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  #1  
Old March 21st, 2018, 09:55 PM
RickM
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Rick Mabus
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Another code 44 and missfire question.

Hello all. So this is my quick question. My truck is throwing a code 44 but most importantly was running horribly. Definitely felt like it was missing one or more cylinders. Could a bad o2 sensor cause a missfire when it is cold and or hot?

Here is the backstory. My truck was leaking like crazy from all over the place. I took it to this wonderful older gentleman who worked on it for a long time meticulously going over it. One of those leaks was from the cover of the T-case. He had to get the exhaust off the truck to address that. He put it all together and now it seams to have an exhaust leak and was throwing a code for a bad o2 sensor. BTW. It ran pretty well before I took it in aside from the leaking. The gentleman worked really hard to fix all the leaks and I think he has done a fantastic job of that. I am not about to give him a hard time on here because my truck is a restoration project waiting to happen. So...I ordered two nftew O2 sensors, but I am a little curious as to if anyone has had a O2 sensor cause this missfire. FWIW I did search the forum, on this and the feedback was promising but slightly different.
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  #2  
Old March 22nd, 2018, 06:48 AM
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Bill Adams
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I don't think an o2 sensor will cause misfire. The job of an o2 sensor is to "sniff" the exhaust for rich/lean condition and adjust the fueling to correct. This only happens after the engine reaches operating temp, not during idle or warm-up.
I would look toward the distributor. Maybe out of time or a faulty ignition amp module. But yes, you should replace the o2 sensors if you are getting the code.
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  #3  
Old March 22nd, 2018, 07:52 AM
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Jeff B
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I agree w/ Bill re the O2 sensors.

Have you asked the old gentleman about the rough running condition?


.
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  #4  
Old March 22nd, 2018, 08:23 AM
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Also, I wouldn’t rule out that both issues are unrelated and something just went wrong unrelated to the old guys work. That can also happen. But an exhaust leak or malfunctioning MAF can through that code along with fueling issues... or it can totally be the old guys fault— and he should be flogged :-)

Code 44 means that o2s are outside their limits and not necessarily bad. Check for vacuum leak, check hose between plenum and MAF particularly the bottom for dry rot and any holes. Check o2 sensor plugs and wiring. Even overfuelling from bad pressure regulator or lack of fueling from bad pump can throw that code. Check MAF plug and swap it out if you have a known good one. Check o2 sensors are tightened. Avoid throwing parts at it...
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  #5  
Old March 22nd, 2018, 01:47 PM
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Robert Lynch
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Code 44 is drivers side o2... check to see if itís damaged or unplugged.. either way it is contained to the one side and not a whole engine problem (such as a MAF, or plenum leak which makes both sensors go out of bounds)
To test and see if you o2 is bad, switch it to the other side.. usually they are not bad unless damaged physically, and itís just not able to send a signal to the computer.


This is unrelated to the mid fire, this is likely a loose lead, or internal issue with the distributor cap, and is likely confined to one cylinder..

Normally what I do is check the leads at both ends and if they are all right and the problem is still present I replace the leads and the cap (leave the rotor button on)
Usually does the trick - the leads start grounding sparking when they are worn out, or the sheath gets worn away..

Anyway itís 2 issues.. ignition is totally separate from the fuel computer
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  #6  
Old March 22nd, 2018, 03:42 PM
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Rick Mabus
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I Thanks everyone. My large hose to my Plenum to my intake fell off during a test run. It had given me fits forever and has wires poking out of the intake end. When I noticed this during my pickup, I mentioned it, and he said he had to do some rigging to make it work. So... I just installed that hose new, which was in import from Europe. It is all good on that end. May disconnect the battery and try again one step at a time. Wil report back.
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  #7  
Old March 22nd, 2018, 03:47 PM
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Cool -

to read the codes - here is the process

1) locate the white plug in the passenger side cubby box (along with the ECU)
2) Key to ON position - take note of the code
3) unplug the white connector
4) turn key to OFF position - wait until ECU relay drops out (about 5 seconds or so - you will hear it click)
5) reconnect White plug
6) Turn Key to ON position
7) read next code - if any...

Repeat until you have read and cleared the ECU codes


No need to disconnect the battery unless you want to do them all in one shot but you may miss some - the display does not cycle through codes - it only displays one at a time
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  #8  
Old March 22nd, 2018, 06:02 PM
RickM
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Ok. So to reset the fuel air mixture though, do you have to disconnect the battery?
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  #9  
Old March 22nd, 2018, 06:51 PM
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Robert Lynch
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What? Just reset the codes as above .. or pull the battery cables

The ECU is stupid it does not ďlearnĒ... clearing the codes is all it needs and it goes back to the optimal map. When a code is triggered it defaults to the base map..

No magic in the ECU
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  #10  
Old March 22nd, 2018, 07:34 PM
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Ok. Latest update. So I got under my truck. I changed out the O2 Sensor. I also checked to see if it is throwing any codes. No codes. No service engine light. I then fired it up. I let it run for a while and it does not sound right. That said, I know for certain I have a bad exhaust leak on the front pipe of my muffler. BUT, you put your head under the hood and it sounds pretty normal. Then I went to the back and noticed a pretty good flow of condensation coming from the exhaust. My first thought was oh crap. head Gasket. I was envisioning that when this mechanic did the intake gasket he somehow damaged the head gaskets or something along those lines. Then the condensation dissipated almost completely. It never had an oily look and did not smell like anti freeze. So I am hoping I am ok there. Regardless the truck sat running in my garage for 10 or so minutes with no codes etc. So dumb question. Will a Miss fire of any kind throw a code? Will a head gasket issue of any scale throw a code?
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  #11  
Old March 22nd, 2018, 07:50 PM
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the exhaust leak "could" throw a CEL 44 or 45 - but honestly its unlikely..

The ECU codes only relate to Fuel injection so it would have to be pretty bad to throw a code. - Let it warm up enough to switch to the Optimal map (engine warm so about 15 minutes or so) it switches to using the O2/lamba sensors to adjust the fuel delivered.

Here are all the codes that it has

CODE 02

THE ECU HAS JUST BEEN RECONNECTED.
Switch on the ignition to clear the display.
Clearing the display. Switch ignition on. Disconnect serial link mating plug, wait 5 seconds, then reconnect.
Switch ignition off, wait for main relay to drop out.
Switch ignition on. The display should now be reset. If there are other faults, the next one will be displayed. Otherwise the display will be black.

If there is more than one fault, repeat steps 1-4 to clear each fault until the display is blank. If no LEDs are on: Good news, nothing is wrong. Either that or the LEDs are burned out or the display isn't getting any power.


CODE 12

AIRFLOW METER
Refer to service test 19, continuity test procedure.


CODE 14

COOLANT THERMISTOR
Refer to service test 14, continuity test procedure.


CODE 17

THROTTLE POTENTIOMETER
Refer to service test 17, continuity test procedure.


CODE 18

THROTTLE POTENTIOMETER INPUT HIGH/
AIRFLOW METER LOW
Refer to service tests 17, 18 and 19, continuity test procedure.


CODE 19

THROTTLE POTENTIOMETER INPUT LOW/
AIRFLOW METER HIGH
Refer to service tests 17, 18 and 19, continuity test procedure.


CODE 21

FUEL TUNE SELECT
Identifies that the tune select resistor is open circuit - refer to tune select resistor test in service manual.


CODE 23

FUEL SUPPLY
Check fuel system pressure - test 20 of continuity test procedure.


CODE 25

IGNITION MISFIRE
This code indicates that an ignition system misfire has been detected. Codes 40 and 50 indicate on which bank the misfire has occurred.


CODE 28

AIR LEAK
Check for air leaks in the following areas:
Hose, air flow meter to plenum
Breather system hoses to plenum
Brake servo hose
Vacuum reservoir hose (fresh air solenoid)
Distributor vacuum advance
Hose, purge valve to plenum
Injector seals
Joint - bypass air valve to plenum, plenum chamber to ram housing, ram housing to inlet manifold, manifold to cylinder head


CODE 29

ECU MEMORY CHECK
If detected, all other fault codes are unreliable and must be ignored.
Procedure:
1. Leave battery connected
2. Switch ignition off
3. Wait for approximately 5 seconds
4. Disconnect ECU plug
5. Reconnect ECU plug
6. Switch ignition on and check display unit
If fault code 29 is detected again, swap out the ECU for another one and retest.


CODE 34

INJECTOR BANK A
The display will indicate if the injector(s) are causing the engine to run rich or lean. If the bank is running rich, check for faulty injector wiring and connectors, stuck open injectors. If the bank is running lean, check for faulty injector wiring and connectors, blocked injectors.


CODE 36

INJECTOR BANK B
Same testing and procedures as Code 34, except relevant to bank A injectors.


CODE 40
CODE 50

MISFIRE, BANK A (LEFT BANK)
MISFIRE, BANK B (RIGHT BANK)
If both codes are displayed, check the following components common to both banks:
Distributor cap
Rotor arm
Coil
Electrical connections
Pick-up (air gap)
Amplifier
Injectors (if code 34 or 36 is displayed)
If just either code 40 or 50 is displayed, check components specific to that particular bank that the misfire has occurred on. ie - spark plugs, HT leads, distributor cap.


CODE 44
CODE 45

LAMBDA (OXYGEN) SENSOR A - LEFT BANK
LAMBDA (OXYGEN) SENSOR B - RIGHT BANK
If one of these fault codes is displayed, check the wiring to that particular lambda sensor. If both codes are displayed, the voltage supply to the heater coils of the sensors must be checked. Refer to test 26, continuity test procedure.


CODE 48

STEPPER MOTOR
Check base idle speed - see setting procedure. Refer to tests 15 and 16 of continuity test procedure. Check road speed sensor - refer to test 25 of the continuity test procedure.


CODE 58

GROUP FAULTS 23/28
This indicates that a fault has been registered that is caused by the fuel supply or an air leak but the exact fault cannot be identified. Check all items outlined under codes 23 and 28 (above).


CODE 59

FUEL THERMISTOR
Refer to test 13 of the continuity test procedure.


CODE 68

ROAD SPEED SENSOR
Refer to test 25 of the continuity test procedure.


CODE 69

GEARSWITCH
Refer to test 24 of the continuity test procedure.


CODE 88

PURGE VALVE LEAK
Refer to test 9 and 10 of the continuity test procedure.
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  #12  
Old March 22nd, 2018, 08:09 PM
RickM
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Rick Mabus
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Interesting. So if I look at this, a missfire should then throw a 40 or 50. That is extremely helpful and you are kind to post this.
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  #13  
Old March 23rd, 2018, 04:18 PM
RickM
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Rick Mabus
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So update. Exhaust leaks fixed. I went to drive it and it still did not feel/sound right. Sooo, took it back to the mechanic. After letting it cool down he insists by touching the exhaust headers on fire up that it is firing on all 8. Left his shop, and almost immediately it spit out a code 50. I am at a loss. I want my leaky good running truck back!! I am going to check the wires and plugs this weekend and see if there is some odd reason one is not right. Ironically though, I have no idea if this is the only code as I cannot the check engine light to go off and clear the code of the diagnostic box.
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  #14  
Old March 23rd, 2018, 10:01 PM
RickM
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Rick Mabus
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Well kids. The verdict is in. And the winner was a loose enjector lead on the pass side (missfire 50). The number 6 cylinder to be specific. I think it was close enough that it was not totally out all the time. Thanks everyone for all the help.
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  #15  
Old March 23rd, 2018, 10:50 PM
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That's awesome! Congrats! Occam's Razor raises its head yet again. Been following along and glad you got it finally figured out. Very gratifying I'm sure! Now go for a spirited and pleasurable drive! ;-)
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