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Volvo 740 electrical gremlin help

34 messages,  Last post on Jun 23, 2012 at 1:36 PM

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What is this discussion about? Volvo 740, Electrical, Wagon

Messages Page 3 of 4

#15 of 34 dash service light comes on then off by horseexpress

Jun 18, 2007 (10:25 pm)

For the last six months or so I have noticed that my service light in my 1990 Volvo 740 GLE wagon comes on when I first start up the car and then it goes off after about five minutes of driving it. I am hoping that that is just a routine thing since it is an older car and it has over 224,000 miles on it, but could that actually mean that there is something wrong with it?

#16 of 34 88 740 fuel pump by rstoner

Sep 25, 2007 (9:25 am)

Hi,
After running dry our '88 740 has recieved a new relay, pump (regency style) and filter but to no avail. No power to the pump, is there a shut off switch for this somewhere I need to reset?
thanks

#17 of 34 Re: 1990 740 sw non turbo stalling problem [texholdem10000] by rexc

Mar 11, 2008 (5:07 pm)

Replying to: texholdem10000 (Mar 26, 2007 7:12 pm)
i have an 89 wagon, it does about the same, thing it will run good for awhile and then start cuting out, back firing, to where i have to park it for several hours and it will run again for a while, i replaced plugs wires distrubter, still does it its driving me nuts, have you found the problem with yours? thanks rex

#18 of 34 Volvo 740 GL Beeping by volvo740

May 13, 2008 (5:16 pm)

Started car and the seatbelt, headlight, et whatever keeps beeping
even as seatbelt on... headlights off, etc...
 
Short of pulling fuse 9, not know what to do to muffle it..... cut wire?

#19 of 34 Re: 740 problem [fred43] by snookman05

Jul 13, 2008 (7:21 am)

Replying to: fred43 (Mar 02, 2006 4:18 pm)
The oxygen sensor in your vehicle is what is causing the rich fueling problem. The brainbox (ECU) receives messages from the oxygen sensor and adjusts the the fuel mixture. The oxygen sensor is supposed to be good for the lifertime of the vehicle. It seems that something might have gone wrong wit it and it is sending back wrong info to the ECU which is causing the fuel nixture to cone out rich.

#20 of 34 Odometer and Trip odometer not working by snookman05

Jul 13, 2008 (7:52 am)

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.

#21 of 34 Fixed my 740 stalling problem, at last by electricguy

Aug 26, 2008 (12:32 pm)

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.

#22 of 34 Re: Odometer and Trip odometer not working [snookman05] by volvo740

Aug 26, 2008 (1:28 pm)

Replying to: snookman05 (Jul 13, 2008 7:52 am)
I have replaced my odometer twice in 350k miles.. or is it 400k?
 
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.

#23 of 34 Re: 740 problem [snookman05] by electricguy

Aug 26, 2008 (1:31 pm)

Replying to: snookman05 (Jul 13, 2008 7:21 am)
I was able to fix a similar problem on my 740, please see post #21. If you do still have the problem, it's not much work to clean the oxygen sensor.

#24 of 34 '90 740 GL sedan stalls once in a while by jamis18413

Sep 23, 2008 (3:02 pm)

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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