Volvo 940 warm/hot start problem | Technical matters | Back Room Forum

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Tue 15 Oct 2002 08:40

Volvo 940 warm/hot start problem - volvoman

For some time now my 940 se turbo has had a minor problem starting when the engine is hot/warm. This is most evident when we take a trip to the out of town shopping centre and have to drive between stores. The car will usually start fine but then immediately die and this may happen several times. It's not a major problem, mainly annoying but I recall a similar fault on my old Rover 800 which was much harder to restart and was never resolved. Other than this, the car runs fine (touching wood as I type !!!).

ps. The MAF sensor was recently cleaned and replaced following an engine management (lambda) warning light problem which has not recurred to date (more touching of wood).

Anyone got any ideas as to what mught be wrong ??

Ta, as always.

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Wed 16 Oct 2002 20:44

Volvo 940 warm/hot start problem - MG

my 940 has the same problem but in the case of cold starting. This could be due to the 222000 miles it has covered but more likly to be the fuel flow problems my mechanic says. He reckons its to do with it evapourating or draining out of the pipes or the pump at temprature or summit??

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Wed 16 Oct 2002 21:06

Volvo 940 warm/hot start problem - volvoman

MG - Mine (1991 H plate) has done 138k and had suffered from this problem for some time now. I recently had and MAF sensor fault diagnosed following the appearance of the dreaded amber engine management light (lambda) so I'm wondering if that has something to do with the poor starting. Let's hope one of our more technical pals can shed some light on what's wrong.

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Wed 16 Oct 2002 22:40

Volvo 940 warm/hot start problem - 659FBE

Check very carefully the relay which supplies the fuel injection system, often mounted on the coolant tank. It develops broken soldered joints inside, and will test ok on a multimeter, but goes high resistance when supplying current to the cold start valve and/or injectors. For some reason, Volvo did not fit a Bosch relay, but used some East European junk. This fault can be very hard to find.

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Thu 17 Oct 2002 08:32

Volvo 940 warm/hot start problem - volvoman

Thanks 659FBE.

I'm not sure it's connected but on the odd occasion we have a hot day and the car has been left in the sun all day it also shows similar symptoms of difficult starting i.e. it starts then cuts out almost immediately.

Any more thoughts ?

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Thu 17 Oct 2002 09:39

Volvo 940 warm/hot start problem - Peter D

Had his been there on my volvo. In my case the engine would not fire at all then 10 15 minutes later bingo no problem. No fault light and no smell of fuel Important point.

Turned out to be a marginal sensor on the Flywheel housing that controls the timing and TDC. This sensor had a slightly now output waveform at cranking speed thus no injector action no spark. I have also heard of this being the cause of the start then instantly stop problem. The sensor was redesigned and has the same partnumber but a different colour band on the cable. Speek to Volvo on this issue. Cost £22

Good Luck Peter

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Thu 17 Oct 2002 18:38

Volvo 940 warm/hot start problem - 659FBE

Peter, You are dead right. I've met this problem with the speed probe on the flywheel too. In my case, the tip was covered in magnetic swarf caused by ham fisted starter operation. Volvo are not too clever at these things (fancy putting the relay on a coolant header tank), but the mechanical bits on these cars last so long that the interesting and infuriating electrical problems tend to show up. The Bosch bits are generally reliable. Try cleaning the probe first.

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Fri 18 Oct 2002 08:34

Volvo 940 warm/hot start problem - volvoman

Thanks for the help so far guys !

Could any of the above be the cause of my problem starting when the car's been out in the sun all day ? The odd thing is the car will restart fine after dying and providing I keep the revs up to say 1500 for a short time (say 20 seconds) it will then run OK.

I've never noticed any smell of petrol but the symptoms when starting after the car has been driven around a bit and when it's just been in the sun for a long time before I need to start it seem to be identical.

Thanks for all the feedback ;-)

ps Had a fault with the MAF sensor a few weeks ago which was cleared and hasn't reappeared, could this be relevant ?

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Fri 31 Oct 2014 19:50

Volvo 940 warm/hot start problem - andy50220

Ok I know this message was posted 12 years ag, but I'm answering here because it features very high in a google search for this issue.

Hot start issues are common on Volvo 940, happily they are easy to diagnose and fix.

If the car starts perfectly when cold, but refuses to start when hot (often after a short stop) the it's almost certainly one of three components. 1/ The Fuel Pump relay, located behind the ashtray, cheap to replace.

2/ The RSR Relay, often next to coolant tank. This provides power to the fuel system when starting.

3/ The crank position sensor. All three components can fail on older volvo 940s and cause hot start issues, it's good preventative maintenance to just change all three and be done with it.

If the car starts after a long time cranking and then runs rough for a while then it's most likely the fuel pressure regulator. Again this is cheap and easy to replace.

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