VN V8 Wont Crank over when Hot

[madA69]

Please Help or Advise....

My VN V8 has had this problem for a few years now & I & the Mechanic I goto dont know why -

The motor refuses to crankover when it reaches its normal operating temperature. I can start the engine cold just fine but if I shutoff the ignition after say 10 or 15 minutes of easy driving then try & start it again it wont crankover - sounding like the batteriy is flat. If I wait perhaps 1 hour it has a better chance of turning over.

I have tried to find the problem for a longtime now & Im basically stumped on what to do !

A brief history of what I've done - (in order of what I've done)
- Replaced & increased number of Earth Straps from Batery -ve to Chassis & Engine (now only about 60mv float between -ve post & engine)
- Replaced the battery (3 times now) - yes Im a slow learner
- Replaced Alternator as it did go faulty at one time
- Replaced the Starter motor (as it was actually burnt out/ melted over time)
- Replaced the main power cable from Battery to Solenoid with a seriously better one
- My mechanic replace the ignition coil as it refused to start at all at one stage & also some other associated sensor as the car wouldnt start (but turned over OK when cold) unless I manually turned the distributor & then reset it back again once started - I assumed this has little to do with my current ongoing problem.

Finally my suspision is something like Water from radiator getting into a cyclinder & vapour/water lock causing problem OR similiar as the car is losing some water but this can thru a faulty radiator which Im currently repairing. The engine itself runs fine doesnt use oil & fires well all the time on all cyclinders. I havent done a compression test as yet

I've read the crank angle sensor may be a culprit but I dont know if this applies to a V8.....

Any advice would be greatly appreciated.

thanks,

[pathfinderus maximus]

keeping in mind what youve done sounds like cas to me.

same thing with a bloke i know, all fixed now.

[madA69]

Just after I posted I went thru my manual & there doesnt seem to be a Crank Angle Sensor on a V8. I remember the mechanic changed the MAP sensor with the coil - however this problem sounds mechanical - it feels like the starter motor is really straining under load but only at normal operating temp. When its cold its just fine.....

[vsuterus]

try changing the ignition module which is the round chrome looking thing surrounded by the big metal heatsink. On the passenger side just in front of the airbox. Apparently when these go the car wont crank over. So it cranks, but doesnt fire, or doesnt crank at all? Even check the connection to this module as there might be corrosion in it. Borrow one off a mate to test before buying a new one as I think they're a couple of hundred bucks.

[madA69]

Apologies for not being concise - It cranks over but very slowly sort of like the engine's seized. On the very odd chance it cranks over fast enough the engine fireup straight away. So its not fuel (unless its flooding the cylinders when at normal temp??) & its not Spark. It just sounds like a 3/4 flat battery trying to start. Another mechanic said its got to be the starter circuit (battery,cable,starter motor & return earth/ground) but I've replaced these at least once. Ive had this car for 11 years now, cammed,chipped, extractors all were fun times but this times its really thrown me a hard one.....

[VTSSDUDE]

Are those V8s self timed? Do you have to time them your self. Maybe want to re-check the timing. While the motor is cold and warm. See if there is any difference.

[minux]

I had the same problem after rebuilding my SS, it wouldnt fire when warm, turns out it was caused by the oil pump, so set of cams, lifters valves etc and one new oil pump later, never had the problem again.(only found the problem after the pump completly shit itself and wore down lobes on cams on #4 )

[madA69]

Thanks for the advice - The timing is mechanical via the distributor. I shorted out A-B on link & rechecked as OK 10Deg BTDC. Re the Oil Pump - I never thought of that as it might be "sticky" causing the beast not to turn over when warm.

[jdd]

If you can find somebody with a clamp on ammeter (most auto-elec’s), you could measure the starter motor current and compare to another similar car.
Low current would indicate electrical problem while high current would indicate the problem is not electrical. That is assuming the starter is not the problem but it sounds like you’ve already eliminated that.

[STEALTHY™]

Have to agree with vsuterus about the ign module. I had that problem on my Calais, as well as having the coil problem.

Definatly look into it, as its a common problem on the 5L Motors.

[madA69]

Im feel im getting closer now. When I crank over the starter when its cold the voltage at both the battery & starter contact is ~ 10.4 volts. After I have run the car & made it difficult to start the crankover voltage drops to around 10.00 volts. The manual says nothing about voltage requirments at the solenoid. When I jump start the car when its hot the voltage goes backupto 10.5 volts - perhaps its another battery needed. When its running with highbeam & fan & a/c on (basically full load) the voltage at the battery is 12.9 volts. With all lights & fans off its 14.33 volts at idle so its not the alternator - perhaps the batterry's just not able to supply the current under load i mean i lose 2volts at the battery when trying to crank it over

[BlackVXGTS]

Do you have an engine immobiliser fitted? Didn't think they were installed as standard on a VN except on the Calais model and I see that yours in an Exec. I had a similar problem which took a long time to diagnose but turned out to be a problem with the battery in the remote that controlled the power windows and immobiliser. This might not be the cause of your problem. A good way to narrow down the causes would be to reproduce the problem near to another car or a spare battery that you can connect to your car using jumper leads. If your car starts then the problem isn't with the fuel system, coil or ignition trigger module.

[jdd]

When lead acid car batteries heat up (due to under bonnet temperatures), the internal resistance of the battery increases. The higher the internal resistance, the lower the current the battery will be capable of delivering. This would account for the drop in cranking voltage when hot. In addition to this, the internal resistance increases with battery age. It’s the heat reason that many taxis have their batteries relocated to the boot.
There are a few variations of car batteries around now (in addition to capacities and CCA ratings), I would speak to a battery specialist or autoelec to find which one is most suitable for your application.
I used to have this exact problem with my VN V8 until I changed battery types.