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Thread: Difficult Ignition Cutout Problem

  1. #101

    Re: Difficult Ignition Cutout Problem

    I haven't read through the whole thread, but right now you still having the car stumble. Have you determined what you are losing when this happens? ie. You need fuel, spark and compression. Starting with the assumption that you are not losing compression (ie. valve hanging open.) That leaves fuel and spark.

    Fuel: a fuel pump failing will behave similar to what you describe. Fuel pressure gauge hooked up will tell you that. Bad injector driver/wiring harness issue could cause something similar. Wiring (backprobing or piercing probe) a light in you can see if there is complete failure. Oscilloscope would show sporadic issues. If it is a wiring harness issue, you might be able to press on the harness lightly and get it to happen at idle...

    Spark: Again you could wire in some test lights and see if power to the spark or ground side switching goes away.

    Once you figure out what is going away, you can determine the why it is going away...

  2. #102
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    Re: Difficult Ignition Cutout Problem

    I just read the whole thread. If you have a laptop and USB data cable, try connecting with MPScan and create a layout of just all the inputs to the LM (MAP, O2, CTS, TPS, Knock, Batt Temp, etc..). Inspect each value and be sure the ranges and behaviors match expectations. This may not yield anything useful, but given the magnitude of effort already given...

  3. #103
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Difficult Ignition Cutout Problem

    Quote Originally Posted by c2xejk View Post
    I haven't read through the whole thread, but right now you still having the car stumble. Have you determined what you are losing when this happens? ie. You need fuel, spark and compression. Starting with the assumption that you are not losing compression (ie. valve hanging open.) That leaves fuel and spark.

    Fuel: a fuel pump failing will behave similar to what you describe. Fuel pressure gauge hooked up will tell you that. Bad injector driver/wiring harness issue could cause something similar. Wiring (backprobing or piercing probe) a light in you can see if there is complete failure. Oscilloscope would show sporadic issues. If it is a wiring harness issue, you might be able to press on the harness lightly and get it to happen at idle...

    Spark: Again you could wire in some test lights and see if power to the spark or ground side switching goes away.

    Once you figure out what is going away, you can determine the why it is going away...
    I think I'm most definitely losing spark, as the tach cuts out when it does this. I'm not sure the cause, but it apparently causes the computer to freak out and kill the ASD relay.

    Quote Originally Posted by jpcturbo View Post
    I just read the whole thread. If you have a laptop and USB data cable, try connecting with MPScan and create a layout of just all the inputs to the LM (MAP, O2, CTS, TPS, Knock, Batt Temp, etc..). Inspect each value and be sure the ranges and behaviors match expectations. This may not yield anything useful, but given the magnitude of effort already given...
    I'll try to hook up my MPSciLink device again. It was running well enough yesterday that I thought about getting it going. I should probably take the power from the battery to avoid it resetting when the ASD dies. It seems to reset and not be able to connect whenever the miss happens anyway.

    I'll be reading up on on using an oscilloscope over the next couple of days. I will have everything to install the later K frame and front suspension for my minivan arriving, but after that, the Lancer is the full time gig.

  4. #104
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Difficult Ignition Cutout Problem

    Cordes, can you give a better description of when it is cutting out?

    I've read through the thread and best I could find was when you were merging into traffic.

    So is it only under acceleration? (load) that this happens? Any specific RPM?

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  5. #105
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    Re: Difficult Ignition Cutout Problem

    Quote Originally Posted by Shadow View Post
    Cordes, can you give a better description of when it is cutting out?

    I've read through the thread and best I could find was when you were merging into traffic.

    So is it only under acceleration? (load) that this happens? Any specific RPM?
    Unfortunately, this is the most random problem I've ever had. It does it more often than not when under load, but there have been many times which the car could hardly run around the block. It also seems like it could happen more often with a throttle input, but it does it plenty at other times too. It has struggled to run at idle in the driveway many times. It's the worst electrical problem I've ever been a party to in any way.

    I have a 4 channel oscilloscope now. What should I log? Power to the LM? TPS? HEP? I have an inductive pickup for ignition which came with it. and enough probes to be dangerous. I don't think the momentary problem can escape me now. It's just a matter of trying to most efficiently determine what's going wrong and how to work back to the source.

  6. #106
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    Re: Difficult Ignition Cutout Problem

    Seems like itís still not determined if the cutout is spark or fuel related.
    I would hook up a fuel pressure gauge and tape it to the windshield.
    the O scope channels I would pick would be:
    HEP
    Secondary ignition inductive pickup on coil wire
    Power supply to LM
    MAP sensor

    i feel like one of those would catch the issue. If not directly, then indirectly. Example, you could tell a lot of the engine is running rich or lean by a change in secondary ignition pattern and that could lead you down the right path. I found a similar issue on my Charger once by reading secondary ignition.

    - - - Updated - - -

    Seems like itís still not determined if the cutout is spark or fuel related.
    I would hook up a fuel pressure gauge and tape it to the windshield.
    the O scope channels I would pick would be:
    HEP
    Secondary ignition inductive pickup on coil wire
    Power supply to LM
    MAP sensor

    i feel like one of those would catch the issue. If not directly, then indirectly. Example, you could tell a lot of the engine is running rich or lean by a change in secondary ignition pattern and that could lead you down the right path. I found a similar issue on my Charger once by reading secondary ignition.

  7. #107

    Re: Difficult Ignition Cutout Problem

    On the scope, did you also get a means to access the signals in the wires? ie a piercing probe or a means to back probe? (T-pins from Wal-mart can be a good way to back probe a connector.)

    Given that this problem is a little random any setup you do will need to be secured so it doesn't rattle free and give bad data.

    How much record time does the scope have? how many channels does the scope have? It sounds like you are going to have to drive around till it happens and then review the data...

    RattFink's list is a good start (especially if you have a 4-channel scope.) Once you notice some oddities you may want to change up the list (ie if you see something on MAP, it would be good to correlate it to the throttle position to confirm...)

    Have you considered making a YouTube video of the event?

  8. #108
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Difficult Ignition Cutout Problem

    My first inclination is to ask you if you can remember when this first started, and if you had done/ changed anything recently before the first symptoms?

    The 3 most common issues I've found over the years with rough idle and break up under load;

    1. MAP sensor

    Usually happens after whole set-up has been taken apart and all vac line broken, or just broken vac lines and put back together. In the process, the MAP ends up getting the last feed of manifold or worse, last feed of of T'd vac source and ends up getting inadequate reference. This is what lead to use giving the MAP sensor a large dedicated reference unmolested from any other sensor. How important is the MAP sensor in the total scheme of things? Important enough that by the time the NSRT 4 came out, it was mounted directly to the intake mani.

    2. A/M o2 sensors

    I can't even list how many different issues I have found from a non Chrysler o2 in one of these engines. everything from intermittent idle/ run to severe break up under load and total break up over 4k rpm. I'm not saying I've never see an A/M o2 work OK, just that I've seen so many issues that we stuck strictly to OEM o2's from very early on.

    3. Bosch platinum/ Ford Autolite and other off brand spark plugs.

    NGK and Champion are the only spark plugs that I have seen zero issues, unless plugs are simply worn out or damaged/ defective.

    Bosch plugs I can tell as soon as vehicle arrives, as they would effect right at idle, giving rough and intermittent stumbling.

    Autolite I have only encountered twice. Once on a T3 Iroc R/T that no one could figure out why it would break up over 4k rpm and once on an 8v that would break up intermittently anywhere along the curve.

    On the R/T I got lucky, cuz just looking it over, the Ford plugs stuck out like a sore thumb. Pulled them and they looked like they were burning 4 different heat ranges. Slapped in some Champions and problem solved.

    When I saw them in the 8v it was simple, since I'd already encountered it before.

    I can't remember if the MAP's Always threw a code, so maybe that ones not to likely, but thought I would just throw these up there for starters, as I've not often found Major wiring issues unless someone or several individuals have really butchered the car.

    Also, because these are such simple things that most would never suspect, they seem to fly under the radar almost all the time. Just like all the mechanics that would put the timing belt on wrong, then not even go back to dbl check if they'd made a mistake because it was an insult to them that they could possibly do something that simple, Wrong

    I know you are no stranger to this platform, so most likely you are aware of some if not all of these, just throwing it out there in case it was overlooked and because I didn't see any of it mentioned in the thread.

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  9. #109
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    Re: Difficult Ignition Cutout Problem

    I do have ways to access the signals. I need to get some T pins and perhaps some new probes in general for my specific application. The scope has 4 channels.

    I'll try to make a video for you guys. It acts just like a bad HEP when it cuts out. Loss of tach, car very momentarily dies, etc. Many functional HEPs, a new one, different connectors for the HEP wiring, and a couple entirely different harness combinations tell me it's not the hep itself.

    ETA: I bought this car from another member who couldn't get it running. That was pretty easy for me, but a ton of small mechanical things needed fixing in order to have it ready for the road. The kicker is that the car had an engine fire, so that obviously makes the electrical gremlins come out in force. Most everything I've pulled apart so far has looked at least as good as anything else I have in the stable.

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    Re: Difficult Ignition Cutout Problem

    OK, the apparent key to solving this issue is hooking up a 4 channel scope to it. I'll drive around more today in order to hopefully trigger the fault. In the mean time, here is the picture of what I had going on.

    Click image for larger version. 

Name:	map 12v ign sync.jpg 
Views:	18 
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ID:	66306

    Channel 1 is the voltage to the LM, 2 is the inductive ignition deal, 3 is the map sensor, and 4 is the ignition reference sensor. It looks pretty great in my uneducated opinion.

  11. #111

    Re: Difficult Ignition Cutout Problem

    What's with the ignition reference having a double pulse in the center? Is that right? (can't tell since another one would be off screen.) Quick reading indicates that is not right...

  12. #112
    ...if you know what I mean... Turbo Mopar Contributor csxtra's Avatar
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    Re: Difficult Ignition Cutout Problem

    Quote Originally Posted by c2xejk View Post
    What's with the ignition reference having a double pulse in the center? Is that right? (can't tell since another one would be off screen.) Quick reading indicates that is not right...
    I am guessing that is the tooth with the cutout in the distributor.
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  13. #113
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Difficult Ignition Cutout Problem

    Have you checked the distributor plate to make sure the rivets havenít come lose?

    Robert Mclellan
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    Worlds fastest 8v MTX Shelby Charger
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  14. #114
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    Re: Difficult Ignition Cutout Problem

    Quote Originally Posted by Shadow View Post
    Have you checked the distributor plate to make sure the rivets havenít come lose?
    Good suggestion. I have done so, and this one is actually pretty nice.

    I drove the car again tonight and It went about 25 miles with relatively little cutting out. It's a real pleasure to drive when it's running correctly to say the least.

    That said, I'm thinking I need to adjust my trigger to the falling edge and use the 12v to the LM since it feels like I'm just totally losing power to the LM so I can maybe capture this waveform problem. Does that sound right? Does the ASD relay kill power to the whole LM when it's not energized? I'm open to any and all suggestions on how to catch this thing in action.

  16. #116
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Difficult Ignition Cutout Problem

    Been years and wish l was more up on the LMís, as most of the stuff we worked on became SMEC and newer.

    I do remember a cpl asd issues and donít remember it ever going back to the LM, so l donít think the asd sends power to the LM, think it powers fuel pump and sensors etc.

    For some reason lím remembering something wrong with a fuel pump, was internally shorting and tripping the asd but not enough to completely short the pump. Or maybe the connection at the pump. If lím remembering it right, that one was a bit of a bear to figure out.

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  17. #117
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Difficult Ignition Cutout Problem

    Have you run it and driven with 02 unplugged? Guessing the 87 LM has the ability to run at predetermined center with 02 unplugged like SMEC.

    I know lím coming at it with very simple sounding stuff, but 90% of the time líve found its usually something simple, overlooked or strange/ bunk that youíd never suspect.

    I know with the 02ís that ground runs through almost everything. When líve seen A/M O2ís cause issues, they short the ground at intermittent rpmís and take down everything else that ground runs to.
    Last edited by Shadow; 06-09-2023 at 08:34 AM.

    Robert Mclellan
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    10.04 @ 143.28mph (144.82 highest mph)
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  18. #118
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    Re: Difficult Ignition Cutout Problem

    Quote Originally Posted by Shadow View Post
    Have you run it and driven with 02 unplugged? Guessing the 87 LM has the ability to run at predetermined center with 02 unplugged like SMEC.

    I know lím coming at it with very simple sounding stuff, but 99% of the time líve found its usually something simple, overlooked or strange/ bunk that youíd never suspect.

    I know with the 02ís that ground runs through almost everything. When líve seen A/M O2ís cause issues, they short the ground at intermittent rpmís and take down everything else that ground runs to.
    That may be one of the few things I haven't done. I generally find that the cars run poorly with the O2 disconnected. If the car starts breaking up badly, I might try that as a quick way to see if it will alleviate the issue. I believe I have some spare O2 sensors around, so I might just throw one in for fun. I need to check what type of sensor I have on hand, as I know it's a 3 wire sensor in the car.

    Thanks for the great suggestion.

  19. #119
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Difficult Ignition Cutout Problem

    I know you said you added some grounds. This reminded me of an LM rough run issue from very early (25 years ago?)

    The firewall ground was attached to the fuel regulator mounting bolt IMS. Relocated it to the fuel rail and same bolt as the harness ground as I believe that's the way it was from factory.

    Solved the issue and we made sure from that day forward to have all grounds in place and especially the firewall to fuel rail on the LM cars.

    Robert Mclellan
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    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
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    New clutch combo is the SH!T!

  20. #120
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    Re: Difficult Ignition Cutout Problem

    Quote Originally Posted by cordes View Post
    Good suggestion. I have done so, and this one is actually pretty nice.

    I drove the car again tonight and It went about 25 miles with relatively little cutting out. It's a real pleasure to drive when it's running correctly to say the least.

    That said, I'm thinking I need to adjust my trigger to the falling edge and use the 12v to the LM since it feels like I'm just totally losing power to the LM so I can maybe capture this waveform problem. Does that sound right? Does the ASD relay kill power to the whole LM when it's not energized? I'm open to any and all suggestions on how to catch this thing in action.
    From some quick reading and looking at wire diagrams:
    It looks like the LM gets power directly from the PM. The LM actually controls the ASD which supplies power to fuel pump, coil, injectors, and portions of the PM. If the ASD was turning off, fuel pressure would drop. That is why I would have a fuel gauge hooked up while driving.

    Since you are losing the Tach... Either the HEP signal is dropping out, or the LM is completely shutting off. If the cluster was losing signal from the LM, the car would still run fine when the Tach drops out, so that is not the case. It sounds like the HEP circuit is pretty rock solid at this point after your repairs. I would backprobe the power feed
    wires at the LM and see if I am losing 12v at any time when it cuts out. If so, trace those circuits back to the PM. If you are not losing 12v, backprobe all the LM grounds while driving and you should see 0v. If you see 12v on any ground, then you are losing the ground.

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