Brothers, Help!

Hello,
I have exhausted my search efforts on here, google and other sites. 2001 Taco 2.7 138k.

Problem:
DTC P0402

What i have done..(all testing methods were from previous searches on this site as well as others before making a thread)
1. Tested and replaced faulty VSV. Tested new one prior to installing.
2. Tested and removed carbon from EGR Temp sensor.
Retested, confirmed it is now within parameters.
3. Removed EGR Valve, confirmed its seats properly and operates smoothly.
4. Tested EGR Modulator, it freely blew through the filter area.
5. Removed and Inspected every vaccum line that is in contact with all three previous items.. as well as the air box-hard line above radiator to evap system. Confirmed they were put back in the right places.

I am at a loss of ideas. The truck runs great, idles great, gets good gas mileage. Need emmissions insp. done.
One last thing...i was unsure about how on the EGR temp sensor, occasionally at random testing points, I would only get a reading at 2000K ohm setting. The reading was in parameter, but I thought I read somewhere you should not get a reading over the 200K ohm setting on a meter or it is considered a sensor short?
Also, can someone on here point me in the right direction of using a 10ohm resistor on this temp sensor to cheaply diagnose if this is intermittently acting up? The resistor goes on the wiring harness plug and is taped shut.. Is it that cheap and simple or am i missing something else?

 

My EGR modulator tested in 'spec' but wasn't. There is a cheap Dorman Chinese knock off of the modulator on Amazon, I think. I bought it, (I know I know not OEM, I justified it by reminding myself there is no electrical connections, etc lol ) and it's still working. I had replaced the bad vsv and my code went from P0401 - insufficient EGR flow, to P0402 - excessive egr flow. That's when I thought I'll try the cheap modulator. I'm hesitant to recommend it, even though it works for now, because it's cheap crap. But this might be a spot on the truck that cheap crap is okay to use. Just the modulator, though. The VSV you'll for sure want the Aisin brand OEM quality. Sorry for long reply.

 

My VSV replacement is the OEM green one. im all for cheap troubleshooting as all these parts are very expensive. At this point I am considering going to a junkyard and purchasing all three for cheap and swapping them out just to diagnose. Hell, I even stopped at 2 bone yards already to do that, but they didn't have any 3RZs. Im beyond frustrated. Its becoming a true demon to me, due to my pet peeve being no diagnostic dash lights on!!

 

I guess you have a hand operated vacuum pump to test things since you said the EGR valve operated smoothly. If not, then you can buy a cheap one.

There are two things that come to mind. First is make sure the exhaust pipe leading to the EGR valve and from the EGR valve to the intake is not clogged with soot.

Second, the old rubber diaphragm in the modulator can start leaking causing the modulator to stop working correctly. The repair manual doesn't give this as a test, but you can apply a small amount of vacuum to the bottom port (the feedback port coming from the bottom of the EGR valve). If it doesn't hold vacuum then the diaphragm has a hole and the modulator should be replaced. I say to apply only a small amount of vacuum because if the diaphragm is old and brittle but still working, applying a large vacuum could damage it.

See this thread EGR modulator disassembly on another forum, in particular the 7th picture showing the broken diaphragm. All the modulators work the same. They are just different sizes for different engines. There is no way to fix it, but it lets you understand why modulators break.

If the diaphragm is leaking then the metal pipe coming from the bottom of the ERG valve to the bottom of the modulator can get filled with soot. Normally the port just senses the pressure, so no exhaust gases (and soot) pass through it, but with a broken diaphragm the gases will carry soot into that pipe.

In summary:
1) Check that the EGR pipes are not clogged.
2) Check that the bottom port of modulator holds vacuum.

 

This absolutely has to be made into a stickie.

 

Yes, DrZ great help.
I would think number one would be associated with P0401, but I will definitely check anyways.
Number 2, I have not done, but it sounds promising and will hopefully be the culprit. I did not see that advice on any other posts or through numerous searches. Thank you. And when I get my truck back from a relative later this week I will certainly check them. If only you guys knew how peeved I get with dummy lights. I usually lurk on forums to gain knowledge with little participation in topics. But this situation has me quirked lol.

 

I'll add that the bottom port of the modulator is a little bigger that the pipe on a vacuum pump, so you may need to use 2 different size hoses and an adapter or just force a small hose on. If you don't have a tight seal you might lose vacuum from the hose and misdiagnose it as the diaphragm.

And you're right, the clogged passages would cause P0401 not P0402.

 

Soo... update.. I got the truck back today off my relative... noticed no DTC.. thought to my self eh what the hell, hooked it up to my scanner 8 out 8 readyness monitors no DTCs. No Pending, nothing. I don't know what to think, but im gonna hurry up and get it inspected and emissions done just incase. This truck is awsome, maybe it didn't like its previous owner, so it threw a temper and made them chase ghosts. I still want to check those things but im afraid to touch anything. Thanks again to the guys who responded.

 

Awesome dude, lucked out.