QuestionQUESTION: its not a constant issue, the engine runs fine when the dash is working but as soon as it goes out it runs horribly. it is a 95 deville with the 4.9l pre northstar engine, and i cant get trouble codes currently because i dont have the car in my possession at the moment
ANSWER: Hello,
The reason your car is running rough when speedo goes out is that you are now in open loop and computer is in limp mode.
A bad speed sensor could cause this issue, but don't go running out and getting one.
Reading the codes will do you little good because they cascade. One code will set off another and another, so to try to diagnose by pulling up codes could be frustrating.
Since it is intermittent, my guess would be a connection problem somewhere in which a vibration or a bump in the road can create the problem.
Just to start out, I would pull the dash cluster and check the main connection. Then spray with brake cleaner or electric motor cleaner and put die-electric grease on the connection and reassemble.
This can be a very difficult problem to locate. For all we know, you might have a cracked circuit board in the cluster. That is a real and frightening situation with the frustration involved. You may also want to go under the driver's dash to the bulkhead that takes all the wiring into the engine area, passenger compartment and trunk area. Should be one bolt holding together. Pull bolt and remove connector. Spray an install grease.
See, in your situation, the codes are an after effect from the dash circuit failure and not the cause. The codes are only going to insignificant to your diagnoses. Even if plugged into a Tech II (Scanner for reading computer), it's going to tell us dash failure. We already know that!
Once the cluster circuit is repaired, it will purr like a kitten, but you need to find what is causing the dash read out to go out at times.
Check the cluster circuit board behind the speedo well. You might even want to contact some electronics repair store to check it out for piece of min and to eliminate that first from being the issue. All you need is a hair line crack that opens up when driving and goes back together when it cools off. These are electronic nightmares! I am just giving you ideas where to look.
Good Luck!
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QUESTION: Also i just remembered they said it started when they plugged something in to the cig lighter could that help narrow it down?
ANSWER: Hello,
Who did what and why? How long has this been going on?
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QUESTION: Not really sure it was the previous owner but they said it blew the fuse and after that this started happening
AnswerHello,
This is useful information believe it or not. Cigarette lighter circuit should supply power to radio memory which links up with the dash.
I really want you to consider the possibility of a cracked circuit board on the back of the speedo. PC could have over heated for a short amount of time.
Connection issue and wiring not that big of deal now. At least I would be looking at the board before doing anything else.
That makes more sense than anything else. If you don't see a crack, it does not mean it isn't there. Take to someone who has the equipent to check it out. You might get luck and see an anomaly in the board. A burned spot or brownish area.
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