Not a major find compared to what you other guys find and post on here but thought I'd put it in as i quite happy with the outcome
Got in a Citroen 2001 C5 2000, 16v (RFN) owner said its been to 2 workshops, 1st workshop fitted a new coil, 2nd workshop said it needed a new coil, owner complained of a hesitation + a yellow lamp flashing up on dash when driving and every now and again at idle depending on how far \ long the car had been driven for, mil (yellow lamp) would go out after stopping & restarting engine. I plugged in diagbox done a scan and got a P0351\2 Ignition Coil A Primary/Secondary Circuit Malfunction,
1st thing was to check compression, change plugs & check "new" coil, Compression was good, plugs fitted didn’t look to old & coil was good. Fitted new plugs & cleared the codes, let it idle for 10 \15 mins, no mil, I gave it a 10 min drive, slight misfire, on come the mil again, same codes appeared, stopped restarted the engine mil off, let it idle while sitting in the car and looking at live data, the data stream was a little slow, I was waiting for the misfire, when it did misfire I got this:
Time to get the Pico out.
Chan A, Primary
Chan B, Coil current
Chan C, Coil feed:
as you can see it dont look to bad for an 11 year old car, Zoom in on the green trace and you can see a just under 300mv voltage drop for just over 3ms as the coil is charging.
Sitting looking at screen waiting for misfire not a lot happened, I then got a slight misfire, I stopped the scope went back and found this:
After waiting and checking I then realised this misfire was happening everytime the cooling fan started, you can see a little difference there, coil feed (chan C) has dropped from 14 volts down to just under 12v, Chan B current has dropped from 8.7 to 6.2 amps, I switched off Chan A & B, slowed everything down and waited for the fan to start again, you can see nearly a 3 volt drop for just under 3 sec's on the coil feed when the cooling fan starts:
Next was to amp clamp the fan feed using the 60amp clamp:
you can see its off the screen, I clamped the feed again with the 600 amp clamp, set on 100-200 amps + Chan C on coil feed:
when the fan starts its drawing neary 110 amps, 1st thought was bad fan motor or bad battery, I put a good battery on just incase, I also checked the fan was spinning nice and free with no noise. I plugged in Diagbox again, selected actuator test, 1st was to check the high speed cooling fan, that worked, next was low speed fan, that didnt work, I checked all wiring, relays and fan resistor & found the thermo fuse in the fan resistor had melted
If the fan started on the lower speed then switched to high when needed it would no have been supping that much current & causing the missifre. I have ordered a new fan resistor, when thats in and fitted I'll check current draw and voltage drop again but Im 100% sure that will solve the problem
I may have if I'd used my brain realised that the cooling fan starting on full speed is going to draw lot of current but its better to use the Pico and be 100% sure + it helps save what little brain I have left