Bull Bar Cowboy Posted September 22, 2005 Share Posted September 22, 2005 I don’t post very often but here is an interesting fault ! The V8EFI has been intermittently misfiring lately …… not on any one of eight, but on all eight, just like the ignition has been turned on and off in a nanosecond. It was due for a service anyway and I had recently fitted a new ignition amp (it was doing it before it was changed) so I changed the dizzy cap, all the plug leads, king lead & coil. I then rewired from the dizzy to the coil and coil to ignition switch. Also I checked and reset the air-gap on the dizzy hall sensor – dizzy is a 35DLM8 series...... and had a nice warm smug feeling that I must have fixed it as theres F*** all left to change. The fault still persisted ……. I knew it was electrical as I could see the misfire on the rev counter……a good tip for those not in the know ….. if you have misfire and the rev counter is steady, then look at the fuel system. It would misfire from a cold or warm start but only for a few seconds and then be OK all day. However, I noted that if I was out at night the misfire would come and go intermittently. Tonight whilst out shooting, the bl00dy thing was driving me crackers ……. Continual intermittent missing ….so I abandoned the ‘harass the bunny’ and set my diagnostic mind to work together with a few electronic instruments ……… and within 30 minutes I had discovered the problem, which left me with a ….….â€yes that makes sense, but bu55er me I would have never looked there in a thousand years†type of feeling. I have now fixed the fault …………. No prizes but who is gonna get it right ? Ian Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted September 22, 2005 Share Posted September 22, 2005 Dodgy wire from the ignition key/loose battery terminal? Quote Link to comment Share on other sites More sharing options...
Les Brock Posted September 22, 2005 Share Posted September 22, 2005 Resister jobbie from the coil to the ECU ?? Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted September 22, 2005 Author Share Posted September 22, 2005 No & no ................. not even close I think that les may well get it in the end though ....but has nowt to do with the ECU. Ian Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted September 22, 2005 Share Posted September 22, 2005 I think that les may well get it in the end though ....but has nowt to do with the ECU. Aha... you've got a cylinder head gasket problem. Easy Quote Link to comment Share on other sites More sharing options...
Les Brock Posted September 22, 2005 Share Posted September 22, 2005 So it sounds votage related, as it does it when there is a load being drawn on the electical system or damp or am I still way off ? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 22, 2005 Share Posted September 22, 2005 An earth or lack of? Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted September 22, 2005 Share Posted September 22, 2005 Ok, had a think Throttle pot plug connector Resistor pack plug / damp King lead earthing out on rocker cover etc Overun switch wiring shorting etc Water in dizzy Am I close ? Nige Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted September 22, 2005 Author Share Posted September 22, 2005 Les, Almost ……..sparky minds think alike Here are the clues. When you start the engine from hot or cold the starter motor draws a large gob full of amps from the battery that have to be replenished. At night you drive with the lights on. During the summer months when my lights are on main beam there is a 610 watts on the front (4 driving lights and two headlamps) ………… I take 2 of the lights off in the winter because we use the lamp power for shooting during the summer months (makes the bunnies stay still ……. Difficult to run when your blinded ). The common denominator to the above is the alternator ………….. a quick check with an oscilloscope showed that one of the diodes had blown, which causes large spikes on the DC output (almost like half AC). Under light load conditions the battery (acting like a large capacitor) would mask the fault by smoothing out the ripple …… but under load I was detecting some nasty spikes…. with the 100Mhz scope some were 30V + !! . Whilst the battery would not mind this at all (lead acid wet cell battery chargers are a very rough DC supply), the ignition amp was getting very, very, upset about it. That’s probably why I had an ignition amp pack up on me a week or so ago. New (secondhand) alternator and problem solved. Ian Quote Link to comment Share on other sites More sharing options...
white90 Posted September 23, 2005 Share Posted September 23, 2005 Fit a TDI prob solved Quote Link to comment Share on other sites More sharing options...
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