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Discussion Starter · #1 ·
I rebuilt my 258 to stock and installed the California legal Howell TBI. It passed smog after getting running, but has never run great. It has had poor throttle response, horrible fuel mileage, stumbles off of idle occasionally, but the most annoying problem has been a back-fire (technically an after-fire) out of the exhaust when the throttle plates close while shifting gears. Occasionally I could detect a little pinging with distributor set to the recommended 8 degrees.

I noticed that this backfire only occurred after the engine warmed up. Either when the ECM went into closed loop or the dual CTO valve opens up introducing the EGR and the charcoal canister to ported vacuum. So I isolated the EGR valve and charcoal canister and found that the backfire was gone. I re-introduced the charcoal canister and verified that the EGR valve was the issue. With the ported vacuum to the EGR disconnected and plugged the Jeep runs so much better. No backfire, better throttle response. The 258 seemed much happier cruising at the 2400 RPM needed to achieve 55 MPH with my 4.11's. So I put a vacuum pump on the EGR valve with the engine running (only at idle) and found that I couldn't hold a vacuum on the diaphragm. Viola!! I was so excited to have discovered my problem. Or not.... ( I since learned that the engine needed to be at 2000 to 2500 RPM for this test, but I haven't tried it yet.) So right or wrong, I deduced that my backfire and other poor running issues were caused by the distributor being robbed of vacuum advance by a blown EGR diaphragm. So I ordered a new EGR valve Napa CRB 226099 for CA emissions and manual transmission $230. Yikes. So I tried to bench test the new EGR valve and found that it doesn't hold vacuum with a hand pump either.

I've since researched the forum and discovered that the 258 EGR requires back pressure form the exhaust to assist the ported vacuum in opening the EGR valve but have been unable to answer my questions by reading the posts. Hopefully someone here can further enlighten me so here are my questions as I'm hoping not to install a $230 EGR valve if the old one isn't bad. Also I have not had success in the past of removing the orifice washers from the EGR valve once it has been staked in place with a chisel so I hope not to experiment with washer size.

The current EGR valve was new from Rockauto when the motor was rebuilt. The numbers on the previous EGR valve did not match any of the numbers in the orifice selection chart so I chose a washer with nearly the same ID as the washer in the original EGR. It currently has a #37 which was one of the smaller if not the smallest size in the ket. The original EGR number doesn't match any of the numbers in the chart for the new Napa EGR either. One question I have is whether the orifice size affects how much exhaust back pressure is applied to assist in opening the EGR valve?

Also, with the proper exhaust back pressure on the valve, will the diaphragm hold vacuum with a hand pump? Again, I suspect most of my run-ability issues are caused by the distributor being robbed of ported vacuum, except the occasional pinging being caused by high combustion temps due to the EGR not opening.

In regards to exhaust back-pressure. I don't detect any exhaust leaks. I am running a stock exhaust manifold. I'm running 2" exhaust, through a catalytic converter, glass-pack, and then 2" out the back. I remember the OEM exhaust was slightly crimped above the rear axle. I've seen this on at least one other Jeep so I suspect it was done OEM to increase back-pressure. Has any one else seen this?

I plan on going out and re-installing the old EGR valve to do some more tests before installing the $230 Napa one. Hoping someone could walk me through some of this. All I know is that the Jeep runs way better with the ported vaccum disconnected from the EGR valve and plugged. Any assistance would be much appreciated.
 

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Discussion Starter · #2 ·
Further food for thought. I just went out and checked the original EGR valve that was on it before the engine was rebuilt. It does hold vacuum on the diaphragm. Just testing it on the bench.
 

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Discussion Starter · #3 ·
My original EGR appeared to have 17075662 written on it. So it had probably been replaced at some point. I bought the Jeep with 74Kmi on it back in 1990. Who knows what someone put on it in its first 8 years of life.
 

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Discussion Starter · #6 ·
Since my original EGR valve was not a positive back-pressure type, which is incorrect, and it had approximately a #37 washer. How do I determine a proper washer size when I install the proper positive back-pressure type? What size washers have some of you members used? Since the washer is in the exhaust side of the valve, will a bigger washer orifice provide more back-pressure assist to help open the valve?
 

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Discussion Starter · #8 ·
I appreciate the feedback. I'm in California, however, so I need to keep this valve functional and need to get a better understanding of the effects that the washer size has on operation. I may have to use some trial and error with different washers.
 

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To pass CA emissions, is the EGR function only on the visual/mechanical part to show it is connected, or do they actually connect to it and test if it is working?
Or is it how another machine connected somewhere else can tell if the EGR is connected/working?

With that thought, I found the same issue with my MC2100 carb here in AZ, that I needed to disconnect the EGR so the engine would run correctly. To go through emissions in AZ, all the charcoal canister/EGR is part of the visual/mechanical inspection. When I get ready to test here again (currently registered out of state), I will go into the EGR vac hose with something to plug the line internally, then connect that plugged line back onto the EGR to show visually it is in service.
The vac line will be connected at both ends, but if you tried to blow through it, nothing will pass either way.

Not sure, but hear that CA emissions to pass is getting tougher all the time, so just asking! No intent to imply that anyone would deceive the Government just to pass emissions, and be able to drive what they want short of persecution and/or arrest, but sometimes these rules really reach a bit too far!

Hope you get it figured out sooner than later!
 

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Discussion Starter · #10 ·
I'm not sure if the physical check the operation here in CA. Possibly not since it passed smog with the current EGR, which doesn't seem to work correctly, on it. If I don't get any further advice, I think I'm going to switch from the smallest washer that is on it, to the largest washer size to see what the effect is. Then follow guidelines for testing a positive back-pressure type valve. Then take it from there
 

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Discussion Starter · #11 ·
If anyone is paying attention, I went out today and replaced the #37 orifice with a bigger #54 orifice. Brought the engine up to temp and tested the EGR as follows:

Verified that I had at least 5 to 8" vacuum at the EGR with the engine above 2000 rpm. Can't see my tach so I'm going by ear. While holding the rpm steady. I disconnect and plugged vacuum to the EGR. Rpm went up slightly. With the Throttle still steady above 2000 rpm, I reconnected the EGR vacuum and noted a slight decrease in rpm. So I think the valve appears to be working.

Went for a test drive and noted that the backfire was present when the Throttle plates closed while shifting gears. Poor Throttle response and engine performance. Some lagging or stumbling when applying throttle. Disconnected and plugged vacuum to the EGR and verified once again that while not perfect, it runs much, much better with the EGR disconnect.

I may try the biggest washer next, or no washer at all. I still have a brand new EGR to try if that doesn't work. Stay tuned.
 

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There are two tests that you should have carried out before fiddling with the restrictor.

Firstly at operating temperature and idling, blip the throttle to 1500rpm. You should see the diaphragm of the EGR valve move. if not, hose or valve or CTO valve is broke.

Secondly at operating temperature and idle you can press on the back of the diaphragm and you should hear the engine roughen. If always rough the EGR valve is not stopping the flow of exhaust gases to the inlet manifold.
 

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Just grasping for straws here, and I may have this wrong but, I'm pretty sure the EGR is suppose to be connected to a ported vacuum. Make sure you're on the correct port.
You don't want it open when the throttle is closed.

Rectangle Font Slope Line Parallel


Are you connected to a vacuum source that has no vacuum when the throttle is closed? Check to make sure.
Is your throttle closing completely?
Is one of your throttle plate bent?

Basically the way it works is the backpressure from the exhaust runs up through the hole in the pintle. This forces the control diaphragm up against the vent valve. This seals the area where vacuum is applied pulling up the power diaphragm. In order to release the power diaphragm, you have to cut off the vacuum.

If you have it connected to a manifold vacuum, then once the EGR is open, it won't close again. So it won't matter what size washer you put in there.
It will idle rough and run poorly.
Font Parallel Slope Illustration Rectangle


If the EGR is working correctly, the combustion temperature is lowered and will reduce pinging and cut down on NOX pollution.
It will also helps with low octane fuel by keeping it from pinging.
 

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Discussion Starter · #15 ·
There are two tests that you should have carried out before fiddling with the restrictor.

Firstly at operating temperature and idling, blip the throttle to 1500rpm. You should see the diaphragm of the EGR valve move. if not, hose or valve or CTO valve is broke.

Secondly at operating temperature and idle you can press on the back of the diaphragm and you should hear the engine roughen. If always rough the EGR valve is not stopping the flow of exhaust gases to the inlet manifold.
I will try these tests next weekend when I get a chance to work on it.
 

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Discussion Starter · #16 ·
There are two tests that you should have carried out before fiddling with the restrictor.

Firstly at operating temperature and idling, blip the throttle to 1500rpm. You should see the diaphragm of the EGR valve move. if not, hose or valve or CTO valve is broke.

Secondly at operating temperature and idle you can press on the back of the diaphragm and you should hear the engine roughen. If always rough the EGR valve is not stopping the flow of exhaust gases to the inlet manifold.
I will say that the idle is pretty smooth with or without the EGR plugged in. I appreciate the feedback. I will try these tests next weekend when I get back to it.
 

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Discussion Starter · #17 ·
Just grasping for straws here, and I may have this wrong but, I'm pretty sure the EGR is suppose to be connected to a ported vacuum. Make sure you're on the correct port.
You don't want it open when the throttle is closed.

View attachment 4133625

Are you connected to a vacuum source that has no vacuum when the throttle is closed? Check to make sure.
Is your throttle closing completely?
Is one of your throttle plate bent?

Basically the way it works is the backpressure from the exhaust runs up through the hole in the pintle. This forces the control diaphragm up against the vent valve. This seals the area where vacuum is applied pulling up the power diaphragm. In order to release the power diaphragm, you have to cut off the vacuum.

If you have it connected to a manifold vacuum, then once the EGR is open, it won't close again. So it won't matter what size washer you put in there.
It will idle rough and run poorly.
View attachment 4133624

If the EGR is working correctly, the combustion temperature is lowered and will reduce pinging and cut down on NOX pollution.
It will also helps with low octane fuel by keeping it from pinging.
I
I am definitely connected to ported vacuum per the Howell diagram and not getting any vacuum to the EGR at idle. This EGR valve, which I believe I got from Rockauto, doesn't a hole in the middle of the pintle. I will have to check my records to see what the part number is. I have a new Napa one that I haven't installed yet. It is supposed to be for CA emissions with manual transmission. It also doesn't have a hole in the middle of the pintle, but is a positive back-pressure type, I believe, because you can't pull vacuum on the diaphragm with a hand pump either. I would like to narrow down the washer size before installing it so I dont have to install and uninstall different washers. It kinda beats up the face of the valve un-installing the washers.

The EGR that was on the Jeep when I bought it in 1990 had 17075662 on it, although it was hard to read. Interestingly, that valve has a hole in the pintle, but doesn't appear to be a positive back-pressure design because I can pull/hold vacuum on the diaphragm with a hand pump. The pintle on it is flush with the gasket surface of the valve. The Rockauto and Napa valves pintles stick out past the gasket surface. The 17075662 (Thats what is written on it) seems to cross to a EGV 524, which I think is for Federal Emissions rather than California. Im not sure if the EGV524 is a positive back-pressure design, if it is, then the PO marked the EGR valve incorrectly.

Could my exhaust be too open with the glass pack to provide back pressure to the EGR?
 

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Found some info here:


More Information for STANDARD MOTOR PRODUCTS EGV524 (Alternate/OEM Part Number(s): 04778472, 17075662, 33004383, 4778472, 8933004383B, EF8933004383B, J3240097)
 

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Discussion Starter · #19 ·
Found some info here:


More Information for STANDARD MOTOR PRODUCTS EGV524 (Alternate/OEM Part Number(s): 04778472, 17075662, 33004383, 4778472, 8933004383B, EF8933004383B, J3240097)
Thanks for the response. I have read the above post. None of the valves that I have have the protruding ring in the middle. I will post pictures of the valves I have when I get the chance.
 

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Discussion Starter · #20 ·
The first two pics show angles of the Napa CRB 2250 Valve $230 that I have new in the box. I have not yet installed and tried it yet. It has a protruding pintle with 2 small orifices in the sides it. I don't have pics of the valve that I have been troubleshooting so far, but it is a OMIX 17712.01 and appears similar in design with the protruding pintle. Im not sure it it has the orifices in the pintle. I will check later. The next two pics are of the valve that was installed by the PO and was on the Jeep until the motor died 15 years ago. It appears to have 17175662 written on it. This one will hold vacuum with a hand pump, therefore, not a positive back-pressure design. Its pintle is recessed into the body of the valve and has a large hole through the center of it.

I currently have a #54 washer, which is pretty large compared to the #37 that was in the PO installed valve.

There are two tests that you should have carried out before fiddling with the restrictor.

Firstly at operating temperature and idling, blip the throttle to 1500rpm. You should see the diaphragm of the EGR valve move. if not, hose or valve or CTO valve is broke.

Secondly at operating temperature and idle you can press on the back of the diaphragm and you should hear the engine roughen. If always rough the EGR valve is not stopping the flow of exhaust gases to the inlet manifold.
I did the above tests the BagusJeep suggested, which worked correctly as described.

I noted that with the EGR connected I pull 5 to 10 inches of vacuum between 2000 to 2500 RPM. I noted with the EGR disconnected and plugged that I pull more like 10 to 14 inches between 2000 to 2500 RPM. Note sure if this is significant, but im wondering if this is affecting vacuum advance.

The final pic shows a 13/16 socket that I clamped in the exhaust as a backpressure experiment. I had the drive of the socket plugged so I estimate that I restricted the exhaust by 25 to 33%. This MAY have shown some improvement on a test drive, but still had some back-firing and poor performance.

I think I am going to reluctantly install the new $230 napa valve with a #37 or smaller washer to see what happens. What do you guys think? Any suggestions? What do you think about washer size?
 

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