Stalling in hot weather Topic is solved

[Oitsujosh]

Ok I'm stumped on this one. My 98 XC70 a few weeks ago on a day above 75f while sitting at a light after driving about 20mi, the car just stumbled and died. After sitting a bit the car started and ran fine. Unable to recreate the issue, i drove the car the last few cooler weeks No problem. Friday it happened again to My wife at A drive thru after A 20mi trip on A day above 80f. I got it there and started and drove back home. I checked the battery when I got home and found it was low on voltage and two end cells were a little down on fluid. I suspected it as it was an older battery. Put A New battery in it today above 90f and while on My way home from a 20mi run it did it again. Once it stalls if you try to start it right away it May start and run 10-20 seconds and stumble and die. After it sat a few minutes it started and made it home I let it run and it didn't die. I'm hesitant to take it out as it's going to be above 90 the next few days. I am overdue for an oil change and it's down A bit but still within the marks on the stuck. I noticed when it was stumbling the oil light was flickering, is it possible the oil is thinning out and losing pressure causing it to shut down? Otherwise where else should I look?

Thanks in advance,
Josh

[misha]

Fuel pump relay,most likely.
Jump it and try it like that for a few days.
Info is in the repair database.

[Oitsujosh]

I'm sorry I forgot to put it in the first post, the first time it happened I checked for pressure at the fuel rail by removing the blue cap and pressing the insert before checking the battery. I wasn't able to check it while cranking though, would that make a difference?

[erikv11]

So you mean there was pressure at the rail, even though it wouldn't start? I agree that makes the fuel pump relay idea seem less likely, but I would still check it out with a jumper wire like misha suggested. It is cheap and easy to check (but you risk getting stranded out there).

The bottom line is, this looks and smells like an electrical problem: when the engine compartment gets hot, some electrical component increases its resistance too high (e.g. due to a failing solder joint in a relay) and no longer conducts enough current to do the job. Most common electrical items to fail, in approximate order:
1 fuel pump relay
2 Cam position sensor
3 fuel injection system main relay (although you 98 probably doesn't have one)
4 Crank sensor
5 something else

If jumping the fuel relay doesn't solve it, then be more systematic (or be systematic now!): look at the no-start thread pinned to the top of the sub-forum, when it is disabled you need to go through checking for spark, fuel and compression. The problem is most probably spark or fuel here.

[Oitsujosh]

Erikv11, after attempting to start I checked the fuel rail. I don't have a pressure gauge but when I pressed the insert there was a good amount of pressure with fuel coming out. I it seems electrical to me as well I was there were known heat related culprits. I only seem to have a few minutes when the conditions are present to try and diagnose it.

[Oitsujosh]

Ok, I had to run to my work to pick up my multimeter when I car ran fine getting there. so I checked the crank sensor there and it was over 375 ohms. On the no start thread I saw it should only be 300 +- 40, I checked again 20 min later and it only dropped to 360 ohm. so I'm thinking that is the culprit I'll keep you guys posted.

[rguzz]

Miles and fuel pump replacement history? On every car I have ever owned this is classic fuel pump badness, +- related relays. When it gets hot it is stressed, cools down and is okay for a while. If the history is unknown, get the fuel pressure properly tested. Could be some other Volvo thing but I'd want piece of mind on this one, you'll need that anyway even if it checks out fine. Avoid shotgun (expensive) replacement of items as guesswork.

[Oitsujosh]

Rguzz, 155k miles and I've replaced the fuel pump and sending unit in the car about a year ago that's why I've more or less skipped by it. They way it stumbles makes me think it's electrical, Once it starts to go the throttle seems to have no effect on it at all. My local volvo dealer should have the crank sensor the morning. It appears original so either way probably nut a bad idea to do it anyway.

[misha]

It doesn't matter if it's still original.They are not prone to failure at all if they aren't damaged somehow.
It would be a good idea to read the codes if check engine light is ON,before you start spending money on guessing.
Bad crank sensor will throw a code,but bad fuel pump relay will not.

[misha]

...3 fuel injection system main relay (although you 98 probably doesn't have one)...

I may be mistaken,but if i remember correctly...Lee once said that it is still present in s,v,c,xc70 cars.Probably up to '99.