EGR VSV and Vacuum issues

Ok so I've been looking through the forum for people with similar EGR issues as me and can't seem to find anything so far. I figure instead of bugging the guys in the daily thread I would make my own post. I have a 1995.5 2.7L 4x4 Tacoma.

I think I've narrowed down the issue to two possible factors as to why my EGR system failed on a recent smog test. I haven't had any CEL or OBD2 codes since resetting it (couple hundred miles) and doing some work on the cluster (unplugging battery) so I'm not sure if I need to worry about this before re-testing.

I followed the instructions in the FSM and on a Youtube video linked in other threads on how to diagnose the EGR and two problems show up in mine.

1. The VSV for EGR functions correctly when plugged into the battery and holds vacuum when the truck is off but when I turn my truck to "on" with the key or it is running at idle the VSV is open, so no vacuum is restricted to the EGR system. (This is an intended OEM function) I am able to plug and unplug the VSV with the truck turned to on without the engine running and can hear and feel it click when the contacts on the plug are made. I checked it for continuity to its body and it's all clear, it also has a resistance of 37.5 (within spec.)

2. Vacuum line R on the throttle body does not show any vacuum at 3500 RPM per FSM spec. I have sprayed TB cleaner and blown it out but still it pulled no vacuum. Both ports P and E do show vacuum. Port R is the one going to the VSV's intake port. (Seems to not be an issue with EGR function, port R may be a return vacuum line. If all else fails with your EGR maybe look into this, but my truck runs fine regardless.)




I'm sitting here scratching my head at this point as to problem #2 because the port is just a tube, how is there vacuum next to it but not on that line? Even blowing air down the tube I can feel it come out from the front of the throttle body.

The only "symptom" I may be noticing beyond failing smog for EGR function is a slightly rough idle once it's warm. It will sit around 750 rpm, which would make sense given the fact the VSV is open and possibly causing the EGR to do its job of recirculating exhaust. (I confirmed in the FSM that idle is within spec.)

Any advice on what to do next?

 

You could start by adding your Yoda info to your profile so members know which year, model, engine, Or add that info to your post every time. You will increase your chances of attracting assistance from others with same specs/issues.

 

Oops, yeah I realized that afterwards. I will edit the post.

 

Have you removed and thoroughly cleaned the EGR valve and air pipe and replaced the 3 gaskets with NEW gaskets?

 

No not yet. Should I be concerned about the VSV opening as soon as I plug it in though?

 

VSV should only get power when Temp sensor is at operating temp. If engine is COLD no voltage should be at VSV with engine off,key on. If VSV is on with cold engine off key on the temp sensor is faulty.

 

Love it when I read posts from someone who knows what they're talking about

 

Step 1 Maintain a clean engine and compartment.

 

Thanks for this. I figured it was either the temp sensor, ECM, or a short somewhere in the wires. I will be taking the Temp sensor off to check if it is faulty using the FSM method of oil temp testing soon.

I should have checked it one more time this morning when the engine was COLD.

I agree, can't wait to start going through everything and make it run smooth and stay clean.

 

I pulled the temp sensor and cleaned it off, VSV is still opening when leaving temp sensor connected and open to air temp outside. I checked the resistance of the temp sensor while it was off the truck so it was at outside temperature and it was showing 100k+ Ohms. Resistance specs from the FSM for the temp sensor are on page EG-156. I don't think I have any way to safely heat up oil to check it at the FSM temps though, but considering it was showing higher resistance at room temp it should be telling the ECU to keep the VSV closed no?

 

BTW I did notice I had port R from the throttle body connected wrong, it goes to post R on the EGR vacuum modulator not the VSV as I had it in the first port. Still there is no vacuum on port R of the throttle body at 3500 RPM per page EG -138.



I suspect I need to clean it out. Going to do that this weekend when I get the new gaskets for the throttle body and the EGR.

 

Put that temp sensor out of its misery. I think when you see/test a new one you will agree.

 

Sounds good. I ordered a new VSV for good measure as it's only $30, but I have a source for a $200 OEM temp sensor. Was hoping it wasn't going to be that but might as well at this point.

 

The EGR temp sensor is not used to control the EGR valve. It's only used to monitor the system to make sure it's working. If it stays cold when there's supposed to be EGR flow it will throw a code and CEL. (May be 2-trip logic.)

The coolant temp sensor may be involved. ERG system may not operate until coolant is above a certain temp.

 

Hmm interesting. I mean my real issue is no matter what, cold or hot the VSV is open. So the computer or something else is thinking it needs to actuate the EGR always. Or the VSV is faulty even if it is within resistance spec.

I am still going to pull the EGR and clean it because the carbon on the temp sensor makes me suspect it's got massive buildup in the system itself.

The only other issue I saw was when I first got the truck is it had a code P0136. And I notice it still isn't showing the O2 system as being ready for emissions testing after a couple hundred miles of driving. Does that come into play for the EGR system at all?

 

Which code did you get? The egr excessive flow or the egr insufficient flow?
The way the ecu thinks there is insufficient or excessive flow is through the temp the egr temp sensor reports to it.
If it's too hot for set parameters, logically the ecu would think there is excessive egr flow because that is where the heat comes from, the recycled exhaust gas out of the exhaust.
Many times the insufficient flow DTC can be corrected with cleaning the carbon out of the vac lines and air passageways and even the VSV.
Insufficient egr flow means temp sensor is getting hot enough, not enough egr gas getting to temp sensor.
So if sensor is reporting temp accurately, I'd ensure carbon is all cleaned and new lines. Then I'd move into the VSV and modulator and egr valve. Rare for the egr valve to fail. I've actually only replaced the egr valve once for a customer and it was bad because customer jacked around with it and pierced the diaphragm. Anywho, sounds like you already had a grasp of this stuff. It helps me retain the info more when I get to type it out in a post on someone's thread

 

Actually funnily enough I don't have any codes regarding the EGR at all. The code I got was related to the O2 sensor bank 1 sensor 2. I saw that potentially was just due to bad gas, and the tank was empty when I bought the truck so I cleared it and haven't seen it since.

I feel like I'm running in circles with this EGR issue. The only two things I notice that caused it to fail the smog test was the VSV is always open, and there doesn't seem to be enough vacuum to port R on the throttle body to activate the EGR. I don't see any vacuum to activate the EGR when I tap into port Q on the modulator when at 3k+ RPM either. Which still makes me think it might be port R.

 

How did the smog test determine that the EGR failed since you don't have any codes related to it? Or did they say the EGR system readiness monitor was incomplete? You should have a printout of exactly why it failed.

 

The only note is that is failed for the MIL, which is fixed now. But in the systems information it shows the EGR also failed functional test, which as far as I understand is them hooking up a vacuum gauge in order test it. Same as I have been doing. It will of course fail because the VSV is staying open preventing the EGR from ever being actuated.

*edit* actually maybe I have this all wrong and the VSV needs to be closed at above idle to let the EGR get vacuum to open? I am going to check this after work.

 

If I understand it right, you shouldn't have any EGR flowing at idle. But at WOT and heavy acceleration, I believe, is where the exhaust gasses get routed back into the intake. I think.
You would have the MIL on if the EGR wasn't operating to spec. Not sure how that dude determined it wasn't operating correctly.