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I decided to post this problem separately, rather than hijack someone else post, but I see that there are two other people having a speedo problem as of the present time. Sorry but this is going to be lengthy. My reason for posting this is in hopes of someone seeing something obvious that I cant -- guess I'm sick and tired of working on Volvos.
Here are the facts: 91, 740 Sedan, Non-Turbo, Auto, Regina Electronics, 190+k miles
The OE speedo for this car did not ever have any problems. I took it out to replace some bulbs and clean it up in various spots -- a big mistake! I messed up the paint on the thing while cleaning it and it ended up looking too crappy, so I got a speedo from a salvage yard. The car has been sitting without use for about 18 months. When I finally got it operational to take the car for inspection, the speedo went nuts at any speed over 15-20 mph, flittering, jerky, fluctuating up and down as if it didnt know what the speed really was, and also telling me I was going 60 when I was going about 20-30, then dropping to the correct speed, and then going nuts again [this is just my general observation from driving it a few times]. I dont recall it ever dying completely, but in hindsight who knows if it did or would have. First thing I thought was I got a bad speedo from the junkyard.
When I read the FAQ about the leaky capacitor issue, and looked at the salvage yard donor speedo, I saw blackened spots at the base of the C6 capacitor and at the prongs of the IC chip aside of it. Everything else looked ok. Is the blackened stuff from the acid leakage? Is that what to look for? Btw, I looked over the OE speedo and it too has blackened stuff on the board, but only at one place, at the base of one of the prongs of the C6 capacitor, but it always worked before I took it out. Now it doesn't work. Can removing the speedo cause the acid to leak? Does the presence of the black stuff mean the speedo will have a problem?
As to whether it was the wrong year Regina speedo, I dont remember if the donor volvo was a 91 or 92. Volvo says the speedos for the 91 and 92 Regina's are different part numbers [of course, I'm wondering if Volvo does that deliberately], but does that mean the speedo is different? They look identical to me, but when I looked them over it was not with the intent to see if they were identical, so I cant say 100% for sure. I just assumed they were from general observation.
So, I put the OE speedo back in, and now I got problems with that one. The difference is the symptoms: The OE now works normal but then just dies. There is no jerkiness like the donor speedo had. So, now I'm wondering if taking a speedo out causes a problem ? ... did I accidentally break something off that I was not aware of ? ... or something else entirely? I assumed that I connected everything back correctly and snugly. The cluster connectors are all different so it is obvious where they connect. I placed the rear end on stands and spun the wheels in drive, and watched the OE speedo work normally for approx 5-15 seconds, until it dies. However, I'm not able to do this all the time, sometimes it just stays dead, and I have not attempted to do it more than a few times, so I dont mean any of this in any scientific way. Btw, the speedo, the odometer, and the tripometer all die together -- that is consistent. I read the archives where Art Benstein said that is a clue to look to the rear.
Since the OE speedo has historically always worked ok, than I assume that the VO-W wires to the ecu are connected and ok. I see no point in doing a continuity test on that wire. Alldata [aka, partialdata] indicates the VO-W as being two separate wires.
I tested the transmitter in the axle for ohms, and got 1.38Kohms, which according to Haynes is 1k under what it should be, but Haynes has typos, but more often than not, unless I got an extremely high or infinite resistance reading, it is always my luck that the sensors were ok and functioning fine, so I'm done with throwing parts on a car trying to get lucky.
The outside plastic body of the Transmitter Sensor connector [at rear axle] is cracked on the top corner on one side, but even while holding it in place while someone watches the speedo did not make it function normally. So, I doubt the problem is that simple.
I tightened up the Transmitter Sensor electrical connector at the rear axle. That was the first time I saw it go back to life and thought I had it fixed, but it died the next day. I had someone watch the speedo while I moved the connector halfs and the wiring, but it did nothing. So much for that.
The wiring looks ok from the trunk to the connector end, and the connector end looks ok. And I would be just floored to discover that there is a just a bad wire from the trunk to the cluster, but maybe a ground issue, because one odd thing happens. When
I put the OE speedo back in after taking out the salvage yard speedo, I noticed that the rheostat for the lights did not work unless, I pushed the gearshift lever forward a little bit. I thought ... mmm ground issue. So, I removed the gear shift plastic cover, ash tray, etc., to have a closer look at things. I moved a few wires around here and there looking for something loose, but did not see anything obvious. So I reassembled the area and now the rheostat works normally. So, I dont know what I did to fix it. How this ties into the speedo, is that, every so often when I start to move the gearshift out of Drive toward Neutral, the speedo needle starts to come to life. The wiring diagram from Alldata shows wiring to and from the speedo being connected to the following areas: Rehostat, the electrical distribution unit, the ground earth busbar, solenoid shift lock, ground point right A-post, 4 pole connector gearshift selector, overdrive relay, BUT Alldata doesnt show any pics and there are tens upon tens of parts and wires in these same places, so of what use is it to know that? Maybe someone can post some pics for the Regina ground points, since speedo issues are an occurring problem.
I also tested the ecu to see if it would set a 311 code when I disconnected the connector. It didn't. Bosch OBD I, doesn't surprise me.
The primary reason why I have not checked theses things out is that I have bad luck with mechanical stuff -- Murphy's law, misery loves me.
thanks, diyer
PS. if I think of anything significant I'll post it as an answer to my post. If I fix it I'll post what I think it was (fingers crossed Murphy doesnt interfere)
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My plan is to do these additional tests:
I dont have an oscilloscope, but a Volvo master tech friend of mine told me to hook up a analog meter to the speed sensor and to turn a rear wheel to see if it generates any voltage.
Check the connectors once again at the instrument cluster, and clean and tighten them if needed, and check the screws for good contact. Randy Starkie told me to do this. Its worth trying but I will say that this cluster was spotless and never an issue in that regard. Actually I was very surprised how newish this looked compared to a 240 cluster I have.
Try a sensor from a salvage yard if I can find one that reads 3k ohms
Keep looking at the gearshift lever area
Check the grounds at the right and left A post
Test the wires from the trunk to the sensor connector end for continuity
Test the wires from the trunk to the cluster for continuity.
Things I wont bother trying to do:
I will not be replacing any cpacitors, because the info I am reading is that the people who have done that now have speedos that wont go over 45mph.
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