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- #21
I got a new VSV today but the wife took the 80 out of town tonight so I will try tomorow to get it in. I will disembowel the old one 
kurt
kurt
Its back...Code71 (1 Viewer)
- Thread starter landtoy80
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I'm taking an advanced FI course for Fords this week and today we talked about EGR for a bit. Fords have terrible EGR systems too, so I learned a lot. Some problems they are having with low flow include small cracks in the EGR tube, Their version of the VSV, and their pressure monitoring system. They no longer use the temp sensor, but use a MAP type piezio crystal sensor. Their VSV gets plugged on the vent that releives the vacuum to the EGR when the valve shuts. I assume that's what the modulator does on the Toyota system. That would account for high flow, though. I wonder if a leaky modulator would not let the EGR open enough?
Gumby,
Here is a general description of how Toyota's EGR systems work.
http://www.autoshop101.com/forms/h61.pdf
-B-
Here is a general description of how Toyota's EGR systems work.
http://www.autoshop101.com/forms/h61.pdf
-B-
>> I wonder if a leaky modulator would not let the EGR open enough? [i.e., "stuck closed"]
Personally, I think Gumby is paying attention and is going to get an A in this course
After six months of mucking around with the P0401 (Code 71), I tried something different involving the vacuum modulator... and it seems to be working. I am departing on a week+ road trip to the Sierra Nevadas, and if I get back without another MIL, I'll report back in detail (I've eaten far too much crow already on this EGR business to be too premature...).
Cheers, R -
Personally, I think Gumby is paying attention and is going to get an A in this course
After six months of mucking around with the P0401 (Code 71), I tried something different involving the vacuum modulator... and it seems to be working. I am departing on a week+ road trip to the Sierra Nevadas, and if I get back without another MIL, I'll report back in detail (I've eaten far too much crow already on this EGR business to be too premature...).
Cheers, R -
Spent some time on it today.
The EGR is working. The temp sensor is working. It's changing values as it heats up. I would like to see a chart to compare the rate of change to factory specs, but I don't have that info, and I believe it to not be the problem. The modulator is actually a backpressure sensor and it works as it's supposed to. A quick drive with a vacuum guage from the EGR feed stuck under my w/s wiper showed NO vacuum to the EGR at driving conditions that should trigger EGR action. I did not have a Toyota scan tool on the vehicle to confirm ECM signal to the VSV, but if I had such a fancy peice of equipment, I'm sure I'd have had this sucker repaired long ago.
I am feeling fairly certain it is the VSV. If it is not and it is in the programing I'd bet there is a flash reprogram to fix it.
Meanwhile, the tech that was working on it with me said that if it doesn't ping, chances are I'm getting better performance out of it with it in-op.
I just have to clear the codes less than two drive cycles before emissions testing.
The EGR is working. The temp sensor is working. It's changing values as it heats up. I would like to see a chart to compare the rate of change to factory specs, but I don't have that info, and I believe it to not be the problem. The modulator is actually a backpressure sensor and it works as it's supposed to. A quick drive with a vacuum guage from the EGR feed stuck under my w/s wiper showed NO vacuum to the EGR at driving conditions that should trigger EGR action. I did not have a Toyota scan tool on the vehicle to confirm ECM signal to the VSV, but if I had such a fancy peice of equipment, I'm sure I'd have had this sucker repaired long ago.
I am feeling fairly certain it is the VSV. If it is not and it is in the programing I'd bet there is a flash reprogram to fix it.
Meanwhile, the tech that was working on it with me said that if it doesn't ping, chances are I'm getting better performance out of it with it in-op.
I just have to clear the codes less than two drive cycles before emissions testing.
Todd,
Unfortunately that ECM is not flash programable. Toyota didn't introduce that until about the 2000 MY, IIRC.
Dan.
Unfortunately that ECM is not flash programable. Toyota didn't introduce that until about the 2000 MY, IIRC.
Dan.
That's too bad. There sure are a lot of fixes for Ford and GM that include flashing the EEPROM.
I'm going to hook the scan tool up to it today and drive it for the weekend to see if I'm getting any knock sensor activated timing retard. I don't think I am and I'm running 10 degrees base timing with mid grade fuel. If not, fixing the P0401 will be just to see if I can do it.
I'm going to hook the scan tool up to it today and drive it for the weekend to see if I'm getting any knock sensor activated timing retard. I don't think I am and I'm running 10 degrees base timing with mid grade fuel. If not, fixing the P0401 will be just to see if I can do it.
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- #28
Gumby.As for getting better performance when EGR not working. From what I understand is that the timing will be retarded if motor is pining. So not hearing the ping could mean that it runs fine without the EGR or the timing is retarding. I don't know if you can check timing at the rpm that is needed to open the EGR?? If so then you could check it.
My CE light comes and goes. After pulling and checking the VSV without removing the intake chamber, it stayed on. I looked under there and 2 hoses were off. It is not fun trying to hook up vacuum hoses with one hand in that tight area.. I finaly got them and the light is off. I am sure they will fall off again when I replace the VSV :'( I thought there was something wrong with the preformance, think it was the EGR I didn't check. One of the hoses went to the throttle body and causing a vacuum leak.
kurt
My CE light comes and goes. After pulling and checking the VSV without removing the intake chamber, it stayed on. I looked under there and 2 hoses were off. It is not fun trying to hook up vacuum hoses with one hand in that tight area.
. I finaly got them and the light is off. I am sure they will fall off again when I replace the VSV :'( I thought there was something wrong with the preformance, think it was the EGR I didn't check. One of the hoses went to the throttle body and causing a vacuum leak.kurt
You can't check the timing advance and retard due to knock sensor input with a timing light because the ECM looks at a number of criteria before opening the EGR VSV including coolant temp, TPS, MAF, run time, gear selection and road speed. I can check timing advance and knock sensor input with my scan tool through the data stream while driving and that's what I intend to do. Unfortunately, when I was at work today i could not find the little chip that allows my scan tool to read the Toyota OBDII signal. Somebody borrowed it and returned the tool without all the parts.
That guy has since been canned so i don't think I'm getting my chip back.
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- #30
I took apart the VSV. It is just a electromagnet. There is a diaphrgm, a tiny spring and a tiny metal downut thing that vacuum goes through.It is pulled back when electromagneti is triggered, stopping the vacuum. Very simple but $$$$.
It is a real pain in the 'birfield' to get the new VSV back in but it is possable. If me kan do, u kan too 8)
kurt
It is a real pain in the 'birfield' to get the new VSV back in but it is possable. If me kan do, u kan too 8)
kurt
- Thread starter
- #31
I GIVE. The wife call and said the CE light is turning on and off now. I thought the new VSV would solve the #@%& problem
kurt
kurt
- Thread starter
- #32
After cleaning the intake chamber and replacing the VSV, the check engine light now is on about 1/4 of the time. I will reset the light and it will stay off for miles and then out of the blue it will come on for a while then go off.
I plan on hooking up a vacuum guage to the EGR and put the guage in the cab to see if the vsv is letting vacuum get to the EGR while driving.
What else can I check? Could the new VSV be bad?
kurt
I plan on hooking up a vacuum guage to the EGR and put the guage in the cab to see if the vsv is letting vacuum get to the EGR while driving.
What else can I check? Could the new VSV be bad?
kurt
I'd check the temp sensor and the wiring to it. The item used is called a thermister. Regardless of the application they are all the same basic design and I've seen plenty that will change in the sensing range producing a small shift in resistance. This would acount for the on/off of the light as it might be borderline ok. The VSV might be the most likely suspect but I doubt it is some kind of magic bullet that will fix all EGR error codes.
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- #34
How do I check the temp sensor?
kurt
kurt
- Thread starter
- #35
Not so good pic of vsv.
The red thing diaphragm has a tiny spring that opens the VSV so vacuum will flow. When the VSV is powered, the electromagnet pulls the red diaphragm to close the VSV stopping the vacuum.
kurt
[attachment deleted by admin]
The red thing diaphragm has a tiny spring that opens the VSV so vacuum will flow. When the VSV is powered, the electromagnet pulls the red diaphragm to close the VSV stopping the vacuum.
kurt
[attachment deleted by admin]
We checked my temp sensor the last time I was messing with mine. Hook a ohm meter to the sensor across the terminals. Run the engine to about 2000 RPM and open the egr with a vacuum pump. The ohm meter will drop resistance in a fairly linear fashion. Glitches would indicate a bad thermistor.
I hooked a vac guage to the EGR line and ran it to under the w/s wiper and drove it around. No change. My VSV can't be working right. The next step for me would be to back probe the ECM to see if the ECM is sending voltage to the VSV, or hook up a voltmeter to the VSV plug to see the same thing. The problem is the ECM will not activate the VSV unless it sees the vehicle moving.
I wonder if I could devise a relay that would be active when the ECM asks for EGR and would switch from a "cold" resistance curcuit to a "hot" one so the ECM sees what it wants to.
I hooked a vac guage to the EGR line and ran it to under the w/s wiper and drove it around. No change. My VSV can't be working right. The next step for me would be to back probe the ECM to see if the ECM is sending voltage to the VSV, or hook up a voltmeter to the VSV plug to see the same thing. The problem is the ECM will not activate the VSV unless it sees the vehicle moving.
I wonder if I could devise a relay that would be active when the ECM asks for EGR and would switch from a "cold" resistance curcuit to a "hot" one so the ECM sees what it wants to.
The important thing to check with the temp sensor is it's resistance when hot. The wrong resistance and you'll get a wrong temp indication to the ECM. The "ONLY" way to check it is to remove it from the vehicle heat it to the correct temperature and then check the resistance. This info is in your FSM. Once you've confirmed that the sensor is correct then you can check the operation of the system by spot checking it's resistance while driving. If the proper amount of gas is recirculating than the resistance should be within that same range.
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- #38
This info is in your FSM
Not in my 94 FSM, at least not in the EGR section. It shows the temp sensor but not how to test.
The check light will come on and stay on when driving and will stay on after I turn off the motor. I will start it, light will be on, then after a while it will trun off.
kurt
Not in my 94 FSM, at least not in the EGR section. It shows the temp sensor but not how to test.
The check light will come on and stay on when driving and will stay on after I turn off the motor. I will start it, light will be on, then after a while it will trun off.
kurt
I have a 96 so there might be differences but I'd expect the same detail in yours. Placing the sensor in an oil bath, and heat monitoring the temp:
at 122 deg F res = 64~97kOhms
at 212 deg F res = 11~16kOhms
at 302 deg F res = 2~4kOhms
The manual jumps around a little but start at the engine troubleshooting section at the error code. It will take you through the steps in identifying your specific problem. I haven't seen the actual part but from the picture and experience with these sort of sensors if there is a build up on the tip of the sensor this will act as an insulator and make it slow to react to temp changes, so look for something like that also.
I use a good old Coleman camp stove and old pot for these types of tests. You'll also need a mercury thermometer to monitor the oil's temp.
at 122 deg F res = 64~97kOhms
at 212 deg F res = 11~16kOhms
at 302 deg F res = 2~4kOhms
The manual jumps around a little but start at the engine troubleshooting section at the error code. It will take you through the steps in identifying your specific problem. I haven't seen the actual part but from the picture and experience with these sort of sensors if there is a build up on the tip of the sensor this will act as an insulator and make it slow to react to temp changes, so look for something like that also.
I use a good old Coleman camp stove and old pot for these types of tests. You'll also need a mercury thermometer to monitor the oil's temp.
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- #40
I cleaned the temp sensor, it was black with carbon. The EGR vacuum modulator was full of sand sized carbon that could plug the tiny ports. Can the modulator be cleaned with carb cleaner?
kurt
kurt
