P0401 help- For the millionth time...

[JBSTRD]

My buddy has a '97 80. He received a p0401 code a couple of weeks ago so to the forums I went. I have read countless threads on the Egr topic. I replaced the VSV and cleaned the TB. All of the vac hoses appear to be in good shape. So, I reset the code. The 0401 reared it's ugly head again.

So, more reading brought me to a vid that showed how to test the EGR valve. I started the engine and pulled the vac line on the passenger side of the EGR valve. I sucked on it and there was no change in the RPMs at all. I pinched off the vac line on the driver's side of the EGR valve. This is supposed to kill the engine......nothing. I am not feeling any vacuum coming through the lines.

I also pinched the line coming off of the VSV. This is also supposed to kill the engine....nothing.

When I had the TB apart, I checked the port that runs along the top of the intake plenum to the EGR valve. There was some carbon, but it did not appear completely plugged like some people have described. I also checked the other tube that runs through the plenum from the VSV to the EGR valve. It does not appear to be plugged either.

So, my question is, what does this mean when there is nothing running through the vac lines to the EGR valve. Where does the vacuum start. Obviously there is a plug somewhere, but I am unsure which direction to start from.

Another question I have is about the EGR temp sensor. I was going to clean it off, but the 14mm hex head is very tight in there. I am worried about stripping it. Is there a trick to get this off?

Thanks and sorry if this has all been covered before.

Jason

 

[JBSTRD]

Bump

Does anybody have a PDF of the EGR diagnosis steps from the FSM?

Thanks in advance.

 

[bsmart82]

When pulling vacuum on the egr valve you need to look and see if the valve is actually opening. If it doesn't, then the valve is bad likely due to a bad diaphragm. If it does open, bit there is no change in the engine, like lowered rpm or stall, the the egr passage is clogged.

 

[JBSTRD]

I am assuming the vacuum starts with the two hoses connecting from the EGR modulator to the top of the TB. Is this correct?

Is there a chance there is no vacuum because (1) the two lines coming out of the top of the TB are clogged or (2) the EGR modulator is bad? I disconnected those, but I don't remember if the engine was running at that time. The only hoses I remember disconnecting when the engine was running were the two running off of the EGR valve itself. When I did this, there was no air flow either way and the engine did not change RPMs at all when I messed with these.

Hope this helps.

Jason

 

[Pin_Head]

When pulling vacuum on the egr valve you need to look and see if the valve is actually opening. If it doesn't, then the valve is bad likely due to a bad diaphragm. If it does open, bit there is no change in the engine, like lowered rpm or stall, the the egr passage is clogged.

X2

I The only hoses I remember disconnecting when the engine was running were the two running off of the EGR valve itself. When I did this, there was no air flow either way and the engine did not change RPMs at all when I messed with these.

P0401 means insufficient EGR flow. The potential causes are (in order of liklihood):


1. Plugged EGR passage in intake manifold.
2. EGR valve bad/stuck closed.
3. Bad VSV
4. Bad EGR modulator.
5. Bad temp sensor.
6. Bad wiring.

When you pull a vaccum (suck) on the EGR actuator line, the valve actuator rod should move up about 3/8 inch. If the EGR passage is clear, the engine should also stumble or stall. If it passes this test, then move on to 3, 4, 5, 6.

 

[JBSTRD]

So if I clean/ream out the large port on the intake minifold (from the area of the TB to the EGR Valve), I should start feeling vacuum in the vac lines running off the top of the EGR valve. If I don't feel anything in these vac lines, as it sits now, there is most like a problem with the diaphragm inside the EGR Valve.

Does this sound right?

Thanks for the replies.

 

[Pin_Head]

So if I clean/ream out the large port on the intake minifold (from the area of the TB to the EGR Valve), I should start feeling vacuum in the vac lines running off the top of the EGR valve. If I don't feel anything in these vac lines, as it sits now, there is most like a problem with the diaphragm inside the EGR Valve.

Does this sound right?

No. You are thinking about it bass ackwards. Vacuum on the EGR lines causes the EGR valve to open, which sends exhaust gas into the intake manifold. The vacuum is controlled by the VSV and the EGR modulator. You only see vacuum on the actuator lines when the EGR valve needs to be open. It is the lack of exhaust gas flow that causes the P0401 code.

 

[JBSTRD]

Gotcha. I appreciate the help. I am going to do a thorough cleaning on the main port running to the EGR Valve. I will report back when I do that. Hopefully this cures the issue.

Thanks

 

[JBSTRD]

So I removed the Throttle Body and EGR Valve again and cleaned the port running between the two in the intake plenum. It was not completely blocked as some have described. It was mainly black on the walls so I reamed it out and shot some carb cleaner into it. I also removed the EGR Temp sensor and cleaned it off. I replaced the vacuum hose running from the VSV to the EGR Valve. I bypassed the metal piping that runs through the Intake Plenum to alleviate that issue.

So, when I sucked through the vacuum hose running from the EGR Valve to the EGR Modulator, the engine stuttered as it is supposed to. However, when I pinched off the vacuum line between the EGR Valve and the VSV, the engine did not die like it is supposed to. In fact, nothing happened.

I am keeping my fingers crossed that the cleaning and hose replacement I did will be the fix, but I am wondering why the engine is not cutting out when I pinch that vacuum line. Does this only happen when you rev the engine up? I was pinching the hose at idle.

The only things I have not replaced are the EGR Valve and the EGR Modulator. Everything else has been cleaned, hoses replaced, and the VSV is new.

Any help would be appreciated.

Thanks

 

[Stevesnj]

I had the same code, sealed the leak in one of my cats and haven't had the code since.