Intake Manifold Question (1 Viewer)

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I am troubleshooting my PO401 code and I have a question concerning the amount of vacuum that I am getting out of my intake manifold where the 2 lines from the EGR modulator plug into. I have run throuth the testing accoring to the FSM and I have come to the conclusion that either the VSV is bad or that the vacuum ports in my intake manifold are blocked. How much vacuum should be at those two ports? I have great vacuum at what was called the gas valve on a FJ40 so it makes me think that I may have clogged intake ports.

Please chime in with any info.

Thanks
Scott
 
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It actually depends on the day. I have seen it drive for quite some time before the light comes back on. The last time I reset the light it probably ran 20 to 30 miles before it came on. I think I will pull the intake tommorrow as well as the VSV and I will test the VSV(and probably replace) and I will clean the intake. I was trying to avoid pulling the intake, but I guess I will just to it. That just means I am going to have to change the PHH as well. I hope it isn't as bad as I have heard.

Thanks
Scott
 
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I don't think you'll need to pull the intake. I'm sure someone will chime in and make a liar out of me, but the intake vacuum ports won't clog. They'll build up a bit of crud around them, but the opening in the intake won't close off. I'd pull the throttle body and look at the VSV and nearby vacuum lines for a leak/rotted/loose one.

Also, when discussing your vehicle, good info for us is year and miles as the systems are different between years.

DougM
 
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Sorry, it is a 95 FZJ80 with 145,000 miles. The Cruiser has been very well kept, fluids, service etc.... It has also passed Utah emission without any problems. I have checked all vacuum lines associated with the EGR system, they were all leak free. One of the reasons I considered pulling the intake was because of the possible carbon buildup that I read about in other threads. The reason I was curious about the amount of vacuum from those ports is because of how much I am getting out of the other port with the gas valve. When I run the FSM test I get no vacuum with a warm engine. When I run the vacuum guage directly to those ports I never read any vacuum. According to the FSM I should have high vacuum at 2500 RPM at the R Port of the Modulator, I have zero. That leads me to believe that those ports are clogged. I hope I am trouble shooting this correctly, I hate to go through all of this work to have the light come back on. Anyway thanks for the advice.

Scott
 
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Can you get a thin wire into the intake ports in question? I'd consider doing that as if indeed the port has been covered over, even a tiny pinhole will provide vacuum. Obviously a worry would be knocking something loose, but it's worth knowing that what gathers there is a soft oily accumulation, not hard carbon particles like you might find in the cylinder environment. In other words, from the two intakes I've had off, I would have no worries about knocking a chunk of it loose while punching through it with a needle. The stuff would go right through valves and such.

It is strange that you get no vacuum at the ports. I'm assuming they're not some kind of non-vacuum ports that simply allow the system to have an open air component so the vacuum generated elsewhere can move the air to do the 'work' the vacuum is supposed to do.

DougM
 
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I was wondering if it was an open air component as well, but after testing like the FSM states I don't see how that would be possible(unless I am misreading the test in the FSM, very possible) and to me the ports look like the are directly entering the intake/throttle body so at some point there should be some vacuum. I was concerned about putting something down the hole because I wasn't sure what was in there(ie. some kind of filter etc...). I will re-read the FSM tomorrow and see if I can make any better sense of what is being asked. I am definitly going to test the VSV first to see if that is the problem, the I will proceed from there. I will let you know what I find out tomorrw, I may be able to shed some better light on the subject.

Thanks
Scott
 
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Scott,

At least one of the ports back there looks like you're going into the manifold from the top, but it's actually just a pass through that exits as a hose on the bottom and then goes somewhere. Someone else recently had quite a post on this and discovered that. It had great photos, etc. Be sure you're not talking about those same nipples on the #5 or #6 intake runners. The FSM doesn't make this clear.

DougM
 
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IdahoDoug said:
Scott,

At least one of the ports back there looks like you're going into the manifold from the top, but it's actually just a pass through that exits as a hose on the bottom and then goes somewhere. Someone else recently had quite a post on this and discovered that. It had great photos, etc. Be sure you're not talking about those same nipples on the #5 or #6 intake runners. The FSM doesn't make this clear.

DougM

Yep, Doug speaketh the truth. My pass-through was clogged 100% when I pulled the intake. I suspect it was the cause of my troubles although I replaced the VSV and EGR modulator while I was in there. It wasn't me who took the pics though...
 
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I decided to pull the intake so I could see and access all of the ports, hoses and parts associated with the EGR system. I have gone throuth all the hoses, ports, parts(including the VSV, EGR Modulator, and EGR valve) and they all work within the specs of the FSM. The only thing that seemed to be out of spec is the Gas Temperature Sensor. I took it out and tested the resistance at certain specific temps. From cold it was fine, but as it heated up it never got down to the correct Ohms reading. It seemed to be working, by this I mean that the resistance would decrease, but not very fast and not down to the numbers specified. About 30,000 miles ago this part was taken out and cleaned by a Toyota dealer as a result of the light comming on and the PO401 code. I decided to just replace the part which I hope will fix the problem. I will find out tomorrow or saturday if this is the case. I wish I would have tested the part before I disassembled the intake, but I guess I have the piece of mind knowing that the intake is clean and all of the ports are clear.

This diagnosis does sound like it could be the problem, and would explain why the light would stay off until it was driven for a while.

If anyone has a picture of the port that was clogged, or know where I can find the picture please let me know I would hate to miss something like that especially while the intake is off.

Thanks for the help
Scott
 
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I see that the VSV idea has passed but yes, you can change it w/o taking off the top manifold. Pull the TB and it's not bad from there. Either use a flex ratchet or bend up a 12mm a little and your in.
 
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Portal_tek said:
... and would explain why the light would stay off until it was driven for a while.

Scott,
P0401 is a 2-trip logic meaning that the MIL will not illuminate every time the system detects a P0401. There are a few other factors that define a "trip." I can't recall the details but it is something like:
The vehicle has to reach 50 MPH and sustain that speed for 5 minutes. You have to do this twice and the failing condition has to occur on both trips.

The VSV for EGR can be R&R'd without removing the throttle body or the intake. It can be accessed from below for one of the bolts and from above for the other.

-B-
 
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Thanks for the help, I did remove the intake and tested all the ports, hoses, vsv, and everything else I could think of while in there. The only thing that was out of spec was the Gas Temp Sensor. I decided that I would replace it since it was the only thing that was not within specifications. I hope this helps for what that little sensor cost, plus I am going to drive 1250 miles to Oklohoma tomorrow and I don't want to have any issues. I will let everyone know if this does the trick.

Thanks
Scott
 
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I just wanted to let everyone know that I replaced the temp sensor and so far no more PO401 Error. I have driven to OK and have been driving around town now for a couple of weeks. I just wanted to thank everyone for their input.

Thanks
Scott
 
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Good news Scott.

My first attempts at erradicating a P0401 produced ~6 months before the MIL came back and when it came back it was no longer intermittent. I absolutely hate that damn P0401 code.

-B-
 
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I am hoping it stays off, I would hate to start all over again in 6 months. Mine was a constant light to begin with, so I hope maybe this was it. I hope you figured it out the second time and this time for good, what a pain!

Thanks again for all the help
Scott

PS. Now I just neet to figure out the dome lights and the errant locking of the doors.
 
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It's Back

Well, like my previous post I really didn't want to start all over again, but I guess I have no choice.

If you have read my previous posts you can see what has been done to repair the issue, so I really don't know where to start. I thought about just purchasing the VSV to count that out, but I hate to throw parts at the problem. The funny thing is that it will stay off for about 4 days then come back on. I am going to start going through the FSM and begin troubleshooting again, but I thought I would ask what you guys think and where you would suggest I restart.

Thanks
Scott
 
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The part that fails most often is the VSV for EGR. The most common cause of the P0401 is clogged passages or EGR or hoses. You've checked the passages and you've replaced the temp sensor (I don't think anyone has ever permanently fixed a P0401 by replacing the temp sensor...)

If it were me, I would replace the VSV for EGR. You said you tested it but test it again. I believe Raven is fighting an intermittent VSV problem in another thread.

Good Luck and keep us posted!!
-B-
 
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I will see if I can find the thread that Raven has going to see if I can get any more ideas. Has anyone used the Toyota Hand Held Tester? or does anyone know where a person could rent one?

Scott
 
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My EGR port was completely clogged in the upper intake. A quick run with a .5 inch drill fixed it. Most complicated part will be the time to remove the intake, and keeping the carbon out of the lower intake.

I also had a mechanic previously clean the large EGR tube for the same reason.

I had to remove the upper intake to accomodate a HG job, and that is when / how I found the clog. If I were you I would clena all ports out. I bet this will fix you right up.
 

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