QuestionQUESTION: I will be inheriting a 1991 740 Turbo that apparently has an intermitent problem with the gas guage and speedometer (maybe other guages?) not working. I saw one suggestion about a bad ground behind the panel or bad circut board - is this the best place to start? Any directions toward on line instructions would also be appreciated.
ANSWER: I've seen alot speedo problems because of bad/broken wires at the speed sensor mounted on the differential.I've also seen many bad speedo heads.Does it function at all? Does speed work sometimes and then not others or is it just the odometer portion not recording mileage? The gas gauge function could also be affected by several things, most likely a bad level sensor, but the gauge should be checked also...sometimes it just needs the connections cleaned and tightened at the gauge.You can check the speedo wires by gently pulling on the wires at the sensor. Next you would have to remove the instrument cluster and jack the car up to check for the signal at the speedo head. It is an AC V signal.If you have a signal the problem is in the circuit board or speedo head.Very rarely have I seen a bad speed sensor.
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QUESTION: i don't have the car yet, should have it shortly. I've heard that it was taken into a shop and everything worked for them but now it doesn't again. It sounds like multiple gauges at the same time which leads me to suspect a ground on the instrument panel - ideas where to look? BTW - thanks for the other ideas, very helpful and insightful.
ANSWER: Also check the ground wire at the chassis. Go to the battery ground side. Follow ground cables, it splits into two,follow them all the way to where they attach. Larger cable should go to block and smaller lead to chassis ground, also check the alternator ground wire.I've seen some crazy things happen because of those being bad.Also remove the instrument cluster and tighten the connectors with a small pick.They are push on pinch type connectors so just push the pick in from one side and pinch it closer, on all wires.Let me know your progress
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QUESTION: I was able to get my hands on the 1991 Volvo 740 turbo wagon. Most grounds seemed ok at
both A posts. All of the meters work but the speedometer and fuel gage. There may be a
problem with intermittent loss of ground on the coil but that's for another time.
I think the problem with the fuel meter is either a stuck float or the sensor - the meter
goes to and stays at ~3/4 full when powered and it dropped to empty when I disconnected
the wire to the meter itself back in the rear tire well where it runs out to the tank.
Question is: how do I get to the fuel sensor/float? I saw something about it being under
the seats...
As for the speedometer, it appears to not work at all although I've seen some mileage on
the trip meter a couple times after someone else drove it (I think). I checked the speed
sensor at the differential - it looks rather 'old' and someone had cut the wires to it
and used electrical tape to reconnect them but nothing significant to they eye. I did
not do anything under the car but did disconnect the wires running to the sensor at the
wheel well. I did not get any voltage signal (AC or DC) when I put a meter across the
connector with the car running. That's as far as I got.
I did not see an easy way to get the instrument panel out. There are two square
openings on either side of the panel cover that appear to have push type clamps behind
them. However, the panel did not seem to want to come out. Do I really want to get
behind the panel or should I leave it to someone who knows what they're doing? Do I
disconnect the battery ground prior to trying to get it off again? If I do get the panel
out, how do I test the speedometer head?
I have a wiring diagram which seems correct as far as I can tell - although the wire
colors are different. Thanks.
AnswerI would take apart that previous repair of the wiring and do it over to make sure that isn't the problem. You can buy the rubber insulated bullet connectors at the dealer and cut out a good six inches of the cars wiring to make sure you have a good repair.Yes that instrument cluster is a bit difficult to release, push in on the clips and get a hook behind it and pull.But I'll bet the fuel gauge problem is the sensor, it is located under the rear decking.Remove the decking and there is an access panel held in with four bolts.Release the hoses and unscrew the retainer, the sensor will pull out, you can buy the whole thing at the dealer (sensor, pump filter sock) as a unit rather than have to piece it together.If the speedo is registering miles but no speed look no further the problem is in the head.
