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Thread: EGR Codes

  1. #1

    Default EGR Codes

    Iím having issues with EGR codes 31 and 33. I get code 31 when I run a KOEO test and 31 with 33 when I do a KOER test. I checked continuity between all three pins on the EGR position sensor and the corresponding pins on the ECM. Everything was good. I have 4.99 volts between the 5 volt reference and ground at the EGR position sensor. I also backprobed the signal pins on the ECU connector for the position sensor while running a KOER test. Voltage started out around .9 volts and ramped up to about 3.5 volts. I even jumped the 5 volt reference to the signal pin and still got codes 31 and 33!

    None of this makes any sense. The EGR position sensor is working but these codes persist. Could my ECM be failing? This is my first car with eec-Iv so I donít know if this is a common failure mode when they go bad.

    My car is an 85 Crown Vic. Thanks!


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  2. #2

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    Update...I found a 60 pin EEC-IV breakout box on eBay this morning and bought it. I was getting my butt kicked trying to fit my hands down by the ECM connector to backprobe it. When it arrives Iíll check to make sure Iíve got good powers and grounds to the ECM. If they check out then Iím going to call it bad. SIA electronics in Illinois will rebuild it for about 170 bucks.


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  3. #3
    all the CFI are belong to me
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    31: the voltage the computer sees coming back from the EVP is out of spec (too low or too high to be in the valid range of values). This is an extremely common code and most people (anecdotally) do not bother trying to fix it, but it's certainly one I try to fix and I will not tell you to not fix it.

    33: the computer does not believe (using the EVP sensor) that the valve moved when it was given vacuum (if it is a memory code, this could have been an intermittent/it only happened one time problem).

    I would approach this as follows:

    Ensure the minimum voltage coming back off the EVP is at least [edited out bad data - refer to gadget's post below, I didn't have good data at my fingertips earlier when I wrote this]

    Using a hand vacuum pump if available, verify the smooth and consistent operation of the EGR valve itself. Make sure that it is not jammed with carbon and that it does not leak back closed again, and that while closing it fully closes without getting stuck. Unlikely to affect your issue but you're in there anyway.

    It is far more likely to me that your EVP sensor is out of spec, or maybe is being made to look out of spec by some condition of the valve itself. If it were just the 31 I would say there is almost no chance this is a bad computer, but the 33 makes it not impossible. Still far less likely, maybe thousands of times less likely. The EVP is a variable resistor (a potentiometer), and the nature of how they work makes them wear out in ways that make them lose accuracy and go out of spec while still overall "working".

    Breakout box is a nice tool to have and I agree with your plan to check out the power and ground.

    It is also worth mentioning that EGR issues of this nature (that is, it isn't stuck open) should not affect the running quality of the engine, so if you are chasing a performance or drive quality issue, solving these codes will not likely be your magic bullet.
    Last edited by kishy; 08-31-2020 at 10:47 PM.

    83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 CS | 85 Ranger +trlr | 86 GM | 91 GM POTM 12/2017 | Junkyards
    Gone: 97CV | 83 TC

  4. #4

    Default EGR Codes

    Thanks Kishy! Iíll pickup a hand vacuum pump to manually operate the valve and watch the voltage. Itís quite possible I missed something or connected my test equipment wrong since I was backprobing connectors with T pins in cramped spaces. Iím a big guy so it wasnít easy lol. Iím going to repeat all the tests when the breakout box arrives so I know I have proper connections.


    Iíll pull the EGR valve off the spacer plate and give it a good cleaning in the meantime.

    I donít have any drivability problems currently. I found these codes by accident. I picked up a ford super star 2 tester and was trying it out.

    Do these engines ping at part throttle in stock configuration with no EGR?


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    Last edited by matth825; 08-31-2020 at 12:06 PM.

  5. #5
    Wagon Addicted Tiggie's Avatar
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    Quote Originally Posted by matth825 View Post
    Do these engines ping at part throttle in stock configuration with no EGR?
    My experience with a clogged EGR passage: LOTS LOTS LOTS OF pinging.

  6. #6
    I'm an air-conditioned gypsy gadget73's Avatar
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    Is it the grey EGR sensor? There is a grey one and a black. You should have the grey.

    http://www.grandmarq.net/oldfuelinjection/page35.html

    has a chart with the expected voltages. Looks like fully closed should be 0.5 volts. If you're at 0.9, either it has some vacuum, or the valve isn't closed fully. Or the sensor is bad. There is a gasket or O ring under that thing, if its missing the position sensor will sit in further than it ought to and will read over voltage. If the gasket and such is fine, file the end of the sensor down until its in range and it should quit giving you codes.


    Clogged EGR passage with a functional valve will act differently than when you get codes. If the ECM has no faults for the EGR, it will add extra timing and lean out the fuel mix because it assumes you have EGR flow. It has no way of knowing if anything is actually flowing, all it sees is the valve opening. Later engine setups use a DPFE sensor to verify its actually getting gas flow rather than just relying on the valve moving.

    If there is a fault code, it will not bump the timing or cut the fuel so it probably will not ping.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

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    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  7. #7

    Default EGR Codes

    Thanks for the link! Iíve actually got the black sensor. I checked my parts catalog, looked up the emissions calibration page and the part number listed for the sensor matches the number on the installed sensor. I didnít know there are two different color ones so I wanted to check to make sure someone didnít install the wrong one at some point.

    I pulled the EGR valve off tonight. There was some carbon but the valve was fully closed. My .9 volts is what the black sensor is supposed to output per the spec chart when the EGR is closed so thatís one good thing. I also verified the EGR valve moves by using a handheld vacuum pump. I watched the sensor output voltage as I did this and it ramped up as the valve opened with no dropouts.

    My breakout box should be arriving this weekend. Once it does Iíll verify that the signal is making it to the ECM. If that checks out along with the ECM having solid powers and grounds is it safe to call the ECM being the culprit?


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    Last edited by matth825; 08-31-2020 at 10:10 PM.

  8. #8
    I'm an air-conditioned gypsy gadget73's Avatar
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    hm, I've never seen a black sensor on one of these but I have somewhat limited CFI experience. If thats what the book says I guess maybe its right. I'm guessing you're looking in the special specifications book, or are you using the master parts manual?

    Might be worth confirming the ECM is what the calibration says it should be.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  9. #9

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    Iím using the master parts manual. I got the info from section 93 which was ďemission parts by calibration.Ē Once the breakout box arrives Iíll do my final electrical tests. Iíll then pull the ECM to verify itís correct for my year and calibration. If that checks out Iíll open it up and look for bad solder joints, leaky caps, etc.

    If the ECM is the culprit then Iíve got to decide which way to go with repairs. Considering the age of all the electronics and the fact I have CFI makes me lean towards a carb conversion. I was looking at a 390 cfm Holley 4160 with an Edelbrock performer dual plane manifold.


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  10. #10
    all the CFI are belong to me
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    If you decide to get rid of CFI, and your disposal method for the CFI parts would not get you any money (e.g. trash can), I would gladly expand my hoar- um, collection of CFI bits and pieces. Computer and engine harness being the priorities, throttle body less-so but still welcome. Not sure where you are so costs could get irritating in that respect.

    I do think that ditching CFI is sort of a "throwing the baby out with the bath water" thing to do, but I am in a small minority when I say that.

    Not sure of which sensor (black or grey) is on my two; I'll take a peek and report in later.

    83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 CS | 85 Ranger +trlr | 86 GM | 91 GM POTM 12/2017 | Junkyards
    Gone: 97CV | 83 TC

  11. #11

    Default EGR Codes

    Kishy- Youíve got first dibs if I decide to ditch the CFI. Iím located around the Chicago area. Shipping may not be horrendously bad. Iíll be interesting to see what color sensor is on your EGR.

    Once I complete the diagnostics and sleep on things Iíll know more about which way I want to go. I really need to sit down and evaluate where Iím going with this car long term as well....thatís going to determine what I implement for a fix.

    I have thought about moving on to a different panther thatís cleaner for a long term car. This one came from Pennsylvania so itís got some rust issues but no rot thankfully. I had the underbody painted with rust encapsulator last summer and rust is already starting to poke back through. I knew it wouldnít last forever but one year has got me kinda bummed.


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    Last edited by matth825; 09-01-2020 at 01:19 PM.

  12. #12
    Lost and driftin' Arquemann's Avatar
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    CFI is great! The complexity of an efi system and only slightly better driveability and MPG!
    I replaced almost everything on mine to get things running proper. Though I have my doubts about my EGR's functionality, no codes but I have it plugged and disconnected anyways. I get 15-16mpg all day every day so it might have something to do or its just my driving.

    Only thing is I'm starting to yearn for more power...
    1985 Mercury Grand Marquis LS
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  13. #13
    I'm an air-conditioned gypsy gadget73's Avatar
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    If the BOB doesn't give you anything, I'd be real tempted to toss a grey sensor on it before going with ECM problems. Its very rare that they actually go bad. Not impossible, but it would be the absolute last thing I'd go for.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  14. #14

    Default EGR Codes

    Arquemann - I was wondering how yours turned out. I remember all the issues you were having. Glad itís all sorted out.

    Gadget - I like that idea. I can probably pick a grey one up locally.


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  15. #15
    GMN Regular DerekTheGreat's Avatar
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    Hey, I liked my '85 with CFI. Hated it at first, but that was just my ignorance. I miss that car, it met it's maker so shall it rest in piece or something profound like that.
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  16. #16

    Default EGR Codes

    Quote Originally Posted by DerekTheGreat View Post
    Hey, I liked my '85 with CFI. Hated it at first, but that was just my ignorance. I miss that car, it met it's maker so shall it rest in piece or something profound like that.
    I actually kind of like it too. It has its quirks but when it works it works well. My reasons for potentially wanting to ditch it are because of long term availability of replacement components. Iím still not ready to make that decision yet however. Breakout box should be arriving today so if Iím not too tired after work I plan on continuing diagnostics.

    What were your main issues with it?


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    Last edited by matth825; 09-02-2020 at 09:42 AM.

  17. #17
    all the CFI are belong to me
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    Black sensor on both of my EEC-IV CFI cars (84 and 85).
    I do not know if codes are set on either currently/recently, but I seem to recall there was at least a time where the 84 had no codes.

    83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 CS | 85 Ranger +trlr | 86 GM | 91 GM POTM 12/2017 | Junkyards
    Gone: 97CV | 83 TC

  18. #18

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    Quote Originally Posted by kishy View Post
    Black sensor on both of my EEC-IV CFI cars (84 and 85).
    I do not know if codes are set on either currently/recently, but I seem to recall there was at least a time where the 84 had no codes.
    Thanks! I appreciate you checking!


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  19. #19
    GMN Regular DerekTheGreat's Avatar
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    Quote Originally Posted by matth825 View Post
    I actually kind of like it too. It has its quirks but when it works it works well. My reasons for potentially wanting to ditch it are because of long term availability of replacement components. I’m still not ready to make that decision yet however. Breakout box should be arriving today so if I’m not too tired after work I plan on continuing diagnostics.

    What were your main issues with it?
    My car ran really well once I sorted it out. It had quirks too, one being I had to toe in the throttle ever so slightly when hot or else it would crank and crank with no results. I never liked how it didn't seem to compensate for a cold engine fuel mix wise. Ford had a carburetor like 2,100 RPM when cold spec if I remember right. I was able to get that down quite a bit with no weirdness but that required a lot of fiddling with the choke pull-off mechanism and stuff. I was happy with it when by the time I sold it. Never realized the dashpot which adjusted the idle was adjustable sensitivity wise- it always kicked the idle up too much when I ran the A/C. 3.8 CFI cars had an IAC valve, don't know why Ford didn't give us 5.0 crowd one..

    I liked how compared to SEFI cars, everything is accessible with minimal fuss and it looks old school under the hood. Everything that plagued my car initially was EGR, throttle position sensor, choke pull-off, fast idle and vacuum routing related. I don't know how one screws up the vacuum routing as there is a sticker on the fan shroud. Oh, the TV bushing was trashed and was the adjustment. I think my car was pretty rare, was an '85 with the first digit of the vin being a "1". Ain't never seen that since.

    Sold it to a guy who later junked it and in a twist of fate, I stumbled upon it at the yard it wound up in. Met a sad fate towards that end, it had been "ghettoized." Poor car.
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  20. #20
    Lost and driftin' Arquemann's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    My car ran really well once I sorted it out. It had quirks too, one being I had to toe in the throttle ever so slightly when hot or else it would crank and crank with no results. I never liked how it didn't seem to compensate for a cold engine fuel mix wise. Ford had a carburetor like 2,100 RPM when cold spec if I remember right. I was able to get that down quite a bit with no weirdness but that required a lot of fiddling with the choke pull-off mechanism and stuff. I was happy with it when by the time I sold it. Never realized the dashpot which adjusted the idle was adjustable sensitivity wise- it always kicked the idle up too much when I ran the A/C.
    Before I had mine sorted, it was always like starting a cold, cranky carbed motor, hot engine was only slightly better. Needed quite a bit of throttle input every single time.
    Nowadays it starts without throttle probably 75% of the time, always fine when hot. Sometimes when cold it just cranks and sputters but doesn't catch on. With throttle it fires up perfect every time.
    My choke and pull-off are sitting in a box in the garage, as I broke the tab on the throttle body unit.

    Also what!? The dashpot is adjustable? How about idle speed overall?
    My main gripes of the engine currently is the RPM stays kinda high all the time. AC compressor off and idling in gear is okay, ac kicks in it's high. Also idle in park is high, for some reason it keeps the RPM high for couple of minutes or so before it lowers to an tolerable speed.
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

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