Electrical Problems on 84
Thread Starter
Intermediate
Joined: Aug 2003
Posts: 25
Likes: 0
From: Deltona FL
Electrical Problems on 84
I have an 84 with some electrical problems. At about the same time, the cooling fan stopped coming on automatically (motor tested and good), odometer doesn't work and the digital display stopped working. I was wondering if all these problems were connected. I replaced the vehicle speed sensor and the coolant temp switch but still no luck. I can't even drive it now because it overheats quickly without that fan and Florida temperatures don't help either.
Any help or advice would be really appreciated.
Thanks for your help
Ben Davis
Any help or advice would be really appreciated.
Thanks for your help
Ben Davis
Last edited by bmtdavis; May 20, 2006 at 09:30 AM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The fan is turned on by a relay, so you should next ground the green/white wire on the relay with the ign sw in run and see if you can hear the relay click and with a voltmeter determine that the relay switches 12v to the fan motor. Then check for 12v at the fan motor connector. Check the condition of the ground wire on the fan motor connector. The ECM turns on the fan relay when the coolant gets to 228F from a temp sensor. On my 87 the temp sensor is on the front of the block, top, and under the MAF. I don't know where it is on an 84. A scan tool can tell you if the temp sensor is sending correct temp info to the ECM. The ECM could also be the problem.
Which digital display stopped working? speed? The speedometer and the odometer are operated by the ECM from pulses from the speed sensor in the transmission. First determine if you are getting pulses at the cluster connector from the speed sensor while the rear wheels are turning. If so, then your cluster needs to be repaired at a service center.
Which digital display stopped working? speed? The speedometer and the odometer are operated by the ECM from pulses from the speed sensor in the transmission. First determine if you are getting pulses at the cluster connector from the speed sensor while the rear wheels are turning. If so, then your cluster needs to be repaired at a service center.
Thread Starter
Intermediate
Joined: Aug 2003
Posts: 25
Likes: 0
From: Deltona FL
I'll check the relay. I know the fan motor works because I spliced into the motor wire and wired it directly to the battery with a switch so I could temporarily drive. The entire display is out and you can't see anything no matter what angle you look at it. Could the entire problem be a bad ground? Sounds like all of the problems could be ECM. How do you test for that and is it a costly repair?
Thanks for your response; you were a lot of help.
Ben
Thanks for your response; you were a lot of help.
Ben
Last edited by bmtdavis; May 21, 2006 at 12:07 AM.
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
In between the #6 and #8 cyl on the engine is the temp sensor that controls the temp of when the fan will turn on. More than likely this is the culprit. It has two wires to it, make sure that they are both good and you have good connections
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Check the clstr fuse and the lcd fuse which supplies power to the cluster. You could have a broken ground on the cluster, but usually when this happens the turn signal lamps stay on. If you have to remove the cluster, check that the wiring harness connectors are seated fully. The cluster ground on my 87 is a black wire that goes to ground behind the instrument panel near the LH side of the steering column.
Guest
Posts: n/a
Check the 2 fusible links coming off the posative batery cable by looking for voltage on the side away from batt.. Also look closely at all the fuses and try to find the major grounding points. If every-thing went at once then it is PROBABLY all related to one electrical problem. I know that this is not much help but it should tell you to save money by not looking for one sender or sensor by changing them all. Good luck and let us know if you see any-thing that doesn't look right in the wiring. LOOK CLOSELY!
Heel & Toe
Joined: May 2004
Posts: 23
Likes: 0
From: Navarre Florida
The temp sensor on the '84 is between 6 & 8 and has only one wire running to it.
Check it for continuity to the relay. Does the fan come on
with the A/C? This would rule out the relay and point to the wiring to
the temp sensor or the sensor itself. You can disconnect the wire at the
sensor and ground it with the ignition on. This will check out the wiring.
Also check the main ground at the back of the driver's side head. There are two wire there.
There are also several (I think 3) that go
to ground at the lower drivers side of the block above the oil filer.
Good luck. Been there and had that happen to me after and engine
swap on my '84.
Check it for continuity to the relay. Does the fan come on
with the A/C? This would rule out the relay and point to the wiring to
the temp sensor or the sensor itself. You can disconnect the wire at the
sensor and ground it with the ignition on. This will check out the wiring.
Also check the main ground at the back of the driver's side head. There are two wire there.
There are also several (I think 3) that go
to ground at the lower drivers side of the block above the oil filer.
Good luck. Been there and had that happen to me after and engine
swap on my '84.
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Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The temp sensor is a thermostatic switch that closes when the coolant temp gets to 228 F which then grounds the fan relay coil turning on the relay which switches 12v to the fan motor . If you short the wire to the temp sensor to ground, the relay should close and the fan should come on. The fan relay I believe is located on the firewall below the brake master cylinder just like on my 87, but I am not completely sure of that as I don't have the service manual for an 84. I covered this in my first post!!!!!!!
