93 yj 4.0 electrical - JeepForum.com
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post #1 of 17 Old 11-25-2019, 09:10 PM Thread Starter
mudd1966
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93 yj 4.0 electrical

hello does any one know what pin 19 in the ecu is //12 volts or 8 volts .pin 19 is ignition but does it give 12 or 8 volts out or in ..no power to cam or crank sensor .
pin # 3 battery -good
pin # 9 start/run - good
pin # 19 ignition --- no power at ecu in or out
pins 11 - 12 are grounds - good

thank you

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post #2 of 17 Old 11-26-2019, 04:48 PM
WestfieldMX5
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Pin 19 is the coil driver so that would be a ground signal (and only when it sparks). When it doesn't spark you measure 12V on it, feeding back from the coil.
Pin 6 is 5V feed for the TPS sensor
Pin 7 is 8V feed for the cam and crank sensor
Pin 51 is ground for the fuel pump


If the 8V output from the ecu is defective, try connecting the sensors to the 5V output. The sensors probably work fine at 5V as well.
You don't want 8V on the tps because the pcm is calibrated for 100% TPS @ 5V. A 8V signal would cause wrong tps readings. The pcm thinks you're at full throttle when you're about halfway.
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post #3 of 17 Old 11-28-2019, 07:52 PM Thread Starter
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thank you i think the ecu is no good
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post #4 of 17 Old 11-29-2019, 05:33 PM
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Originally Posted by mudd1966 View Post
hello does any one know what pin 19 in the ecu is //12 volts or 8 volts .pin 19 is ignition but does it give 12 or 8 volts out or in ..no power to cam or crank sensor .
pin # 3 battery -good
pin # 9 start/run - good
pin # 19 ignition --- no power at ecu in or out
pins 11 - 12 are grounds - good

thank you
FWIW if you do not have 8 volts at the cam or crank sensor it could be because the Vehicle Speed Sensor is shorted internally. These three sensors share the same 8 volt circuit BUT if the VSS shorts internally you get no power to the cam or crank sensor. If the crank or cam sensor send no movement signal back to the ECU you get zip for start up. BTW this condition does not cause any fuse to blow either.
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post #5 of 17 Old 11-30-2019, 07:55 AM
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I’m always totally amazed at the knowledge that flows here on JF

[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #6 of 17 Old 11-30-2019, 10:51 PM
Gausswave
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Originally Posted by laybackman View Post
FWIW if you do not have 8 volts at the cam or crank sensor it could be because the Vehicle Speed Sensor is shorted internally. These three sensors share the same 8 volt circuit BUT if the VSS shorts internally you get no power to the cam or crank sensor. If the crank or cam sensor send no movement signal back to the ECU you get zip for start up. BTW this condition does not cause any fuse to blow either.
That makes sense. From a trouble shooting perspective If you disconnect the VSS will is start as usual? Do any codes show?
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post #7 of 17 Old 12-01-2019, 07:37 AM
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I believe it will start fine, throw a code, and not run as well warmed up going down the road but I defer to the other two guys who apparently have sat around with Que and recited wire colors and voltages. I think unplugging it would be a worthwhile test.
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[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #8 of 17 Old 12-11-2019, 10:09 AM Thread Starter
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thank you
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post #9 of 17 Old 12-11-2019, 07:33 PM
jsawduste
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Originally Posted by fishadventure View Post
I believe it will start fine, throw a code, and not run as well warmed up going down the road but I defer to the other two guys who apparently have sat around with Que and recited wire colors and voltages. I think unplugging it would be a worthwhile test.
Correct Fish, no VSS signal. The ECM will have issues trying to adjust the AFR mix especially on coastdown. It will remain pig rich till the IAT/RPM adjust itself to clear out the excess fuel.


It`ll run fine in the driveway but sucky on the road. Not to mention the cylinder walls don't like getting washed down with all that extra fuel.


I run a Autometer WB O2 sensor. Coming off the throttle the WB will show a 17:1 AFR. Richens right back up to 14.7-15.0 right away at stop.


One things that keeps me up at night is thinking about the long gradual downhills. You know, where you have an extend downhill where your pushing through compression and on the brakes rather than the gas.


17:1 all the way down the WB says.


Engine is not under any load but it still makes me wonder what's going on heat wise on the piston crown and exhaust valves.


Speaking of Darryl. Been a couple years since we have talked. He only lives about an hour away and works even closer. We used to meet by his work and have dinner once twice a month. He got married and started doing a bunch of family stuff. Drifted apart I guess.
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post #10 of 17 Old 12-12-2019, 10:36 AM
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93 Wrangler YJ Code 47 Fix

Hey there new to the forums, but in need of some help.

Im fixing/repairing a 93 Wrangler YJ and have run into the same issue multiple times and dont have a clear solution yet.

My Jeep continues to display both code 47 and code 12 and the battery gauge only reads around 11 volts. I have since replaced the battery, alternator, starter, and ignition coil. All brand new parts and yet still having the same issue.

Has anybody found any other alternatives or solutions to this problem? I thought it was just a simple alternator replacement, but it seems to be more. Would really appreciate any help and /or feedback. Thank you
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post #11 of 17 Old 12-12-2019, 02:37 PM
laybackman
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Originally Posted by scrummy914 View Post
Hey there new to the forums, but in need of some help.

Im fixing/repairing a 93 Wrangler YJ and have run into the same issue multiple times and dont have a clear solution yet.

My Jeep continues to display both code 47 and code 12 and the battery gauge only reads around 11 volts. I have since replaced the battery, alternator, starter, and ignition coil. All brand new parts and yet still having the same issue.

Has anybody found any other alternatives or solutions to this problem? I thought it was just a simple alternator replacement, but it seems to be more. Would really appreciate any help and /or feedback. Thank you
First problem....Start your own thread concerning your YJ. QUIT throwing parts at the problem. You'll only make the parts guy rich.

FWIW....Take the + battery cable end off of the battery and ground it out for 30 seconds or more. That dumps any learned memory in the ECU....the brain. See what it does then.

Do you know what was good about the good old days? I wasn't good, And I wasn't old!

Senators and Congressman should wear uniforms like NASCAR drivers so we could identify their corporate sponsors....
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post #12 of 17 Old 12-12-2019, 07:31 PM
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Originally Posted by jsawduste View Post





One things that keeps me up at night is thinking about the long gradual downhills. You know, where you have an extend downhill where your pushing through compression and on the brakes rather than the gas.


17:1 all the way down the WB says.


Engine is not under any load but it still makes me wonder what's going on heat wise on the piston crown and exhaust valves.

What will really bend your mind is if you can monitor total ignition timing at the same time on decel. It is not uncommon for total timing to go above 50 degrees of advance. So what is melting down then???

Low manifold vacuum equals acceleration or load such as going uphill. It requires less timing and more fuel to not detonate. The opposite is true. Going downhill or decel requires less fuel and more timing to burn the mixture thoroughly.

Leaning out on decel and maintaining air flow helps emissions, prevents backfire, keeps cats from loading up, and prevents stalling. Go back to the original feedback carbs and idle solenoids, etc. Even the theory behind pulse air systems. Air injection reaction systems. Etc.

I am a tech, not an engineer. But...... When the throttle closes, manifold vacuum is very high. Manifold vacuum has EVERYTING to do with load on the engine, thus fuel and timing requirements.

You make more heat under acceleration than deceleration. It is really hard to lean out an engine under a no load situation such as decel. Thus why some modern engines go into total fuel cutoff from the injectors when in decel mode.

I get what you are saying but the science is true and has worked for years.


Good lord. I will not sleep tonight trying to remember all I have learned and know about this. Thanks.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #13 of 17 Old 12-13-2019, 05:17 PM
jsawduste
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Thanks for the comments Bo. We speaketh the same ideology with what's melting.


Indeed it would be interesting to see what the EGT`s in the long decel situation.
Plenty of folks do this downhill maneuver on a daily basis in a variety of vehicles. Just unsettling to see those carefully programed fuel trims set for load do the opposite under no load.
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post #14 of 17 Old 12-13-2019, 05:41 PM
Boojo35
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New O2 sensor science is off the charts. Voltage ranges changed, speed of the feedback changed, hard to currently monitor and diagnose. It is too fast for a a modern factory scanner to diag. Welcome to the modern world.

I agree with you on EGT and I have always wondered why individual cylinder EGT is not monitored in the modern OBDII world. It would surely help sort out some of these other software driven logic codes that just suk camel nuts to figure out sometimes. But. EGT seems to be exclusive to only the diesel world but is yet used on many sophisticated gas engine dynos. Hmmm.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #15 of 17 Old 12-14-2019, 05:40 AM
jsawduste
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Old man here, this new fangled stuff is incomprehensible in many factions. Still trying to get my head around the pricing structure that has evolved with advent of each new year.
On one hand you have a machine featuring astounding capabilities. On the other you don't want to lean too hard against the fender for fear of denting it.




Still don't like seeing that WB showing 17:1 whilst running closed throttle down the side of a mountain. Even though it isn't hurting anything it just seems like.............wrong...........
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