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

[98 SNAKE EATER]

OK, here's a little update...


It's been a week since I installed the Camry modulator and she has yet to throw a code

Anyhoo, here's the testing procedure I went by (AllData)



EGR VACUUM MODULATOR INSPECTION

1) Disconnect vacuum hoses from EGR vacuum modulator.

Disconnect these vacuum hoses:

(1) Vacuum hose from R port
(2) Vacuum hose from Q port
(3) Vacuum hose from P port


2. Inspect EGR vacuum modulator operation.

(a) Block ports P and R with your finger.

(b) blow air into port Q and check that the air passes through to the air filter side freely.

(c) Start the engine and maintain speed at 2,500 rpm.
(d) Repeat the above test. Check that there is a strong resistance to air flow. If operation is not as specified, replace the EGR vacuum modulator.


3. Reconnect vacuum hoses to EGR vacuum modulator.

Connect these vacuum hoses:

(1) Vacuum hose to R port
(2) Vacuum hose to Q port
(3) Vacuum hose to P port





With that said, I'd like to add that removing the modulator altogether and testing vacuum on the bottom port to see if the diaphragm had any leaks was more straight forward in my case and should probably be added to the testing procedure

 

[motelcambodia]

OK, here's a little update...


It's been a week since I installed the Camry modulator and she has yet to throw a code

Anyhoo, here's the testing procedure I went by (AllData)



EGR VACUUM MODULATOR INSPECTION

1) Disconnect vacuum hoses from EGR vacuum modulator.

Disconnect these vacuum hoses:

(1) Vacuum hose from R port
(2) Vacuum hose from Q port
(3) Vacuum hose from P port


2. Inspect EGR vacuum modulator operation.

(a) Block ports P and R with your finger.

(b) blow air into port Q and check that the air passes through to the air filter side freely.

(c) Start the engine and maintain speed at 2,500 rpm.
(d) Repeat the above test. Check that there is a strong resistance to air flow. If operation is not as specified, replace the EGR vacuum modulator.


3. Reconnect vacuum hoses to EGR vacuum modulator.

Connect these vacuum hoses:

(1) Vacuum hose to R port
(2) Vacuum hose to Q port
(3) Vacuum hose to P port





With that said, I'd like to add that removing the modulator altogether and testing vacuum on the bottom port to see if the diaphragm had any leaks was more straight forward in my case and should probably be added to the testing procedure

Where are P and R ports located ? When I had my code checked the macaninc pulled off the lines before I had time to see the lines but I dont think he got them back on right I think P and R may be swithed . After replacing mine the code come back.

 

[98 SNAKE EATER]

Where are P and R ports located ? When I had my code checked the macaninc pulled off the lines before I had time to see the lines but I dont think he got them back on right I think P and R may be swithed . After replacing mine the code come back.

They're marked by number:

(1) Vacuum hose to R port
(2) Vacuum hose to Q port
(3) Vacuum hose to P port

 

[Rivera5]

I replaced my modulator - i now have the blue top: part # 25870-66011 I am pretty sure that I connected hoses correctly. I followed the R & P hoses from the modulator to their connection points. Where they connect there are 3 letters stamped. Standing on the drivers side left to right they are P R E

I have the R going to R, and P to E Is this correct?

I too am frustrated with this same issue on my 97'.

 

[RavenTai]

I replaced my modulator - i now have the blue top: part # 25870-66011 I am pretty sure that I connected hoses correctly. I followed the R & P hoses from the modulator to their connection points. Where they connect there are 3 letters stamped. Standing on the drivers side left to right they are P R E

I have the R going to R, and P to E Is this correct?

I too am frustrated with this same issue on my 97'.

Yes
R-R
P-E
Q-EGR valve
bottom - exhaust pressure.

If you have the original hood you should have a vacuum sticker above the battery that shows it.

 

[Rivera5]

Yes I have the original hood and the the vacuum sticker - thanks for the heads up. I will tackle the VSV next.

 

[98 SNAKE EATER]

OK, another update....

It's been about 4 weeks (a little over 4000 miles) since I installed the Camry modulator and she finally spit out another 401 code

So I went ahead and ordered a new blue top for her

As you can see, the updated modulator is a bit different than the older ones

The entire body is plastic, it doesn't have a metal trim ring around it and it's also slightly larger...

Also, the cap on top doesn't look like it can be removed to inspect the filter (perhaps it can, but it felt like it would break if I try to force it)

 

[Bluetribal]

How much for the part. I think I am going to begin my P401 saga this weekend. It has been 11 months on so I better get started on this before it's registration time AKA smog check. I have the FSM to run through the tests but just curious what I am getting into if I have to replace parts.

 

[98 SNAKE EATER]

How much for the part. I think I am going to begin my P401 saga this weekend. It has been 11 months on so I better get started on this before it's registration time AKA smog check. I have the FSM to run through the tests but just curious what I am getting into if I have to replace parts.

Lists for $68 bucks, got it for $42 at the dealer next door to my shop (CDan could probably do better)

 

[edog's 80]

About how much vacuum did you have to apply to make the engine stumble? I tried this morning by sucking on the tube to create a vacuum and the engine ran fine, does it take a really strong vacuum pump?

 

[98 SNAKE EATER]

About how much vacuum did you have to apply to make the engine stumble? I tried this morning by sucking on the tube to create a vacuum and the engine ran fine, does it take a really strong vacuum pump?

It doesn't require much vacuum at all...

See the test video in post #37

The engine should give you a slight stumble when you just apply vacuum...

When you apply vacuum and pinch the opposing tube leading to the intake port, the engine should stumble hard and stall...


Rick

 

[Beowulf]

About how much vacuum did you have to apply to make the engine stumble? I tried this morning by sucking on the tube to create a vacuum and the engine ran fine, does it take a really strong vacuum pump?

I don't think sucking on the tube is a good vacuum test. Unplug the fuel pressure regulator and plug in the hose to the EGR modulator to that intake port.

-B-

 

[edog's 80]

Well, I just went out and tried it and I could not get it to stumble hooked up to the Fuel Pressure Regulator, but giving it a quick suck did the trick, I was able to get it to stumble. I am still suspecting my EGR though because it won't hold vacuum and the engine did not totally die nor stumble when I pinched the other lines leading into the EGR. I may take it off and give it a once over, I am sure at a minimum it needs to be cleaned even if it ends up being the VSV for EGR. My truck is idling rough when it's in park or neutral after it has warmed up, so something is amiss I think.

 

[RavenTai]

E-dog, The EGR valve is rarely the problem, there are two lines to the EGR valve, you need to cap the other side of the egr vavle before you can aply vac to it.

 

[Beowulf]

Well, I just went out and tried it and I could not get it to stumble hooked up to the Fuel Pressure Regulator,

To get vacuum, you are supposed to run a hose from the EGR Modulator to the same intake port used by the FPR, not hook it to the FPR.

-B-

 

[edog's 80]

To get vacuum, you are supposed to run a hose from the EGR Modulator to the same intake port used by the FPR, not hook it to the FPR.

-B-

Good to know. Either way, when I applied vacuum I got it to stumble so I am thinking that gets the EGR in the clear, and based on Raventai's advice, the EGR is not usually the culprit anyways. I just did the air pressure test on the vacuum modulator and according to the FSM it passed, so it looks it could be the VSV for me as well as many others.

 

[98 SNAKE EATER]

I just did the air pressure test on the vacuum modulator and according to the FSM it passed, so it looks it could be the VSV for me as well as many others.

Did you remove the modulator and check the bottom port to see if it holds vacuum?

When I tested my old modulator using AllData's instructions (I assume it's the same as the FSM?), it seemed to be working fine, but I wasn't sure if the test was adequate cause I had nothing to compare the results to

It just says strong resistance when running at a given rpm, but doesn't go into detail as to how much is considered strong

That's kinda like saying an oil filter should be installed hand tight while talking to little girl and a bodybuilder

However, when I removed the modulator and checked the bottom port, it became very clear that it was bad because the diaphragm wouldn't hold vacuum

Not sure why that test wasn't added to the testing procedure cause it's much more straight forward

Definitely worth a shot if you haven't done so already...

 

[edog's 80]

Did you remove the modulator and check the bottom port to see if it holds vacuum?

When I tested my old modulator using AllData's instructions (I assume it's the same as the FSM?), it seemed to be working fine, but I wasn't sure if the test was adequate cause I had nothing to compare the results to

It just says strong resistance when running at a given rpm, but doesn't go into detail as to how much is considered strong

That's kinda like saying an oil filter should be installed hand tight while talking to little girl and a bodybuilder

However, when I removed the modulator and checked the bottom port, it became very clear that it was bad because the diaphragm wouldn't hold vacuum

Not sure why that test wasn't added to the testing procedure cause it's much more straight forward

Definitely worth a shot if you haven't done so already...

Well I think the FSM has you do essentially the same thing, you plug the two holes (P and Q I think?) on the back side and apply air (I just blew into some spare vacuum tubing I have) into the incoming tube from the EGR. The FSM has you do this while idling at 2500 rpm and mine stopped all air flow going into the Vacuum modulator. I think that indicates that it is holding vacuum and functioning correctly. Either way, I wil try what you said because it is very easy to take off I want to make sure I order the correct part.

Thanks for all the help.

 

[edog's 80]

Well I think the FSM has you do essentially the same thing, you plug the two holes (P and Q I think?) on the back side and apply air (I just blew into some spare vacuum tubing I have) into the incoming tube from the EGR. The FSM has you do this while idling at 2500 rpm and mine stopped all air flow going into the Vacuum modulator. I think that indicates that it is holding vacuum and functioning correctly. Either way, I wil try what you said because it is very easy to take off I want to make sure I order the correct part.

Thanks for all the help.

Update: This morning I took the Vacuum modulator off and ensured that the bottom port held vacuum by attaching a vac line on it and sucking-it held vacuum pretty well. All of my tests so far have shown that the vacuum modulator is ok. I ordered the VSV for EGR today from CDAN. My fingers are crossed that this solves it!

 

[Beowulf]

I ordered the VSV for EGR today from CDAN. My fingers are crossed that this solves it!

Start reading up on the VSV for EGR R&R without removing the intake. Takes about 20 minutes with some dexterity in your hands.

-B-