EGR interchange
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 15 of 18
HT4100 4.1, 4.5, 4.9 Discussion, EGR interchange in Cadillac Engine Technical Discussion; My '85 4.1 has long had a very slight stumble at tip-in, which I'm trying to narrow down. I've been ...
  1. #1
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
    Automobile(s): 1985 Sedan DeVille
    Join Date
    Aug 2007
    Location
    Southern Maryland
    Posts
    1,487

    EGR interchange

    My '85 4.1 has long had a very slight stumble at tip-in, which I'm trying to narrow down. I've been reading up on EGR tech and am now wondering if I should switch to a valve for a later model.

    Specifically the 4.1 uses a negative back-pressure valve which uses a combination of ECM control and exhaust pressure to modulate the valve. Basically the engine computer commands the solenoid to pass vacuum to the valve when certain criteria are met, which then causes the vacuum to suck on the diaphragm. However there is a secondary valve that holds the diaphragm closed, which is forced open by exhaust back-pressure. This way the computer can make dumb ON-OFF selection based on operating criteria (throttle position, coolant temperature, etc) but leave actual operation to the back-pressure created by the engine running.

    Due to the performance mods that I've made my back-pressure at low RPMs is kind of high, so the valve starts modulating sooner than intended. I suspect that this is causing my problems with stumble at tip-in.

    What I am wondering is if I could take a valve from a 4.5 or 4.9 and get higher mechanical resistance to the back-pressure, so that the valve did not come on until later.

    I've looked at the data I can find but can't seem to locate the specs on this stuff. Anybody have any ideas?

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): none
    Join Date
    Oct 2004
    Location
    WI
    Posts
    5,280

    Re: EGR interchange

    Performance mods to a 4.1??

    What makes you think the backpressure with your current setup is significantly higher?

    Have you tried cross referencing part numbers to see if the valve is different between engines?

    Have you tried blocking off the egr to see if the stumble disappears?

  4. #3
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
    Automobile(s): 1985 Sedan DeVille
    Join Date
    Aug 2007
    Location
    Southern Maryland
    Posts
    1,487

    Re: EGR interchange

    Quote Originally Posted by drewsdeville View Post
    Performance mods to a 4.1??
    timing, ignition, Borla exhaust and Magnaflow cat, whatever is available I have done it

    What makes you think the backpressure with your current setup is significantly higher?
    I think it's higher at low RPMs (which is where the stumble occurs) because that's a fairly common byproduct of these kinds of mods.

    Have you tried cross referencing part numbers to see if the valve is different between engines?
    Yes I did the obvious stuff already. The part numbers are different. The parts are externally identical and will obviously physically interchange. What I am trying to figure out is if the 4.5 or 4.9 valves would have higher spring tension on the back-pressure side of the valve. I ass-u-me it would since the increased combustion size should put out more exhaust pressure but I'm trying to get more definitive.

    Have you tried blocking off the egr to see if the stumble disappears?
    Yes and I've replaced it too. Everything is doing what it should be doing, except that the back-pressure side of the valve is opening too soon.

  5. #4
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
    Automobile(s): 69 Thunderbird | 90 Seville | 89 Marquis | 72 Torino
    Join Date
    Oct 2008
    Location
    Palm Bay, FL
    Posts
    2,022

    Re: EGR interchange

    Quote Originally Posted by ehall View Post

    I think it's higher at low RPMs (which is where the stumble occurs) because that's a fairly common byproduct of these kinds of mods.



    How do you figure that? For one, a magnaflow cat will have significantly less backpressure than oem as will a borla exhaust( or really any aftermarket exhaust.) If you have high back pressure at low rpm, its only going to increase at higher rpm.

    Did you block off the EGR and the problem went away or did it remain?

  6. #5
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
    Automobile(s): 1985 Sedan DeVille
    Join Date
    Aug 2007
    Location
    Southern Maryland
    Posts
    1,487

    Re: EGR interchange

    Quote Originally Posted by Sevillian273 View Post
    How do you figure that? For one, a magnaflow cat will have significantly less backpressure than oem as will a borla exhaust( or really any aftermarket exhaust.) If you have high back pressure at low rpm, its only going to increase at higher rpm.
    I don't have problem at high RPMS so I'm not addressing that part of it.

    I chose a muffler size with the intention of keeping torque at the low end. I did not buy a 3" exhaust that would optimize flow at 4000 RPM since I don't spend any time in that part of the power band. Instead I focused scavenging in the bottom part of the band aka back-pressure at low RPMs.

    Did you block off the EGR and the problem went away or did it remain?
    I blocked off the vacuum plug and the problem went away. I know how to test

  7. #6
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): none
    Join Date
    Oct 2004
    Location
    WI
    Posts
    5,280

    Re: EGR interchange

    Quote Originally Posted by ehall View Post

    I blocked off the vacuum plug and the problem went away. I know how to test
    This is NOT correct.

    What you did there is confirm that the EGR SOLENOID is probably shot. If you plugged the vacuum line and your symptoms went away, the solenoid is applying vacuum to the valve at all times. It is stuck or leaking.


    As you said, the valve itself uses exhaust backpressure as well as engine vacuum to operate. There are two diaphrams, either can leak. You can't tell what's up with the valve by disconnecting the vacuum line. You have to remove the valve and block off the EGR port on the intake manifold. THEN if the symptoms disappear, you can suspect the valve is defective.

  8. #7
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
    Automobile(s): 69 Thunderbird | 90 Seville | 89 Marquis | 72 Torino
    Join Date
    Oct 2008
    Location
    Palm Bay, FL
    Posts
    2,022

    Re: EGR interchange

    Quote Originally Posted by ehall View Post
    I chose a muffler size with the intention of keeping torque at the low end. Instead I focused scavenging in the bottom part of the band aka back-pressure at low RPMs.
    I gotcha, you left that part out. But still, backpressure will only increase from there. Do you think your new exhaust flows less than the OEM did? And did you notice the problem right after installing it?

    Quote Originally Posted by ehall View Post
    I blocked off the vacuum plug and the problem went away. I know how to test
    When you do that, the suspected over-backpressure can still act on the valve. If I were you I'd block the valve off with a plate to be 100% sure. Personally I think you problem lies elsewhere but I'd still go for the plate to be sure.

  9. #8
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
    Automobile(s): 1985 Sedan DeVille
    Join Date
    Aug 2007
    Location
    Southern Maryland
    Posts
    1,487

    Re: EGR interchange

    I have tested vacuum pressure from the solenoid separately, and it is doing what it is supposed to do. There is a very specific area where the back-pressure valve is fluttering and I am trying to find a valve with a stronger back-pressure spring.

    Go read these if you want to know more pay attention to the negative back-pressure type since that is what we have

    http://www.asashop.org/autoinc/nov97/gas.htm

    http://www.asashop.org/autoinc/dec97/mech.htm

  10. #9
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
    Automobile(s): 1985 Sedan DeVille
    Join Date
    Aug 2007
    Location
    Southern Maryland
    Posts
    1,487

    Re: EGR interchange

    Quote Originally Posted by drewsdeville View Post
    As you said, the valve itself uses exhaust backpressure as well as engine vacuum to operate. There are two diaphrams, either can leak. You can't tell what's up with the valve by disconnecting the vacuum line. You have to remove the valve and block off the EGR port on the intake manifold. THEN if the symptoms disappear, you can suspect the valve is defective.
    I REPLACED the valve first try, both were AC Delco correct parts

  11. #10
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
    Automobile(s): 69 Thunderbird | 90 Seville | 89 Marquis | 72 Torino
    Join Date
    Oct 2008
    Location
    Palm Bay, FL
    Posts
    2,022

    Re: EGR interchange

    Quote Originally Posted by ehall View Post
    I REPLACED the valve first try, both were AC Delco correct parts
    Not trying to be a wise ass but as I see it, If your exhaust makes too much backpressure for your oem valve to operate correctly, then replacing the valve with the same part would yield the same result. Right?

  12. #11
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): none
    Join Date
    Oct 2004
    Location
    WI
    Posts
    5,280

    Re: EGR interchange

    Exactly, replacing it isn't the same as eliminating it.

  13. #12
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
    Automobile(s): 1985 Sedan DeVille
    Join Date
    Aug 2007
    Location
    Southern Maryland
    Posts
    1,487

    Re: EGR interchange

    Quote Originally Posted by Sevillian273 View Post
    Not trying to be a wise ass but as I see it, If your exhaust makes too much backpressure for your oem valve to operate correctly, then replacing the valve with the same part would yield the same result. Right?
    You were arguing that the valve was defective, which I addressed by trying another valve.

  14. #13
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): none
    Join Date
    Oct 2004
    Location
    WI
    Posts
    5,280

    Re: EGR interchange

    Unless you are talking about another thread that I haven't read, I think Sevillian is arguing the same thing I am...It's most likely NOT the EGR valve.

  15. #14
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
    Automobile(s): 69 Thunderbird | 90 Seville | 89 Marquis | 72 Torino
    Join Date
    Oct 2008
    Location
    Palm Bay, FL
    Posts
    2,022

    Re: EGR interchange

    I'm arguing that the egr is not your issue and the ONLY way to be 100% sure is to block it off. I've been through this before which is why there is a block off plate sitting in my tool drawer.

    edit: yeah, what he said.

  16. #15
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
    Automobile(s): none
    Join Date
    Oct 2004
    Location
    WI
    Posts
    5,280

    Re: EGR interchange

    Quote Originally Posted by Sevillian273 View Post
    the ONLY way to be 100% sure is to block it off.
    Yes

    Again, I can't stress this enough, you did NOT confirm your theory by replacing it or disconnecting the vacuum line. It needs to be removed from the engine, EGR port on the intake blocked off. THEN run the car and see where you are at.

    I think you are overstating your backpressure changes. These are four stroke engines and aren't terribly sensitive to backpressure changes to begin with, especially the minor ones you made. This isn't like two strokes that need a tuned exhaust with expansion chambers.

    The only time backpressure changes really throw an EGR out of whack is extreme cases like clogged catalytic converters or crushed/collapsed pipes. If you chose an exhaust system that can generate as much backpressure as a clogged cat, I'd suggest replacing your exhaust before you burn the valves.


    I'm sure your backpressure is just fine, your EGR valve working correctly. I'd look elsewhere.

    If you are really curious about it, before spending money on parts and screw in a backpressure gauge.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting