Strange engine fluctuations

Website · Post by **antiekeradio** » 11 Oct 2006 06:15 pm

you might want to read the following message once more....

antiekeradio wrote:OWWW...... thát problem... new diagnosis ->

its well possible that the 'tacho relay' has a broken soldering inside.

this is a known problem and can be fixed by opening up the tacho relay and resoldering the relay connections on the printed circuit board.

the weight of the relay is only supported by its electrical connections, which causes these to be stressed quite severely. liberal use of solder prevents the problem occuring again.

PS "the switch to fix the revs" is called the "low gear ratio hold switch" (or, translated literally from dutch; hill brake switch)

Post by Ed » 11 Oct 2006 06:27 pm

Hi,

I dont have a tacho meter in my volvo, i only have the clock and speedometer. im assuming this tacho relay is on the instrument panel?

Website · Post by **antiekeradio** » 11 Oct 2006 06:32 pm

nope, its the control unit of your transmission.

situated near the control valve, under the bonnet driver side, close to firewall/inner wheel arch.

good luck fiddling it open.

Post by Ed » 11 Oct 2006 06:39 pm

ok,

im with you now! which relay would it be as my manual doesnt name all the relays. is it the inhibitor relay?

Website · Post by **antiekeradio** » 11 Oct 2006 06:42 pm

its NOT a relay in the fuse box.. please look further than your nose's length or get someone 'in the know' to help you out...

Post by Ed » 11 Oct 2006 06:48 pm

well you seem to be in the 'know' so why dont you help me out! you called it a relay i assumed i was looking for a relay.

ok ive found a picture of the electromagnetic vacumn valve, there are 7 parts to this, what you are talking about is the vacumn control unit? is this correct or am i still looking in the wrong place

Website · Post by **antiekeradio** » 11 Oct 2006 10:17 pm

its a black plastic box about 5 x 5 x 1 1/2 inch.

it has a 8-pin electrical connector.

it is mounted on the same mounting plate as the white plastic vacuum valve (electromagnetic vacuum valve)

it says 'BOSCH' and 'drehzahlrelais'

Post by Ed » 12 Oct 2006 07:21 pm

checked that and found nothing wrong with it. i re tightened the nuts on the carb, checked all pipes for splits and that they are connected to something and all is fine.

any other suggestions?

Website · Post by **antiekeradio** » 13 Oct 2006 10:13 am

what did you check? have you taken it apart?

Post by **pettaw** » 15 Oct 2006 09:25 pm

How did you check the tachometric relay? Did you take it apart? Did you look at its connections?

IMO the easiest way to check the tachometric relay, is to check its function. The function of it is to open the side of the solenoid valve that controls the change-up function. It does this after 1700 rpm. Trouble is I can't remember whether it will do it all the time or whether you have to be in gear for it to work

Erm anyway, what to do is the start the car and let it idle...if it works as I remember it, what to do is to rev the car slowly up to 1700-1800 rpm when there should be a loud click from the relay...if so its working properly. If not then it isn't.

If its intermittently faulty, then you need to take it apart, because, as Wouter says, they can break the solder contacts and/or develop dry joints.

There are other possibilities as well. Come back to us with any further questions.

I would say if you're not sure then you would be better off taking it to a garage for diagnosis, but try finding a garage that understands these systems. Even most Volvo main dealers haven't got a clue of how they work or diagnosis of problems!

Post by Ed » 16 Oct 2006 10:53 am

Yes i took it apart, and i checked all components in case something else had come loose or burnt out. The relay i checked all joints and all legs, relay is solidely connected to the pcb board. i checked the points on the relay and gave them a little clean as they were a little grubby.

I was driving down the road yesterday and the engine started playing up again, so i switched the low gear switch on and off to see if there is a difference in rev pitch and there is. when the engine plays up it revs higher than when the switch is on. but when the engine is playing up switching the low gear on doesnt affect the engine it still over revs. when the engine returns to its normal state of running you can then notice the switch coming on and off.

The car did exactly the same last year at this time of year throughout the summer its fine.

I will try out making sure the relay is working later and come back to you

Ed

Website · Post by **antiekeradio** » 18 Oct 2006 09:54 am

the loud click does not come from the relay, but from the vacuum valve.

gear position is of no influence, when testing one should always use N with handbrake applied.

another possible cause is the connector/switch assembly in the interior, where the throttle cable passes trough the firewall. the connector should be grounded solidly except when full throttle is applied. (then its circuit to ground should be broken)

sometimes the connection gets a bit oxidized etc, and will play up.