VR 5.0 Litre won't crank when hot

[kemikall]

Hi All,

I have just spent the last couple of hours looking at threads but nothing seems satisfying enough for my issue.

I have a fully rebuilt 304 in my VR, not a massive compression jump but much bigger cam, rockers, flat top pistons etc. It has extractors as well. Rebuilt auto with 3000 rpm stally.

A real screamer, built specifically for drags.

Now, only recently started getting problems starting when hot, so have done all of the following things, in order of appearance;

1. New battery
2. Second new battery
3. New Bosch Hi-torque starter
4. Wrapped the extractors all the way from headers to past the starter
5. Wrapped the starter
6. Fully cleaned all battery terminals and connections.
7. Checked the alternator, charging at around 14.5 v
8. No big voltage draw at rest
9. No error codes at all, only flashes 12, in the past has complained about running too rich so I know the ECU is showing codes.

Now, it always starts well when cold, and will start when I haven't travelled very far, but after a decent drive it won't over as if the battery is flat. Let it cool and it will start OK.

Its an auto, and jumper leads from another car will allow it to turn over and start very easily, no drama at all, always fires immediately.

It used to run quite hot, prob at 3/4+ on the gauge in traffic, but replacing the thermostat and wrapping the extractors has helped and it will sit at half way now.

I have run a jumper lead from the positive terminal to the starter and turning it over but it doesn't seem to help, although it is hard to get a decent connection.

The starter motor cables seem fine, there were some cracks in the smaller solenoid cable but the main power cable is OK, I checked it all when the extractors were off.

Could voltage drop be coming from something else that is less than obvious ?

I have heard talk of ignition modules, IAC, CAS (not sure in 5.0l) etc, the car doesn't idle very well after replacing the throttle body, but without getting the car chipped I would expect a rough idle with the cam work.

Its massively annoying and I can't go to the drags due to fear of stalling in the Pit lane, any decent suggestions for me to try without referring to an auto-electrician ?

Thanks in advance.

[Brett_jjj]

Id try earthing the engine to the body and to the battery with heavy wire and see if that makes any difference.I helped a guy fix a problem he had with a slow starter motor when the engine was hot.He had renewed starters and batteries etc with no difference.We tried running a thick earth wire from the battery to the body,and another from the body to the engine and it wound over fine.He fitted the thick earth wires permenantly and hasnt had a problem since as far as I know.

[TheIceman]

I have a fully rebuilt 304 in my VR, not a massive compression jump but much bigger cam, rockers, flat top pistons etc. It has extractors as well. Rebuilt auto with 3000 rpm stally.

and theres the tell tale sign were looking for. engines been out, maybe forgot to put earth strap back on. ive seen that done in the past.
and as he said it starts ok jumping it, you would normally put the negative lead on the engine so there we go, theres logical proof, we have a crap earth as mentioned.

[VR38]

Yeah I would have said bad engine earth.

[BlackVXGTS]

Bad earth or bad (+ve) wiring between battery and starter motor. Replace the (+ve) wiring with a heavier gauge wire.

[VrWagz1]

Having just read this i was going to suggest running a jumper lead from the starter body to the batt - terminal, the post reads like you only did the + side of things. Seems though you might be onto this by now. Was it the bare wire that fits in near the air box to the motor missing??

If that wasnt it, maybe try seeing your battery voltage during cranking. If it drops more then what would be considered normal then it would suggest the starter is doing all it can and the engine is tight for some reason. If it stays up then it suggests a high resitance somwhere. Try (while cranking) measuring from the batt - terminal to the starter body. If you see about 2> or greater volts theres a good chance your - side is the issue. Failing that it could be the actual contact in the starter.

[Redroostr]

I had the same prob with my Senator. Always started well when cold but slow cranking when hot. Replaced battery with a higher output one and then to a high torque starter motor, total cost $480. Problem was a dirty engine earth connection and took 5 mins to fix.