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| | |-+ Error code 21 but everything checks out. Questions on error code 41 causes also.
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Author Topic: Error code 21 but everything checks out. Questions on error code 41 causes also.  (Read 304 times)
Armorican
4 Banger
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Location: Sierra Nevada, California

« on: November 11, 2017, 07:36:09 pm »

Hi guys,
I have had my Frankenstein project (89 GT the PO threw in the towel on) on hold for around 2 years but recently decided to buy a reliable ECU so I am back at it.
Yesterday I was down to code 21 and 41 on KOER  and code 95 on KOEO.
After checking fuel pressure (around 37-38, holding pressure including under acceleration) I decided to leave that code 94 alone and work on the other 2.
Regarding code 21, I had an extra ECT sensor, so I swapped them, but the code remained. I have then checked continuity from the connector to pin 7 as well as resistance. Everything is fine. checked signal return wire from connector to pin 46, and it checked also.
What may be weird is that the ECT sensor felt barely wet. I checked the tube and found it didn't have much  water in it. Maybe it does fill up only when the engine runs as it is quite high?
In any case, I am stumpted there.
Regarding code 41, there is something I may not understand. I have conflicting information regarding  its cause. Some web sites it means "passenger bank/side lean", other times it is explained as an issue with the "O2 sensor not switching". I bought  new O2 sensors when I got the car years ago on PO's advice, so I installed them this morning in hopes of an easy fix. Code 41 is still there.
I first changed the driver side one (easy reach, old one not throwing codes but looking beat up) and ran the codes again, with no change (was expected). Not happy with gravel hurting my back  during the operation, I drove the car on the garage's  concrete pad  and operated on the other side(The exhaust seems custom and I had to remove the starter to access the sensor.) After reconnecting the battery, hell broke lose: the engine would barely  start and refused to idle, even more so accelerate (engine warm). It did start fine when cold though.  I checked KOER codes with cold engine and  I still have 21 and 41.

Can someone send me in the right direction as to what code 41 really means and what I should look for?
and if someone has a hunch what is plaguing me, please let me know!


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89 Mustang GT Manual transmission.
Known mods: bored .030 over to a 306,  MHP173-311 kit.
BBK shorty headers, h pipes with under-car exhaust tip (exhaust happens beneath rear passenger seats, not at the back of the car).
RunninHorse
Big Block
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Location: Floresville, Texas
Órale!


« Reply #1 on: November 12, 2017, 10:14:01 pm »

Have you read this thread?http://sbftech.com/index.php/topic,29608.0.html

"A code 21 is normal to get logged if a KOEO self test is performed with a cold engine or coolant temp is below 50°F. A code 21 is also normal to get logged if a KOER self test is performed with the coolant temp below ~160°F."
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I'm Rob.  Working on my '93 Reef Blue coupe.  Stock internal 302, 80 MAF, 75 TB, Victor 5.0, High Ports, 30# inj., B303, 1.6s, Tremec TKO 3550, Quicktime bell, Fidanza Al flywheel, stage 3 ceramic clutch, & 4.10s.  12.68 @ 111.69
'66 F100 shortbed, 352ci, 3 on the tree - on hold
'65 Coupe rolling chassis - on hold
Parts I'm selling: 
Hardened Push Rods - Trick Flow 6.2" .080 - $60
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Armorican
4 Banger
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Location: Sierra Nevada, California

« Reply #2 on: November 13, 2017, 11:20:41 am »

Hi RunninHorse!
Thanks for taking the time to answer my questions again. Last time was a year and a half ago I think!
I did not take you up on your offer for harnesses then as I had all the time in the world to find cheap ones at various junkyards waiting for Joel to work on my ECU.
back to the present, I did not find the thread you linked when I looked, so thank you, I'll do more testing, but chances are that It is a non issue with codes 12  and 21 as temperature did drop recently around here.
For the code 41, I have no clue what could have happened when I changed the last O2 sensor, as now the car doesn't want to start even when cold. I thought there might be a logical explanation and was wondering if the engine ran before only because it was pig rich as the computer was trying to compensate for the lean condition, and once the condition (potentially) fixed, the  engine might be  fuel starved or something along those lines.
I have found a 'crank but no start' check list so I'll follow it step by step assuming this is an un-linked condition I was unlucky to develop in the few minutes the O2 sensor swap happened.
thanks again, I'll probably be back after some tests.
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89 Mustang GT Manual transmission.
Known mods: bored .030 over to a 306,  MHP173-311 kit.
BBK shorty headers, h pipes with under-car exhaust tip (exhaust happens beneath rear passenger seats, not at the back of the car).
wbrockstar
2stroke
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« Reply #3 on: December 02, 2017, 12:23:52 am »

The o2 sensor trouble shooting info is listed at the link below.
http://sbftech.com/index.php/topic,29771.0.html

The Hego ground wire being loose or corroded can cause code 41.Its located at a rear lower intake bolt or the crossover pipe bolt on the back of the cylinder head.

Code 21 popped up because the engine was still cold.
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