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How to Diagnose Stalling Problems

diagnose stalling

MVS forum member NateR documents a recent experience he had while commuting. He talks about his 89 Volvo 740 Turbo having issues with sudden drops in rpm. The car never actually stalled but came close. How can we come together to diagnose stalling problems with our Volvos? Chime in to add to this great discussion.

I’ve had my 89 Volvo 740 Turbo for a few years now, always running great. Recently, I started commuting to college, about an hour drive each way. Shortly after the heavy highway use began, driving 65-75 mph, I would notice an occasional (maybe 2 or 3 times per trip) sudden drop in RPMs (and power), for a quick second, then a regaining of power. It wouldn’t actually stall, but seemed to come close. My mechanic asked me if I would then hear a backfire or pop, and I said no.

I kept driving it, then yesterday it happened again, the needle dropped to zero, engine still running, I pumped the gas pedal, it regained RPMs, and then popped or backfired out of the exhaust.
I made it home safely. Then, in town, at a stop light, it stalled for the first time ever. I tried to turn it over, but it wouldn’t start. I pushed it to the side of the road, waited 5 minutes, and she started right up. Drove through town and made it home.

As a student, I don’t have a ton of money. My mechanic said instead of just randomly replacing parts, we need it to actually fail to find out what’s wrong. I could let it idle at his shop the whole day and hope it fails, but I’d would greatly appreciate any advice on what may be causing this problem. The last thing I want is for it to fail on the highway when I’m driving up to school to take a mid-term 😳

MVS forum member dmf volvo freak asks:

Hi – I am having somewhat similar issues with my 88 760T wagon. So far it always starts back up and I experience strange erratic rpm on the tach when it is acting up. It sounds like from my research that we are both suffering from ignition issues particularly related to the hall sensor (88) or RPM sensor in the disrtibution (89 is RPM) , the potential for shorts in the wiring harness or bad connections in the ignition, and also a failed or fluky ignition power boost unit. Not that I am advicating radom changing of parts to find the bad one, but I picked up a ignition power boost with nothing but a screwdriver and $10 at the junk yard off a nice 9 series – same part number etc. I installed and yet to see if that solves, but if $10 gives me a 1 in 3, it is well worth it. Careful on the sensor connector on the back of the distributor, I may have just screwed that up sufficiently for me to think about replacing the distributor itself.

How to Dignose Stalling Problems

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