Hi folks, After 7 years of trouble-free ownership - generally how it works when you keep up maintenance yourself - my QV has developed a sudden problem. Once up at a good operating temperature, when I go to hammer it, the ignition intermittently cuts in and out. I'm not talking burpy, farty misfire, I mean both banks, completely dead. It lasts for maybe a quarter of a second at a time with the cutouts getting more and more frequent. I can keep it at bay by driving at a cruise with no load on. After another 10-15 minutes it just gets impossible to drive. Pull over, let everything cool down and it's good to go and then it all starts over again. Not having anything resembling a wiring diagram - plus I hate electrical stuff - i took it to a local "expert" and they are talking about replacing coils, dizzy caps, HT leads, plugs, everything. But I'm trying to convince them that, because its the WHOLE engine cutting out, it's got to be a power cut somewhere before the coils, not after. I was hoping someone may have had experience with a similar problem. I'm thinking crank angle sensors, a relay, a fuse... Because it's heat-related, does anyone know if there's anything else in the ignition circuit that could be heat-affected at 36 years old? Thanks in advance for anyone who has any idea about this. Cheers Greg
The fuel system is the only part shared by the entire engine. The ignition has two of everything. The fact that it happens when you hammer it would suggest fuel starvation to me. Pressure check would be my first test.
Thanks for the thought. I understand and I'll follow up, although the shop I sent it to did say that "the fuel system was fine". It's so sudden and so "total" that it feels like ignition AND the tacho drops off too. Before getting to the "two of everything", would there not be a common power supply?
Yes, it's a common power supply for both banks. The wiring diagram is in the 308QV OM. One thing to check is the condition of the fuseblock for melting/rivets getting loose for the ignition fuse position, but the easy functional test would be to connect a voltmeter between terminal 15 of one of the coils (the terminal on either coil with the yellow wires) and ground (and have the meter in the cabin with you so you can see it when the trouble occurs) = it should always be +12V whenever the engine is running. As you noted, the RPM sensor is shared by both banks of ignition so that would be the next suspect if it isn't an upstream +12V power problem (and you are loosing both banks of ignition at the same time). Good Hunting!
I agree with Steve. If the tach is cutting out when it happens, then it is most likely electrical. You may find some nice color wiring diagrams online as well. Paul Bennett has a nice collection, I payed for access. It was worth it. Look for him.
The tach signal is generated by one of the Digiplex boxes, not the TDC sensor. The TDC provides the input to the Digiplex. If you're losing the tach signal, you could be losing: Power to the Digiplex boxes One of the Digiplex boxes The TDC sensor To eliminate the Digiplex boxes, switch their position...and see what happens. Take a look/see at the Digiplex harness in the LHS wheel well, after you pull the fender liner.
Thanks again for the great input/suggestions. Having been over the wiring diagram last night, I discover that, although the three crank sensors may look the same and they are referred to interchangeably in other threads as "crank sensors", they have three distinct labels in the diagram: 1-4 TDC sensor 5-8 TDC sensor RPM sensor If the problem were to be one of the sensors, it could logically only be the latter of the above. out of the three - 3, 7 and 11 o'clock - do you know which is which?
Steve, not only is that great information - THANK YOU - but it also means that the one that may be my problem child is the easiest one to get to!!
Since you are focusing on the RPM sensor, have you confirmed that it is not an upstream +12V power problem? I should correct myself as I wrongly wrote: "...check is the condition of the fuseblock for melting/rivets getting loose for the ignition fuse position..." when there is no ignition fuse. What I should've written is: "...check is the condition of the fuseblock for melting/rivets getting loose where +12V comes into the top of fuse #2 from the ignition switch on the A wire and is bridged over to the top of fuse #1 where it exits to the coils on the G wire".
Oh no, Steve. I will definitely be looking at the power supply first LOL before I go and spend GBP50 on a sensor I might not need!!
