EGR valve operation (1 Viewer)

[gthaines]

I have a question regarding the EGR valve operation on a carb'd 1986 fj60:
First off, I have failed CA emissions for NOx, at the 15 mph only, with super low co and hc. The 25mph test passes great (350 nox) 15 mph fails badly (1450 nox). I got the FSM, and Emissions manual, replaced all vacuum lines, at least all the smaller sized ones, ran the tests and the only thing I have found is this: when I hook up the T to read the vacuum from the modulator to the valve, I get a reading of 2.5+/- no matter what the rpm or throttle valve is doing or if I hook it directly to intake vacuum per test (supposed to show a high vacuum, but doesn't) . Modulator valve passes the test and kills engine when vacuum is applied, so its at least working. Modulator tests to be functioning properly and is 4 months new. If i read vacuum straight off the modulator (not connected to the valve) then I get various strengths of strong vacuum.

So it appears that the valve itself is killing some vacuum, is this how it is supposed to be? Is this a symptom of something else? Manuals do not really say what to do if high vacuum is not showing on this test with intake connected. I'm stumped, any help would be great.

Also anyone with any suggestions for why it would pass at 25 mph and not 15mph?

 

[Output Shaft]

What were the engine RPMs at those speeds? Try testing in 2WD low range.

 

[gthaines]

What were the engine RPMs at those speeds? Try testing in 2WD low range.

View attachment 1275163

2wd low, is a possible good idea thx.

I thought about this line in the book, but the clincher is the line about the throttle valve positioned above the R port. The vacuum in mine from the R port does not come on until 1800-2000 rpm suggesting that the valve is not making it past the port until then (right?). That is also measured straight from the carb, and with the port cleaned out. Could it be a throttle valve problem, or perhaps choke or linkage? Not super competent with this as it has been a while, but I usually can catch up pretty quick.

It passed with 350 nox values for both 5 months ago with 1539 rpm @ 15 mph, and 2428 rpm @ 25 mph. Failing now with 1430 @ 1586 rpm (15mph) and passing with 143 (seems way low and probably choking on it) @ 1562 rpm (25 mph). All of this with the same setup plus a new VSV that I determined was bad.

 

[Output Shaft]

If you're measuring vacuum directly off the R port on the carb and you're not seeing vacuum till around 1800 rpm, what you're really seeing is vacuum once the throttle angle passes the R port. It just happens to occur at 1800 rpm at idle because it takes that much throttle angle. Vacuum from the R port on the carb is RPM independent. It's governed by throttle angle.

What you need to see is if you're getting vacuum above 1800 RPM (or so) off the R vacuum hose going into the modulator.

I wouldn't place to too much trust in the absolute accuracy of the 2F tach.

 

[Output Shaft]

Test to make sure the EGR valve diaphragm is not leaking. If you apply vacuum to the valve with a vacuum pump (or your mouth) it should hold vacuum indefinitely. No leaks.

 

[gthaines]

Test to make sure the EGR valve diaphragm is not leaking. If you apply vacuum to the valve with a vacuum pump (or your mouth) it should hold vacuum indefinitely. No leaks.

I will try valve diaphagm test, thanks. Might just be the culprit.

I have been using a digital tach and vacuum guage.

As for the vacuum from the Ports, I get it all the way from the carb thru all the lines and then out the Q of the modulator, so enough vacuum is getting to the valve. Its just odd that once its there and I use a T to test it (instead of a direct measurements of 5-15 from Q) it goes down to 2.5 and stays there no matter what. I have also verified that the vacuum is maintained thru each piece of pipe/line/switch until it gets there.

 

[gthaines]

valve diaphragm appears to be good, no 2wd low that I know of.

one thought though is that if your at 15mph and 1500 rpm then you are probably in second gear with nearly no throttle. Not sure if this translates to the dyno though.

Seems to be driving very well once warmed up, but sputters and chokes a bit at lower rpms & speeds. I just reset the timing to stock, idle mixture and idle speed, and am thinking that the mixture might need a very minor adjustment.
What direction would most likely improve the sputter issue listed?
Also, if smog tech is reporting it running a bit lean anyone have any suggestions about how much one would try to adjust the mixture (or something else) to get it slightly richer? My thought was maybe 1/4 turn or so?

 

[Output Shaft]

If you've been tinkering with the idle mixture then it's most likely out of whack for a smog test. Only way to accurately dial it in for smog is with a wide band O2 sensor. That was the reason the idle mixture screw was capped at the factory.

 

[gthaines]

any other suggestions on how to get the vacuum engaged from the throttle valve to happen at a lower rpm?

 

[morganism]

this is usually a buildup of carbon deposits on the EGR plug.

Try using a length of vac hose, and your mouth, not vac pump to pull hard a few times and see if you can get the carbon chunks to drop down the pipe to the oil pan. Tap the EGR w screwdriver handle at same time..At idle it will kill the engine unless you have a friend on the pedal

 

[morganism]

by the way, where is your temp sensor sitting at regular driving? You need it up around a third of the way to get good combustion. Also adding a colder thermo will gut your gas mileage. I thought the desert was a good reason to have a cooler temp, but it really hurts operation, and seems to increase carbon buildup engine wide.

It also seems to be better to adjust your timing to change your lean/rich mixture , rather than messing with the idle mix. I typically am 2 deg over so i get better accel, and better altitude performance.

there is a thread in the last couple months on "i passed emissions in OR" here...

 

[gthaines]

thx.
I ended up replacing all vacuum tubing, dialing the timing back down to stock, fixing the hole in my exhaust pipe just before muffler, idling slightly rich (while carb is set slightly lean at speed), dialing the idle speed down to closer to 500rpm (seemed to help engage vacuum earlier, although still not totally clear why), taking the car and testing it cold for the first time and giving it a few screwdriver love taps to the egr just before testing. numbers dropped down from 1400 nox to around 145....Im sure I will be doing this again in 2 years. I also now have some time to pull the egr and clean it out if needed.

 

[gthaines]

Well, its been 2 years and I am once again chasing smog problems . It would appear my vacuum modulator is not working well and causing the egr to remain open for to long or too quickly. Based on the emissions manual proceedures everything checks as working, except the test at 2500 rpm to confirm the modulator shuts off from the exhaust pressure build up from J pipe & cooler (if I am understanding the concept correctly). Long story short, at mid rpm 1500 +/-, egr valve is opening, but then staying open and not alternating as it should be (based upon pressures. see chart above). I havent fixed it yet, but hopefully it will help someone or someone will correct me, hah.

 

[gthaines]

Just a note to anyone going through this smog bananza: when cleaning the egr, make sure to clean the small tube that sends air for backpressure to the modulator. This small tube gets the same nasty air as the egr, and is 1/4 the size and susceptible to buildup which messes up your modulator functions. I cleaned mine with a oven cleaner, and a small but firm wire and a bunch of nastyness came out of it. See multiple posts of people stripping the screw that holds this little tube/port on, so I just left it on while cleaning.

 

[NeverGiveUpYota]

Just a note to anyone going through this smog bananza: when cleaning the egr, make sure to clean the small tube that sends air for backpressure to the modulator. This small tube gets the same nasty air as the egr, and is 1/4 the size and susceptible to buildup which messes up your modulator functions. I cleaned mine with a oven cleaner, and a small but firm wire and a bunch of nastyness came out of it. See multiple posts of people stripping the screw that holds this little tube/port on, so I just left it on while cleaning.

Good of you to follow up. Thanks!

 

[4Cruisers]

@CenTXFJ60