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EGR valve testing

10K views 43 replies 9 participants last post by  *sean* 
#1 · (Edited)
I'm testing my EGR valve to eliminate it as a possible cause of my MPG issues.

First questions:
(1) What is "herky-jerky"? I experience a very mild jerkiness in lean mode. Hard to differentiate it from normal road vibrations; however I can tell because it is a front-back movement instead up-down. I only notice it because I drive the car regularly; others would not.
(2) Have some people with "herky-jerky" cured it with an EGR valve replacement?
 
#2 · (Edited)
I'm testing my EGR valve to eliminate it as a possible cause of my MPG issues.

First questions:
(1) What is "herky-jerky"? I experience a very mild jerkiness in lean mode.

Basically it feels like the engine looses power for an instant and then runs normally for an instant. Hence the nickname "herky-jerky".

The engine needs to be thoroughly warmed up to have a smooth lean burn. My car won't go into lean burn until I see at least 154° F coolant temperature with my OBDIIc&c with the ambient air temperature above ~68°. At that point I may feel the slightest amount of "hesitation". A few more degrees of coolant temperature rise and the engine smooths out.


(2) Have some people with "herky-jerky" cured it with an EGR valve replacement?

I found a new looking 1997 Acura 3.0 CL V-6 Siemens EGR valve at my favorite junk yard for $5. It cured my herky-jerky.


I measured the sensor voltage while driving with my OBDIIc&c. While in lean burn the sensor measured a constant 0.9 volts.

Unfortunately I don't remember what the max sensor voltage was when I was checking the valve[edit] OUT of[/edit] lean burn. I seem to remember something like 3 volts. But that wouldn't be the applied voltage to the solenoid.

Do your tests show that the valve is open at all with a 0.9v sensor reading? I haven't tested my original EGR valve to determine that.

I bought used 2001 Accord valve (ebay, $18 ) to experiment with. Same connector, same mating surface, but wider top and it did not fit without some "encouragement" (I have not tried to fully install it yet).

I found a way to bench test the Accord EGR valve by holding it open with 6 V, then pushing it closed with my finger while monitoring the potentiometer leads (from the connected, EGR not opened). (It takes 0.6 volts at 6 V and 1.8 amps at 13.8 volts but I have a feeling it is not designed for constant operation at the higher voltage, so I would not advise extended operation at a high voltage.)

I would guess that the voltage to the solenoid is a pulse width modulated X volt signal. Your 6 volt DC applied voltage would amount to 50% PWM drive if the peak voltage is 12 volts DC.

Also since the EGR plate has a restriction plug in the passage to each cylinder, the EGR valve probably has very little movement to reach the maximum flow rate that the restrictions would allow.

Please explain what "It takes 0.6 volts at 6 V ..." means. Is 0.6v the sensor output voltage at 6 volts or perhaps you mean the solenoid current is 0.6A at 6 volts?

I found that the valve's resistance changed linearly through most of the travel, but when partially open, it deviated from this straight line, indicating that the wipers may have cut through the material in this area, where the valve most likely operates most.

This means that the Accord EGR, a junkyard special, is No Good. It gives erroneous position readings in the range it would be used most. The ECU would then command it to reposition. Could this cause "herky-jerky"? Thus the questions above.

Sure sounds like it could. But that assumes that the bad area is used mostly in lean burn. That raises the question of which wears out the sensor's resistance the most, moving to the 0.9 volt lean burn spot or the normal variation of the sensor voltage when not in lean burn.

You could answer that question by varying the solenoid voltage to give a ~0.9 volt sensor reading and see if that is in the bad area of output voltage.

The next step is to run this test on the Insight valve in the car. I have a feeling it will behave similarly just from having read about potentiometer wiper problems being common. I am working out a way to test it without removing it from the car.
Use a OBDIIc&c. One of the things it measures is the "EGR feedback" which must be the sensor output voltage.

Since you have a known defective Accord EGR valve you can correlate my 0.9 volt steady reading in lean burn with where the bad area of the sensor output is at and what solenoid drive voltage gives that reading.

I wouldn't expect that Honda would have the wiper on the sensor completely at the "zero" end of it's voltage output range when the valve is depowered. In that case the 0.9 volt reading I saw might be a very low or no PWM being applied to the valve.

Hopefully Peter or someone with the complete Insight electronics test bed can fill us in on this.
 
#4 ·
Do you have any EGR harnesses? I am getting ready to build an EGR valve tester.
 
#8 · (Edited)
You don't need to go on my behalf, but if my tester works, lets just meet up locally.
 
#9 ·
Sean,

I assume that the EGR solenoid winding has a 0-12V range. Think that might be correct? The solenoid signal comes from the the ECM, so it "could" have most any range.
 
#11 · (Edited)
Fully open is well below 12 volts, and supplying 12V on the bench could damage the solenoid.
 
#14 · (Edited)
An Arduino configured to drive a used EGR valve on the bench and measure the resulting position provided data that resulted in the plot below. The discontinuity is a clear sign that the position sensor has an intermittent section where it travels most and needs to be replaced.

Blue Text Plot Line Font
 
#18 ·
Well this is promising...
I let this one run a little longer... the bad section of the pot really stands out. This valve is straight from some junkyard and I've made no attempt to clean the carbon from it. So it will be interesting to see how it behaves after a good soaking.

View attachment 77205
Interesting, nice contribution to the forum, keep up the research.

Assuming the horrible variations are at the slightly valve open end of the track, that fits in well with worn potentiometer symptoms in the critical lean burn stability area..

The ECM gets confused by the non linear wildly varying feedback at the worn part of the track in the EGR, and then commands the EGR with wild movements trying to compensate.

Result can vary depending on how bad the carbon track is, between mild lean burn stability issues to horrible herky jerky and kangarooing...

Fix = replace EGR or repair and fix/flip feedback potentiometer in valve top.
 
#15 · (Edited)
This is the EGR valve in my Insight. Didn't have to take the valve out of the car to test it.

This valve was not throwing codes or giving me herky-jerky, and the EGR plate was relatively clean. But replacing this led to a noticeable MPG improvement.



This valve is clearly faulty and needs to be replaced.

The shifting track explains why the position sensor is needed: the supply voltage cannot be used alone as a reliable indicator of valve position.
 

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#16 ·
Test harness:

 

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#17 ·
Very interesting development. I assume the X axis to proportional to solenoid voltage and the Y axis is proportional to measured resistance across the variable resistor??? I might furnish a loaner of a new EGR valve, depending on how much I have to pay;)

Re a meet, if your friend could square the library room, then I assume the library would condone some diy equipment brought in?
 
#19 · (Edited)
Confirming that sensor wipers were indeed at fault. This sensor still needs to be replaced.

 

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#21 · (Edited)
<not relevant to the technical discussion>
 
#22 ·
Amazing! This is obviously a breakthrough. Now EGRs can be tested in a definitive way - no more guesswork.

It will be interesting to see how long the reversal of the wiper fingers will hold out. Probably dependent on the starting damage level. Jeff652 did this at one time and furnished the refurbished EGRs. Never quite sure why he quit, but probably the availability of the cheap Accord EGRs
 
#23 ·
Those are wonderful before-and-after graphs. It's cool to see such a definite change!

Y'know... I once owned a used MT '96 Accord EX. I drove it extra-gently and enjoyed the very good (+43 mpg). One day, on the way home, the CEL popped on.

The Honda mechanic told me that "the EGR valve needs cleaned."

I had never heard of such a thing, but he said it would make the problem go away. They did so and charged me the going rate, which was steep.

When I picked the car up I asked what had caused the problem and if there was anything I could do to avoid it.

He hemmed and hawed a little and then said "the only cars with this problem are ones owned by little old ladies. It's a Honda. It likes to be driven. At least once a week, when it's warmed up, run up the RPMs and take it through the gears. Blow things out." Then, he gave me a little smile and said "To be honest, you're the first guy that's ever come in with it."

So, I've done that with every car I've ever owned and never had any trouble (like that), again.

Question: What do you think of the advice he gave me?
 
#25 ·
It's a Honda. It likes to be driven. At least once a week, when it's warmed up, run up the RPMs and take it through the gears. Blow things out."

There is a ~2 mile stretch of road near my house that many years there was nothing but cow pastures around it with several side streets along one side of the road. I had an XKE Jaguar that I'd blow the snot out of it by running it up to 120 mph in 3rd gear and then put it in neutral & turn the key off and coast to the street I had to turn off to eventually get to my house.

Well one time there was a State Trouper that I didn't see siting off the road on one of the side streets so he took off after me. When I slowed down he finally caught up to me and turned his siren on.

He kept asking me how fast I was going and of course I didn't want to tell him. He finally said, "I'm just going to give you a warning but I'd really like to know how fast you were going."

So I told him I was going about 120 mph when I turned the motor off and coasted to my turn off street.

He said, "WHAT?! I was wide open and you were still leaving me!"

So for years I've told the story how I outran a State Trouper and my motor wasn't even running (and I didn't get a ticket either). :D


So, I've done that with every car I've ever owned and never had any trouble (like that), again.

Question: What do you think of the advice he gave me?
Keep an eye out for State Troupers. ;)
 
#24 · (Edited)
<not relevant to the technical discussion>
 
#26 · (Edited)
I've done some bench tests on my original [bad] Honda EGR valve to see what the EGR sensor voltage (Vegrp) is vs increasing the Vdc applied to the solenoid (Vegr). The graph below shows the results.

I also used my OBDIIc&c to test the 1977 Accord EGR valve on my car now for Vegrp under various driving conditions.

Test conditions:
---------------------=-
Ambient temp = 80° F
Coolant temp = 170° F
No breeze or drafting
Tire pressures: 55 psi front, 50 psi rear
Max speed = 45 mph in light urban traffic, long stretches of open road
Segment mpg = 87.4 (includes lower warm up mpg)

Results of tests:
Condition ..... Vegrp
-----------------------
Idle .............. 1.00
45 mph ......... 1.00 in lean burn
Short purge ... 1.14 at 40 mph
Acceleration .. 2.40 max at medium throttle change

If car supplies PWM signal to solenoid with 13.8 volt max supply voltage, the PWM would be ~54% at 2.4 Vegrp. (13.8 volts is the typical specified automotive battery test voltage.)

From the above test and a shorter test I did years ago there should be no EGR valve action happening during lean burn. Of course if the Vegrp varies due to a bad sensor resistance trace then who knows what the ECM is doing about that. It would seem that it would just command the Vegr to go back to 1.00 volt.

We need someone with an OBDIIc&c AND herky-jerky to do the EGR test while it is happening to see if the OBDIIc&c responds fast enough to see any change in Vegrp.

Sean: What is the max Vegrp voltage your graph represents? From my DC tests we can see what the Vegr voltage is when Vegrp first changes to Vegr drive. Also what is your max Vegr voltage? That would give us two reference points to correlate the rest of the chart.

What model Arduino are you using?
 

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#28 ·
The challenge is reading the potentiometer while the valve is being opened/closed. When I was making static measurements the data seemed to fit. It was only when I had power applied to the valve and I was pushing it in and out did I see the meter jump - and I was using an analog meter since this would be really hard to see with a digital ohmmeter. So to see the discontinuities you had to do it while dragging the wiper along the valve.

Second, you need a fair number of samples because the damaged area can be small enough to miss if taking individual samples, since the ECU is generally going to run the valve in the same spot once the valve warms up. When I first built the tester I thought that such damage might take multiple wipes to discover. However, it seems you can see it in one open/close cycle.

As for making this a test you can do in-car: I am thinking that the ECU should have a command where you can write a value that sets the EGR drive voltage to that value, and another command for reading the EGR position value. Then, you could sweep the valve open and closed through the OBD-II port and do my test without touching the engine.

Well, according to Peter, we do know it has the latter measurement. The former probably exists in dealer-grade diagnostic software. Or, could be found if there is a "write value" command where the addresses map to hardware outputs. You just write to many locations until you find the one that moves the EGR. One would need to try this on an ECU set up on a bench so if you apply voltage to the injectors, VTEC, etc while trying to find the EGR valve solenoid, it won't hurt anything.

I wonder who has a setup like this? :)
 
#30 ·
The challenge is reading the potentiometer while the valve is being opened/closed. When I was making static measurements the data seemed to fit. It was only when I had power applied to the valve and I was pushing it in and out did I see the meter jump - and I was using an analog meter since this would be really hard to see with a digital ohmmeter. So to see the discontinuities you had to do it while dragging the wiper along the valve.
The confusing thing about comparing my tests and the data on both our charts is that the discontinuities of the upside down sliding contact in your charts are not in the normal lean burn Vegrp location which ought to be in the flat area of the left side our charts. Of course at that time the valve is closed and can't be pushed if there are bad areas to be seen.

What is the Vegrp & Vegr voltages on the left side flat area of your chart? From my bench test Vegrp ought to be in the 1 volt range.

Perhaps you could slow down and restrict the Vegr range in your test setup to see if there is a Vegrp discontinuity around 1 volt by using my Vdc data to see what voltage range you need to examine.

Also, from what I can determine by watching the OBDIIc&c Vegrp readout is when my car goes from normal cruising into lean burn I didn't see any change in the ~1 Vegr value. In that case there should be no movement of the valve anyway.

A sure fire way to stop the valve from moving in lean burn would be to hack the OBDIIc&c to tap the lean burn voltage to the green LED to remove the PWM signal to the EGR valve. That would guarantee that the valve is closed.

It would just take a transistor circuit to control a relay to turn OFF Vegr when the lean burn LED is lit (basically open the pink wire at the valve itself).
 
#29 · (Edited)
There isn't a write value command for the Insight ECM accessible via the OBDII port AFAIK. :(
Not even in the Honda software.

Also variations in ECM's would mean it is not likely in the same place in all the variants, US/UK or years.. So all would have to be tested.

The easy way to test the egr is unplug it, does herky jerky go away? Y/N.
If Y clean and replace or repair feedback resistor/egr. .
If N it's not the EGR.
 
#32 ·
Update on cleaning

An update on my repaired EGR valve. I noticed some herky-jerky in lean burn. This could be many things but since the EGR valve is now easy to test, I retested it.

Compare to post #19, made after the initial repair. Note that there are small jumps as the valve opens and closes, particularly near the bottom of travel, where the EGR spends most of its time. Also note the steep jump where the valve "pops open".

Before anyone concludes that repairing an EGR is not effective long term (and it probably is not), two theories:
1) Residual graphite, which I used to lubricate the valve when it was open, has gotten onto the potentiometer.
2) The fix really is not that great and the potentiometer is failing again.

The next step is to open the valve, and blow it out then clean it thoroughly, and then reassemble it.

Before that, perhaps I should see if herky-jerky coincides with EGR movement, using an accelerometer, a really smooth road (where???, but fortunately the acceleration is back and forth so road vibrations could be filtered out) and measuring the pulse width going into the EGR, the voltage from the potentiometer, and perhaps at the same time, the AF sensor, injector PWM and timing, to see if those are factors.

A test that does not require the alternator would be to see if the EGR valve is sensitive to vibration. From the data, it appears that it takes a measurable reduction in voltage before the valve starts closing, which suggests internal binding. If the engine is on, its vibrations might cause it to close or open more erratically. So perhaps that needs to be a new test: set the valve to a certain position, let it stay there with the engine on, see if it moves. Repeat and plot.

Here is the valve after about a month and 1600 miles:
 

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#33 ·
Sean: I see something that can't be when I was curious what voltage the valve is closed on your post #32 chart since it seems the valve is still moving when it flat lines.

In post #31 you said, "In the horizontal axis I am using 12 bit PWM to control the voltage to the solenoid, from a voltage source set to 10 volts. In other words, 4095 = 10 V, 3072 = 7.5V "

That means that 1 digit horizontally is; 10/4095 = 0.00244 volt.

Using that conversion number on the chart in post #32 indicates that the valve is closed (flat line) at the left side of your chart from 3600 (8.784 volts) to 3700 (9.028 volts). Obviously that can't be right. I'm sure it's just some conversion error and the graphing is correct.

Nevertheless ..........

An update on my repaired EGR valve. I noticed some herky-jerky in lean burn. This could be many things but since the EGR valve is now easy to test, I retested it.

Compare to post #19, made after the initial repair. Note that there are small jumps as the valve opens and closes, particularly near the bottom of travel, where the EGR spends most of its time. Also note the steep jump where the valve "pops open".

Before anyone concludes that repairing an EGR is not effective long term (and it probably is not), two theories:
1) Residual graphite, which I used to lubricate the valve when it was open, has gotten onto the potentiometer.
2) The fix really is not that great and the potentiometer is failing again.

Could it be that the wiper doesn't have enough contact pressure now?

Assuming the valve isn't leaking, as long as the sensor voltage has settled near 1 volt when the valve stays closed for a few seconds the output voltage shouldn't cause herky-jerky since in use the valve closes and the sensor voltage should be settled long before the car attempts to enter lean burn.

Of course the sensor voltage jumping around while the valve is moving (as your graphs clearly show) when not closed is a good indication of a damaged pot.

It seems that in driving the car the voltage deviations from a linear curve wouldn't affect lean burn since the valve only opens when not in lean burn. Your graph indicates that the slight resistance changes with the valve closed might get the ECU's attention and it does something other than move the valve (perhaps it changes the AFR). When my car had herky-jerky it felt like the engine lost power for an instant.

On my car the sensor voltage usually sits at 1.01 as per the OBDIIc&c. Sometimes it is 0.99 until the next opening/closing event. But it doesn't vary from whichever number it settles on until after the next "open" command. I've never seen it change once it settles. And if you are driving at a steady speed the valve is closed for quite awhile before lean burn is initiated.


The next step is to open the valve, and blow it out then clean it thoroughly, and then reassemble it.

The service manual says to use carburetor cleaner on the valve itself.

I looked very closely at the valve and valve seat with a magnifying glass but couldn't really tell if it had been leaking or not. The valve contact width is very small. Maybe 0.025" ?


Before that, perhaps I should see if herky-jerky coincides with EGR movement, using an accelerometer, a really smooth road (where???, but fortunately the acceleration is back and forth so road vibrations could be filtered out) and measuring the pulse width going into the EGR, the voltage from the potentiometer, and perhaps at the same time, the AF sensor, injector PWM and timing, to see if those are factors.

Just as a check, you might want to check the total resistance of the sensor pot. My defective valve and the newer Accord valve are both ~4.43k ohms.

I would first eliminate the EGR valve affecting herky-jerky by temporarily placing a piece of thin metal shim stock under the EGR gasket then install the valve to absolutely make sure no exhaust is getting into the intake system through the valve and then check for herky-jerky. Leave the EGR connected so the ECU doesn't have a fit.

If the car settles down in lean burn you have better proof that it is only the valve causing the problem and not other things. And it might be proof that the valve is leaky when closed.

The next thing may be to check the crankcase ventilation valve that it isn't stuck open or closed.


A test that does not require the alternator would be to see if the EGR valve is sensitive to vibration. From the data, it appears that it takes a measurable reduction in voltage before the valve starts closing, which suggests internal binding. If the engine is on, its vibrations might cause it to close or open more erratically. So perhaps that needs to be a new test: set the valve to a certain position, let it stay there with the engine on, see if it moves. Repeat and plot.

Hit valve with a small hammer while it's on the bench??? As an old timer machinist once told me, "Don't force it, ....... use a bigger hammer."

When I bench tested my defective valve I tapped on it with a short metal rod before reading the voltage after each change in drive voltage.

If the 1st or 2nd tap did cause a change, the voltage change was very small. After the first few taps the output voltage didn't change with more taps.

I also pulsed my bad valve ON/OFF at ~1.5 times per second and it was really clapping shut from a little opening each time. The sensor voltage as shown on a Tektronix scope just settled to the closed value with no problem. Yet that valve had bad herky-jerky.


Here is the valve after about a month and 1600 miles:
The strange thing is that your tests seem to show the sensor is changing voltage when the valve should be mechanically closed before starting to open again. That is definitely not right. Or the wiper needs more pressure to insure it's making good contact.

How long does the sensor voltage keep changing if you just pulse the valve open/shut one time and continue to read the sensor?
 
#34 · (Edited)
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#35 · (Edited)
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#36 ·
My egr valve played up terribly on my recent trip to France so I just unplugged it for the duration.
You don't get a code for several drive cycles and even when it coded lean burn still worked.

Today I took it off and disassembled it.
It had the classic pot wiper on wrong way round fault..
Scraping back and forth along the carbon pot tracks :(
I've flicked it over cleaned the tracks with alcohol and reassembled.

Seems to be working fine again.

I also have a failed accord egr and one of the cheap chinese $30 ones to take apart for research purposes.
 
#38 ·
@*sean* (or others), is there a consensus from this testing whether EGR valves start to go bad, BEFORE the "herky jerky" starts? If so, are there any symptoms, other than herky jerky, that a driver should be watching for?

(I suppose I'm just curious if there would be any reason to replace an EGR valve if a driver isn't experiencing herky jerky and wasn't having problems getting into lean burn?)

Thanks,
Bryan
 
#41 ·
Hi Bryan,

Yes, the valves can definitely degrade and eat away at your mileage before herky-jerky starts and before they throw a code. I have recorded evidence of a badly performing stock valve that when measured at around 150K miles with my EGR valve tester was found to have an improperly performing sensor. No codes or herky-jerky. Replacing it was responsible for a few MPG improvement. I've tested a purportedly younger valve that had similar degradation. Hope this helps!
 
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