740 turns over but occasional no start.

Lakai07 · Post by **Lakai07** » 10 Jan 2013, 16:23

Ok so my volvo has been giving me trouble starting...it will turn over just not start At times. So I googled other reasons why it would do this before replacing the spark plugs and wires and such and I came across a thread suggesting to locate two black boxes under the hood and switch them (one goes to the cooling fan) they said if it starts right away to switch them back and replace the bad one. Can someone tell what those boxes are???

Post by **JDS60R** » 10 Jan 2013, 16:40

Sounds like electrical relays for the fan and starter motor. It sounds like your starter is working fine. You need the codes if any from your computer and check , compression, fuel and spark.

Lakai07 · Post by **Lakai07** » 10 Jan 2013, 18:55

That sounds about right thank you

Post by **chrism** » 06 Feb 2013, 15:35

One of those relays powers the cooling fan, the other is called a Radio Suppression Relay (RSR). The RSR provides electrical power to one of the wires on each of the fuel injectors. The other wire on each injector runs to the ECU which provides the switching to ground to open and close the injectors. Failed RSR's are common, generally due to failed solder joints on their internal circuit boards (which can be re-flowed if you are skilled with a small soldering iron). By swapping the wire on the relays, you are temporarily "borrowing" the fan relay to provide power to the injectors.

There are a handful of components that typically fail on those cars with old age. You really need to do some diagnosis to determine if the problem is on the ignition or on the fuel delivery side of the house, like check for spark, check the fuel pressure, etc. This will cut the possibilities in half and hopefully help you zero in on the problem.

The last thing you want to do is start throwing expensive parts at the car hoping to hit on the problem. In many cases there are ways to jumper an electrical component in order to determine if it was the weak link. One of the best forums to get help with that model car is brickboard.com (RWD).

richieb · Post by **richieb** » 14 May 2016, 16:35

Looking for a driveshaft for a 1987 740GLE Sedan. I want to put a M 47 5 speed manual in place of the M 46 4 speed with electric overdrive. Anyone out there who might have one you can e-mail me at [email protected] Thanks Richard

lummert · Post by **lummert** » 14 May 2016, 20:07

If you start a new thread you may have better luck.

93Regina · Post by **93Regina** » 14 May 2016, 22:24

chrism wrote:One of those relays powers the cooling fan, the other is called a Radio Suppression Relay (RSR).

I'm not sure if all years were consistent with that setup, iirc.

If both are the same, then yes, it can be done.