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V10 no start when hot

2974 Views 65 Replies 8 Participants Last post by  Professor Eggman
So I'm almost able to drive my 2006 V10 after a year, but I cannot get the engine to start after the coolant gets up to temp. When the engine is cold, or slightly warm, I can kill it and it will start right back up. When it's up to temp, if I kill it and immediately try to restart, it just cranks. I'm reaching the end of my ideas to figure this out. Here is what I've done so far to try to change this:

Fresh fuel
Removed and cleaned fuel pumps/filters, new fuel filter
Hardwired fuel pump to run continuously
Added jumper cables to another running engine to add starting power
Released pressure in coolant system
Opened PCV to atmosphere
Removed coolant temp connector
Removed coolant return temp connector
Opened ECU to check for corrosion: appears all intact, no areas of damage or corrosion
Checked all fuses and relays

Currently, cam position sensor is still reading "signal out of range", so signal return wire has been removed from ECU wire harness. This leaves "no signal" fault.
Also, Steering Angle sensor is not working despite all wires being intact and voltages present, leading to steering and steering wheel electronics faults.
Batteries and related grounds are in good condition, with batteries being kept on a charger/tender.
I'm also posting before and after scans of the hot no-start, as well as video of it cranking while hot.
If I can solve this, I'll finally be able to drive this beast on a regular basis.
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Log rpm while cranking.
You need something like 275 or 295 before the ECUs fire the injectors even when everything else is good.

Might be a weak or struggling starter that just doesn't have the grunt once it get all heated up.

Obviously CPS issues are also a contributor.
The VW tech bulletin I've seen references all TDIs..... Not sure I've seen a separate V10 one
One last Rando thought. You were messing around with the ECUs if I understand correctly. I think behind #1, there's a critical ground to the body that is often not properly reattached or damaged during work. Without that ground, your injectors won't fire. Might be worth checking it and cleaning it.

Do you smell fuel when cranking?
Good point... I'm just grasping at straws since he didn't mention if he smells fuel or not. As long as he has compression (he does since it runs) he only needs fuel and air... So it sounds like he's not getting fuel.... This makes me think it's injectors not firing since he's bypassed the fuel relay. The only reason why they wouldn't fire that I can come up with is insufficient Cranking rpm (which he's dismissed) and this injector ground.

Do you have any suggestions?
I'm fairly certain that your cranking RPM is too low. I know the ECU maps typically have a cutoff point, but I don't know what it is for the v10. That being said, does it still start when cold? Maybe another v10 user can measure their cranking RPM as a point of comparison. Since you're not smelling fuel, I will stick to my suspicion that you've hit "fuel cutoff" on the starting map.
That sounds like the classic Crankshaft position sensor failure
I just went through this whole thread again as there's a lot of flaky info in it.
I don't even know how both you and the OP have gone to the Crank sensor, when the codes are for the CAMSHAFT
scan said:
012295 - Camshaft Position Sensor (G40)
P3007 - 000 - No Signal
What am I missing?
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Anyways, now that I'm actually reading the scan and not following random stuff, the G40 sensor won't cause you to not start. The signal from the G28 is used instead..... G40 loss will cause longer crank until start, but will not impede starting.
Professor, you keep getting the codes 012545 and 012546 intake flap valve motor problems, you don’t suppose they are stuck closed when hot? Or perhaps the ECM needs to know they are open before it fires the injectors. Random thoughts, not to well organized! Best of luck Prof
Very unlikely as the intake flaps are mainly used for regulating intake\exhaust pressure difference required for proper EGR function.
Have you done voltage drop tests on the starting system? You could just have a crappy wire\connection that flakes out once it gets hot.
There was also a famous failure in the early TDI days (unsure if it impacted v10)... Trying to remember the darn component name. Ah yes, relay 109. Does the v10 have one?
The power supply replay is a thing on small 4 banger TDIs.... not for this beast!
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So what's he getting his hot rpm readings from? The same failed hot sensor?
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Before a new starter, look into the cable/wiring. Voltage drop test the system. Some bad connections will heat up and fail or become flaky after initial use (aka initial start)
20+ year old wires tend to rott and need replacing or at the very least connectors/terminals need cleaning up. You'd be shocked how often voltage drop is a thing.
Everything can be redone if the drive to do it is there. They are just machines. We build them!
Make sure you isolate the correct problem component/connector .... It could be the power cable, its connectors, the grounding between the starter casing/mounting bolts, block, the engine ground strap, battery terminal connectors, etc.
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Progress is good.... especially when the parts cannon is still empty. :p
Going to replace the cable from the jumper to the starter.
Wait a second.... are you talking about the jumper post?
(like where you hookup jumper cables when the batteries are dead)
Isn't the power supplied off the Terminal 50 Voltage Supply Relay?
Something like C20 in the E-box?
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