I have a non turbo 1988 volvo 740 automatic wagon. I love the car. it only has about 160K on it. Ive owned lots of volvo 240's and I have a 122 as well.

it started having an issue with intermittent stalling. it seems to just die very suddenly. the tach drops suddenly and motor tries to quit. sometimes/usually it keeps running but it's dangerous to drive it like that. I got stuck in traffic a couple of times and was able to restart and go but Im scared to drive it now. it could die in the middle of a left turn or something.

I replaced the fuel pump relay first. then the gas tank pump and the main pump. I think I ruled that out and it doesn't seem to stumble like I would expect if it was running out of gas. To me it feels more like an ignition problem, maybe something grounding out or a bad connection somewhere, maybe a faulty electronic component. the way it quits feels like an electrical fault because it is so abrupt. Im sure it isn't anything mechanical in the engine, it runs and sounds fine otherwise. the problem ocurrs about every 15 minutes or so at random intervals and it doesn't seem to depend on how Im driving. It won't run out of gas on a long hard climb. Its not overheating or showing signs of a bad head gasket like water in oil or oil in water or water in tailpipe so I think the head is ok.

I noticed the relays seem to get a bit warm. right in front of the relay for the fuel pump there is one marked "J". it seems warm around there and around the new fuel pump relay and I have a spare fuel pump relay that's new but I don't think the relay is the issue , I already replaced it for this issue. maybe the warmth is from the coils in the relays but it seemed a bit warmer there than I would expect. they aren't cooking or frying the wires or anything so severe. no bad smells. I do have a spare set of all the relays from another 740


I replaced the O2 sensor, that made no difference but I figured it wouldn't hurt to change it and the fuel pumps for reliability.

I ordered the crankshaft zero position sensor. On all the 240's I have owned it lived right behind the block above the bell housing. I know it's a tight area but now I have the thing in my hand and can't see it on my 740. This car has the distributor at the back of the block. I dont' know if it doesn't exist on this engine or if it is perhaps part of the distributor ? im pretty sure it's on the back of the block in this area on my 1990 volvo 244

Im not sure if this 1988 volvo 740 has the ability to make the fault codes? I looked for the little plug thing with the jumper wire and couldn't find it. I know where it is on my 240.

so at this point I'm kind of stuck so I thought maybe someone could help me decide what I could check next. maybe I could hook a little light to the coil wires and see if it seems like the light goes out when it dies?

Ive been hoping I can just buy an older rusty or body damaged 740 to swap parts from like the ignition computer, or the mass meter or the central computer but I haven't' been able to find any used ones cheap . I could admit defeat and tow it in to the shop but if there are more things I can check I'd rather that as money is a bit tight now.

I do have a working 1990 volvo 240 so if there are any parts I can swap for troubleshooting Im open to doing that. Im not sure if the computers or the mass meter are compatible? the mass meter on my 740 has a little plug with two dots on it. I hear there are two types, adjustable and non adjustible. are they compatible with each other?

I noticed it seems to be weeping oil a bit. Ill have to get under it and wash it to see if it's a loose pan gasket or something but I know old volvos can have an issue with the screen located under the intake manifold plugging up and causing it to pressurize the crankcase. part of me wondered if It could be leaking from the back of the crank or cam and flinging oil around and maybe blocking the crankshaft sensor but I don't know if that theory holds water.

I've also had some little issues with the blower fan. Its easier to access thant the 240's but for some reason mine seems to have a little hose that collects water from the cowling area and twice I took the motor out and it was sitting in the plastic housing and soaked with water. the second time I replaced that motor ( again totally sitting under water) left the bottom half of the housing off so it can go on the floor rather than collect inside the motor. maybe there is a drain inside the cowling that's plugged.. without the bottom half of the plastic cover it still blows enough to clear the windows but it doesn't put out as much heat.
the carpets aren't wet or anything but I could have some water issues in this area and it's near the computers for timing and the CPU for the motor.

any help appreciated .
can I read the codes or is this not possible on this 1988 740? maybe I just can't find the plug thing?

the fuses all test ok. Im ok with checking anything with a meter.
Are there any parts that I can swap from my 1990 244 automatic? like maybe the mass meter or ignition computer? or the engine computer or ?

I bought a new timing belt and tensioner but I know that the issues arent' related. Just tthought I'd do it while Im doing some maintenence.

I replaced the plug wires rotor and cap a couple of years ago. I guess I cpould swap those or maybe wash them in alcohol and examine for carbon tracking or anything noticeable. wiggling wires and stuff didnt' seem to help locate the issue.



Phil

 

The '88s don't have OBD, so no plug to tell you.
I'd look at the Hall Effect Sensor in the base of the distributor and the coaxial cable that comes from it into the wiring harness.

 

Thank You Lev.
that led me to researching the hall sensor
I found some info here ;
Electrical-Ignition

I've replaced these sensors on machinery as I worked as a printing equipment technician but not cars. Usually they only went bad if they got rubbing on the disc. I do have an oscilloscope so maybe I could hook that up at the connector and see what the trace does when it momentarily dies. not sure which wire but I guess probing the plug connector shouldn't hurt anything. also hooking a bulb up to the distributor leads and watching for it to blink off might help.

it tells how to replace the sensor, and I'm thinking it could just as likely be a bad ignition module. I saw no evidence of cable damage but Ill examine closer.

i'm thinking swapping out the distributor or ignition module with a used one might quickly prove the fault if I can't isolate the issue with electrical testing. Hopefully I can get lucky and find one at the wrecker. any idea if these parts would be common to any volvo 740 before 89 or so with the distributor at the back of the block? any difference with the turbo models? or standard models or would they all share the same module?

it looks like my crankshaft sensor isn't used on my 88 but I have a 1990 240 so it can get a new crankshaft sensor rather than returning it.

do I need to worry about the position of the distributor affecting the timing if I pull it out for an examination or is it the sort of thing that is either right or 180 degrees out? I'll plan to take pictures. maybe it wouldn't hurt to pull it and change O rings.

If I can't get my hands on a used distributor or ignition module maybe I can just buy the sensor from digikey or somewhere. I wonder if the module could suffer from cold solder joints or maybe bad capacitors?

I've been racking my brain over this issue for quite a while and driving my van because I don't' trust it. That little bit of direction has helped more than you know. Thank you !

Phil

 

The dist. goes one way, there is a bit of "notch" to get into, not bad...
I don't think it's the ignition module. This type of behavior is usually due to bad crank sensor or Hall sensor.

 

this page
http://easyautodiagnostics.com/misc-...o-case-study-3

shows the pinouts to check pin number 5 - Input circuit for the Triggering Signal for the ignition control module by the air filter box. it looks like a yellow or maybe a white wire.

I was thinking that maybe if I could put my scope on pin 5 and run the car then If the hall sensor is bad I'd expect to still see a pulse but I'd also expect to see the trace get interrupted and maybe drop off at the same time the motor quits. If this is the case then I could go on to trying to find out where I can buy the hall sensors.

I do have an independent volvo shop near me so I'd try there first since I don't' have any part numbers to research.

that other document talks about difficulty in swapping the hall sensor. I'm a millwright not an auto mechanic but I think I should be able to find my way through swapping the sensor once I get one.

I'm not ignoring your comment that it's more likely to be the sensor at fault. I appreciate the input and have no experience with this to draw on.

in the document I linked to it turned out to be the ICM but in that case it was a no-start and in my case it is an intermittent issue where it appears it just stops firing completely, but momentarily.

I'm thinking that if I can prove the distributor hall sensor is at fault by seeing an intermittent signal I will also know the cause before I go monkeying with the distributor. You may be a step ahead of me having seen this in the past.

Phil

 

that previous document I linked to said the ignition module was near the air cleaner. Mine goes into the wiring harness so I assume it's just a difference between years and mine must be down to the left of the drivers feet.

I guess the system I have was short lived as they went to the TDC sensor that looks at the flywheel plate shortly after.

in this document he explains to open the wiring harness and to me that sounds like a lot of extra work, I think I'm comfortable just splicing the sensor wire instead.. it means opening the sheathing but I can just repair the sheathing with a little copper foil or substitute a few wraps of solder wick. Even if I had to replace the cable I think it would be better to leave the harness alone and just clip any unused wire.

http://www.stepbystepvolvo.com/Resou...or%20Cable.pdf

The symptoms sound the same in this document, the car runs fine and periodically quits, usually just for a short period of time.

Now I just need to figure out where to get new hall sensors. If anyone had a cross reference to the part number of the sensor or even the volvo part number it would be helpful. Ill visit my local independent volvo dealer but I don't know if he is just going to try to sell me a new distributor or if he'll have the part available. Ill find out but I bet this same sensor is used all over the place in other applications.
phil

 

I decided to just order the hall sensor from rock auto its 90 for the sensor or I found I can get. The "reluctor plate" which is the distributor plate with hall sensor and connector

I'll report results after I try that
Thanks for the advice
Phil

 

I changed the timing belt and seals. One of the seals had a lip that was flipped over. I installed the smaller one then the cover, then the crank seal. It seemed easier to get the cover back with the seals oriented properly. Shows it pays to check under the seals with a little mirror..

The distributor was oily I ordered the hall sensor pre mounted on a new distributor plate and was able to find o rings to fit.

The main issues seem to be resolved I need to check the timing the idles a tad high but it seems to have stopped stalling thank you all for the help

I'll still need to find the flame trap thing to check if it's clogged.

At least I have new fuel pumps and a new relay timing belt. O2 sensor.. Changed most of the rubber bushings for the alternator etc.. Runs better now

Thanks again
Phil