Riddle me this car geniuses

NeX

You're after my robot bee
Club Member
ok i am sick of this volvo now, i want it sold, i would happily pay £50 to the person who can solve this problem!

here's the problem,

the volvo starts every time, if i roll it down a hill and bump start it.

if i take the thick red cable from the starter motor and connect it to a separate battery, and earth that battery to the engine, and then join the small wire from the starter motor to the positive on the battery, the starter motor is now totally isolated from the rest of the electrics, the engine goes round but doesn't start.

there is nothing different between when it starts by being bumped or when i turn the starter with a separate battery.

i put the small wire on the separate battery and it goes round but doesn't fire at all, then i remove the small wire so the starter is no longer running, and push it down the hill (not changing anything at all, the bonnet is still up with the two batteries inside and everything) and it bump starts and runs, i reverse it back up the hill, switch the ignition off, switch it back on, reconnect the small wire to turn the starter and it doesn't fire.

the electrics are totally separate, i found a live feed to the injectors also attached to the starter motor so i took that off and connected it to the first battery, so the starter is fully isolated.



explain how an engine can start from a bump but not from being turned round by a motor?
 
I must say, this riddle has me completely stumped :eek:. Doesn't make any sense at all, surely there's got to be something faulty with the electrics, possibly ECU?
 
the ECU is fine because of course the engine runs when bumped. i took the ECU apart and reflowed all the contacts and checked for damages but its fine, i also checked its ground contacts and that is fine, but either way it shouldn't be a problem because it is getting the same amount of power when bumped as it is when i start the engine with a separate battery

the thing is NOTHING changes, the key is in the same position, the battery is in the same position etc,

now that i think about it there is one thing that is different, it is in gear with the clutch up when bumped.... hmmm maybe it has a neutral sensor that is stopping it from running...
 
maybe? If the starter is worn maybe it turns but not enough to fire the engine? My motorbike does this if the battery is low. I know you tried a different battery which is why my money is on an iffy starter motor.
 
maybe? If the starter is worn maybe it turns but not enough to fire the engine? My motorbike does this if the battery is low. I know you tried a different battery which is why my money is on an iffy starter motor.

yep i have tried it with 3 different batteries, the battery and starter work so well that normally i can drive the car up the hill by leaving it in gear and running it on the starter motor, then i just roll it back down and it starts. so the starter is fine, then engine goes round at normal speed (i have a second volvo to compare it to) the battery can turn it round for ages with no problems and it will still start from a bump, i used one battery to drive it up the hill twice and then used the same battery to start my micra straight after (so i could charge it back up)
 
i dont think it's the starter maybe the fuel pump may is knackered, fuel filter blocked? are sparkplugs dirty/gapped wrong? wet?, engine maybe flooding somehow whilst turning on the key.

bloody cars :grinning:
 
i dont think it's the starter maybe the fuel pump may is knackered, fuel filter blocked? are sparkplugs dirty/gapped wrong? wet?, engine maybe flooding somehow whilst turning on the key.

bloody cars :grinning:

yeh fuel pump on the way out
fuel pump relay
ignition switch gone
 
ign switch maybe sticking/old so may not be sending power to the ecu etc whilst in Start position but is ok when in Ign position?
take it out, check with a wiring chart that its making the right connections with multimeter in the Start & Ign mode, clean and check switch contacts for wear, regrease together..or just replace it.
 
does the other volvo run? have you tried swapping the starters over...what happens then
the other one starts fine, but is a daily driver, i don't have time to swap the starters over

i dont think it's the starter maybe the fuel pump may is knackered, fuel filter blocked? are sparkplugs dirty/gapped wrong? wet?, engine maybe flooding somehow whilst turning on the key.

bloody cars :grinning:

fuel pump makes a noise, also there is fuel pressure in the pipe, the injectors are firing, spark plugs are brand new, engine isn't flooded as it turns round fine. everything to do with the engine running is fine because on bump it runs perfectly.
yeh fuel pump on the way out
fuel pump relay
ignition switch gone

i swapped the fuel pump relay, no problem, and the ignition switch is in the same place as it is when i bump it, so the ignition switch is fine and has been changed recently anyway.

ign switch maybe sticking/old so may not be sending power to the ecu etc whilst in Start position but is ok when in Ign position?
take it out, check with a wiring chart that its making the right connections with multimeter in the Start & Ign mode, clean and check switch contacts for wear, regrease together..or just replace it.

ignition barrel does some times stick when in the start position, but even in just the on position its fine because it bumps, but not if i force the starter motor manually (with a wire direct to the battery instead of the key)

i really could do with a wiring diagram, there is supposed to be a resistor pack for the injectors but i have no idea where it is.


thanks for the help guys i have certainly got some new ideas to try tomorrow, but still just shooting in the dark, i am going to see if i can quickly swap over little bits like the injectors from the working car, maybe the fuel pump if there is time.
 
Are the teeth of the starter motor actually engaging with the flywheel?

yep, i can drive the car on the starter if i put it in gear and turn the key, the fan and belts are all going round fine
 
maybe try turn to key to Start while a helper connects the starter to the seperate battery so during cranking, the ecu is given a signal that ur cranking (guessing maybe it makes the ecu adjust its starting mixtures according to its cranking map?)
 
Id say its a duff ignition switch, when the switch is in ignition on mode and you bump start it it goes fine, but wont start on the starter,

Id bet that when your turning the starter using the key the ignition is going off and not allowing the car to start. I would take out the ignition switch and run a permanent feed to the wire to keep the ignition turned on then try start it with the key
 
Id say its a duff ignition switch, when the switch is in ignition on mode and you bump start it it goes fine, but wont start on the starter,

Id bet that when your turning the starter using the key the ignition is going off and not allowing the car to start. I would take out the ignition switch and run a permanent feed to the wire to keep the ignition turned on then try start it with the key

he has duff'd it turning it too much :grinning:
 
Id say its a duff ignition switch, when the switch is in ignition on mode and you bump start it it goes fine, but wont start on the starter,

Id bet that when your turning the starter using the key the ignition is going off and not allowing the car to start. I would take out the ignition switch and run a permanent feed to the wire to keep the ignition turned on then try start it with the key

i think he said he tried powering the starter with the key on IGN mode and didn't fire but yet it did fire when he bump started with key in IGN mode.
am I right Nex that you tried the seperate starter battery with the key on IGN mode with dash lights on?
 
Hmmm sounds nearly like the same problem as my Fiat Marea if i do not let the injection cycle run, possibly blaming it on a faulty stepper/idle motor as i can sometimes get it firing by throttle blipping however it doesn't idle correctly, only idle at 100-200 rpm (No idea how) and then picks up only if i drive it for a while or it decides to snap out of it!

But yours seems like the starter motor is turning the engine fine but everything else is completely ignoring it! o_O, can you tell if sparks are going or theres petrol/diesel whatever it is being fed correctly?


I'd say re-assemble the system back to stock, ignition and all,

Then i think you should if your volvo allows it, put the key in and run the starter immediately (Dont even wait for dashboard electronics) and fire her up, i'm guessing it'l turn over but not fire up, so try blip the throttle to see if you can get it going at all, and then if it doesnt start, i'd try let a full injection cycle occur and see if it'l turn over, i'd also take your plugs out and check the condition again since you've been turning it over with no success!

Good luck, this is an interesting thread!

Friend told me it could be a cheaply made starter with a damaged tooth? not sure if that makes any sence.
 
it involves a hole load of creeping

maybe eng fuse like stani's problem?
lol

well i don't think it can be a fuse otherwise the engine would not start at all.. but i have checked all the fuses and they are fine.

So it's not starting when you turn the key? But if you put it in gear and turn the key it does?
no it just doesn't start on the key no matter what.

maybe try turn to key to Start while a helper connects the starter to the seperate battery so during cranking, the ecu is given a signal that ur cranking (guessing maybe it makes the ecu adjust its starting mixtures according to its cranking map?)
but thats where its not working, if the key is in the ON position then it will bump start fine, if the key is in the start position so the starter is going round, it wont fire, i haven't tried bump starting it whilst turning the key but i think that might break something
Id say its a duff ignition switch, when the switch is in ignition on mode and you bump start it it goes fine, but wont start on the starter,

Id bet that when your turning the starter using the key the ignition is going off and not allowing the car to start. I would take out the ignition switch and run a permanent feed to the wire to keep the ignition turned on then try start it with the key
thats what i thought, but when the ignition is in the ON position (the same position that it is in when it bump starts and runs fine) and i manually start the starter motor by connecting it directly to another battery, it doesn't start, so the key position doesn't change.
he has duff'd it turning it too much :grinning:
lol maybe, this car has spent more time driving on its starter and bumping than actually driving.
i think he said he tried powering the starter with the key on IGN mode and didn't fire but yet it did fire when he bump started with key in IGN mode.
am I right Nex that you tried the seperate starter battery with the key on IGN mode with dash lights on?
yea exactly, and with the second battery doing just the starter motor, the lights didn't dim like they do when you normally crank a car, because it had all the power it needed.
see prehaps to test the ignition switch try sorta hotwiring it!

could tell you its the ign switch without ripping it apart
i have hotwired it, but it has had two ignition switches in its time, but either way the ignition switch doesn't change, i just leave it in the on position and either start the car by rolling it down a hill or try and start it by forcing the starter to run manually with a second battery.

Hmmm sounds nearly like the same problem as my Fiat Marea if i do not let the injection cycle run, possibly blaming it on a faulty stepper/idle motor as i can sometimes get it firing by throttle blipping however it doesn't idle correctly, only idle at 100-200 rpm (No idea how) and then picks up only if i drive it for a while or it decides to snap out of it!

But yours seems like the starter motor is turning the engine fine but everything else is completely ignoring it! o_O, can you tell if sparks are going or theres petrol/diesel whatever it is being fed correctly?


I'd say re-assemble the system back to stock, ignition and all,

Then i think you should if your volvo allows it, put the key in and run the starter immediately (Dont even wait for dashboard electronics) and fire her up, i'm guessing it'l turn over but not fire up, so try blip the throttle to see if you can get it going at all, and then if it doesnt start, i'd try let a full injection cycle occur and see if it'l turn over, i'd also take your plugs out and check the condition again since you've been turning it over with no success!

Good luck, this is an interesting thread!

Friend told me it could be a cheaply made starter with a damaged tooth? not sure if that makes any sence.

thanks for that, i will give it a try,

the car has all the things i needs, spark, compression, injector signal etc. but i am going to double check again, i think i want to wire something directly to the injector connector to see if it works, because all i got was a blip from my multimeter to say there was a signal, but it didn't say it was good enough to fully open the injectors,

but yea i think you are right, some how the car knows that it is being turned over by the motor and then decides to cut the fuel (fuel pump is running, and there is spark, but maybe no injectors) but why it would do this or how it knows is beyond me.

bliping the throttle doesn't work because it does not fire at all, the engine sounds like its going round with no HT leads on or with an immobilizer on (not that it has any at all) because it just goes round and round without stuttering like it does when it fires once or twice. so with the throttle open or closed it doesn't fire because something is not there,

its like the ECU is not opening the injectors enough or something... when its running i can remove the air mass sensor and it still runs, i can also disconnect a positive feed which goes somewhere to the engine, both of these things cause it to run rough but still run,

as for the starter, i am 100% sure the starter is fine, i drove it up a hill in reverse by putting it in gear and just turning the key, it drove up the hill no problems, then i rolled it back down and gave it a bump and it started. the starter is amazingly strong, it will move the car in any gear, and the battery will power the motor for about a minute constantly, before starting to die.



anyway thanks again for the help guys, i have got some great ideas about what to try next, i am starting to lean towards something with the transmission, as it has a 4 speed gearbox with an electric 5th gear overdrive, when in 5th there is a little light but taking it out of gear in to neutral the light goes out. so the ECU knows if its in gear or not, and i wonder if it is choosing not to start the engine if its not in gear and the clutch is down.... or something
 
It has to be electrical then, have you checked for burnt out wires?

i have checked what i can, obviously the stuff behind the dash is a little hard to get to, there was one burnt fuse holder but that was for the tape player, and its fixed now anyway.
 
GOD DAMN THIS MOTHER####ING CAR!!!!!! i put the battery back in, wired it all up as normal, now it starts on the key, first time every time...... i didn't even get a chance to try any of the ideas because it works fine!!!

it might be that it is cold? i am going to drive it and see... i just hope that it decides to work when people come to look at it.
 
right i just drove it to the shops, no problems, then after shopping it wouldn't start, got a helpful bump start from a nice old man, and after getting it home ready to start fault finding, it starts first time again.... i hate this car so much!
 
ooh i hate it when it plays tricks on ya too
sounds like some electrical connection has been slightly re-established after reinstalling the battery and on the edge of working/not working
 
ooh i hate it when it plays tricks on ya too
sounds like some electrical connection has been slightly re-established after reinstalling the battery and on the edge of working/not working

agreed, at first i was thinking that the engine starts when cool and not when warm, but i have it starting when warm too... i am going to look at the "big 3" wiring and maybe put some new stuff in just to see.
 
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