Car wont start help

[spesh]

hi dont know if anyone will know but got to be worth a shot, my 850 t5 wont start, when you turn the key the engine turns over but doesnt fire, BUT the strange thing is that the rev counter goes up to 3000 rpm and back down to 1000rmp and up and down, but the engine is only at cranking over speed, i have fuel to the rail but the spark seems to be half hearted, think it might be the coil (new one coming tommorrow), but why is the rev counter goin up and down, is this a sign of any sensor failing (cam sensor maybe), the are no fault codes either, i dont think there is a loose connection as ive checked everythng with a plug, any help would be great, thanks

[jonno12]

normally the sign of a dodgy lead

[nobananas]

Where are you checking the spark from Spesh ?, coil lead or plug lead ?. If threre's a fat spark at the coil lead but weak spark at the plug lead then a dizzy cap and rotor arm maybe in order.

[spesh]

the leads are newish magnicor ones rotor arm and dizzy cap all new, this happened all of a sudden like someone flicked a switch, checked spark on each lead spark end, the is no damp in the cap, everything seems ok, but the rev counter wouldnt jump around if it was a plug or lead or cap, cause as soon as it failed then the rev counter was all over the place,

[nobananas]

Could well be cam or crank sensor then, or possibly a ignition module/coil problem but I wouldn't have thought that would cause your rev counter madness either. Have you checked all your earths as a dodgy earth can cause all sorts of weirdness and the Volvo's seem to be blessed with several earth points !

[spesh]

well ill fit the new coil when it comes tommorrow, then look down a faulty earth root, thanks

[t5 stealth]

fuel pump relay....u shld hav a lot of pressure at the fuel rail if its working.....if its not a lot of pressure and it only has a small dribble (i know the feeling) lol its probly the relay...the rev counter will flick about cos its still gettin a signal & sparks etc...its just missing the fuel bit .

[t5 stealth]

sit in the car with the door shut & in quietness...turn on ignition...u should hear the fuel pump buzz for about 4 seconds then stop...if you dont hear it buzz then id say the relay aint working mate..............

[spesh]

new fuel pump and new relay, pump is priming just fine when the ignition is on, thanks though, next idea, lol

[Alan M]

I have a cam position sensor spare if you want to try that. Send me a PM and I'll sort something out, you will just need to post it back when you have finished.