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Tell me about how awful it is to change an impulse sensor on this model.[740-760/1989] posted by Jarrod on
Wednesday, 19 August 1998, at 3:56 p.m.
I still don't have a manual for my car. I don't know what I'm waiting for.
My car has been stalling too much so I have been biking for a week now. (My woman's car...my old 240 runs better and is more reliable!) I finally got my hands on the impulse sender (otherwise known as the Hall effect thingy...and get it at your dealer...well you have no choice). So I'm ready to start work but I know that damn distributor is back by the firewall, behind the engine.
Any tricks to getting at this? What tools will I need?
I should do some background here: the car suddenly stalls with little warning. Actually it now goes off...on...off..on in very rapid succession and then blamo or whisper it stops running and I coast to the side of the road. I sit there for maybe a minute or so and it starts right back up. Well it stalls too often now to tolerate. I have posted here before about this and many have told me it's the device I just bought that goes flakey.
One would guess that it is the fuel pump relay but often one is wrong(in fact on Cartalk they lost "Stump the Chump" when they told a woman to change the fuel pump relay and it did nothing.
So I just bought the impulse sender.
My car has 140k or so so a new fuel pump wouldn't hurt I suppose. I just might do what my grampa would do(though he would never have bought a fuel injected car), I'm going to pry the relay apart (if needed) and clean it with tuner bath and emery.
I'm kinda just talking here but any advice would be appreciated.
-jarrod
Re: Tell me about how awful it is to change an impulse sensor on this model.[740-760/1989] posted by abe crombie on
Wednesday, 19 August 1998, at 6:40 p.m.
If your car is a non-turbo 89 model then it has a flywheel reading RPM/Position sensor that is down below rear of cyl head stuck through a bracket retained by one bolt that should be a 10mm head on a 89. If it is 89 turbo then it has the hall switch that is in distributor. The hall switch is kinda tough as it requires that you knock out a pin and pull out shaft, then VERY carefully drill out a couple of pins that retain hall switch. Then you have to be very carefull about supporting the dist base while bradding the retainer pins to retain the new hall switch. If you slip while bradding the pins then you punch out hole ins in dist base and the you need a new dist.
Re: Tell me about how awful it is to change an impulse sensor on this model.[740-760/1989] posted by jarrod on
Wednesday, 19 August 1998, at 10:01 p.m.
It's a non-turbo (GL).
So the hall switch does not exist on this model?
I am very confused about this "RPM/Position sensor." Is it easy to remove? Sounds like it. I would guess it's hard to get at judging by your description of where it's located. I should mess with the fuel pump relay first. Do these RPM/Position sensors get replaced often?
I finally got the '82-'88 Haynes 740-760 manual. Helps some.
So the volvo dealer sold me a hall sensor for a non-turbo which doesn't exist? I suppose I could have been better informed but they should catch stuff like that with there fancy pants computers (Borton has some cool boxes).
-jarrod
Re: Tell me about how awful it is to change an impulse sensor on this model.[740-760/1989] posted by abe crombie on
Wednesday, 19 August 1998, at 11:32 p.m.
The turbo/nonturbo thing probably slipped by the counter guy.
The sensor is not hard to remove on a cold engine usually. They can swell and be hard to get out. The fuel pump/sytem relay inside behind ashtray and the auxiliary relay in eng compartment are both worth a look.
To check for possible aux relay trouble use a volt meter between one of the green wires on any of the injectors and the batt pos post. It should be less than .3 V (<300mV).
To check for possible fuel pump relay failure go between center of cig lighter plug and fuse 11, should be less than .5 V (<500mV). Excessive resistance creates voltage drops that will exceed these values. The volt drops will be high due to poor contact points in relays or the solder joint problems.
It is best to check these volt drops after it has run for a while as that is when the failures usually occur.
Re: Tell me about how awful it is to change an impulse sensor on this model.[740-760/1989] posted by Jim Bradley on
Wednesday, 19 August 1998, at 7:13 p.m.
First a comment on the tuner bath and emery. Forget it. If your problem is in fact the fuel pump relay, just replace it. The old clean and file approach won't work on this sensitive low current relay. I had a similar problem on my '89 780, and the problem was, in fact, the fuel pump relay. Try this. If the car quits and won't restart, try banging your fist or similar thumper on the left side of console, at about ash tray height while cranking the engine. If it starts, the relay is probably flakey. It sounds wierd, but that's how I found my problem. If you want to be more sophisticated, use a volt meter to check the voltage to ground at the injection ballast resistors. You should see 12 volts when you turn the key on. If not, thump the console. If the voltage comes on, it's the fuel system (pump) relay. $29.75 with VCOA discount.
Back to the issue of the hall pick-up. Changing that is not for the novice. It is riveted into the distributor. Some dealers offer rebuilt exchange on the distributors. Before you jump to the hall sensor, carefully examine the wires from the firewall to the distributor, which sometimes break inside from years of flexing. These can be repaired with a little work. Also, check the brittle plastic connector where the wires go into the distributor. This can cause intermittent shorting. The plastic fitting is Volvo PN 1346793, about $3.00 as I recall. If you are going to remove the distributor for any reason, carefully scribe a mark to return it to its exact former position so as not to change the timing (the holes in the distributor are slotted).
Good luck. Hope this has been some help.
Re: Tell me about how awful it is to change an impulse sensor on this model.[740-760/1989] posted by Don Foster on
Wednesday, 19 August 1998, at 9:24 p.m.
Jarrod ---
I agree with Jim, sort of. You'll do absolutely nothing useful with tuner clearer or filing the contacts. In fact, you may damage it more -- replacing is a very good option. However, because I'm a cheap Yankee, I prefer to fix when possible. (There's an element of pride in that, outsmarting the parts man!)
The Bosch relays can be resoldered very easily by anyone handy with a soldering iron and soldering gun. And a little experience. Remove the plastic relay cover and examine the foil side of the printed circuit board (on the flip side from the electronic components). With a magnifying glass you'll probably see the solder cracked, crystallized, and overheated around the heavy connections to the actual relay -- they look like little "buttons" coming through the silvery solder.
I use a soldering gun the heat & resolder these heavy connections, and a small 25 Watt iron for the other connections. Be very careful not to form a "solder bridge" between adjacent foil traces. George Swift suggests drilling several holes in the plastic case for ventilation -- a good idea.
--Thursday, 20 August 1998, at 6:12 p.m.
I believe the relay that Don is referring to is the older type with the circuit board inside as was used in the older 240's. I don't think that the relay in the '89 740-760 has the circuit board. My '89 just has two small relays inside.