83 Jeep CJ5 Ignition cuts out

Robert Diagnostician California Posted   Latest  
Resolved
Pico Technology
Driveability
Electrical
1983 Jeep CJ5 4.2L (C) 4-spd (T176)
Ignition Cut In And Out

Hi guy,

I need to pick your old brains on this old system. LOL

Got this running and seems to run ok at higher RPM but still can act up at higher RPM. After the choke opens and the engine drops to base idle many times it just stalls. When it stalls the ignition coil just stops firing. sometimes it almost dies and catches again and cuts out and catches and cuts out and catches then stalls. When it cuts out the Ignition coil just stops firing. I replaced the Ignition module after taking this capture and figuring the module was faulty. 

Yesterday I took a capture looking at the positive side of the ignition coil and noticed that as the problem started to happen sometimes the module would start regrounding the coil before the coil could fully discharge until it was just grounding it all the time. The pickup coil signal looks the same and the MCU signal to the Ignition module looks the same but the module keeps grounding the coil.

My question is what tells the Ignition module to reground the coil to get ready for the nest firing event? I don't see a signal from the MCU to accomplish that.

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Interesting
Brandon Diagnostician
Pennsylvania
Brandon
   

You never lose control so that proves the PCM is functioning properly. Check for positive voltage available at the coil simultaneously, in your next capture. That may explain your loss of Drive

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Robert Diagnostician
California
Robert
 

It has positive voltage at the coil from the capture I took at the end of the day Friday. When ungrounded reads battery voltage and grounded reads 8 volts because of the ballast resistor wire. That is how I could tell the module was turning on the ground early sometimes and just leaving the ground on when no spark. The capture is on the computer at work so can't post that right now. I have not…

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Ray Diagnostician
Ontario
Ray
 

I remember one where the tach circuit interfered with the coil negative.

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Robert Diagnostician
California
Robert
 

I disconnected the aftermarket tach. still same problem.

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Ugwoke Owner
Singapore
Ugwoke
 

What is aftermarket tach

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Robert Diagnostician
California
Robert
 

tachometer to show RPM. Was added to the jeep on the steering column.

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Richard Owner/Technician
Missouri
Richard
 

I agree with Brandon, you're not losing the control side. These used a very simple system and I don't recall them being very problematic. If you aren't losing supply voltage it may be the primary windings in the coil separating intermittently.

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Robert Diagnostician
California
Robert
 

I have been reading the Jeep forums and there are quite a few people complaining of the quality of the replacement modules and ignition cutting out. I hope it is not a part quality issue and an issue I can fix. On my capture, on Friday the supply voltage showed the load of the coil is grounded so the coil could not be open on the primary side. I think I need to check grounds on the block…

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Interesting
Brandon Diagnostician
Pennsylvania
Brandon
 

A coil ramp will certainly help

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Brandon Diagnostician
Pennsylvania
Brandon
 

I see now, it appears the coil control continues to dwell during the failure (does not release). Place your amp probe at the control module and if the failure occurred and current is present, the module is responsible for the excessive dwell. if no Current is available, you have a short to ground present in the harness between coil negative and control module

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Robert Diagnostician
California
Robert
 

I tried another module and still the same problem. I will try a current ramp on Monday and see how many amps it pulls and if the amperage is different when it cuts out.

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Gary Owner/Technician
Colorado
Gary
 

Robert, Looking at your wiring diagram, you should have the old Motorcraft ignition with the blue-grommet module and a Carter BBD feedback carburetor. The module is identified by the color of the grommet holding the wires to the module. The MCU basically controls air/fuel ratio via the oxygen sensor and other inputs. As I recall, the MCU shouldn't be controlling control spark timing. The only…

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Interesting
Helpful
Robert Diagnostician
California
Robert
 

The Pickup coil goes to the MCU and the Purple wire is not connected to the module. the Orange wire is connected to the MCU that triggers the module. It is a blue coded module. The Vacuum advance has intake vacuum to it and from what I have read on the forums is the computer controls timing by regarding it from max advance with the vacuum advance pulled full at idle. Information on operational…

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Gary Owner/Technician
Colorado
Gary
 

You're correct, Robert. The Jeep must have a California emissions certification, which could be more sophisticated than the 49 states engines. Sorry about that, I didn't notice that when I looked at your diagram. You're also right that there was next to nothing published in those days regarding operating strategy. That said, coil negative still goes directly to module pin D4 via the green wire…

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Allan Instructor
Manitoba
Allan
 

Robert I have had issues with the old Ford system where the starter solenoid was grounding the coil causing a stall. Unplug the red wire on the solenoid, the ignition by-pass, and see if that makes a difference. Easy enough to try.

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Robert Diagnostician
California
Robert
 

easy enough to try. I will try it.

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Nelson Diagnostician
North Carolina
Nelson
 

Be sure to check for any distributor shaft end play causing the loss of ignition. I remember an older, high mileage Ford Ranger years ago than caused me to chase my tail a while on a similar problem. A new distributor shaft was the fix

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Brandon Diagnostician
Pennsylvania
Brandon
 

Nelson, Viewing the waveforms it can be seen that the coil primary remains grounded at the time the stall occurs. This proves the fault is not a loss of ignition do the shaft play but A control issue. The coil circuit is shorted on the control side. Whether the short is internal to the control unit, the coil itself or the circuit in between is what is to be found

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Robert Diagnostician
California
Robert
 

If I have a current flow, I will check for current flow at the positive side of the coil and also by the module. That will help narrow down what is causing the grounding. If it is the module, why? It is the second new module on the car doing the same thing.

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Brandon Diagnostician
Pennsylvania
Brandon
   

Been there more than once. But, that is the beauty of testing, ”no guesswork”! if you monitor current at the module, ans voltage at the coil negative, it will tell the ENTIRE story. the voltage will say when the fault is present and the current will say one of two things: -“its the module” Or -“its NOT the module”

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Robert Diagnostician
California
Robert
 

Unfortunately, my gut is telling me it is junk aftermarket china parts. I did find new old stock Motorcraft modules on eBay, So maybe there is hope.

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Brandon Diagnostician
Pennsylvania
Brandon
 

Why are you going with your gut? Perform a test to prove it, Robert. It’s a simple as that. There is absolutely no need to guess, that’s Makes no sense. Especially on a site like Diag​.​net  Besides proving the fault you will also learn something. A valuable test that applies to everything we work on

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Robert Diagnostician
California
Robert
 

I will test it and find out, I just think the test may show the junky aftermarket parts we have to deal with. If it is something else great I will fix that.

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Brandon Diagnostician
Pennsylvania
Brandon
 

AWESOME!!! 🤜🏻🤛🏻😎

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John Mobile Technician
Illinois
John
 

Robert, I have a few observations regarding your pattern. The voltage seen in the primary pattern after the spark line and oscillations is about 17.5 volts. This is open circuit voltage, and should be charging voltage. There could be a few reasons for this; the location of your scope ground, overcharging, a battery charger is connected, or maybe a bad ground. If you take a close look at the…

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Interesting
Agree
Helpful
Thanks
Robert Diagnostician
California
Robert
 

Great catch! I looked at where it starts to fire again at the end of the waveform and see the voltage coming back down again. Maybe I have a voltage drop on the ground circuit causing the trigger voltage not to be crossed on the module.

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Ugwoke Owner
Singapore
Ugwoke
 

For what i observed from what you narrated is that the PCM is not ok you have to fix another one

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Robert Diagnostician
California
Robert
 

This jeep was sitting for 20 yrs, so may have corrosion on some of the grounds. The scope was hooked to the battery so the negative voltage readings could be grounding problems between the body, engine and battery. The module is bolted to the fender but grounded to the distributor. the MCU(PCM) is behind the glove box, and I will need to find out where it is grounded.

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Gary Owner/Technician
Colorado
Gary
 

Good catch, John Battery to engine ground is just behind the distributor and he should have a body ground to the engine somewhere in the same area…

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Robert Technician
Oklahoma
Robert
 

Does this have a factory tachometer I had a simular problem yrs ago and bypassed tach and problem gone. Also check grounds around right side of block/ head they would be loose I found on middle to back side of head also check pick up coil in dist found some that rivets come loose and pick up hits trigger wheel

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Robert Diagnostician
California
Robert
 

Has an aftermarket tach that I unhooked to see if the problem would go away and it did not. Will be checking all the grounds on Monday after seeing the voltage shift in the waveform.

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Robert Technician
Oklahoma
Robert
 

what engine is in jeep

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Robert Diagnostician
California
Robert
 

4.2l in the car build info.

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Gary Owner/Technician
Colorado
Gary
 

Robert, Your battery to engine ground should be on the side of the block just behind the distributor. This is also where the ECM is usually grounded. You should also have a battery to body ground and a ground strap around the RH engine mount from block to frame. If the engine has ever been removed, one or more of these grounds is usually missing….

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Robert Diagnostician
California
Robert
 

The Battery to body ground was broken when the jeep came in. I fixed that one when I put the new battery in. I have not checked/cleaned the others. I suspect I will find them loose/rusted or missing.

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Gary Owner/Technician
Colorado
Gary
 

Going back to John T's observation on grounds, Quite frankly, I didn't look closely at your waveforms because too many scopes on these forums aren't set up to correctly read signals. But I had a Ford TFI (later model ignition system) lose spark because the module wasn't pulling the square-wave signal all the way to ground. The engine would die during warm-up and recover. It took me a while with…

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Robert Diagnostician
California
Robert
 

I am thinking of hooking up 3 of the channels to the different grounds and the ignition. Start it and see what voltage drop I read on the different grounds till the problem occurs. Then clean and add redundant grounds if needed and recheck. I think it will be interesting to see the results.

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Gary Owner/Technician
Colorado
Gary
 

That would be a good learning experience, to say the least. The most important thing I've learned from 40 years of troubleshooting electronics is first, have a battery in good state of health and state of charge. Trying to boost a bad battery for diagnostic purposes will corrupt the diagnostic process. It's also a waste of time because I've had some PCMs lose their adaptive memories and…

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Robert Diagnostician
California
Robert
 

I have the feeling the engineers of Dura Spark set the thresholds of the switching control voltage too close to the min and max of the signal. So voltage shifts from bad grounds can break the system. That signal is going into negative voltage and I have no idea how that affects the internal calculation by the module. Modern day communication lines set the on-off voltage well within the range of…

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Gary Owner/Technician
Colorado
Gary
   

Back 1974 when Dura Spark was introduced, practically all OEM modules failed within 50,000 miles. Ford's only solution was to change the coil because they felt the coil primary winding could be shorting and drawing too much amperage through the module. Of course, all we had back then were big-box ignition scopes that had no lab scope capacity. Our testing was limited by what little service…

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Bentley Manager
California
Bentley
 

Both the primary voltage and module control, when grounded, go below the 0 volt level and their voltages rise as the are held to ground, are both of these events caused by a bad ground or grounds?

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Robert Diagnostician
California
Robert
 

The scope was grounded to the battery negative. So it a component has a bad ground, and tries to ground something my scope will read the difference between its ground and battery ground. As the ground heats up and gains resistance, the component will start losing ground and the voltage will rise. A good example of that is some of the newer O2 sensors that have a floating ground in the computer…

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Randall Technician
Pennsylvania
Randall
 

Robert, Don’t trust any of the grounds, take them apart and clean all you can find. Battery to engine to body to frame all need to be equal. I believe that you will find it. Randy

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Ray Diagnostician
Ontario
Ray
 

Looking thru my files, I found this capture of an 82 jeep 6 cyl. HTH

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Robert Diagnostician
California
Robert
 

Must be federal emissions, you don't have the square wave signal from the computer. The current ramping is helpful for when I check it tomorrow.

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Gary Owner/Technician
Colorado
Gary
 

Hello, Ray. Robert is right, this is a 49-state federal emissions configuration. The current ramp seems to be right on the money at ~5.0 amps as is the pickup signal…

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Troy Owner/Technician
Washington
Troy
 

I ihad kinda the same senerio 4.2 jeep had been sitting for 20 years customer wanted to drive it and after carb replacement I was still having issues, behind the battery there was or is a resister pac that the battery acid took out and I want to a local computer ship they gave me the resisters I needed and the ground at the block to battery was bad after that all was well

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Stephen Owner/Technician
Ontario
Stephen
 

this sounds like parts cannon but my experience with those older ford ignition systems was that ignition modules and coils should be changed as a pair​.​On more than 1 occasion I have changed a module only and had a faulty coil take out the new module.

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Gary Owner/Technician
Colorado
Gary
   

You're entirely correct, Stephen, as per Ford's recommendations back in the day, bad coils were part of the problem. Practically all of the initial crop of Ford Dura Spark modules failed very early. The standard test was to thump the module with a soft hammer and if the engine started and ran, the module was defective… :0)

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Robert Diagnostician
California
Robert Resolution
   

Well, I hooked the scope up this morning and the jeep started and ran fine and did not cut out. I did take some captures and this is what I got. diag​.​net/file/ff7ixqssr… diag​.​net/file/f2gt7x4te… The engine ground has lots of noise when the RPMs are raised up. Also, the battery voltage is about 18 volts. Yes, I confirmed that the voltage at the battery was 18 volts. I cleaned the grounds at…

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Randall Technician
Pennsylvania
Randall
 

Robert, Old feedback carburetor systems, sometimes used a coolant temperature switch for closed loop. Some remain in open loop at idle. Sometimes the vacuum switches want to see steady part throttle loaded cruise. I think that the Mixture control is an air bleed on these. If you have a S.O. Vantage the component tests usually describe the functionality of each device. Even for stuff this…

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Gary Owner/Technician
Colorado
Gary
   

Grounds make a huge difference, Robert. The alternator was over-charging because it couldn't accurately sense voltage. As Randall S. said below, feedback carbs had to see at least 160*F. coolant temperature to go into closed loop. I would begin by changing the oxygen sensor because most back in the day were contaminated by silica and ethyl lead in the gasoline and by phosphorus in the engine…

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Robert Diagnostician
California
Robert
 

Even with the grounds fixed the alternator was still overcharging. After I replaced it the voltage was normal. I put a rebuilt carb on it already since the automatic choke was frozen in the choke stat part. I had tried soaking it in penetrating oil, but would not free up. I would not be surprised if the coolant temp switch is bad and causing it not to go into closed loop. I need to pull up the…

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Gary Owner/Technician
Colorado
Gary
   

Sounds like you have multiple problems related to age and neglect. I've serviced these old Jeeps since they were brand-new. Even the fuel control system is pretty simple. They're not hard to repair providing nobody has deleted all the emissions controls…

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Robert Diagnostician
California
Robert
 

Well, I was checking the fuel control and it never went into fuel control. The temp switch did close at 157 deg and the blue wire showed .07 volts and there was a battery voltage supply before grounded. I hooked up the snap-on scanner and had to tell it that the jeep is an 84 jeep cj7. The data showed it going from warm to cold and back and forth. The voltage on the blue wire did not change. If…

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Randall Technician
Pennsylvania
Randall
 

Robert, I couldn’t get the video to run on my iPhone. I can try tomorrow on my PC. When dealing with pre-OBD2 and an aftermarket scan tool, I don’t put 100% faith in the data. Need to find what all is needed to enter closed loop. Besides temperature, possibly a specific amount of time?vehicle speed? The proper vacuum level at the switches, and the WOT switch not indicating full throttle. I am…

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Gary Owner/Technician
Colorado
Gary
 

I can't read your video because it's vertical rather than horizontal. I'll pull up a wring diagram tomorrow morning. If I recall, you should have a temp sensor for the dash gauge and a two-wire sensor located just ahead of the carburetor for the ECT data. Again, if I recall from working on my 1983 CJ7, a disconnect should show -40F. and jumping the two wires should show nearly 300F. on the data…

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Robert Diagnostician
California
Robert
 

It uses a temp switch to tell the computer it is up to temperature. I tested the stepper motor for power to it and through each step motor. With the temp switch closing and grounding, the computer never tries to control the mixture. When I have worked on other Ford feedback carbs, when you raised the RPM up to 2500 the stepper motor would move in and out as it was controlling the mixture. The…

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Randall Technician
Pennsylvania
Randall
 

Robert, I am seeing a six pin connector with 5 wires for the mixture control. It does show separate idle and part throttle solenoids. Connect your scope to watch both solenoids and the O2 sensor. As you indicated the part throttle solenoid (pins1&2) should have varying voltage fully warm and over 2500 rpm. The idle solenoid (3&4)should be varying at idle. If not what O2 sensor voltage…

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Robert Diagnostician
California
Robert
 

I already installed a new O2 sensor and it reads .9 volts. I have not tried grounding the o2 sensor wire to see if I get a response. I will check the other switches to see they change when they should. At the end of the day, I pulled out the MCU and cleaned the connections at the computer, and blew the dust and dirt off the circuit board. The mixture stepper motor has not moved in or out and is…

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Randall Technician
Pennsylvania
Randall
   

Robert, Check for open circuit bias voltage. I am thinking MCU system is.5v But it could be 5v. Think of the zirconia O2 sensor as a battery, it generates its own voltage. Randy

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Gary Owner/Technician
Colorado
Gary
 

As long as the O2 sensor is reading .9 volts, the stepper motor will be in the wide-open position trying to lean the mixture out. Pull a vacuum hose or lean the idle mixture out by turning in the mixture screws 1-2 turns and see if the stepper motor extends.

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Gary Owner/Technician
Colorado
Gary
 

Robert, your Jeep should have a single-wire zirconia O2 sensor. I assume you have a new O2. If you don't, your old one is likely contaminated with silica and ethyl lead if it's the OE sensor. The contamination seals the sensor thimble and kills the voltage output. At idle, the O2 cools below 700*F. and won't generate a signal. At 2,500 rpm, theO2 should be generating a signal because it's at…

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Robert Diagnostician
California
Robert
 

It is a one-wire sensor and it is new. I am using my fluke to read the voltage when checking for fuel control. After cleaning the connections at the computer and blowing it out. I started it at the end of the day today and warmed it up. The temp switch closed and it did not go into fuel control. I tried grounding the O2 sensor wire to see if I could get the computer to do anything. The sensor…

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Randall Technician
Pennsylvania
Randall
 

Robert, Unplug the O2, check for bias voltage from the computer. Without being able to see the O2 in a data list it is a clue if the computer is capable of recognizing the 02. Randy

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Gary Owner/Technician
Colorado
Gary
 

Robert, I'll look at the ECT on a wiring diagram in the morning. The ‘83 CJ I was working on had a Howell (General Motors throttle-body) injection conversion, so none of that information really counts. Had a busy day, I have a tough electronic problem to solve on a ’98 Dodge automatic transmission at our local transmission shop, so I feel for ya… :0)

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Gary Owner/Technician
Colorado
Gary
   

Robert, just a reminder: These old systems aren't looking for O2 sensor activity for going into closed loop. What they are looking for is an absolute minimum of 160F. coolant temperature. I'd check the coolant outlet temperature for thermostat function. Should be around 180*F. I think the carb might also have a nose switch to indicate off-idle before it goes into closed loop. Might check for…

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Robert Diagnostician
California
Robert
 

There is no other throttle switches, and it is warming up enough. I added 100 ohms of resistance and the computer is happy to say it is warm. I have a feeling the grounded switch was pulling too many amps for the old computer and it was cycling the biased voltage causing the cold-warm toggling. Still have not gotten the feedback system working yet, but have another carburetor coming to see if…

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Ray Diagnostician
Ontario
Ray
 

This has some info on Open and Closed loop.

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Robert Diagnostician
California
Robert
 

Great information! Thank you!

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Robert Diagnostician
California
Robert
 

Update: After installing the computer back in I started it and tried hooking a resistance decade box to the temp switch wire. When not grounded it reads cold and when grounded it toggles between cold and warm. So I put 10 ohms of resistance and it stayed warm. I added 100 ohms and it stayed warm, but when I added 10k ohms it switched to cold. So I changed it back to 100 ohms and tried to see if…

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Gary Owner/Technician
Colorado
Gary
 

Hello, Robert. I looked at my diagrams today and they turned out to be the old black-and-white factory wiring diagrams with the 4-cylinder system superimposed over the 6-cylinder system. So it's hard to read. I did notice that the ECT is a single-wire sensor, other than that, the diagrams were more confusing than informative. I also didn't see a California certification. Back in that day, the…

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Robert Diagnostician
California
Robert
 

It has a WOT switch and that is it. The O2 sensor is reading .9 volts till I snap the throttle and on decel goes to .1 volt. I am hoping the replacement carb has a good stepper motor. The stepper motor seems stuck on the rebuilt carb I put on. Do you know how it pulses the stepper motor to move it? I was trying to ground each one in a circle around the connector to get it to move, first…

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Gary Owner/Technician
Colorado
Gary
 

I saw the WOT on the wiring diagram. I can't tell you how it pulses the stepper motor. On my diagram, it shows only two wires on the stepper. That doesn't seem correct. I test the stepper by creating a major vacuum leak (lean) or squirting some carb or throttle body cleaner or propane into the carburetor (rich). The stepper motor should respond to extreme rich or lean by changing direction.

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Ray Diagnostician
Ontario
Ray
 

There are 3 tests for the stepper motor and the first photo is test 1, the second photo is test 2 and the third photo is test 3

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Ray Diagnostician
Ontario
Ray
 

The first photo is the 02 sensor test 1 and the second photo is test 2 The third photo is the stepper motor connector and the fourth photo is the MCU connector. The last photo is the wiring diagram.

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Robert Diagnostician
California
Robert
 

Good information! I got another Carburetor and took the stepper motor off it and hooked jumper wires to it to test it. I was able to get it to move in and out grounding the different terminal in sequence. I couldn't do that with the one on the jeep. The one that worked was an original stepper motor and the one on the jeep was a replacement one. I also noticed that when I hooked my test light to…

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Robert Diagnostician
California
Robert
   

Well, I got a “new” in the box MCU from Deadjeep​.​com The box looks 37 years old and after I cleaned off the dust on the connections I could see it had been plugged in before. This was old stock from a dealership that they had bought, so I guess they tried a new module to see if it fixed a jeep years ago and the part sat on the shelf. I plugged it in and had someone tap the starter and…

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Gary Owner/Technician
Colorado
Gary
 

Hello, Robert, My experience is that the old Ford computers (unlike General Motors C3) were pretty durable units. In fact, during 35 years of working on these vehicles, I've replaced only maybe 3-4 of these computers in 35 years, compared to a boat load of GM computers. My 1985 Ford 4x4 Ranger which I bought brand-new and just recently restored, has a 2.8L engine with a Motorcraft feedback…

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Robert Diagnostician
California
Robert
 

What use Lewis's favorite tool! I will pull out the WPS and hook it to the Pico and take a vacuum reading. LOL

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Gary Owner/Technician
Colorado
Gary
   

While I have a half-dozen scopes and several transducers in my tool box, I'm a big believer in Keep It Simple, Stupid (KISS) by using a vacuum gauge to adjust idle mixture on a carburetor. Nothing to zero, don't have to interpret waveforms. Just look at the needle. Duuuh… Keep in mind that Lewis and I were fixing these "new" 1983 Jeeps with a vacuum gauge and a Fluke 88 long before Pico ever…

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Thanks
Robert Diagnostician
California
Robert
 

Back when I started working on cars (1988) I had to tune a few for emission testing. I used my ear and carb cleaner to adjust the carbs. I have not used the Vacuum gauge enough, because I did not have a mentor to show me that. This jeep has the feedback so I will need to adjust it so the mixture control is in the same area as at the cruise speed. I don't want the hesitation of it being too lean…

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Olle Instructor
Minnesota
Olle
 

Interesting how the module is re-energizing the coil before the falling edge of the square wave from the MCU.

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Robert Diagnostician
California
Robert
 

Well after fine-tuning the Carb, getting the Exhaust replaced and the Air injection connected, fixing the O ring in the rollover valve it finally passed the California Dyno Emission test. the Jeep is finally going home!

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Ray Diagnostician
Ontario
Ray
 

Good work Robert!

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Gary Owner/Technician
Colorado
Gary
 

Congratulations, Robert! That certainly was an uphill battle all the way… :0)

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