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Wagons Older Volvo Wagons Volvo 740 electrical gremlin help
28 messages, Last post on Oct 31, 2009 at 6:12 PM
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Replying to: fred43 (Mar 02, 2006 3:18 pm)
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My 1989 Volvo GL740 the speedoneter is working and I know it is an electrical speedoneter powered from the differential. I cannot find anything in chiltons on the odemeters. Are they supposed to work seperatly from the Speedometer? Are the speedometer and oddometers supposed to be one unit which are supposed to work together from the one connection from the differential? Are there supposed to be separate connections to the odometers and Speedometer? I have not taken ny dashboard instrument panel out to check and would and would like answers to my questions before I do. My odomete renains at the sane reading since i noticed this when I pushed the button to return the tripodoneter back to zero and it did not put any miles on it since that time and I would like both odometers to be operating again. Would appreciate some answers.
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My 740 (200,000 miles) was cutting out occasionally when you took your foot off the accelerator, so it would stall at intersections, when cornering slowly, even sometimes when coasting if you didn’t keep pumping the pedal. I had the problem for months and it got slowly worse, until the car in the end wouldn’t even hold idle when you started it. This is a hard problem to diagnose because the symptom looks like a fuel supply problem. It was actually due to a blocked sensor that reports no free oxygen in the manifold, the EMC computer is expecting at least some free oxygen so it cuts the gas supply down to lean out the mixture, but no oxygen is ever reported, so it cuts the gas so far down that it starves the engine. I fixed it by cleaning the oxygen sensor. It may have helped that I also replaced some broken capacitors in the EMC computer. I disconnected the battery before doing any of the electrical work. The oxygen sensor on my 740 is a 3-wire type (positive, ground, and sensor) very low down on the manifold, right up against the firewall. I was nervous about damaging it but it’s really tough, just a smooth rubber cylindrical plug with a small metal tip, slides up and out easily once you’ve undone the single retaining screw (there’s almost no room to work, you’ll need a 10mm extended socket and ratchet, but you don’t need the special Volvo tool described in the manual). I did follow the electrical test procedure in the manual. Even though the sensor checked out fine electrically, it wasn’t working because the tip was almost completely gummed up with soot. It cleaned up fine with rubbing alcohol and a very light sandpapering. I also fixed the EMC because the workshop diagnostics said there was an electrical problem, but if I were doing it again I’d clean the oxygen sensor first and then road-test the car before doing any more work. Check the maker/serial on the EMC, I had a 940 Bendix EMC in a 740 saloon, so you might need the 940 workshop manual to check your electrics. The EMC computer is the size of a paper-back book and is behind the plastic wall to the right of the front passenger’s feet. I had to break a coupla glue seals to get to the circuit board once I had taken the EMC computer out of its aluminum case. I used a cheap Radio Shack tester to check the capacitors on the circuit board (caps do age with time, one even broke apart in my hand) and replaced three of them by soldering each new capacitor to the cut-off leads of the old one. The EMC computer is old-fashioned with mostly big parts, so doesn’t require much soldering skill. Caps have polarity, so they must be soldered on the right way round (the short lead and the light-gray stripe mark the negative lead, the one that goes where the circuit board says “-ive”). I’m not a mechanic. I was so fed up with the car, if I could have found a decent recon EMC I’d have happily (well, fairly happily) paid $200 for it. But the caps cost me less than $5 for all three, and took less than an hour to fit, so I came out feeling good. The car runs so well now it reminds me of why I bought it in the first place.
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Replying to: snookman05 (Jul 13, 2008 6:52 am) When it stops your car has less mileage. Hence car is worth more at trade in time. Not a factor in 25 year old cars. Big cities have shops that repair them in a few hours. It seems to be a specialized job and cheaper than buyin a new one. |
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Replying to: snookman05 (Jul 13, 2008 6:21 am) |
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| this 740 stalls out once in a while. we have tried to narrow down what makes this happen and came up with "whenever we go up a hill of some kind and then have a light to stop at at the bottom of the hill or top is when it seems to want to stall." Right after it stalls it's hard to get it to start up...takes a few tries. I thought it was an ignition problem but I tug on the keys and ignition area when it runs and it does not stall. I am thinking it's the fuel filter clogging up. I have had someone tell me it could be the head gasket???? Not sure if that makes sense or not. Any ideas out there or has anyone seen anything similar? thanks. | |
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Replying to: electricguy (Aug 26, 2008 11:32 am) |
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Replying to: rstoner (Sep 25, 2007 8:25 am)
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Replying to: fred43 (Mar 02, 2006 3:18 pm) |
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Replying to: richs (Feb 03, 2009 9:42 pm) |
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