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EGR Excess Flow?? Hesitation w/ EGR Connected, Runs Good W/O EGR!

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6.3K views 13 replies 5 participants last post by  ryanschillinger  
#1 ·
I replaced my EGR vacuum modulator because it was not functioning, and it took care of part of the hesitation, but even with the new modulator it's still causing a hesitation!!
I took my truck to the shop where I used to work, and they adjusted my TPS. That helped, too. I bumped up the timing to 12' btdc, and that made it run better, but still with a hesitation!
Tonight, I went to Autozone and picked up some vacuum caps. I capped off the EGR valve as well as the metal line the other side of the vacuum line connects to. Now the truck runs great! No hesitation at all. Never thought this engine would be so smooth.
Does anyone have ideas what would be making my EGR cause this problem? The modulator is brand new and the EGR is working (when you hook a vacuum pump up to it and give it vacuum, the truck wants to die).
This is driving me crazy!
I've put new plugs, wires, cap, rotor, fuel filter, cleaned the throttle body & intake manifold, adjusted the idle speed, and I'm sure some other stuff I didn't remember to mention...

Thanks for your guys' help! This site is great.

Ryan
 
#3 ·
So you replaced the solenoid valve that sends vacuum to the EGR valve to open it, and you still have too much hesitation? dj99 has a good point, the valve might be partially stuck open from carbon build up or something.
Either that, or there is something else in the system that is making the valve open sooner than it should or at times it shouldn't. Is there anything else controlling the opening of the EGR valve?
 
#4 ·
I'm not sure what else controls the EGR opening. Looking in my Hayne's manual, it looks like maybe the VSV- vacuum switching valve. It doesn't do it when it's first started and cold though, so it would seem like the VSV is working, according to what I've been reading. I think I'm going to clean the EGR valve itself. Sounds like a lot of these Toyota EGRs get pretty gunked up with carbon buildup...
 
#6 ·
The modulator was bad, so I replaced it. It helped the hesitation some, but not much. I just put in the modulator about 50-100 miles ago. Had a shop adjust my TPS. Think it might have something to do with the VSV or what else might be causing this? I'm going to remove the EGR valve and clean it out and see what happens... Oven cleaner works good? Or what is good for the carbon buildup??

Thanks!!
 
#8 ·
I wouldn't use over cleaner, sure, it would eat carbon, but also everything else like seals and the vacuum diaphram if it got on it. A high quality carb or throttle body cleaner like CRC should help loosen it up, and some elbow grease with a toothbrush/pipe cleaners/rags and whatever else should help remove the carbon. You also might want to clean the passages leading to and away from the EGR if you have access, especially the passage TO it. If the EGR was clogged, that passage probably is also.
 
#7 ·
EGR excessive flow code is becuase it is seeing an increase in temp on the EGR temp sensor when it shouldn't. If you have EGR when you shoudn't it will cause a hesitation/stumble.

If it is stuck open all the time it would idle poorly and probably stall.

There is a vacuum switching valve that should keep the EGR from working when the engine is below 48degC and allow it to work above 50degC If this is not working right I would expect to have a problem when the engine was warming up, but not all the time.

Probably you should go over the vacuum hose routing and make sure all the hoses are connected properly. I've seen many different problems on 3VZEs caused by mis routed vacuum hoses.
 
#9 ·
I don't have a check engine light on, but I haven't tried reading the flashing lights on the dash with the jumped terminals. According to the best I can tell, the vacuum hoses are routed correctly (So many of them!!) I was just describing that it seems like the EGR is flowing more than it's supposed to when I said excess flow. Even with the EGR capped off and disabled, I still haven't gotten a check engine light (yet). With the EGR connected, the idle isn't affected much, it hesitates alot when you first step on the gas, like leaving a stop light, as well as losing power, noticeable on freeway uphills especially. Maybe the VSV is working OK since it doesn't do the hesitation really when it's cold and first started driving....
Headache!

Haha thanks everyone for the help and advice!
 
#10 ·
OK, Back to basics....

The purpose of the EGR is to reduce Oxides of Nitrogen (NOx) emmisions. It does this by blending a small amount of exhaust with the intake charge to reduce peak combustion temperatures. This is supposed to occur at part throttle conditions after the engine is warm. If the VSV is not functioning properly, it will either make the EGR work when the engine is cold (may cause hesitation during warm up) or it won't let the EGR work at all which can cause the engine to ping under part throttle, but would not cause it to hesitate.

Here is a link to a pdf that will give you diagnostic info.

http://home.comcast.net/~vbarnett11/Exhaust_Gas_Recirculation_Egr_S.pdf

Check that the system is working correctly.

If it is, you may have another issue that is making the engine run lean and it only shows up when the EGR is functioning
 
#11 ·
Hmmm... Maybe that would explain the "ticking" noise I noticed at very light throttle, like neighborhood cruising speed. I didn't think it was pinging because I've only ever experienced pinging at heavy throttle. I'll hook the EGR back up and see if it goes away. What might make this enging run lean without tripping a check engine light? Sorry for this post going on so long, but I didn't find an answer elsewhere
 
#12 ·
One thing that can cause lean conditions is dirty injectors. Another is an O2 sensor that has voltage leaking through it from the sensor heater.

These trucks are usually a bit slow to throw codes for lean/rich conditions. But if they have dirty injectors eventually they will throw a lean and a rich code.

If you have a good voltmeter preferably a digital one with a bar graph or an analog one. check voltage between the OXY terminal in the dignostic connector and ground. warm the engine up and run it at 2000rpm for one minute then let it idle. the voltage should sweep back and forth fairly steady between about 0.2V and 0.8V about 8 times in ten seconds.

If it hangs up at the higher voltage before dropping down that is a sign of dirty injectors. If it stays high and especially goes over 1.0V swap in a new O2 sensor.
 
#13 ·
OK cool. Thanks for the info. I'll have to borrow the voltmeter from my buddy and check it out. I dumped a bottle of Berryman in the tank when I filled up yesterday actually, so maybe that will help.
BTW- I really like the look of your truck with the shaved tailgate and all. I was about to shave mine along with the door handles and stuff before I painted it, but decided against doing that on a "work truck" with so many miles!! I think your taillights would look really good with a little bit of tinting. I'm going to tint mine or just pick up a pair of the black euros for mine once I get the hesitation issue settled.
 
#14 ·
So I reconnected my EGR, and the pinging went away, but the hesitation is back!! I need to get a voltmeter to check the o2 sensor and stuff. I want to get this truck running better, but this hesitations is pretty persistent...