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Thread: CASE Learn Help - Speedometer Twitches as RPM Raises

  1. #1
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    CASE Learn Help - Speedometer Twitches as RPM Raises

    New poster here, thanks in advance for the help!

    The computer in my dad's 1998 5.7L Express Van flaked out (wouldn't read MAF). We changed it with a new one that is correctly coded for his VIN, and we did the security re-learn process, so it starts and runs great. But, the check-engine light is lit because the computer wants a CASE Learn to be performed. The problem is that each time I start the CASE Learn process and raise the RPM, the speedometer twitches (comes off it's post briefly) and the CASE Learn fails because the computer thinks the truck is moving.

    The speedometer does this "twitch" whenever the RPM is raised to around 3-4000. It shows you're moving 5 mph and then settles back down. Anyone have any idea what would cause this? The truck is in Park with the brake held, so it's definitely not moving.

    I wouldn't care about the check engine light, since the truck runs great. But, the truck won't pass state emissions testing with the check engine light lit. Is there any way to code tune out the CASE Learn code so that the check engine light doesn't come on?

  2. #2
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    Check the coil, wires, cap & rotor. It's been a long time since I worked on those every day but I seem to remember they were prone to burning up the coil button in the cap (and the center of the rotor) and also arcing out the sides of the coil to the mounting bracket. Look for light-colored powdery markings on the coil housing and on the exterior of the wires.

    CASE relearn is necessary for proper ignition timing, it's not something to just be turned off.

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    Quote Originally Posted by blindsquirrel View Post
    Check the coil, wires, cap & rotor. It's been a long time since I worked on those every day but I seem to remember they were prone to burning up the coil button in the cap (and the center of the rotor) and also arcing out the sides of the coil to the mounting bracket. Look for light-colored powdery markings on the coil housing and on the exterior of the wires.

    CASE relearn is necessary for proper ignition timing, it's not something to just be turned off.
    Thanks, I'll take a look.

    The other thing I was thinking is that the alternator/regulator may be flaky and sending out a voltage spike as RPM increases. Might try running it with the alternator disconnected to see if that helps.

  4. #4
    Did it do that with the old PCM? have you driven it with the new PCM? If you drive it and the speedometer reads faster than it should you need another pcm.

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    Quote Originally Posted by Jeff7577 View Post
    Did it do that with the old PCM? have you driven it with the new PCM? If you drive it and the speedometer reads faster than it should you need another pcm.
    I don’t know about the old PCM. It got wet and stopped reading the MAF (wet PCMs are a common issue in these vans). Truck runs great and shows correct speed with new PCM during normal driving.

    I tried again today to do a CASE learn with VCM. It failed again since the speedometer showed 5mph as the engine approached redline.

    I also have a VCX Nano that includes Tech2Win. I was able to successfully do the the CASE learn with that. I think it worked because it only wanted RPM up to 4000, not fuel cutoff. Check Engine light is no longer on, so my dad should be good to go!
    Last edited by CCIE; 06-01-2019 at 12:22 PM.

  6. #6
    Quote Originally Posted by CCIE View Post
    I don?t know about the old PCM. It got wet and stopped reading the MAF (wet PCMs are a common issue in these vans). Truck runs great and shows correct speed with new PCM during normal driving.

    I tried again today to do a CASE learn with VCM. It failed again since the speedometer showed 5mph as the engine approached redline.

    I also have a VCX Nano that includes Tech2Win. I was able to successfully do the the CASE learn with that. I think it worked because it only wanted RPM up to 4000, not fuel cutoff. Check Engine light is no longer one, so my dad should be good to go!
    You were using VCM scanner? Does it tell you what to do or did you assume it was the same as LS engines?

    The service information says slowly raise to 4000 rpm. The moving speedometer a pretty common cluster issue.

  7. #7
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    Quote Originally Posted by Jeff7577 View Post
    You were using VCM scanner? Does it tell you what to do or did you assume it was the same as LS engines?

    The service information says slowly raise to 4000 rpm. The moving speedometer a pretty common cluster issue.
    VCM scanner has a CASE Learn button that I was using. It has instructions that walk you through the process, but it does ask that you slowly raise RPM until fuel cutoff and then release accelerator.

    Tech2Win only wanted 4000 RPM, which matches what you see in the service manual. I’m just glad it worked, since failing emissions would have precluded renewing the registration, rendering a perfectly good truck useless.

    It wasn’t just the cluster that showed 5mph at high RPM. It also showed up in VCM Scanner, so the PCM thought the truck was moving.

  8. #8
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    You should still inspect the cap/rotor/wires. The noise bleeding over is a screaming red flag telling you there's something that needs attention.

    But at least the CEL won't be on when Dad gets stranded on the side of the road, right?

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    Quote Originally Posted by blindsquirrel View Post
    You should still inspect the cap/rotor/wires. The noise bleeding over is a screaming red flag telling you there's something that needs attention.

    But at least the CEL won't be on when Dad gets stranded on the side of the road, right?
    Replaced plugs, wires, cap, and rotor about 10k miles ago. Engine runs like a champ. Tons of power and no misfires, even at high RPM, which makes me doubt that the ignition system is arcing or grounding out.

    I hear what you’re saying. But, he’s realistic about the reliability of a 21 year old vehicle. Doesn’t drive it far and has AAA. Odds are the frame will rust-through and crack before the powertrain dies.