Exhaust leak and p0401

[ccslider]

97 fzj80 365k miles

This thing won't go away.

This stupid p0401 has lived up to it's fame of being frustrating to say the least. The interstate traffic is probably pissed about me trying to do a drive cycle.

Done so far
Replaced vsv with known good and tested continuity per fsm (moved to an easier spot)

Replaced modulator that was clogged

Replaced EGR valve with know good

Pull upper manifold and completely cleaned

Replaced all vacuum lines under manifold, to EGR, on throttle body

Cleaned throttle body butterfly and vacuum ports

Tested / cleaned EGR temp sensor / tested voltage to sensor harness side

Possible issue still:
I can still hear a slight exhaust leak, can this be causing the O2 to enrichen and cause a p0401?

 

[vegasfj40]

Where do you hear the exhaust leak? Is it near the egr valve? Make sure the ports on the tbody are clear. Do you have a FSM?

 

[vegasfj40]

I have a copy of the FSM. If you need to see the pages pertaining to P0401 let me know. I spent a lot of time dealing with my P0401 and had a couple of things wrong in the system. I had to take a sewing needle to the ports on the tbody to clear them out.

 

[jpoole]

The main thing I can pass along is to keep trying as this can be fixed . I was starting to wonder on my truck but finally have gotten it resolved and it's been a long time since my CEL popped up. A few of the non-obvious problems that I dealt with near the end of the process were:

-Little carbon chunks periodically getting sucked into the ports on the throttle body and clogging them. Repeated cleanouts that included pulling the brass/copper elbows and using welding wire to clear the ports along with blowing/sucking the lines out to try to clear the chunks from the system finally resolved this
-Leaky vacuum lines on the EGR valve connections which are a little rough from age. Even with new vac lines I was getting some leaking here but a thin coating of sealant then re-attaching the lines resolved this final intermittent issue on my 80

If you don't know what to check next then you may want to try the vacuum guage on the windshield wiper to troubleshoot what's really happening in the vacuum control circuit as you drive around. You can T the gauge into the vac. circuit with the system intact and then one at a time remove/plug the VSV valve, EGR, Vac Modulator, all the way back to the TB to confirm that your vacuum controls are working properly at each stage in the system. If all of that checks out it's easy to test the EGR valve (just apply vacuum to it while the truck is idling and the idle should drop, stumble and/or stall.

Chances are it's not the temp sender in the intake and it sounds like you cleared that passage so that the hot exhaust gas can pass through. The vsv is pretty easy to test by powering/unpowering it while checking for air passing through it.

After those tests you should know what's up but can always come back to mud for more ideas.

 

[ccslider]

Where do you hear the exhaust leak? Is it near the egr valve? Make sure the ports on the tbody are clear. Do you have a FSM?

Not sure, maybe the manifold toward the firewall.
I sprayed brake clean through the ports with it off and saw fluid spray out all except one, I tried the test on another throttle body I had and it reacted the same way.

I have a copy of the FSM. If you need to see the pages pertaining to P0401 let me know. I spent a lot of time dealing with my P0401 and had a couple of things wrong in the system. I had to take a sewing needle to the ports on the tbody to clear them out.

Yeah I have a copy and printed out the pages for the p0401.

The main thing I can pass along is to keep trying as this can be fixed . I was starting to wonder on my truck but finally have gotten it resolved and it's been a long time since my CEL popped up. A few of the non-obvious problems that I dealt with near the end of the process were:

-Little carbon chunks periodically getting sucked into the ports on the throttle body and clogging them. Repeated cleanouts that included pulling the brass/copper elbows and using welding wire to clear the ports along with blowing/sucking the lines out to try to clear the chunks from the system finally resolved this
-Leaky vacuum lines on the EGR valve connections which are a little rough from age. Even with new vac lines I was getting some leaking here but a thin coating of sealant then re-attaching the lines resolved this final intermittent issue on my 80

If you don't know what to check next then you may want to try the vacuum guage on the windshield wiper to troubleshoot what's really happening in the vacuum control circuit as you drive around. You can T the gauge into the vac. circuit with the system intact and then one at a time remove/plug the VSV valve, EGR, Vac Modulator, all the way back to the TB to confirm that your vacuum controls are working properly at each stage in the system. If all of that checks out it's easy to test the EGR valve (just apply vacuum to it while the truck is idling and the idle should drop, stumble and/or stall.

Chances are it's not the temp sender in the intake and it sounds like you cleared that passage so that the hot exhaust gas can pass through. The vsv is pretty easy to test by powering/unpowering it while checking for air passing through it.

After those tests you should know what's up but can always come back to mud for more ideas.

I didn't pull the Elbows off, I'll try that and see what it looks like.

 

[jpoole]

Before you pull the elbows off you can do a number of things to see if the ports are blocked. The best thing to do is just hook up a vac. guage and then rev the engine up a bit to see if vac. registers on the guage. Perhaps easier is to squirt a bit of brake/carb clean into each of the ports while the engine is running. If there is a change of rpm then you know the port is clear.

I wouldn't pull the elbow(s) unless you know that the ports are clogged. It's not that hard to damage them and it's a waste of time given the easy options for checking that the port isn't clogged.

 

[woodsman 44]

I had the P0401 and it was a crack at the Y pipe.....If you here it leaking its either gasket or cracked Y pipe

 

[ccslider]

I had the P0401 and it was a crack at the Y pipe.....If you here it leaking its either gasket or cracked Y pipe

It was leaking there but I welded it up.. or maybe I didn't.

 

[SaturnAscends]

I have the P0401 issue that seems to afflict virtually all of the OBD2 trucks: is it common for exhaust gases to leak from the EGR system itself into the engine bay? I thought it just meant there was a clog?

I was going to follow along with the steps outlined in the p0401 defeated thread, but is it even worth putting money into it? Some people claim it actually helps efficiency, but others say it was just tacked on to satisfy the EPA and ends up choking the engine.