Close



Results 1 to 5 of 5
  1. #1

    Default '86 CFI 3.8 code 31 error (need help)

    Hello,

    I need help with my '86 mustang LX: The car was running fine at 1st(i am new owner): but now will only consistently start and idle pretty well; any amount of throttle results in the engine stumbling with no rpm increase beyond maybe 12 to 15 hundred and lots of black smoke, so its running too rich.

    There are no obvious vacuum leaks, disconnected sensors, and the wiring seems intact.

    I have run the diagnostic 'engine off' test and get only #31 (egr) error code. The motor does runs slightly better or different with EVP? electrics disconnected, and in the running engine test mode(seems to run fine at 1500 for examle, but the same stumbling occurs with any throttle application beyond that).

    I would just like to get the car running correctly. This is a California emmisions car.

    Running test codes are 44, 94, &31(air pump valve?)

    The egr valve does move with the application of some vacuum. There is change measurable in the electrical resistance on the EVP with application of vacuum. I have shop manuals including the emissions diagnostic Volume H.

    So my real question is what next?

    The manual states that static test (engine diagnostic codes) #31 should be cleared 1st before 'chasing' the running test error codes. There seems to be plently of exhaust volume coming out of the tailpipe, but I cant excluded a partially clogged exhaust as black soot and smaller chunks of ? collect on the ground under the tailpipe.
    The spark plugs were fouled black, but changed(resulting in no change in performance) and probably are fouled again at this point.

    The engine would idle all day long if I let it and it starts easily either cold or hot with an appropriate transistion from cold engine to hot starting at 1500 rpm cold and going to about 650 when warm.

    I want to remove the egr and try to clean it, thinking it maybe partially stuck open(ie wont close completely?) though the egr valve does apparently move if you put some vacuum on it, and moving the valve with some vacuum does make the engine run much worse.

    This car did the same thing once before and I had to limp home at < 20 mph(cold idle on flat ground cold) which miracously did improved to 50mph(because of some throttle responsiveness) & over the course of 150 miles the car finally drove normally again by the time I got back home.

    The car worked fine thereafter for some time (long enough for me to dare driving a longer distance on the highway again)unfortunately the same symptoms returned the next time I got about 50 miles outside of town. It did start to run hot before starting to sputter again, which could be controled by reducing speed to 50 mph, but eventually I had to limp back to town a second time(replaced radiator once back and have tried to 'drive it back to normal' again in town with no improvement over the course of two or three tanks of fuel; I kept thinking I had contaminated gas in my tank as symptoms were intermittant & seemed to be related to rain?; urrgh!!

    I would like some guidance on what to try next ? I dont like buying parts to just test things, hoping to stumble on a 'cure'.

    I have never needed to mess with an egr before and this one seems to bolt into a plate that lives underneath the CFI that is aluminum, so I am alittle concerned I may strip the threads on an attempted removal(bolts look very rusty and im not sure what i will find or even do, if i get the egr off, replace?.......I do think it is best to keep the CFI, so conversion to carb or something like that is not in the cards for me( I would rather sell the car before considering doing that); keeping it completely 'stock' however is not an issue I need care about here; I just would like a reliable good running car.......without too much more headache


    Please help, thanks!
    Last edited by hypercycle; 04-18-2020 at 11:57 AM.

  2. #2
    FEP Super Member xctasy's Avatar
    Join Date
    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,961

    Default

    The specific resistance for test in Volume H must be true at all positions.

    On Mikes wip, the EGR played up, very typical.

    Quote Originally Posted by Walking-Tall View Post
    The next hiccup (I feel like trademarking/copyrighting/coining/whatever that phrase), in the never-ending saga of hiccups that is EEC-IV:



    These sensors are supposed to have, through their range of movement to sensing and relaying the EGR valve's diaphragm's position, as a variable resistor, 5500Ω to 100Ω. Mine has exactly 4.85Ω of resistance no matter where it's stem is, lol. This has been causing the car to run like a can of smashed a$$holes. At first I presumed some bad gas (but 4 different loads (2 premium 91-octane) of ten bucks thrown in? I don't think so), and have retarded the ignition timing 2° twice to 6° BTDC, to no avail. It's also got a somewhat rough idle and off-idle, and pinging/detonation with from anywhere between 20-50% throttle application upon normal acceleration, but only at the lightest of loading, at the top of each gear just prior to shifting. Welcome to EEC land, where I'm suggesting, the ecm's response is to open the EGR when it should be nearly or always closed, and vice versa. That's bass-ackwards, and no, I'm not wasting one more dime on trying to get it to cooperate.

    Thankfully, I have the cure for the hiccups. None of any kind of the above kind of inverted-universe BS will go on with carburetion and Duraspark. Soon.



    so he did a Page 5 Black Spagetti Removal.



    His layout is the same as yours. Sadly, the 2.3 MCU 1-BBL and 3.8 CFi are forgotten about engine combo's you don't see anywhere on the 8 pages of 2.3 Turbo and 5.0 EFi only posts. Good VECI and EVTM shots aren't easy to get.

    http://mustangattitude.com/mustang/1986cars1.shtml.


    The 86's used an 1986 only Port EFi 5.0 style Vacumm manifold on the Passanger Side srping tower, so you have to trace a leak if the TAD/TAB SOLV's aren't working properly.

    Due to the tall deck height of the 3.8 (9.22" instead of 8.206"), FoMoCo were forced to section the SOLV's TAB/TAD to the drivers Outside Fender wall.

    As I understand it, the 5.0 EFi for 86, for example 86Stripper,
    the system is mounted outside the Passenger Side fender wall via a big wire/vac cluster to the parts.




    I'm not sure if your system is the same.


    Quote Originally Posted by 86Stripper View Post
    Vacuum Hose Assembly

    This is the vacuum hose assembly that goes from the vacuum source at the firewall to the switch assembly and then to the Divertor Valve and the Bypass Valve. The blue device on the source end is the check valve. If you look closely at the left plug for the vacuum switches at the bottom of the photo you will see a T fitting. This is where the vacuum canister hose attaches.




    I don't have any pictures of the vacuum canister. If I have the inner fender panel off one day I'll take a photo.


    That is all I can think of for now. Let me know if you need anything else.

    This is Mikes, yours should be the same.

    It may have a big old 1978-1979 3.3 Liter Ford Six vac amplifiyer mounted outside the Drivers Side fender wall via a big wire/vac cluster to the parts.



    The rest looks the same as the 5.0 Port EFi placement.

    The whole kit includes the TAB/TAD in the box on the far right of the screen, and the wire to the control SOL's are the same place






    Due to the condensor hose, and noise of the clicking parts, it was shifted in 1983 to a spot where it was with the 86.

    The CFi was the lynch pin to pave the way to the Port EFi postions, 95% of everything TAB/TAD and AIR and EECIV and fuel pump wise was all there.

    Mikethe80sFanatic



    Make sure the HVAC and solenoids work first, then try the stock combination. IMHO, removing anything TAB/TAD related it won't answer your fault codes dilema.

    On a car this age, you have to check backpressure in the two catalysts first. Blockage is common.That is done by left and right bank drilling a 14 mm spatk plug adaptor like on my 81 Ford 3.3 six. You can braise it up, and then ensure backpressure at 3500 rpm is less than 6 psi.

    Failure of the electronic EGR valve readings often occurs. Like the TPS sensor, dead zones can happen, causing the upstream air to default in the wrong position.

    It is probable that the manifold inert gas stove is blocked.

    The checks are probing the combined Evap EGR sensor for its charted resistances. Normally, its a leak in the vacuum fittings or gummage from the EGR port to the CFi's throttle body baseplate.

    AIR recirculation differs on tall deck 3.8s. The key checks are no catalyst blockages, no Evap/EGR sensor failure, no EGR heat stove issues. Then go back down through the engine idle control and TPS and technical service memorandum for the CFi throttle body to Manifold gasket.

    The codes are in WalkingTalls posts. Its very involved only because the aluminum heads cause a lot of oxidizing corrosion in the intake section. Ford got everything well ordered, but only a service tech can easily check.

  3. #3
    FEP Super Member xctasy's Avatar
    Join Date
    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,961

    Default

    CFYI. Catalysts were blocked. When the Scared Cows stop the other Cattle on the List, you get multiple code violations...

    Quote Originally Posted by JACook View Post
    There's a long list of parts that -might- cause your problems, so replacing parts in hopes they might fix
    something is pretty likely to only lead to frustration. You need to follow the data.

    Have you considered checking the fuel pressure? CFI is pretty picky about fuel pressure, and you've got
    codes saying it's running lean. Should be 35-45 PSI, but most run best between 39 and 42. If the pressure
    is low, you might try a new fuel filter, otherwise you need to diagnose why the pressure is still low. This
    could be a voltage supply problem, a grounding problem, or the main or in-tank lift pump may be failing.

    The EGR codes are all complaining about the position sensor. But don't reach for a new one just yet. If the
    valve is not seating, you need to correct that condition. But the 31 code suggests that's not the issue.
    Whether or not the valve is seating, you need to understand why the EGR valve position sensor is out of
    range.

    First, measure the resistance between the EGR position signal pin, which is the one next to the flat on the
    connector (Brown/Light Green wire) and sensor ground, which is the connector pin opposite the signal pin
    (Black/White wire). With the valve at rest, the resistance should not be greater than 5500Ω. Using a hand
    vacuum pump, or by mechanical means, gradually operate the valve. The resistance should smoothly
    decrease to no less than 100Ω. At no point in the valve travel should the sensor resistance read open.

    If that checks out, measure the voltage between the VREF pin (orange/white wire) and sensor ground
    (Black/White wire), with the key on. You should have between 4V and 6V. If the sensor voltage is low, try
    moving the sensor ground probe to engine or battery ground. If the voltage increases, you have a sensor
    ground issue. Most likely that would be the ECU ground pigtail connection on the negative battery cable.


    Quote Originally Posted by 86frankenstang View Post


    there are the codes from my last check.



    Sent from my iPhone using Tapatalk
    WalkingTall had the same experience, but his catalysts weren't the problem.

    Quote Originally Posted by Walking-Tall View Post
    Update: Tested suspected MAP sensor...

    VREF test: key off, disconnect MAP connector; measure voltage between VREF and SIG RTN at connector; KOEO - got 4.95v, good.

    MAP/BP Sensor test: connect MAP connector; with digital multi-meter, back-probed MAP connector MAP wire with (+) and battery negative with (-) - got 2.50v, not good.

    According to a table of MAP/BP voltage specs, this MAP sensor thinks it's a couple thousand feet below sea level. Maybe what the car needs is a periscope?

    The frequency testing went as follows: 160Hz with no vacuum - perfect; 110Hz with full vacuum - supposed to be ~93Hz.

    NOW, AFTER the above testing, is the FIRST TIME EVER getting a K.O.E.O. code 22 (MAP/BP out of self-test range), and it's been guzzling gas but not really showing signs of it besides the fuel gauge needle, and acts sluggish and hesitant upon acceleration with taking it for one spin around the block so far. I swear this car is possessed, with somewhat of a sense of humor, and likes to play games with me. Anyway, I need to find another MAP sensor... a used one that works, because new ones appear to be hovering around the the ridiculous amount of 90 bucks around here.

  4. #4

    Default

    Thanks for your very prompt response: the pictures are very helpful(they confirm from what I can tell, an exact match to what I have) & you have thus provided me with a wealth of new information to chew through, that I may NEVER have gotten from the ford manuals on my own.

    Unfortunately I had to return the vacuum tester that I originally borrowed to test with, so I havent done any further objective diagnostics on the egr/evp itself yet; but I did succesfully liberate the egr/evp assembly from the manifold with much less than expected trouble using some penetrating (or releasing) oil application & patience.

    What i did find was after removing the egr assembly from the car, was an egr valve that, freely moved to open and fully closed merely with the judicous application of biologically generated vacuum, and which was, surprizing clean. I couldnt do anything more precise with the EVP, like measure its resistance under varying vacuum conditions and remain somewhat civil appearing to the newly aririved neighbors that were moving in next door yesterday too.

    I did however yield to my temptations & started the previously warmed up motor and in that observed the following: the engine ran nicely(albeit much louder) at 3000 rpm without any throttle input, AND very surprizingly the engine now had a crisp(normal feeling) throttle response for the 1st time, without any of the above previously described symptoms of stumbling/lack of power & mega black cloud of too rich mixture that I had with the egr on the manifold (all of which very consistently returned when the egr was put back on...... ).

    Hmmmm.......?

    Also the only koeo code again was #31, & #94/44and 31 with the motor running testing as before(this all was somehow an encouraging discovery, because of the change i suppose; but Im still not sure what it all means......); in anycase I feel like the answer and possible cure will be at hand in the near future(progress at last!)

    Ok so after again considering my observations from yesterday and following my 1st study of your answering post, I am wondering more strongly: is the exhaust system significantly restricted to the point that the engine computer/sensors can't do anything but pour fuel into the CFI in response?

    So I will re-obtain the vacuum tester again this week, & am tempted to fabricate an egr block off plate, to see what she does when no exhaust is allowed to howl out of the engine manifold (seems like i have run motors without an egr attached, and i DON'T recall any similar drama, but those days are only very distant memories at this point).

    In the meantime i will educate myself wrt what TAD/TAB etc ......and the other, currently known to me only as acromyn soup, are applicable to our favorite Fords.

    BTW my barn also include running & non-running examples of '85 & '86 svo's, straight 6 and v8 futuras and a little old maverick from 1973;

    Lost to youthful stupidity was my beloved '79 v8 pace car, with which I totally demolished an innocently PARKED camaro(the other strikes, before again achieving zero velocity & accelerations, fortunately faired much better) all this because I elected NOT to put the 'second bolt' of the throttle bracket into the edelbrock, as those didnt conveniently share the same spacing...... this dramtic event did however partially cured me of my immortality self-delusions.as well as teach me a more serious approach to details....C'est la Vie
    Last edited by hypercycle; 04-19-2020 at 10:02 PM.

  5. #5
    FEP Super Member xctasy's Avatar
    Join Date
    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,961

    Default

    see all of WalkingTalls Documentation. Back probing for out of range values is the key redress for each fault.

    Two pages.

    http://vb.foureyedpride.com/showthre...s-Testing-from

    Unloaded, the engine will subjectively sing. With your foot on the brake, and the park brake on, flashing till 3500, it could start a burnout, but that is the way the back pressure should be determined. There is a safety aspect here, I trust your intelligence in this matter. My personal and company liability insurance wont cover inciting stupidity. I trust you more than my neighbors.




    See as well http://vb.foureyedpride.com/showthre...5-0-wont-start

    Page 231 of the first 44 fault codes. 94 indicates Secondary Air Injection Inoperative or Integrated Relay Control Module (3.8L EFI)

    The others 45 to 99 only are found here by Shelby, PaceFever79

    https://www.troublecodes.net/ford/eec-iv/

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •