FJ60 "Classic Stumbling Issue" - EGR Valve?

[RDub]

Finally got good enough weather to try the new vacuum modulator and the Ford VTV. Tried just the Ford part with the original modulator first, and that pretty much took care of the stumbling everywhere. Then I tried just swapping in the new 80-series modulator without the Ford valve and that was a dismal failure, no real improvement over original modulator. I settled on the new modulator together with the Ford part going forward. I’m fairly sure the EGR valve itself has an issue with whatever the design uses to resist vacuum in the valve actuator. I would think the diaphragm would be metal due to temperature, with maybe a spring on top of that, or maybe not. Until I get the energy to find and test a bunch of old EGR valves it’s staying like it is right now. Trying for emissions test pass tomorrow, will be the sixth attempt in two months of trying. Colorado, so similar to CA. Fingers crossed.

 

[OSS]

The EGR diaphragm is rubber. The return actuation to close the sucker is a metal spring.
As I mentioned previously, my conclusion is that the spring gets weak and the rubber diaphragm soft after years of driving - which makes the EGR valve open too soon, too far and close late.
I had to replace a new egr valve (back in 1989) that was only 3 years old. Back then they were still available new.
A few decades later I ran into ERG valve hell again and purchased a few used ones. They were all the same - none worked properly.

The only workaround nowadays is to get the distributor re-curved (for non-EGR use) to prevent pinging when EGR is disabled and run the engine like that between tests. Engine will pass fine with a recurved distributor (better actually) and the EGR system active - for the test.

 

[RDub]

The EGR diaphragm is rubber. The return actuation to close the sucker is a metal spring.
As I mentioned previously, my conclusion is that the spring gets weak and the rubber diaphragm soft after years of driving - which makes the EGR valve open too soon, too far and close late.
I had to replace a new egr valve (back in 1989) that was only 3 years old. Back then they were still available new.
A few decades later I ran into ERG valve hell again and purchased a few used ones. They were all the same - none worked properly.

The only workaround nowadays is to get the distributor re-curved (for non-EGR use) to prevent pinging when EGR is disabled and run the engine like that between tests. Engine will pass fine with a recurved distributor (better actually) and the EGR system active - for the test.

Ugh. That’s

The EGR diaphragm is rubber. The return actuation to close the sucker is a metal spring.
As I mentioned previously, my conclusion is that the spring gets weak and the rubber diaphragm soft after years of driving - which makes the EGR valve open too soon, too far and close late.
I had to replace a new egr valve (back in 1989) that was only 3 years old. Back then they were still available new.
A few decades later I ran into ERG valve hell again and purchased a few used ones. They were all the same - none worked properly.

The only workaround nowadays is to get the distributor re-curved (for non-EGR use) to prevent pinging when EGR is disabled and run the engine like that between tests. Engine will pass fine with a recurved distributor (better actually) and the EGR system active - for the test.

Ugh. Mine failed emissions again today. New Cat so HC and CO were fine, but NOx was about 15% above the limit. I had the EGR connected with the Ford VTV correctly oriented in the line to the valve. Still stumbles at cruise, so I assume the valve is shot. Can a valve that opens too much or often cause high NOx? Is it like leaning out the mixture when it does that? It’s undriveable if the Ford valve isn’t in the system, at least with EGR connected. Disconnected it’s fine. Could the computer be faulty? I did the emissions manual checks and all were “good”. I’m at a loss for what to do at this point.

 

[RDub]

Ugh. That’s

Ugh. Mine failed emissions again today. New Cat so HC and CO were fine, but NOx was about 15% above the limit. I had the EGR connected with the Ford VTV correctly oriented in the line to the valve. Still stumbles at cruise, so I assume the valve is shot. Can a valve that opens too much or often cause high NOx? Is it like leaning out the mixture when it does that? It’s undriveable if the Ford valve isn’t in the system, at least with EGR connected. Disconnected it’s fine. Could the computer be faulty? I did the emissions manual checks and all were “good”. I’m at a loss for what to do at this point.

I live at about 5500’ elevation so the HAC is always on high altitude mode, confirmed by emissions manual tests. I’ve read that retarding the timing can help reduce NOx. Does anyone know if disconnecting the HAC at the distributor will retard timing enough to make it worthwhile for a retest?

 

[OSS]

High NOx is classic malfunctioning EGR. The sole purpose of EGR is to reduce the combustion temperature so that NOx doesn't form.

EGR works by injecting some exhaust gas, which is pretty much devoid of oxygen, back into the intake charge so there's less oxygen in the air fuel mixture - so it burins cooler.
What "could" be happening (big guess here) is when the EGR was connected as normal which created the stumble, it jacked the combustion too much during the test which causes the engine to run too poorly, which jacks the exhaust too.

That Ford VTV or any VTV run inline with the EGR actuation vacuum hose will delay the opening or prevent the full opening of the EGR valve - hampering its function. While the engine may run better when driving, it'll also pollute more. Personally I wouldn't dare have that little valve inline on the EGR vacuum hose during a test. Technically, a vehicle shouldn't pass visual inspection with one installed - but I guess some techs let it pass.

Id connect a vacuum gauge to the intake manifold and verify there isn't a vacuum leak. A vacuum leak will definitely create lean burning which can create NOx. Also a vacuum leak will cause poor engine performance (stumble) and can burn exhaust valves.

Also advanced timing increases NOX. Id set your timing to 5 degrees BTDC instead of the standard 7 degrees. A 2 degree difference is acceptable for a test (in CA). It might be enough to squeak by.

Also - always change the motor oil before a smog test if its kinda old. Its full of combustion byproducts and its blowby ends up in the exhaust stream.

Definitely if you're up at altitude, plug the vacuum hose on the distributor that is utilized by the HAC. Put a bb in the hose. Its undetectable. Doing that will retard the timing 7 degrees right there. Big difference.

 

[ravenplague]

Ugh. That’s

Ugh. Mine failed emissions again today. New Cat so HC and CO were fine, but NOx was about 15% above the limit. I had the EGR connected with the Ford VTV correctly oriented in the line to the valve. Still stumbles at cruise, so I assume the valve is shot. Can a valve that opens too much or often cause high NOx? Is it like leaning out the mixture when it does that? It’s undriveable if the Ford valve isn’t in the system, at least with EGR connected. Disconnected it’s fine. Could the computer be faulty? I did the emissions manual checks and all were “good”. I’m at a loss for what to do at this point.

wierd...Im in California and have the same stumbling issues as you. The tech told me that I could not have a vtv/restrictor or anything on the tube from the EGR to the modulator. So I took it off and used a straight piece before I smogged it and it still passed. So maybe its something else that is not making it pass?

The ford vtv valve works great btw and so far have not heard any pinging. Ill push my fj a little harder and see if I can hear anything.

 

[RDub]

High NOx is classic malfunctioning EGR. The sole purpose of EGR is to reduce the combustion temperature so that NOx doesn't form.

EGR works by injecting some exhaust gas, which is pretty much devoid of oxygen, back into the intake charge so there's less oxygen in the air fuel mixture - so it burins cooler.
What "could" be happening (big guess here) is when the EGR was connected as normal which created the stumble, it jacked the combustion too much during the test which causes the engine to run too poorly, which jacks the exhaust too.

That Ford VTV or any VTV run inline with the EGR actuation vacuum hose will delay the opening or prevent the full opening of the EGR valve - hampering its function. While the engine may run better when driving, it'll also pollute more. Personally I wouldn't dare have that little valve inline on the EGR vacuum hose during a test. Technically, a vehicle shouldn't pass visual inspection with one installed - but I guess some techs let it pass.

Id connect a vacuum gauge to the intake manifold and verify there isn't a vacuum leak. A vacuum leak will definitely create lean burning which can create NOx. Also a vacuum leak will cause poor engine performance (stumble) and can burn exhaust valves.

Also advanced timing increases NOX. Id set your timing to 5 degrees BTDC instead of the standard 7 degrees. A 2 degree difference is acceptable for a test (in CA). It might be enough to squeak by.

Also - always change the motor oil before a smog test if its kinda old. Its full of combustion byproducts and its blowby ends up in the exhaust stream.

Definitely if you're up at altitude, plug the vacuum hose on the distributor that is utilized by the HAC. Put a bb in the hose. Its undetectable. Doing that will retard the timing 7 degrees right there. Big difference.

Thanks. Agree with all except the Ford part. That part is intended to dampen the action of the EGR valve since mine is “too active” in its current state. But it didn’t work for the test, for whatever reason. If I run the engine with EGR setup per the factory it literally can’t be driven. It bogs too hard and the stumbling during cruise, if I could even get to cruise, is horrendous. So the valve just opens way too soon and way too far, and it’s just too sensitive to run stock. When it was failing HC and CO several weeks ago I rebuilt the carb to fix what I think was a stuck power valve. The HC and CO came way down, and with the then no -stumbling EGR system connected NOx was well under the limit. The stumbling started suddenly a bit later, and goes away completely if EGR is inactive.

Options are limited. I may try setting the timing just under 7 degrees and disconnect and plug the HAC vacuum line that goes to the distributor. That will buy me 3-6 degrees of retard over the way it was setup during the test today. I tried testing it with the EGR disconnected the time before this try, but with the timing set around 4-5 degrees advanced and the HAC line plugged. It cut the NOx number almost in half from where it was when I tested it with the EGR disconnected a few weeks ago. But was still 25% over the limit. It passed emissions five years ago with the EGR disconnected, but I’m not sure how, other than a lot of e85 in the tank.

I will swap the computer with a good one a buddy has just to be sure. The cruise stumble seems odd to me, especially since it disappears with the EGR not functioning. It still stumbles a bit at cruise even with the Ford valve in the EGR valve vacuum line. Puzzling.

 

[RDub]

Thanks. Agree with all except the Ford part. That part is intended to dampen the action of the EGR valve since mine is “too active” in its current state. But it didn’t work for the test, for whatever reason. If I run the engine with EGR setup per the factory it literally can’t be driven. It bogs too hard and the stumbling during cruise, if I could even get to cruise, is horrendous. So the valve just opens way too soon and way too far, and it’s just too sensitive to run stock.

Options are limited. I may try setting the timing just under 7 degrees and disconnect and plug the HAC vacuum line that goes to the distributor. That will buy me 3-6 degrees of retard over the way it was setup during the test today. I tried testing it with the EGR disconnected the time before this try, but with the timing set around 4-5 degrees advanced and the HAC line plugged. It cut the NOx number almost in half from where it was when I tested it with the EGR disconnected a few weeks ago. But was still 25% over the limit. It passed emissions five years ago with the EGR disconnected, but I’m not sure how, other than a lot of e85 in the tank.

I will swap the computer with a good one a buddy has just to be sure. The cruise stumble seems odd to me, especially since it disappears with the EGR not functioning. It still stumbles a bit at cruise even with the Ford valve in the EGR valve vacuum line. Puzzling.

Forgot to mention that for some reason the emissions techs here no longer open the hood or check for a Cat. Colorado has adopted the CARB regs for replacement Cats and I did buy one. It seems to be working, the HC and CO numbers are spectacular now.

 

[DFXR]

For reference, the last time I tested (and passed), I could watch the dyno readout and see the Ford VTV work in real time. NOx would read high at initial acceleration, and after 4-5 seconds would drop sharply when the delay was over and the EGR started dumping exhaust gas. At this point the RPMs would be high enough to avoid any stumble, and the NOx would stay low through the 90 sec duration that the tech needed to hold acceleration. All of which tells me my EGR was working but like so many others, opening too soon.

Previous to this, I had the normal stumble like so many others but it definitely wasn't undriveable, especially at cruise. I would think that at cruise RPMs the engine should be able to handle anything the EGR sends it.

Your high NOx, with the EGR functioning, is confusing. Because as OSS pointed out, the exhaust gases burn cooler and thus reduce NOx. It's like one thing is happening at low RPMs (too much EGR too soon) and something else is happening at higher RPMs (?).

Also, I've never asked any tech about the legality of the VTV and none have ever mentioned it. I have always assumed it is not allowed but most techs either don't know or don't care (enough) to bust me.

 

[RDub]

For reference, the last time I tested (and passed), I could watch the dyno readout and see the Ford VTV work in real time. NOx would read high at initial acceleration, and after 4-5 seconds would drop sharply when the delay was over and the EGR started dumping exhaust gas. At this point the RPMs would be high enough to avoid any stumble, and the NOx would stay low through the 90 sec duration that the tech needed to hold acceleration. All of which tells me my EGR was working but like so many others, opening too soon.

Previous to this, I had the normal stumble like so many others but it definitely wasn't undriveable, especially at cruise. I would think that at cruise RPMs the engine should be able to handle anything the EGR sends it.

Your high NOx, with the EGR functioning, is confusing. Because as OSS pointed out, the exhaust gases burn cooler and thus reduce NOx. It's like one thing is happening at low RPMs (too much EGR too soon) and something else is happening at higher RPMs (?).

Also, I've never asked any tech about the legality of the VTV and none have ever mentioned it. I have always assumed it is not allowed but most techs either don't know or don't care (enough) to bust me.

My NOx fail might be due to the profile the emissions test follows. It’s a speed vs time curve, simulating driving on a road with various inclines and flats. There aren’t really any hold periods aside from when the slope of the curve relaxes a bit. I have the graphs of HC, CO and NOx superimposed on the speed profile. It’s easy to see when the tech stood on the gas to keep up with the profile when it would ramp up quickly, and the emissions numbers reflect that. NOx peaks and stays high during the entire time the gas is mashed. I will look and see if I can determine roughly how many seconds the peaks last, because if only 3 seconds or so that may explain why the Ford part caused the EGR to function as @OSS describes.

 

[DFXR]

Well, whatever the cause, I feel your pain and I'm sorry you're dealing with it.

 

[RDub]

Well, whatever the cause, I feel your pain and I'm sorry you're dealing with it.

Thanks! I think the EGR valve can definitely cause stumbling at cruise. The EGR VSV opens when the engine rpm is above about 1500 (mine opens at around 1300) regardless of whether there is high enough exhaust pressure to force the vacuum modulator to open the EGR valve. The emissions manual has a test where a vacuum gauge is teed into the EGR valve vacuum line, and the engine is revved to about 2500 rpm. With port R on the modulator connected to the VSV per factory configuration the vacuum gauge should read some vacuum but not much. Then in the second part of the test the port R line gets directly connected to intake manifold vacuum and at about 2500 rpm the gauge should read high vacuum and the engine should run rough. That tells me the VSV vacuum circuit is restrictive so the EGR valve only sees a low vacuum signal when the VSV is open above 1500 or so, opening the EGR valve a little but not a lot. On mine I suspect the valve opens all the way every time it sees even a little vacuum, hence the cruise stumble. A lot of words there, does my thinking make sense?

 

[OSS]

On a brand new factory 2F engine with all brand new emissions components working perfectly ( 40 years ago), the EGR valve is not supposed to open at full throttle. It remains closed. Reason being that when you need power - to pass, you need it.

This full throttle tigger is controlled by the vacuum. modulator which gets its signal from the little bypass pipe feeding Ito the bottom of it. If the little pipe is plugged , the system will be whacked.

If you are experiencing a stumble at WOT, that part of the system is suspect. At WOT, the EGR shouldn't be open.

 

[RDub]

On a brand new factory 2F engine with all brand new emissions components working perfectly ( 40 years ago), the EGR valve is not supposed to open at full throttle. It remains closed. Reason being that when you need power - to pass, you need it.

This full throttle tigger is controlled by the vacuum. modulator which gets its signal from the little bypass pipe feeding Ito the bottom of it. If the little pipe is plugged , the system will be whacked.

If you are experiencing a stumble at WOT, that part of the system is suspect. At WOT, the EGR shouldn't be open.

That makes sense at WOT.