89 Volvo 740 Random Stalls Ignition Failure

NateR · Post by **NateR** » 09 Feb 2005, 12:10

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 occaisional (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

Thanks!

Guest · Post by **Guest** » 09 Feb 2005, 12:26

I have read this could be the Throttle Position Sensor if that rings a bell with anyone.

dmf volvo freak · Post by **dmf volvo freak** » 10 Feb 2005, 04:34

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.

http://www.swedishbricks.net/700900FAQ/ ... n%20System

Volvord · Post by **Volvord** » 10 Feb 2005, 17:31

Please do a search of this site for the solution, this topic has been covered many many times.

Check here https://www.matthewsvolvosite.com/chat/p ... php?t=2669

Guest · Post by **Guest** » 12 Feb 2005, 00:03

Volvord 784VC wrote:Please do a search of this site for the solution, this topic has been covered many many times.

Check here https://www.matthewsvolvosite.com/chat/p ... php?t=2669

Yes, I see you have had this issue. Care to lend any advice?

Jim Tatler · Post by **Jim Tatler** » 12 Feb 2005, 09:21

Hi folks, seems like I am having a similar problem with my 940. Periodically just stalls, i then sit at the roadside with ignition turned off for about a minute then away she goes as if nothing had happened. Cany anyone shed some light as to how I cure this irritating problem...once occurred on the motorway luckily I was in the nearside lane and could get to the hard shoulder.

RJL-CSUN · Post by **RJL-CSUN** » 24 Feb 2005, 11:17

I found this in a related thread:

my 850 turbo wagon had the same stalling problem. mine usually occured after fueling. after new plugs, wires, ignition coil, etc. - we found it was the valve in the line that sends fuel to the charcoal canister. it was alowing fuel instead of vapor through, and the return line dumping fuel in to the motor was causing the stall.

Does anybody know how to access this part, how hard it is to change, and how to tell if it is bad?

Also, there seemed to be reports that changing the fuel filter, pump, relay, etc. would help. And, throttle body and fuel trap were mentioned! In my case, especially when on the freeway, it can stall and then come back to life after a few seconds, though other times I will have to find a way to the shoulder and wait a few minutes to be able to start it. If I try to start it too soon, it is very rough and quickly dies.

Should I try to change this valve? The fuel filter? (Pump and relay were recently changed at the dealer. I'm not sure how old the filter is.) This is very annoying and dangerous.

Thanks!

LaRy · Post by **LaRy** » 24 Feb 2005, 12:31

It could also be something with the ignition, that is a common problem. Next time it stalls, check the rpm-meter if it drops to zero rpm. If it does, it is most likely the hall sensor or the power module.

LaRy · Post by **LaRy** » 24 Feb 2005, 12:48

Now I have read your diagnostic more carefully. I would say that this is a typical Hall sensor problem or ignition power module. Also the fact when and how it happens is typical. The fact that the tacho is dropping is definitely showing that you do not have any ignition. The tacho is checking the frequenzy of the pulses coming from power module to the ignition coil. If tacho is showing zero or crazy values, with stalled still rotating engine, ignition is also definitely zero! The tacho is actually one of the wires connected straight to the ignition coil pimary side, so it is giving very valuable information of the condition of ignition. It is very hard with ordinary tools to find out if it is the hall sensor or the power module. So I suggest that you should change both.

Guest · Post by **Guest** » 26 Feb 2005, 00:50

LaRy, if you're responding to me, than thank you very much for the help. I'll mention this to my mechanic.