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You shouldn't have to modify the EGR valve to get it to pass. What state do you live in? I thought for a car to fail emissions the inspector has to indicate why it failed and what needs to be done to pass.
You shouldn't have to modify the EGR valve to get it to pass. What state do you live in? I thought for a car to fail emissions the inspector has to indicate why it failed and what needs to be done to pass.
The inspector did tell him why it failed High NOX NOX levels have to be brought down to pass. Inspectors can not be expected to know how to do so. OP is asking for help here because , it is hard to find a mechanic that knows anything about 45 year old cars . Due to a stroke I have forgot more than I know . Due to a recent knew replacement I cant go to storage and find my manuals. They have excellent troublel shooting charts. I am sure one of the mechanics on here who still has their memory can help. Or somebody with the factory trouble shooting charts. Lots of good guys here
Are you sure your EGR ports are clear(not plugged)
I live in California. For this year car, it has to be tested on the "rollers"
OH yeah the engine is rebuilt and everything cleaned up beforehand, ran a wire brush thru EGR port to carb. Engine has 5,300 miles on it , so broken in.. Passed easily before the old EGR failed,, Why I had to get a new one..
So if at 15mph i get NOX readings 18 PPM and at 25 mph I get 1025 PPM Woah! clearly the EGR is not opening at 25mph,
Oh yeah when I can home I got about 20Hg at both rpms at the EGR vacuum hose.
Besides plugging some bleeder holes on the Back Pressure type EGR. I don't think there is a way of taking teh EGR apart and putting in a weaker spring.
Just wondering if anyone else has seen this issue and fixed it.. somehow???
Did you get the correct type of valve, aka same part number as the old one? Original style ACDelcos have an N or a P on them and that certainly could make a difference if you got the wrong type. The Delphis, although close, are not always exactly like the O.G. Delcos of old. Aftermarket valves many times will be ink marked on top with "POS" or "NEG", but not always. Delco ported EGR valves have nothing.
Here's an example of a positive pressure valve. I believe the 289 is the day, the 3 is the year (93??) and 1 is the shift. Which would be Saturday, 10/16/93 first shift. If 1983, it would be Sunday, 10/16 first shift, so that's doubtful but not out of the question. This is a stock ACDelco one for an 84-85 VIN 9 307. It can't be from 2003 because I bought it in the mid 90s. Anyway, at the end, there's the P, thus a positive pressure valve.
If it's a positive pressure EGR valve, simply trying to use a vacuum pump to operate the valve won't work. The way it's set up with dual diaphragms needs the positive back pressure in the exhaust to push up through the hollow pintle valve and stem to the lower diaphragm to raise it against a small inner spring to seal it off to the upper diaphragm. When vacuum is applied to the top of the upper diaphragm during operation, then the valve can come off its seat. The valve opens and shuts based on engine load. Obviously a positive pressure EGR valve can be affected by an aftermarket lower restriction exhaust.
I thought that in 1978, those EGR valves were simple and just operated on ported vacuum. I wonder if the "new" valve is one of those positive backpressure valves. If it is, I don't think it will ever work. Simple to check: just hook up a vacuum pump and see if it opens. Then reinstall, tee in a vacuum gauge and see if you have a gauge reading at part throttle.
I thought that in 1978, those EGR valves were simple and just operated on ported vacuum. I wonder if the "new" valve is one of those positive backpressure valves. If it is, I don't think it will ever work. Simple to check: just hook up a vacuum pump and see if it opens. Then reinstall, tee in a vacuum gauge and see if you have a gauge reading at part throttle.
According to the 1978 Oldsmobile Service Manual it is a backpressure type EGR. Why I dont get why it works at 15mph and not 25 mph, wouldn't there be MORE backpresure at 25mph??? this makes no sense to me...
Just because a part is new doesn't mean that it is good, so X2 on that suggestion of a faulty new part. Another alternative is go with the style valve that was used way back in 73 or 74 and doesn't rely on backpressure to operate.
Just because a part is new doesn't mean that it is good, so X2 on that suggestion of a faulty new part. Another alternative is go with the style valve that was used way back in 73 or 74 and doesn't rely on backpressure to operate.
Actually, it's better to have a backpressure EGR. It cycles with actual load based on exhaust backpressure (assuming positive on this one) which is more in line with load-based EGR action. But I agree, there is something fishy going on with this new valve. Is it a Delco? If it's another aftermarket brand, sometimes they require different "orifice" installation on the exhaust side to regulate the backpressure signal. That way they can use one valve for wider applications just by changing the bottom orifice under the seat. The instructions should tell you whether you need one or not.
If it's an NOS Delco unit, it should just be a bolt on and go.
Exactly what I was going to say. Especially with low demand parts for older cars. I have seen way too much of it lately
How exactly did your old valve fail ? I would try to find an NOS valve on E-bay.
when i went in for the test the first time, it fail NOC at 15 and 25mph. When reving the engine the diaphram would not more up, hence opening the valve. Took out cleaned the pintle, etc etc still the same.. Worked in prior test 2 years before. Guess old rubber gave out.
Found a NOS GM ACDelco 17056387 supposidely correct one.
Not understanding rpms are about the same at 15 and 25 mph why would it not open???
I really don't want to add more exhaust restriction, why I think plugging some of the bleeder holes off might increase the vacuum and open the valve. Funny it works at one rpm and not the other.. Would load from the rollers and a different gear(2nd) make a difference???
I guess I should just try plugging them and see what happens..
I was just wondering if anyone has see this type of problem and fixed it.
The problem I see of fugging around with an EGR valve by plugging this and plugging that could lead to the EGR opening when it isn't needed and really screwing things up. I could see it for testing, but figuring out exactly when your engine needs it on the backpressure side of things should be the engine's job.
March 29th, 2023, 09:56 AM
