Yet another dreaded 401 thread....(few diag questions) (1 Viewer)

[98 SNAKE EATER]

Earlier this week, I got my very first MIL


Ran a scan and came up with a 401 (EGR flow insufficient)

Made a quick check to see if all the hoses were connected, cleared the code and it came back the next day after about 200 miles of driving...

Put further testing off until today and let the light remain all week...


Here's what I've done so far...

1) I checked the modulator using AllData's guide (I don't have an FSM yet) and cleaned the filter using compressed air (it wasn't really dirty at all)

Now, AllData says to "Install the filter with the coarser surface facing the atmospheric side (outward)"

Does this mean facing up?

When I pulled it out, the coarse side was facing down

Checked the one on my 91 LC and it too was facing down, so I'm not really sure if I'm reading it right


2) Applied vacuum to the EGR while running and she stumbled, almost stalling, but the valve wasn't holding vacuum...

Not sure if this is normal, but every other EGR system I've worked with held vacuum when testing the valve unless the valve itself was bad...

3) Pinched the hose leading from the valve to the intake port and when I applied vacuum again, it held solid (pretty much ruling out a bad valve)

4) Pinched the hose on the VSV that loops under the intake (barely visible from the driver's side) and when I applied vacuum again, it held solid...



Anyhoo, that's where I'm at right now...

About to pickup a new vacuum gauge (current one is busted) to give the modulator a proper test, but I'm guessing the VSV is kaput

 

[98 SNAKE EATER]

ttt

I have yet to check modulator with a vacuum gauge, however, since I flipped the filter and cleared the codes last Saturday, the MIL has yet to return (I've put about 500 miles on her since then)





Crossing my fingers on this one and hoping it stays off

 

[IdahoDoug]

What year.........zzzzzzzzzzzzzzzzzzzzzzzzzzzz

 

[98 SNAKE EATER]

97

 

[gray]

ttt

I have yet to check modulator with a vacuum gauge, however, since I flipped the filter and cleared the codes last Saturday, the MIL has yet to return (I've put about 500 miles on her since then)





Crossing my fingers on this one and hoping it stays off

Sounds exactly like my sequence of events, starting a year ago;
cleaned the vac mod; was a bit dirty; some brown flakes washed
out when used carb cleaner, cleaned the filter,etc, etc,
But the P401 came back after ? X hundred miles, cleaned again,
a few hundred miles, P401 again; etc,etc,etc.

G

 

[98 SNAKE EATER]

Sounds exactly like my sequence of events, starting a year ago;
cleaned the vac mod; was a bit dirty; some brown flakes washed
out when used carb cleaner, cleaned the filter,etc, etc,
But the P401 came back after ? X hundred miles, cleaned again,
a few hundred miles, P401 again; etc,etc,etc.

G

Happen to remember which way you installed the filter?

Mine came with the coarse side facing down as well as the one in my 91, but the ALLData guide says to install it upsidedown

 

[gray]

Course side up; the idea is to catch any particles that get through a leaky EGR valve diaphram
before they do any damage downstream

They should not get discolored at all; the filter on top; they do because the EGR diaphragm
is coming apart and exhaust gases are starting to leak through, so I was told by a Toyota mechanic.

And it makes sense; the EGR has a diaphram the moves up or down depending on
what the system lets it do; that is moved by vacuum;
for the vacuum to work, the diaphram has to be intact.

Once it starts to leak, it loses vacuum, and allows carbon through to the Vac Mod,
and then if the Vac Mod leaks, then to the VSV valve: or so I was told.

Same if the Vac mod leaks from below;
to see what I mean; disconnect the lower hose from the bottom
of the Vac Mod and run the engine. I think I am saying this correctly.

G

 

[Riad]

Looks like I am joining this P401 club after all. Started getting the code when I went out for a drive at lunch time. At first glance it freaked me out, I thought it's one of those 300s but after plugging in my OBDII reader I was Relieved a bit. I cleared it for now but I am sure it's gonna be back again. Looks like I have to start the diagnostics this weekend.

 

[98 SNAKE EATER]

OK, I hope I don't jynx myself here, but so far I've put 1700 miles on her since I cleared it and the light has yet to return

I'm just a bit curious about the modulator filter though

Both my rigs had the filters installed with the coarse side facing down

Is this the way they come from factory or did someone mess with them before?





Rick

 

[rove_mcanus]

Please excuse my ignorance, but I assume MIL is not referring to "mother-in-law". Of course she is something i would not want to turn up either.

 

[98 SNAKE EATER]

Please excuse my ignorance, but I assume MIL is not referring to "mother-in-law". Of course she is something i would not want to turn up either.

LOL



Malfunction Iindicator Lamp

It's just a common term used cause not all MIL's are the same (Check Engine, Service Engine Soon, Engine Image, etc.)

 

[alia176]

Aka CEL.....

 

[98 SNAKE EATER]

Today one of our painters was doing some PM work on his 91 4-Runner...

As I looked on, I pointed out some oil leaks and also told him about the filter in the modulator...

Curiosity got to me and I popped the cap only to find his filter was also installed with the coarse side facing down

 

[gray]

You know, now I don't know now; seems like it was course up, I would guess that the coarse side is to ?catch particles? So, from which hole are the particles most likely to come from? I think it would be from the top EGR vac hose; ie: if the EGR diaphram leaks internally??

But on the other hand, if the vac mod leaks internally, then particles, I guess, could be blown up from below.

I've been meaning to tear my old EGR valve apart(and maybe the vac mod) to see what makes it tick.

Anyone do that already to save me me time?

g

 

[Riad]

Well, 1 can of BG44k (with fill up) and a brand new hose seem to have kept the orange CEL off so far. 402 miles of stop n go traffic + multiple trips and it hasn't shown up yet. I have been getting the code on every 2nd trip (and clearing it too) in an 80 mile round trip every day. After the BG and the new hose it appeared only once. Ordered the VSV and some more hoses from Dan last week. They are not here yet but I am pretty sure the CEL will reappear again. I wanna change all those friggin little hoses under the intake. Hopefully I can attack that this weekend. Here are some pix. This is the hose that runs from the top of the intake to the EGR valve. It took me a while to figure out the crack.

 

[98 SNAKE EATER]

Well, looks like I jynxed myself lol

MIL came back on late last night

She's done a little over 2500 miles, so I'm guessing only a minor malfunction

Haven't checked it yet, but I'm sure it'll be the 401 again...


Anyhoo, a few more diag. questions:


1) Should the hose leading to the VSV hold vacuum?

2) I know it's been said that you can replace the VSV without removing the intake, but does that include ALL of the hoses as well or just the VSV?

3) Anyone know if the Modulator from an FZJ80 is the same one used in an FJ80?
I'm thinking about swapping the one out of my 91 TLC for testing, but I can't read the part numbers off of it






Rick

 

[Beowulf]

Malfunction Iindicator Lamp

It's just a common term used cause not all MIL's are the same (Check Engine, Service Engine Soon, Engine Image, etc.)

MIL is also the term used in the Factory Service Manual (FSM) for the 80-Series.

-B-

 

[98 SNAKE EATER]

MIL is also the term used in the Factory Service Manual (FSM) for the 80-Series.

-B-

I kinda figured that (I don't have an FSM yet)


I never like the term "CEL" as I'd always think Central Electronic Locker

 

[98 SNAKE EATER]

ttt


Light went off by itself yesterday and has yet to return (put about 200 miles on her since then)

 

[RavenTai]

1) Should the hose leading to the VSV hold vacuum?

2) I know it's been said that you can replace the VSV without removing the intake, but does that include ALL of the hoses as well or just the VSV?

3) Anyone know if the Modulator from an FZJ80 is the same one used in an FJ80?
I'm thinking about swapping the one out of my 91 TLC for testing, but I can't read the part numbers off of it

1. If the VSV is commanded closed it should hold vacuum, if the VSV is open it will port ambient air defeating vacuum. EDIT: BAD INFO SEE POST # 36 the VSV is powered open so with the truck off it should be closed, the VSV is actually normaly open and power closes it [ / edit]

2. sort of, you may have to remove the TB as well to replace the ALL the hoses, But more importantly the hoses on the other side of the VSV from the EGR valve cannot cause a P0401/P0402, even if fully severed, it wuld not be desireable as dust could got in to the EGR system but the point is theses hoses are not leak critical, it is the hoses between the VSV and EGR valve that need to seal 100% and those can certainly be replaced wile replacing the VSV without removing the intake or TB, it does require some pretty severe hand contortion but doable,

3. dono