Jcox

Hi guys I'm working on a 94 4runner 6 cylinder.
I'm getting a "71" code for egr system. I've changed thr modulator, cleaned egr valve and checked for egr function by sucking down on the hose while running.
It is idling a little lower than it used to, but no real power loss or stalling.
Its failing emissions badly.

25 mph test
Hc(ppm) 215
Co% 3.14
Nox 2164

15 mph test
Hc 266
Co 338
​​​Nox 1944

I dont fully understand this egr system. Its the first toyota I've owned and I'm kinda piecing it together in my head still. Where would you move next if you were diagnosing it? Anything i can do to track down the problem without spending money guessing is a win on my part! Thanks in advance

scope103

As with all things Toyota, start with the Good Book you must. http://web.archive.org/web/201003261...77exhaustg.pdf

A little background might help. Code 71 is triggered by the EGR temp sensor, which is only on California and C&C trucks. Which makes me think you are in California, where you would fail smog instantly by having a CEL with ANY code. How did you get the NOx numbers?

However you got them, the numbers tell you that you have an EGR problem (but the truck already told you that). In addition to the tests in the manual, I would suggest pulling the EGR tube out of the plenum. Here's a picture of a "really clean" one:

The "gunk" is from the PCV system. On some trucks (mine included), this can get so bad over the years that you will have trouble pulling the tube out. If the tube is blocked, exhaust gas will not be admitted into the plenum, your NOx will go through the roof, and your truck will detect it because the temp sensor doesn't detect warm gas going by.

Jcox

In actually in Texas. I can pass inspection here with CEL on OBD1 vehicles. I'll pull the egr again here in a couple of hours and see what i find. My truck does have the egr temp sensor and it could be out too, but would that failing cause my numbers to shoot up? I havent found anything specific in all my searches on the forums

Thanks for the quick response.
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scope103

It sounds like the temp sensor is working correctly. It told you that the EGR wasn't working, you didn't believe it, but the 5-gas analyzer confirmed it.

The EGR system runs on vacuum, so you might want to check that each line actually connects back to a source of vacuum. Use the manual to tell, for instance, whether the throttle has to be opened for vacuum to be on a specific line.

My best guess is that the exhaust gases, which the EGR meters into the plenum to lower combustion temps, is not making it through the tube into the plenum. Tube clogged? Modulator not opening? Let us know what you find.

Jcox

Definitely lots of carbon build up. Thanks for pointing me somewhere specific. Going to clean this up now & see what else i can find that's dirty. Hope that will clear this light and problems. Thanks again

Andy A

Just to throw out another idea. Check all your vacuum lines in the egr system to make sure none of them have possibly clogged up with something, and do a quick test of any vsv's which are egr related. I had the one metal line which runs under the intake manifold from the vsv to the egr modulator clog up on me once, had a devil of a time getting that thing unclogged. A test on the temp sensor would not hurt either, the FSM has good instructions on testing the modulator, sensor, and vsv.

osv

if the truck stumbled at idle when you did the suck test, there must have been exhaust gas getting into the intake system for that test, so that's probably not where the issue is.

you are looking for something that controls when the vacuum is applied to the egr... need to fix that code 71, it does indicate a possible problem with the egr temp sender, which you should be able to unscrew from the egr tubing, and evaluate.

just for drill, how old is the catalytic converter?

Jcox

Went and grabbed a new vacuum gauge tonight after cleaning the egr pipe and cleaning the plenum as best i could. Ran out of light before i could really dive in. Drove it 25 miles before the cel came back. This is my first toyota. Got it a few years back and its been up and down quite a few times. Bear with me while i figure out whats what. Its a new system to me. My dad and I rebuilt the motor and ive done some transmisson related work on it, but every new thing that breaks is another thing i have to learn about. I haven't pulled the catalytic converter yet, but that's not a bad idea. I'm sure its not in tip top shape but i just haven't gotten there yet. This thing was my project until my chevy transmission took a crap but i like this thing when its running right. Going to clean up the plenum better tomorrow and try to isolate the issue with the vacuum guage.



The three parts bottom left (attached at the wheel well),how do they come out? I didnt want to just start tugging on them and didnt see a way to open the mounting bracket. (As)(fpu)(egr)
Do i need to remove the whole bracket before i can remove individual components?
I think everything else i've located except the charcoal canister but I'll find it once its light out again I'm sure.

osv

you should have cleaned out the plenum when you rebuilt the engine, but really, if the suck test made the engine stumble at idle, there is no indication that cleaning the plenum out will help... yes, it may help, but you are just shooting in the dark with it.

the fsm for the 22re has a series of troubleshooting steps for the egr, i would imagine that the fsm for the v6 has the same thing, i would follow that first.

Jcox

So here's what I've found so far.
Modulator was a little clogged so i cleaned it out and the lines between it and the throttle body. Pulled the plenum last night to clean it and the throttlebody properly. Found a bad bvsv with a cracked line. Also when i pulled my canister the evap line wasnt connected at all and the line itself is falling apart.
I'm guessing this line pictured here is where my evap canister goes back to the tank, yes?


If so ive got the bvsv ordered from toyota, and am a plenum gasket and evap line away from being able to put it together and see where it stands. Thanks for y'alls help.

scope103

I can't tell from your picture; perhaps this will help: http://web.archive.org/web/201003261...76evaporat.pdf

The line from the BOTTOM of the Evap Canister is an air intake; it just runs down and dangles near the engine mount. The line back to the fuel tank does depart from the top of the canister.

By bvsv could you mean "bi-metallic switching valve", often called the TVV "Thermal Vacuum Valve"? (They're the same thing.) The TVV sits between the Canister and the throttle body; it's closed when the engine is cold, open the rest of the time. This allows the fuel vapors to get sucked out of the canister into the intake.

Jcox

Got everything back together, new hoses throughout, new bvsv, new air intake hose.
clean modulator. Idling about 1100-1200 rpms continually weather cold or warm (making a noticeable bouncing maybe 30-50 rpms at idle.) Still getting a code 71, but HC went from 215 (fail) to 123 (pass)
CO from 3.41 (fail) to 0.73 (pass) NOx now 2622 @ 25mph & 2879 @15 mph. (Fail) from. 2164 & 1944.

spent a good time reading fsm, chilton, & forum threads with little insight. HC & CO dropping back suggest the egr is functional (correct me if I'm wrong) but still throwing an error code & cant seem to figure out why its still getting high combustion temp.
How do i connect the vsv to the battery? (Using what more specifically)

Jcox

Here's an update. Still a code 71. Still getting high nox [over 3000]
what I've replaced so far.
Bvsv/tvv
Egr vsv
Vac hoses throughout
Cleaned all vac lines and metal lines.
replaced the hose from airbox to the plenum lines & to pair reed valve.
cleaned intake plenum and egr tube.

Im at a loss as to what else could be causing my egr not to function properly.