Need some help with 91 YJ engine codes 75 and 73

c_anthony27

New Member
Joined
Jan 20, 2021
Messages
5
Location
seaford ny
I have a ‘91 YJ with an auto trans

Recently did an engine swap
Jeep has 109k miles on it
new engine came out of a good running 90k miles Jeep
Engine came out of a ‘92

When driving it around town it runs fine
I am noticing that when you give it more than half throttle its not that responsive
On the the highway when you floor it
it does engage the trans kickdown
but it struggles getting up past 50
It has 31” tires on it

I have 3 other jeeps with 4.0 engines including a TJ with 33” tires
none of them are as slow to accelerate as this one is.

So i did the engine light code check thinking maybe its a map sense or tps sensor

I am getting codes in this order
12
75
73
35
55

I cant find 75 and 73 anywhere online for descriptions of them.

Anyone have any suggestions on where to start ?

I also just changed the fuel filter about 25 miles ago

and the trans is not slipping
it shifts firmly in to every gear
 
From what I can find by searching "jeep YJ code 73 75". It looks like one person figured it out to be that his Alternator was the culprit. He changed it out and the codes no longer appeared.
That is this page here: https://Wrangler Forum/threads/yj-codes-73-and-75-wtf.251402/

Here is one more page I found, but it seems it went unsolved: https://Jeep Forum/forum/f12/need-help-yj-fault-codes-also-have-front-end-vibration-1135617/

In the second one it is explained that the owner witnessed vibrations going past 30mph. There was another guy that mentioned that most ODBI codes are the same between vehicles. If that is true code 73 and 75 could be detecting misfires.

I hope this helps. I am sure someone can provide more information.
 
From what I can find by searching "jeep YJ code 73 75". It looks like one person figured it out to be that his Alternator was the culprit. He changed it out and the codes no longer appeared.
That is this page here: https://Wrangler Forum/threads/yj-codes-73-and-75-wtf.251402/

Here is one more page I found, but it seems it went unsolved: https://Jeep Forum/forum/f12/need-help-yj-fault-codes-also-have-front-end-vibration-1135617/

In the second one it is explained that the owner witnessed vibrations going past 30mph. There was another guy that mentioned that most ODBI codes are the same between vehicles. If that is true code 73 and 75 could be detecting misfires.

I hope this helps. I am sure someone can provide more information.
Yeah I came across the same info

The alternator doesnt make sense because the jeep is charging and charging under load

I dont really experience any miss firing at all

When I did the engine swap I put a brand new distributor and of course new plugs and new wires
and the dist came with new cap and rotor

Its really odd that the 75 and 73 codes are not really noted anywhere
 
I have a ‘91 YJ with an auto trans

Recently did an engine swap
Jeep has 109k miles on it
new engine came out of a good running 90k miles Jeep
Engine came out of a ‘92

When driving it around town it runs fine
I am noticing that when you give it more than half throttle its not that responsive
On the the highway when you floor it
it does engage the trans kickdown
but it struggles getting up past 50
It has 31” tires on it

I have 3 other jeeps with 4.0 engines including a TJ with 33” tires
none of them are as slow to accelerate as this one is.

So i did the engine light code check thinking maybe its a map sense or tps sensor

I am getting codes in this order
12
75
73
35
55

I cant find 75 and 73 anywhere online for descriptions of them.

Anyone have any suggestions on where to start ?

I also just changed the fuel filter about 25 miles ago

and the trans is not slipping
it shifts firmly in to every gear
Can you video your codes to make sure you're counting right?
 
I have the exact series of codes present on my 91 xj and also have found all the same articles as well but I'm pretty sure none pertain to my situation either. Has anyone figured this out yet?