On going issue (3+ years now), 850 GLS 1996 non-turbo wagon with B2525S engine, automatic.

It idles fine and revs good. Drives normally until fully warmed up. Then starts stalling when under load. Will usually still trundle along at idle on the flat but as soon as you put foot down it stalls. Then it can be rough to start and misfire badly if it does catch. Cool down after a few hours then it's Ok again. We've replaced plugs, HT leads, coil, fuel pump, and serviced it as much as possible. There is no engine light, although service comes on for a few minutes then goes off. We can't check codes because there are no Volvo dealers or suitable OBD readers in this country.

I wondered if the issue might be due to a clogged catalytic converter? If so, what's the easiest way to check, can I by pass it or loosen the fittings to allow exhaust to escape before the cat? There's no legal issue where I live (small Pacific islands country)

Thanks

 

well if you loosen the fittings you will certainly throw a check engine light code and possibly throw off the reading of the front O2 sensor which controls the fuel trim. You could go cat-free by installing a straight pipe but I don't think a clogged cat would change with temperature. As to getting an OBD2 code reader - they cost about $30 US these days and you can buy one on Amazon (lol, I'm sure they'll ship anywhere!). it'd be a small box so shipping won't be rediculous. GIven you're car seems to change behavior - have you checked the ECT sensor (its right under the thermostat cover - just follow the upper radiator hose back to the block) - You can test without removing from the car - simply measure its resistance from the connector with a VOM. It should be ~3000 ohms cold (assume 25C ambient temp) run the car then measure it warm - should drop down to 200-300 ohms. You can google for a resistance/temp chart to be more accurate.

 

Thanks mt6127. We changed the ECT sensor twice, it is not that. The problem is elusive, I took it out over the weekend and the car drove normally for 2 hours without any hint of the problem. Perhaps it was "one of those things". Still, too early to trust it in busy traffic.

 

Normally cats don't clog unless you've been burning oil or consuming coolant. The fact that you can drive with normal power at full speed also says the cat's not clogged. Two thoughts on what to look at next: I'd be suspicious of air intake or exhaust leaks throwing off the fuel trim or a fuel pressure/delivery issue. Take a look at all your vacuum lines/air boots tubing. There's a Robert DIY vid on Youtube on how to make your own smoke tester. Can you check your fuel pressure cold then warm at both idle and at some revs? A worn pump will draw too much current which can overheat the relay as well so if you find your fuel pressure is below normal, try jumpering the relay to see if it perks up. If it does you need a new relay but its just an early warning that your fuel pump is going to need replacing.

 

Well it did have a head gasket problem that occurred at the same time as the stalling issue emerged. Initially when I first noticed it stalling, there was also boiling over of coolant and dirty coolant. So we diagnosed head gasket. As there was no one here who could change it we left it 3 years but then someone was able to fix the head. The cooling system is now 100%, clean and pressurized. Also we changed for new the timing belt, fuel pump, water pump, thermostat, ECT sensor, vacuum tubes check, etc It now runs fine 95% of the time but is prone to this stalling when driven for 30 minutes or more.

When changing the fuel pump they found a resin like substance in the tank. As the fuel cap was not lockable type, we suspect someone had poured something in (you get that behavior in places like here too). So apart from catalytic converter I wondered if there could be restricted fuel lines clogged up. That may explain why it seems to be getting better (lines starting to flush out). Anyway we'll use it at weekends and see how it goes, if the problem just goes away. thanks for your welcome advice!

.

 

well if you suspect something is crudding up the fuel pump/filter/line, then I'd think that would show up in a fuel pressure test. I'd be inclined to lean toward testing out the fuel pump - ie it may be working too hard so as it warms up it loses pumping capacity or draws too much current and overloads the relay.

 

This one solved. Someone had put contamination into fuel tank, we found resin of some sort at the bottom. The stalling gradually cleared up of its own.

 

the cat should be bolted at one end . Unbolt it if so , grab a construction nail or a long bar with a sharp end , stick it in the cat , take a sledge hammer and ram that bar thru the screen in the cat at both ends . That will open it up . Or replace the cat with a piece of pipe . Weld it in.

 

Took a long time but issue finally resolved, it was a cracked fuel pump housing exacerbated by old HT cables, plugs, leaking vacuum hoses, etc. And a head gasket at the beginning. All replaced and good now, but the cracked pump housing took a long time to discover (replaced fuel pump twice, fuel relays, etc, but it didn't help, until we found that crack.
.