AGU not starting when hot

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manwithtool

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OK so I have an AGU engine in my VW T4 Transporter. Everything has been fine for a year but recently when I turn it off when hot and then try and start it after say 10 minutes it turns over but doesn't fire. Never a misfire when running or even stuck in traffic. So something is not liking the heat build up but only on start up.
Is there something that only comes into play on start up that could be failing ?
 
What's confusing me is that it runs fine. No sign if misfire or anything even when stuck in traffic when under bonnet temps must be similar if not mare than when you park and turn the engine off. I'm a bit old school so not too familiar with sensors etc but I would have thought a crank position sensor would cause problems at all times not just when left for 10 minutes when hot. It re starts after about 10 minutes of me swearing with the bonnet up.
 
Every 6 months or so my AGU point blank refuses to start. I turn it off and swear at it for a minute or two. Then it starts fine.
I think it might be the Immo off ecu I have that randomly does it.
 
Hmm good point. I had the immobiliser removed from the ECU as it's an engine swap. So unless it's cutting in for some reason I don't think it's that, but I will ask the guy that did the change for me.
Thanks
 
manwithtool said:
What's confusing me is that it runs fine. No sign if misfire or anything even when stuck in traffic when under bonnet temps must be similar if not mare than when you park and turn the engine off. I'm a bit old school so not too familiar with sensors etc but I would have thought a crank position sensor would cause problems at all times not just when left for 10 minutes when hot. It re starts after about 10 minutes of me swearing with the bonnet up.
Click to expand...

Just wait a few more months, it'll start cutting out on parking lots or in traffic :D

What happens is, the sensor is within its operational range most of the time. When parked, the heat builds up and the sensor readings go out of bounds. When the ECU sees this, it kills the fuel pump to prevent a fire hazard.

I recommend a VCDS fault code scan, but my money is on the crank position sensor. Cheap and easy fix (depending on how accessible it is in your bay)...
 
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OK I'll have to get it scanned 1 I guess a fault might be logged. But I do know that the fuel pump does run as I can hear it. Obviously being an engine swap it adds complications ! It could be something wrong in the van wiring. It's the van's ign feed that triggers a relay to feed the AGU ECU. There is a chance this feed is dropping out when cranking...which I recall it might have done before !
 
Resistance in things like damaged/failing sensors, relays and ignition coils will tend to increase with heat. Alternatively, some sort of fault might be occurring in the fuel supply system such as pressure loss/evaporation (petrol engine?) from the fuel rail. We're all guessing on an internet forum I'm afraid.
 
The fuel pump will still prime, because until the engine turns over, the ECU has no way of knowing what the crank position is. Soon as you try to start it, the ECU checks the crank position, finds its signal is out of bounds and kills the fuel supply (which it may even do by shutting off the injectors instead of the pump, I'm not sure).
 
Thanks Guys,
I realise there is a lack of info to go in but some good leads to follow !

thanks again
 
OK been a while and it's done it's usual not starting trick a couple of times. Did about 40 miles Sunday and went to move the van tonight and it wont fire. Checked all my wiring and fuses and the ign feed I used from the van and it's all ok. Even swapped ECUs for another I have that I know works. Then read the codes. Looks like 16706 which I think points to crankshaft position sensor. I think I'll try and get one tomorrow and fit it assuming it's not raining ! anything I should know about fitting one ? Access should be ok once I get the tray off the bottom of the engine.
 
Ok so the crankshaft sensor is just behind the oil filter. Easy access but I changed the oil and having the oil filter out of the way makes getting the sensor out easier. It is fairly well stuck in and took a bit of levering out. Plug was a pig to release as well. Anyway it solved the non starting problem. No idea if it has solved the hot starting issue but I suspect it has and that the hot non start was a symptom of the sensor failing.
 
mine did same .. started fine .. once got to 90 died .. was crank sensor .. was running 100% sweet as .. full boost .. no stalling etc .. then over 3 days died all time .. started once cold again but could take up to 2 hrs sometimes lol

as said above .. was rpm / crank sensor .. 90 bux in NZ to buy direct from auto sparky .. ***** to fit but ran sweet ever since
 
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