1991 Volvo 740 stalls when hot, replacing parts by chance

janefinch · Post by **janefinch** » 28 May 2014, 10:10

Hello
My 91 Volvo 740 stalls while driving. Non-turbo at 355,000 kms. Let sit for up to ten minutes and it starts again. Sometimes lately for only a block or two then stalls. Always starts after short time...but never stalls when at the Volvo mechanics place.
Not sure of its repair history, whats old and whats not.

Being on layoff not having anyone that can perform diagnostics I would like to begin changing sensors etc in the hopes sooner or later it will start. I believe I can change repair sensors myself. I dont mind if a boughten sensor does not fix the stall problem because at least I know its new and have a spare.

Any ideas where I should start.
Timing belt was changed recently.
When in the no start mode I can still hear fuel pump whirling and relay by ashtray clicks u7pon turning key so I think I can say that part is working.
Brought to Volvo dealer they checked but found no problem as in was not in its stall mode. They say it had an unreadable code tho.

Thank you
Jane

lummert · Post by **lummert** » 28 May 2014, 13:27

When I had this problem with my 1988 760 Turbo wagon, it was caused by the in-tank fuel pump being inoperative. Does this not happen with a 3/4 to full tank? The under car main pump will be quite noisy if the in-tank pump doesn't run because it has to work so hard to pull fuel from the tank. This problem gets much worse as the summer gets hotter.

Post by **precopster** » 28 May 2014, 15:18

As above try running the car at 3/4 minimum tank all week and see if the stalling stops.

My 740 turbo had a fuel relay problem causing the same symptoms. There are 2 relays in the engine bay (grey boxes)

One of them is the fuel relay.

lummert · Post by **lummert** » 28 May 2014, 15:42

precopster wrote:As above try running the car at 3/4 minimum tank all week and see if the stalling stops.

My 740 turbo had a fuel relay problem causing the same symptoms. There are 2 relays in the engine bay (grey boxes)

One of them is the fuel relay.

Yes, I had fuel pump relay problems too until I got out the soldering iron and fixed it, along with fixing 2 spares.

janefinch · Post by **janefinch** » 28 May 2014, 15:58

Thanks you guys for your responses.
In the no start mode I can hear the fuel pump whirl with my ear over the spout, as well when Its in the no start mode I can feel the fuel relay click upon turning the key.

Regardless of the fuel level it stalls out all the same.

Thanks...I really do appreciate your advice & words.
So then can I rule out the fuel pump & relay or do they still sort of operate even though they are faulting?

lummert · Post by **lummert** » 28 May 2014, 16:36

In the engine compartment are 2 identical relays with 4 barrel connectors each. One is for the A/C pusher fan in front of the radiator. The other is the Radio Interference Suppression Relay. The (RISR) supplies 12 volts to the injectors . This relay is triggered by the fuel pump relay. Try swapping these 2 identical relays.

janefinch · Post by **janefinch** » 28 May 2014, 17:09

lummert wrote:In the engine compartment are 2 identical relays with 4 barrel connectors each. One is for the A/C pusher fan in front of the radiator. The other is the Radio Interference Suppression Relay. The (RISR) supplies 12 volts to the injectors . This relay is triggered by the fuel pump relay. Try swapping these 2 identical relays.

Ok thanks. I just run outside & had a look.
The two identical relays like you describe I found on a bracket attached to the anti-freeze reservoir. ??
Both have 4 pins & reading the same specs & part number.

I will price them & change them both. If still stalling I,m still ok with that as rather have new ones, planning on keeping this Volvo forever.

Thanks!

janefinch · Post by **janefinch** » 28 May 2014, 17:51

I found out just now that when its running fine and idling in the driveway I can make it not start up by turning it off and on again a few times. After keying it on & off a few times its a no start until about 1 minute later than starts fine.

lummert · Post by **lummert** » 28 May 2014, 19:21

janefinch wrote:
lummert wrote:In the engine compartment are 2 identical relays with 4 barrel connectors each. One is for the A/C pusher fan in front of the radiator. The other is the Radio Interference Suppression Relay. The (RISR) supplies 12 volts to the injectors . This relay is triggered by the fuel pump relay. Try swapping these 2 identical relays.
Ok thanks. I just run outside & had a look.
The two identical relays like you describe I found on a bracket attached to the anti-freeze reservoir. ??
Both have 4 pins & reading the same specs & part number.

I will price them & change them both. If still stalling I,m still ok with that as rather have new ones, planning on keeping this Volvo forever.

The A/C pusher fan relay...do I even need that as the air conditioning does not work anyway. Later project. Compressor not turning on. :edited never mind, I think the Volvo needs this regardless of whether the a/c works or not

Thanks!

This is why I suggested swapping out the 2 identical relays. It's a good way to test the relay before running down to the parts store. Those relays are not cheap.

janefinch · Post by **janefinch** » 28 May 2014, 19:30

Ok thanks lummert. I thought you meant swapping out as swapping them for new.
Tomorrow I will try & let you know.