Ignition problem (B230K)

Hi all!

I recently bought a 740 GL -87 with 400.000 km on the clock, but still is in pretty good shape. Amazing cars... However, the ignition system is not quite what it should be. Brief story: The car runs fine for a while, then suddenly start misfiring. The tachometer drops to zero and the engine looses all power, after maybe a second the engine fires again (tachometer needle jumping up), then looses it all over again. This can last anything between one minute (and the rest of the ride is fine) to several minutes and at last stopping completly and not being able to restart.

Reading the 700/900 FAQ, some different Volvo forums and Usenet, I've learned a bit about this fault. I'm quite certain that there are no fuel problems, since the misfirings happens so "fast" - there is no middle ground, there either is spark or there is not. Also, I think that the problem is on the low tension side because of the tachometer dropping instantly when it happens. (I've checked plugs, plug wires, coil, rotor and dist cap - all seem OK. Measured coil resistance just in case, also OK.)

Suspecting the Hall Effect sensor, I dismantled the distributor yesterday. The connections seem fine, pulling the connector when idling does not affect engine (same thing with coil connections). When measuring the voltage at the sensor as described in the 700/900 FAQ the voltage that should be below 0.7 V is 1.9-2.0 V in my car. All other voltages are correct. (I measured this at the sensor and not at the ECU, but I don't think that would matter?)

The strange thing is, after mounting the distributor again the car ran fine for about 5 minutes - then started misfiring. Would a bad Hall sensor really cause this type of intermittancy? It seems more like there is a loose connection somewhere, but I'm not sure where to look. I'll have a look at the ignition power module tonight to see what the connections are like there. I don't think that the module itself is bad, since the misfire has appeared right from cold start a couple of times and it doesn't matter whether I'm accelerating or not. (Spark is either good or non-existant, it seems.)

I'd really hate to spend ~1200 SEK (£90) on a used distributor from the breakers if there is just a faulty connection somewhere. According to the FAQ, replacing just the sensor doesn't look like a job for the fainted hearted, either. :-)

Sorry for the long post, any help is appreciated...

/Andreas

HI ANDREAS,
I HAD SAME PROBLEM WITH MY 740 B200E 1989. ENGINE WOULD CUT OUT FOR A SPLIT SECOND AND REV COUNTER WOULD DROP TO ZERO. I DID CHANGE THE HALL SENSOR WHICH TURNED OUT TO BE NOT VERY DIFFICULT AS LONG AS YOU TOOK YOUR TIME AND WAS CAREFUL WHEN PEINING OVER PINS THAT HOLD IT ON.
THE JOB IS MUCH EASIER WITH PARTNER TO HELP HOLD SENSOR IN PLACE.
NEW SENSOR COST ME £55.00. INCLUDING BLACK HOUSING FOR WIRES FROM MY LOCAL VOLVO DEALER. CAR IS SPOT ON SINCE REPAIR.
HOPE THIS IS OF HELP.
REGARDS JOHN.
:-)

Thank you for your reply. Having checked the power module, which connections seemed fine, I guess it's time to head down the Hall sensor road.

When checking spare parts, there seem to be only one type of sensor. But my distributor does not look quite like the one pictured in the FAQ. Are the sensors still the same or is there different ones depending on distributor type?

Distributor from FAQ:
http://www.brickboard.com/FAQ/700-90...HallSensor.gif

My distributor:
http://www.anlo.net/dist01.jpg

http://www.anlo.net/dist02.jpg

My distributor have the following numbers inscribed, and is manufactured in 1984 according to the "diecast stamp" on the back.
1235102005
0237502001 TH4

/Anlo

Hmm, I just realized that my distributor might look just the same if the shaft is removed.
Can anyone confirm if that is the case?

/Anlo, feeling a bit stupid... ;-)

yes it is same distributor, shaft must be removed. ensure the orientation of drive is checked before shaft is dismantled as it can be replaced 180 degrees out of line. i.e. the two arms on drive are slightly off centre. also note how washers come off and replace same way. take note of other faq replies and you should not go wrong, it helped me to sort mine
good luck. john

[BillB]

In case you haven't ordered a hall yet, I am almost certain that is your problem. As it fails, that lower voltage rises and causes the voltage DIFFERENCE to be too small, causing loss of spark (because the ECU stops triggering). You can substitute a function generator for the hall with a 5v square wave (if you know an electronics person!). You may be lucky in getting a complete distributor from a breakers - they have often been replaced on high milers. I paid £10 two years ago nearly and it's still going strong. When they eventually fail (it is gradual, this being the characteristic of a semiconductor) you may get bad backfiring, but don't wait that long, of course. Regards.

Turned the distributor in to a local Bosch workshop yesterday to have the Hall sensor replaced. Considering the 500 SEK (£38) in labour, I thought it was worth the money not risking breaking the base plate or the new sensor.

Mounted the distributor today and now the car is all fine again. Went for a long drive around town and not a single misfire. :-) I've also had some slight backfiring before, just some "puff-puff-puff" sounds from the exhaust pipe when coasting but I didn't hear anything like that now.

Another question, though. I inspected the throttle microswitch and discovered that the previous owner has tied the switch "arm" so that it always is in the idling position (throttle pedal not depressed). This seems kind of suspect, what would the reaction be if I remove the wire holding the switch in? I guess I'll have to remove it and see if the engine runs better or worse. The fuel consumption seems a bit high too, but it is an old and big car after all (16 liters/100 kilometer, whatever that would be in mpg).

Thanks for the advice

/Anlo

http://pic7.picturetrail.com/VOL188/...8/23744414.jpg


The throttle switch retards the timing when closed to give a smoother idle.

Try releasing it and check the adjustment ( it should click immediately the throttle starts to open )

This may have been done to cure pinking.
If it starts to pink with the switch operating the timing should be checked and reset to standard.

If the fuel consumption you quoted ( 28mpg ) is a mix of urban and main road driving it`s not too bad.
My 740SE ( 2litre injection ) does about 20mpg around town and 30mpg cruising at 80mph + on the motorway.

Colin.

1990 740SE B200E/M47, remote C/Locking.

Yesterday I removed the wire holding the throttle switch in and adjusted it to click just when the throttle opens. I didn't hear any pinking noise, but the car ran very bad.

Normally (with the wire in place), the car hesitates when driving off from standing still. I have to rev it to about 1500 rpm before releasing the clutch, otherwise the engine chokes and almost stops (especially when cold).

This behavior got worse with the throttle switch adjusted correctly. The engine would almost die every time I drove off from a stop light, and didn't run well at speed either (esp. acceleration from low revs).

I guess I'll have to get hold of an ignition timing lamp to see what the timing is really set at. I still have some backfiring when coasting which suggests that the timing is retarded to much, but advancing the timing by adjusting the throttle switch probably wasn't the only thing needed to get the car running OK.

/Anlo

>Yesterday I removed the wire holding the throttle switch in
>and adjusted it to click just when the throttle opens. I
>didn't hear any pinking noise, but the car ran very bad.
>
>Normally (with the wire in place), the car hesitates when
>driving off from standing still. I have to rev it to about
>1500 rpm before releasing the clutch, otherwise the engine
>chokes and almost stops (especially when cold).
>
>This behavior got worse with the throttle switch adjusted
>correctly. The engine would almost die every time I drove off
>from a stop light, and didn't run well at speed either (esp.
>acceleration from low revs).
>
>I guess I'll have to get hold of an ignition timing lamp to
>see what the timing is really set at. I still have some
>backfiring when coasting which suggests that the timing is
>retarded to much, but advancing the timing by adjusting the
>throttle switch probably wasn't the only thing needed to get
>the car running OK.
>
>/Anlo
>



Hi Anlo

I had the same problem as you.
And I replaced the Hull sensor just recently, it is a fairly straight forward job.
The hardest job of all is driving the pin out of the dog drive (I think thats what they call it.) But I also found out that some of the wiring loom which was connected to the Hull sensor was crumblering and had some broken wires in it, so I replaced a short section of the wiring loom .This wiring loom looks like to me very much like coacxal, but with 2 wires inside it and the third woven & platted around the outside and then insolated over the top I just cut out the bad bit, and installed 3 new pieces of wire connected them up at each end taped them up and hey presto it works..

Watering Can