEA is so effective that a very small amount in fuel will keep the injectors clean.

The distributor caps need to be replaced fairly often in the 3VZE, at least as often as the plugs. The crappy aluminum terminals inside the cap get badly corroded and develop a lot of resistance that kills the spark voltage. If the rotor is a Denso, it lasts a little better, but I always replace it with the cap anyway. I would replace these on your motor if they have over 45,000 km on them.

With the miles, starting issues, and rough running, I would add a few things to the list of checks. In no particular order:

ECT - Engine coolant temp sensor. Very important sensor, as it tells the ecu when the motor has achieved operating temp. The ecu will run the motor in "open loop" until the ECT tells it the motor has reached operating temp. In open loop, the ecu ignores O2 sensor input and runs motor on preset mixture and spark timing values. When the ECT says the motor is hot, the ECU switches to "closed loop" mode where it uses input from the O2 sensor and other sensors to calibrate mixture and timing. If the ECT were sending the "hot engine" signal when the motor was cold, the ecu would probably be running it too lean. See the ENGINE - MFI SYSTEM - ECT SENSOR section of the fsm.

Cold start injector - If the motor is hard to start or runs poorly when cold, this could well be the problem. Very easy to test the injector itself with an ohmmeter: there should be 2-4 ohms between the two pins. The test is pretty reliable - if it fails, the injector is definitely bad; if it passes, the injector is usually good.

Cold start injector time switch - even if the injector is working, a bad cold start injector time switch could prevent it from firing. Check the time switch according to specs in the MFI SYSTEM - COLD START INJECTOR TIME SWITCH section.

Compression test - always a good idea in a 3vze. If the compression is no good, there is no sense wasting any money or time on other stuff until the compression issue is addressed. Head gaskets have that nasty habit of blowing, and burnt exhaust valves are not uncommon, either. Compression testers are cheap - just get one that supports 14mm threads, which is a very common size. Instructions in the ENGINE - MECHANICAL - COMPRESSION section. One thing not made clear in the instructions is that you should keep turning over the motor until the gauge needle stops rising.

Coil - Test both circuits with an ohmmeter - specs & instructions in the IGNITION - ON VEHICLE INSPECTION section. This is important since a bad coil will not only make the motor run poorly, but it will also kill the igniter, a very expensive part that otherwise will not usually fail.

Signal rotors & coils - The important crankshaft position and camshaft position signals are generated in the distributor. There are two rotors under the ignition rotor: one with two cams, and the other a starwheel with - I think - 24 lobes. These rotate past three signal coils to generate electrical pulses that the ecu uses to set spark timing and advance. To test them see this post:
pinging

Auxiliary Air Valve - should be called your cold idle increase, since that's what it does. It's a coolant-operated, thermostat-like valve that allows extra air to bypass the throttle plate when the motor is cold, increasing idle speed. It is part of the throttle body, below the throttle plate. When hot coolant hits it, the valve closes, reducing the idle speed. It can get gummed up, either blocking the extra air or causing the valve not to close when motor is hot. To test it, screw the idle speed adjusting screw all the way in (the large front-facing screw on the top of the throttle body) when the engine is COLD. The idle speed should decrease, but the motor should still run. Back the screw out to the original position (so you have to count turns on the way in). When the motor is hot, repeat the process. When the screw is all the way in, the motor should stall or nearly stall. If there is no difference in idle speed with the screw all the way in cold and hot, then your aux air valve is not operating properly. Cleaning it may fix it (see below); otherwise you'll need a new throttle body.

Clean the throttle body - pull the air hose off the tb and see if the throttle plate or other parts of the tb are dirty or varnished. If dirty, use an O2 sensor- and catalyst- safe throttle body cleaner, making sure to get the back of the throttle plate and also give the little air passages in front of the base of the throttle plate a few shots with the cleaner. One of those is the "auxiliary air valve" mentioned above. Toothbrush can help as can a clean rag. Be very careful not to get any of the cleaner on the tps, as solvents can kill it. When you're done, check the E, R, & P vacuum ports on top of the tb to verify no vacuum at idle and vacuum at 3500 rpm. See the throttle body section of the fsm.

Check for vacuum leaks - pass an unlit propane torch along the various vacuum hoses, including the power steering vacuum hose and also around the throttle body and plenum seams and listen for an increase in rpm. You can also use starter fluid.

Now all that should keep you busy, lol. Seriously, if you follow all that I'd give you a good chance of nailing down why the motor is not running properly. But if you're still getting codes, post back and more fun suggestions can be yours.
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Last edited by sb5walker; 03-03-2009 at 09:01 PM.
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Old 03-03-2009, 08:41 PM   #5 (permalink)
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Thanks again, I'm doing all this as my main concern is for fuel mileage. I get about 230 miles to the tank in the winter and 280 in the summer. Mixed city and highway, not much stop and go on my commute though.
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Old 03-03-2009, 09:23 PM   #6 (permalink)
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You're welcome. Yes, improving how a motor runs will always give you better mileage, too. Toward that end you may want to pull your cat and see if it's clogged - that will really kill mileage. If you replace it, get one of the high-flow models. I gained a 20 percent increase in highway mileage - from 20 to 24 - when I installed my Borla cat-back exhaust in 1996. Unfortunately the Borla is no longer available, but replacing that dog of a stock muffler with a performance 2.25" cat-back exhaust can give big rewards. Also, increasing tire pressure will improve mileage.

Aside from gas mileage, I would think you would want it to run well anyway. It should not be running that badly when cold. As long as they have good compression, these motors can run almost as well as the day they drove off the lot.
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Old 03-04-2009, 06:22 PM   #7 (permalink)
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my experience is that when you have codes 25 and 26 on a 3VZ-E if the O2 sensor is OK then the most likely culprit is dirty injectors.

Poor spray pattern causes a partial misfire (and erratic exhaust oxygen content) at idle and prevents the O2 sensor from properly sensing the fuel mixture.

Usually when they get this bad the injectors do not respond to "in tank" cleaners. You may have to use a more aggressive cleaner that hooks up to the fuel supply.

I've had several that took more than one treatment, and a couple that I just ended up replacing the injectors.
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Old 03-07-2009, 12:01 PM   #8 (permalink)
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So I took the measurements on the VAF, and found when I measure between E2 and Vc that I don't have any resistance, the manual states I should have 100-300 ohms. I then tried moving the flap, and when measuring between E1 and Fc I get 2 ohms resistance when it's any position other than closed, while it should be zero. So is my VAF now suspect? All other measurements were within range.
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Old 03-07-2009, 04:37 PM   #9 (permalink)
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Sounds like you were looking in the 22RE section of the manual - that's very easy to do. The 22RE specs for VC are 100-300, while the 3VZE specs are 200-400. Also, if you are measuring the pins labeled on the 22RE meter as E2 and VC you are actually measuring E2 to E2 on the 3VZE meter, and so it's correct not to have any resistance. As far as 2 ohms on the fuel pump switch (FC), that should be fine - that's little enough resistance to qualify as "continuity". Besides, if your fuel pump switch weren't working, the motor wouldn't run at all - there would be no fuel pressure.

Here's a post that may be of some help:
94 4Runner - Hard to Start w/ Black Smoke
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Old 03-08-2009, 01:19 PM   #10 (permalink)
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Checked the Throttle position sensor, it's all ok, checked cold start injector, fine as well, couldn't find the cold start injector timing switch. I talked to another mechanic, and he said it may be the knock sensor, but those aren't the codes I'm pulling. Could this still be the case?
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Old 03-08-2009, 03:44 PM   #11 (permalink)
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The vast majority of 3VZE knock sensors will last over 400,000 km, and when they do go bad, the symptom is excessive pinging. Even for a vehicle that is pinging excessively, knock sensors are rarely the cause. So I think for your issues, the knock sensor is pretty far down the list of probable causes.

Did you retest your vaf meter?

If that's okay, and since the tps checks out and O2 sensor is new, I would certainly heed Vicoor's recommendation - he knows more about engines than most of us around here. I would give Red Line's cleaner a chance, though maybe you ought to fill the tank only 2/3 to 3/4 full, and buy two bottles so you can do that twice. After you've run two tanks of cleaner through, pull your EFI fuse, drive for a few days, and recheck for codes. If you're still getting mixture codes, a logical next step would be to have a competent shop run some of the concentrated injector cleaner directly into the fuel lines as Vicoor suggested, and have them run a fuel pressure test also. If STILL getting codes, you might try working your way down the other recommendations in this thread.

Good luck, and please keep us posted!
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Old 03-08-2009, 04:33 PM   #12 (permalink)
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Yeah my readings for the VAF were E2-Vs = 292, E2-Vc = 282, E2-THA = 5k @ 0 Celsius (I'm guessing this was the temperature of my garage). So everything seems to check.

I picked up a bottle of Red Line, reset the EFI fuse, and am hoping for the best. I'll pick up another bottle once I've emptied this tank. I poured the Red Line in at 3/4 tank and I'll do the same with the next bottle.

I actually found a VAF at a wrecker once I thought mine was suspect, but his readings were 0 as well on what I thought was E2-Vc. That manual doesn't seem to reference whether it's the 22RE or 3VZE I guess? Funny thing was the wrecker said a guy out of WA state bought the engine out of the truck (145,000 km's) as his 3VZE had finally let go (he had over 600,000 MILES on it!!!!) And I thought I had alot of miles at 224,000!

I should also note that there has been a ticking noise coming from my engine forever, which no one has been able to diagnose or even mentioned when I bring the truck in to dealers. Is this normal?

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Old 03-08-2009, 06:29 PM   #13 (permalink)
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If you're talking about the online manual, when you click ENGINE there's a label for 22RE, then all the 22RE engine topics, then the label 3VZE and all those topics. The topics are almost all the same, though, so it is very easy to lose track of what section you're in. It would have been much easier if there had been a ENGINE - 22RE link, and an ENGINE - 3VZE link, but that's not the way he organized it.

On the meter, the manual mentions that resistance between VS and E2 should change "in a wave pattern" as the measuring plate slowly opens. The resistance readings should not have any spikes or dropouts at any point. Sometimes that's the problem: there is a bad spot or two and the signals jump, confusing the computer. The same thing can happen on the tps between VTA and E2. You may be sick of checking those sensors by now, but it may be worth checking that the resistance changes smoothly.

I've never, ever heard of a 600,000 mile 3vze. I'm afraid I would have to see proof before I believed it, and even then I would probably be skeptical, lol. And that's despite the fact that mine still has good compression at 281k miles.

A "ticking" noise generally comes from either the injectors or valves. It's completely normal for the injectors to "tick", but that's not a very loud noise. It will drop out at various times, especially during deceleration. It sounds like your ticking might be a valve which has a bit too much clearance.

If you have not had your valves adjusted in the last 70-80k miles, I would encourage you to have that done. Reason is, burnt valves are fairly common on this motor, and that's a very expensive fix. The cause is probably valves that gradually stretch, until they no longer close. I've checked my valve clearances twice and both times I found that several valve clearances had tightened up to be less than spec. I believe if I hadn't found and corrected those, that I probably would have had burnt valves by now.

Adjusting the valves is not easy - it was by far the toughest task when I changed my head gaskets. I was unable to purchase the Toyota special service tool for depressing the lifters to replace the shims. I bought an aftermarket tool that didn't work well and the neighbors heard a lot of language that day! If you really want to do it yourself, try for the Toyota tool and whether or not you have it, it would be good to have a helper so one of you can focus on keeping the spring depressed while the other plucks out the shim with a strong magnet and screwdriver. And watch your fingers! If a spring closes on one you'll probably lose it.

I hope the Red Line cleaner will make a difference, but I'll be curious to hear either way. Thanks for keeping us informed, and good luck.
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Old 04-04-2009, 08:34 PM   #14 (permalink)
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Well after running two bottles of Red Line through it's still doing it. Seems to take a little longer to go off, but eventually it still does. I inquired on a valve adjustment and a Toyota dealer wanted $800 plus parts. Seeing as a new engine would only cost about $1600, doesn't make it worth it!
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Old 04-04-2009, 10:19 PM   #15 (permalink)
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No, that's an insane price. If there are any independent shops that have a good reputation, you might ask them.

It's possible your injectors are beyond the point where Red Line could help them, as Vicoor suggested. The next thing to try would be having a shop feed the concentrated stuff directly into the fuel lines.

I'm trying to think of other possible causes of mixed lean/rich codes (there are plenty of explanations for lean codes, like an exhaust leak). The only thing I can think of is a bad fuel pressure regulator or possibly a bad fuel pressure damper (also called the "pulsation damper"). A fuel pressure test would tell you if the regulator is bad; it's harder to tell if the damper is bad because it operates as quickly as the injectors open and close, and a fuel pressure gauge is not designed to pick up variations that quick.

You might consider having a shop run the fuel pressure test and do the injector cleaning - since they will have to tap into the fuel line for both.
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