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Thread: Intermittent Spark

  1. #21
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    Re: Intermittent Spark

    Hi, forum. I have a similar problem: 1993 Chrysler LeBaron AA body, 3.0L V6, new manual 5-speed transmission installed 2.5 years ago. Driving along at 55 mph when suddenly the engine quit. There was no juddering, no hesitation, just instant stoppage when it quit, as though the key had been turned off.

    The problem has been traced to no spark. Coil input indicates max of 5v. during cycling. All wire and hose connections I've examined look good. Key: I get no diagnostic codes from the ignition-switch method. The engine light does not come on; only the Check Gages light. All gauges work fine. Cranking 5-10 sec. gives an indication of oil pressure, so the oil sender is okay.

    Disconnected battery for 1/2 hour. Wiggled all wires I could reach. Reconnected battery and while cranking to reestablish possibly lost diagnostic codes the engine started, ran like a top, and 20-30 sec. later quit again. Still gave no diagnostic codes and no 'Check Engine' light.

    I heard a slight moaning sound coming from the right side of the engine compartment while cranking the engine right after it quit after 20 seconds in the above example. The engine light came on briefly and then went off. It has remained off ever since.

    I have all the books and am following the specific instructions in the "Electrical, Fuel & Emissions" book, section 14. Everything I can reach all seems good. There are a few wires I can't get at (snow; wet ground; carport, not garage). Accordingly I have questions:

    1. Would a diagnostic tool get codes I can't get with the ignition key?
    2. I have not, for the past 3-4 years, ever had any sort of alcohol in the gas. Our premium here is alcohol-free. Could this engine stoppage be the result of icing/water? [Temperatures have been below freezing at night and up to just over 30 in the day. The car had been running about 10 minutes down the highway when it suddenly quit.]
    3. I put a can of Heet into the tank last night, which currently is 3/4 full. I.e., 10-12 gallons or so. I cranked the engine for 5-10 seconds to try to circulate the Heet and then let it sit overnight. Today still no luck.
    4. What's the 'LM' mentioned in this thread?
    5. Any ideas?
    Thanks to you all for your kind help in the past.
    ..........RayO

  2. #22
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Intermittent Spark

    The LM is the Logic Module. It's the computer in the passenger compartment of the cars from 84-87. Your 93 should be SBEC II. That's the computer by the battery.

    I don't think you'll get anything from a scanner that you wouldn't from the key dance.

    Does anything else die when the engine dies? I would test the ASD relay to ensure that it's good. I would also check for power there when cranking. As mentioned earlier in the thread, I've had a lot of problems with ign. switches, especially the style in the 90+ columns. I had a Shadow which would kill those switches, but it would cause a lot of intermittent issues before they would finally die for good. My blower motor would draw too much current and kill that bus in the switch. That happened to also feed power back to the ECU and some other important bits. The radio and lights would work though. It was weird.

  3. #23
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    Re: Intermittent Spark

    Thanks a bunch. I too suspect the ASD. It's original, i.e. 27 years old. I still have the original PCM from the auto transmission and plan to try substituting it in a day or so when we get some reasonable weather here in east Idaho. Winter hangs on! Seems like I saw a comment somewhere in this forum that the old relays go to pot in a drastic manner and ought to be replaced. My cooling fan, as one possible example, runs fine if I put power to it, but it has not run automatically in years. Is it the relay??? We shall see. BTW, I'd have answered you last night but it seems the forum doesn't have my new email, which I changed two years ago. I requested help from a moderator how to start a new thread (haven't been here in a couple years) and got no answer. Therefore I tacked this onto this thread.
    Everything else but the engine seems to work just fine. Radio plays, seats move, heater motor is okay. If I disconnect the power to the purge solenoid I get one instance of an error code (12), but it won't repeat. The engine light goes out and won't come on again. Perhaps another clue?
    Thanks again for your notes.

    .........Ray
    Last edited by RayO; 03-17-2020 at 07:14 PM.

  4. #24
    Super Moderator Turbo Mopar Staff 135sohc's Avatar
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    Re: Intermittent Spark

    Code 12 is the battery has been disconnected and the computer senses that. Totally benign unless you did not pull power.

    A scanner will not provide any additional codes in this situation but it will give you a glimpse into what the computer is seeing from the various sensors.
    1994 Shadow Sedan. 2.2 N/A, A568 400,000 miles. "the science experiment"
    1987 Shelby CSX #418. Long term rebuild and restore ?

  5. #25
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    Re: Intermittent Spark

    Seems that RayO and I are in the same boat. I have just replaced the coil with a new one and still quits without warning. No codes. I am leaning towards a faulty ASD and found out that in my 86, it is part of the PM. I replaced the PM with one that I have from another car with no improvement. I have ordered a new ignition switch which will be here Friday. I am at a complete loss and ready to sell the car. Breaks my heart to say that, because when it runs, it runs beautifully and is a pleasure to drive. I just need something that is dependable and reliable to drive and I am losing patience with it.

    - - - Updated - - -

    A new LM perhaps?

  6. #26
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    Re: Intermittent Spark

    elmor353, you have my sympathies. I have an alternate car which is 45 years old and has no computers: 74 LandCruiser that I bought new. If I could entirely eliminate the computers and gadgets in my Chrysler I'd be ecstatic. [Same goes for all the automatic crap in Windows 10 Pro, by the way.] After I got the five-speed manual trans in and started driving the car, I had the problem of the engine stopping after I drove 30 miles to town and hit the first stop sign. The engine would just quit. This went on until I traced it to the new air intake (23 percent larger and a vast improvement in power), which had its inlet flap not quite in the right position. When I fixed that, the trouble went away. Before I found the problem I could keep the car running by revving up the engine at the stop signs, but that wasn't right. Along the way I replaced a lot of other components and found the thermostat had been locked open for several years. Onward....
    .........R

  7. #27
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Intermittent Spark

    I would definitely try another computer before you sell the car guys. The v6 SBEC IIs are all over the place and dirt cheap still.

  8. #28
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    Re: Intermittent Spark

    Well, I got my car running. Have not driven it anywhere yet, but it seems to be very much okay. Bottom line, I replaced the second-hand PCM, the computer for manual transmissions, with the original PCM for the car's original automatic transmission. But I also did several other things that may have contributed. I took off the three relays, for the Automatic Shut-Down (ASD), the Radiator Fan, and the Air-Conditioning. I cycled these with a 12-volt supply (battery charger) and checked resistance across the two terminals that are connected when power is applied. The resistances were all zero ohms with the relays closed. In the course of doing this I cycled the relays a bunch of times. Did that help? No idea. The relays all looked excellent inside (at the base, not inside the box). All three relays are original, i.e., 27 years old. (Approx 115,000 miles.) They've never been replaced. Mom bought the car new and I've had it since 1994, so I know its entire history.

    One 'trick' I applied to the relays, to all the connectors I could get apart, and to all 60 sockets in the PCM connector was to anoint them with a radio-repair fluid called DeoxIT. This is a red liquid called D100L produced by Caig Laboratories [www.caig.com or www.deoxit.com]. This is designed for all metal-to-metal electrical connections such as the pins of tube-type radios and in our cars. A small bottle of this will last lifetimes. I have a 25 ml bottle and in 15 years or so have used a quarter-inch of it, about 15-20 percent of the contents. I see this sells today for $35 a tiny bottle. Is it worth it? It seems to have helped my short-wave radios work better when I rebuilt 'em. Did it help the Chrysler run? Or was it all the PCM? I don't know, but I'd feel stupid if I hadn't used this stuff on all the connections.

    Thanks to you all for your help once again. I hope you all get your problems solved. In the course of inspecting my old car I saw things like rusty gasoline lines that oughta be replaced. So maybe there's a purpose in these happenings. One hopes so. If you're housebound and want a good read, check out "Border Caper" at Amazon.

    .........Ray

  9. #29
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    Re: Intermittent Spark

    Quote Originally Posted by RayO View Post
    Well, I got my car running.
    Excellent news
    I also have Deoxit 5 on my shelf.
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  10. #30
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    Re: Intermittent Spark

    Does anyone know where I can get a top-quality PCM for the 5-speed manual transmission? The auto-transmission PCM is okay but the other gives 500 more rpm and supposedly idles better on cold mornings. FYI, I attempted to pull apart the suspected and very dirty faulty PCM module only to discover it's encapsulated. So I can't look to see what might have failed on it. All that shows is three items that are heat-sinkable (only two sinks), the tops of three capacitors, and a small transformer. I dug into the corner to remove the yellow jello and, while I could rip this all apart for my own edification, I have better things to do. But there's a computer board buried there.
    .........Ray

  11. #31
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
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    Re: Intermittent Spark

    deoxit is the bomb. ive used it for many years to keep all sorts of old vehicles electrical connections going.

    it works well on LM connectors too.

    Brian

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

  12. #32
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    Re: Intermittent Spark

    Quote Originally Posted by Aries_Turbo View Post
    deoxit is the bomb. ive used it for many years to keep all sorts of old vehicles electrical connections going.

    it works well on LM connectors too.

    Brian
    Have you tried the shield version?
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  13. #33
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
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    Re: Intermittent Spark

    not yet. i have the d5 red and gold.

    i ordered some for work too. its cut down our cable replacement in classrooms considerably.

    Brian

    Quote Originally Posted by turbovanman
    This one is easy, I have myself to blame, I rush things, don't pay attention to gauges when I should, change to much stuff at once then expect miracles, the list is endless.

  14. #34
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    Re: Intermittent Spark

    Update. I messed with the ignition switch yesterday and it fired up. Took it out and drove it around for about 20 minutes and it seemed to run okay. Did an 80 mph blast down the freeway and back home. I'm still a little leery about going very far with it, just a little gun shy still. Going out in a few minutes to run some errands and see how it goes today. I will let you all know what happens. Thanks guys.

  15. #35
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    Re: Intermittent Spark

    Okay, I am back at square one. Took it out this afternoon. Ran great for the first 15 minutes and then left me sitting at the side of the road. Tried a jumper wire from + side of the battery to + side of the coil and got nothing from the fuel pump. I thought perhaps, that the system was still pressurized. Sat there for 30 minutes trying to wiggle every wire and connection possible and nothing. Tried starting it many times and it would just crank. As I was about to start walking towards home, I gave it one more shot and it fired. As I was pulling into my driveway, it quit again. I am beside myself. I have replaced the HEP, LM, coil, PM, ignition switch and I've checked all my grounds. I replaced the PM with a spare that I had. I suppose that it's possible they both have an issue, but it's highly unlikely. The car runs sweet, when it runs, but I am to the point that I don't know what else to do. Yes, I have sprayed my connections with DeoxIt. I love driving it, but I don't trust it as far as I can throw it. It's a straight, solid car with no rust anywhere. Has a nice leather interior without any tears. I am at the point of being so frustrated that I am considering putting it up for sale, along with my spare engine and trans and looking for something reliable.

  16. #36
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    Re: Intermittent Spark

    That's great. You have an intermittent problem with the wiring to the pump or pump itself at the least. If you tried to jump the coil and the pump didn't fire right up, I would start with a fuel pressure test. If you hook up a gauge, jump the pump (when it's working) and pinch off the return line you'll probably get well under 80PSI which is the minimum I would look for in a good pump.

    Again, since the jumper wire from the battery to the coil is all that's needed to fire up the pump, you know there is a problem there. I would strongly suspect the pump itself.

  17. #37
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    Re: Intermittent Spark

    I haven't specifically looked in depth at the NY'er wiring harness, but if it is wired similar to L-bodies, this could very well be your issue. Your problem is more than likely in the Z1 circuit, esp. since you've changed out the PM and Hall Effect without finding a permanent solution. This is a dark green with black tracer wire. I recently helped a friend over the phone diagnose his GLHT that also abruptly died much like yours. He quickly narrowed down the problem with me assisting him while on the phone, after doing a few continuity tests. He found his problem where the two wires from the Z1 circuit meet at the bulkhead connector as they pass through the firewall. In his case, the wires pulled away from the connector, no longer being locked in place. Other times, I have found this connector to be very loose, also causing intermittent problems. He was slightly electrically challenged, but found the issue and repaired it easily. Assisted another guy on TD with this same exact problem recently too. Here are a couple pics from our correspondence.
    That green with black tracer wire circuit powers the fuel pump, injectors, and also provides power to the positive side of coil. They tie together from the left and right side of the car at this connection. That's why there are two wires in photo. Think of it as a splice. I would locate these wires and give a tug on them to see if their still connected to the bulkhead connector securely.
    Hope this info helps,
    Todd
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  18. #38
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    Re: Intermittent Spark

    Quote Originally Posted by 4 l-bodies View Post
    I haven't specifically looked in depth at the NY'er wiring harness, but if it is wired similar to L-bodies, this could very well be your issue. Your problem is more than likely in the Z1 circuit, esp. since you've changed out the PM and Hall Effect without finding a permanent solution. This is a dark green with black tracer wire. I recently helped a friend over the phone diagnose his GLHT that also abruptly died much like yours. He quickly narrowed down the problem with me assisting him while on the phone, after doing a few continuity tests. He found his problem where the two wires from the Z1 circuit meet at the bulkhead connector as they pass through the firewall. In his case, the wires pulled away from the connector, no longer being locked in place. Other times, I have found this connector to be very loose, also causing intermittent problems. He was slightly electrically challenged, but found the issue and repaired it easily. Assisted another guy on TD with this same exact problem recently too. Here are a couple pics from our correspondence.
    That green with black tracer wire circuit powers the fuel pump, injectors, and also provides power to the positive side of coil. They tie together from the left and right side of the car at this connection. That's why there are two wires in photo. Think of it as a splice. I would locate these wires and give a tug on them to see if their still connected to the bulkhead connector securely.
    Hope this info helps,
    Todd
    This is a great suggestion.

  19. #39
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    Re: Intermittent Spark

    There are some other points in the Z1 circuit, after passing through the firewall connector, it runs over to the left side of the dashboard into a 25 way connector. Again the connectors can lose strength or get corroded causing the fuel pump to not receive power. In the rear of the car, there is a connector possibly under the rear sea or in the front of the trunk where the left side body harness branches to the fuel pump and gas gauge harness, it will probably be a square 4 pin connector and one of the wires may go to ground at that area. The Z1 and ground are the fuel pump feed and power ground. Under the car are 2 molded rubber plugs on the back side of the fuel tank, the one on the larger of the 2 round "covers" for lack of a better term, will have a 2 pin molded rubber plug with Z1 and a ground (Chrysler used a gray ground wire color on a lot of these cars) this is another problem point as it is underneath and was a waterproof connector 34 years ago. Rust on the pins or the connector "sockets" basically a two sided spring slot the pins go into will cause problems.

    If you find any of the inside the car connectors with discolored pins, that is a sign of being hot due to high resistance.

  20. #40
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    Re: Intermittent Spark

    Okay, that's some good information to start checking out. I myself, am electrically challenged. I see wiring diagrams and get cross eyed. I will start at the firewall connectors and work my way back to the tank. I know that my 77 Dodge pickup has had many issues at the bulkhead connectors, so it makes sense that it could be a problem here. And considering that the car is 35 years old, Lord only knows what things look like underneath at the tank. I will start checking things out and report back what I find. Thanks guys.

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