Ugh! I have intermittent no spark no start. Been going on for a year. 98% of the time it runs. Code says faulty O2 and knock sensor. I replaced O2 with a new one from AutoZone, it still reads faulty. The wire tested OK. I replaced the knock sensor with one from a 90' 740, still reads faulty. Would the knock sensor effect the O2 sensor? The no start usually happens after the engine has been running a half hour or more and usually on damp days. I replaced the coil/power stage twice with new. Before that I would switch out and start, (for a while), with a used one. Still intermittent no start. If you let it sit, most of the time it will finally start. I tested the crank sensor--when it would not start, and it was OK and read within parameters. I've searched for bad wires at connections seems ok. I checked/cleaned distributor cap and rotor. I'm not clear if it is a Hall effect distributor--I don't think so. I don't see the 3 wire connector. Help please. I've searched and read so much, maybe I'm too close to figure it out....

 

I'd check on all the grounds you can. I used to have a problem where on rainy days, when I turned on my high beams, I would lose spark. It seemed that because of a bad ground, the headlights would ground through some other system, causing problems. This is a very different problem than you have, but I've found problems related to moisture and are intermittent are often related to grounding issues.

It could be many other things, but this is something to rule out.

 

Oh, as a side note, 740s usually have hall-effect distributors. I had a white 89, and it was a hall effect sensor. But I don't have my greenbooks to verify this for all 740s.

 

The dizzy on the 89 740 is driven off of the camshaft. It has no sensor in it. Timing is done via the ECM . The dizzy only has a rotor and distributes spark to each one of the plugs. If you continue to get codes for the 02 sensor then you need to check to make sure you have the correct sensor.

 

Jagtoes is right. I double checked, and that is the case on the 740s, unless it is a turbo (which the one I worked on was). Sorry for the bad info.

 

i had same prob. Fix= for me anyway was coil after coil. Could not figure it out for life of me. Turned out for me , where coil conections are was corroded. Cleaned it no prob. Since.

 

I will clean grounds. What about the ignition module I read about--two small black boxes mounted on passenger side. I pulled them off and apart and only found one wire with a slice to the casing. Wire seemed ok. Do they ground to the body because the metal they clip to was kinda oxidized....what do these modules do and are they troublesome? What about the faulted knock sensor?--see first paragraph info. She started normal this morning! Reliability is a problem here. On a less important note, I get only about half heat from heater. It almost feels like the floor heat door is mostly closed very little blowing down there and not too hot. Any suggestions/experience on this? Tky!

 

my 740 gl is the first one ive owned & it has too been a very troublesome car, what kind of distributor is on car? Ive also replased ecm on mine
(thanks to salavage yards) .heater could be vacum , bad heater core, bad thermstat. If you dont know any really cheap junkyards, then my best advice to you would be call a reputial volvo dealership , give them vin of car, describe probs, if need parts start at junkyard. I only paid $600 dollars for my 740 . i now have about $2500 dollars in it. Ive replaced-#1 overdrive solinoid on trans. #2 coil, #3 rearend. #4 driveline,carrier bering, ujoints. #5 ecm. #6 mass air sensor. There,s always a new problem going on it seems like. But i do love my 740 gl. Even though she is a money pit. I hope any of this was helpfull. Im also on twitter & facebook.
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To you heater question: There could be a heat door issue, but the car may also not be coming all the way up to temp. I had that problem a couple years ago on a 740. It turned out to be a bad thermostat in the radiator--it never closed up all the way. If, however, the car does come all the way up to temp on the gauge within about 5 min., and you are still not getting heat I'd check elsewhere.

As to the knock sensor... I can't help you too much. You car has the LH 2.4 fuel injection system, and the 740 I worked on was a turbo, and has the 2.2 (this is also why I thought you had a hall effect sensor at first). But it does sound to me like a computer issue if you have replaced the knock sensor and 02 sensor. I mean, the possibilities are limited here. Did you replace the sensors with new ones, or used ones from a junkyard? The O2 is new, but the knock sensor could be bad from the junkyard. Still... that is lower on the list of possibilities I think. If they are good, then there are a few possibilities left--wiring issues (possible, but not terribly likely) or a bad computer. And the ever possibility of bad grounds. The black boxes you asked about could be an issue, but I am inclined to think not, as the sensors probably go to the computer and not the black boxes. (I don't know what they do of hand... but the reasoning stands. I will look at a 740 I have access to and see if I can recall what they do.) If you have a nearby pick and pull, I'd see if you can get a hold of another computer relatively inexpensively. That may solve your issues. Just be sure you get an LH 2.4 computer, and not on older one. (I've seen people mixing up the systems... the results is a mess...)

Finally, do you have access to wiring diagram for your car? That is SUPER helpful at trying to track down electrical issues. If you don't, I may be able to find one from the greenbooks I have for the 740 I worked on. But, I am visiting family on holiday, and that would have to wait a week or two.

 

So yesterday the 89 740 started normally. I turned it on and off a few times to test it. I drove it 45 minutes then shut it off. 25 minutes latter no start. I was by myself. After many checks and no start I realized I did not hear the fuel pump! I ended up leaving it parked and had wife and kids pick me up. 6 hours later in the dark, we drove back to try again, no sound of fuel pump, no start. We drove home. I will try it Monday, but I may have to have it towed back to the house if it won't start.--I do not relish the idea of pulling the fuel pump parked in town. The fuel pump relay inside center console clicks on/off with the ignition. So intermittent spark, now intermittent fuel pump. Ugh! All the fun is gone when it gets to be so much trouble and struggle.

 

Check your crank sensor. Also, a bad power stage can be intermittent as well.

 

Ok, I realized the fuel pump was not humming. With a neighbor I checked voltage at connector in trunk--7.5 volts or so. We next fussed the relay out in center console it took a lot of wiggling. It looked ok and put it back in. With ignition on we had fuel pump humming for its initial 3 seconds and it started and has been fine for two days. Im not ready to trust it just yet....The pump still reads 7.5 with ignition in on position. That seems odd. Does this pump go on and off while driving? I think there is only one fuel pump on this car. As for the heater issue: It feels like a door/gate thing firstly. But it isn't very hot either. The temp gauge isn't working in dashboard and the sensor is very hard to reach /get at under rear intake area, so I haven't replaced it. This 1989 sat in the dampish barn for a few years... Causing a lot of issues...

 

So my neighbor went over with me to the "won't start 89 740, 189,000, 5-speed". We tried, no start. We pulled the clicking module relay from the center fuse control area. It was difficult to pull out. Finally, it did and looked OK. We put it back in. Turned the ignition and hmnnnnn, the fuel pump was running for it's 3 seconds, we turned the key and it started after 3 seconds or so of turning! It must have been corrosion on the contacts. It starts fine now....
A few days latter... on the way home after driving around shopping, coming up a steep hill in third, it started to squeal.... I got into my driveway and turned it off. There was a strong smell....?..slipping clutch plates??? I drove it the next day, five miles, everything OK.... ?

 

So it has been a while since I've been able to really get on the forums. Did you have trouble with the clutch plates after that? What has happened in the meantime? Did it happen again? Have none of the other issues come back?

 

The squealing noise has not come back. I snugged up the alternator belt too.
The intermittent start still catches us after using the car for 30 minutes. It turns over with no start. I wiggle the fuel pump relay sometimes it will start. This time not. Sometimes it will start when I switch coil units--nope. So This time I let it sit in the Pricechopper lot 2 hours then it started. I used it for an hour without turning it off. I replaced the knock sensor and O2 sensor per code readouts--ran it, no good , lite came on again, codes showed up the same again. Ugh!