97 model 850 stopped. No spark.

[1998v70xcbill]

ecu never go bad, so i hear

[abscate]

ecu never go bad, so i hear

Its rare, but it does happen. We have probably had about 5 on this Forum, but we do expect that the number will grow as these cars reach 25 years of age.

Many garages will give you a bad ECU diagnosis and a $2000 no-guarantee estimate to make you leave when they are stumped and don't want to admit it. They figure you won't take the gamble.

[danger2manifold]

I wanted to thank previous posters for their detailed troubleshooting descriptions, and add a data point for myself as well.
Over the past 8 months my 350k km 1996 850 Turbo developed an intermittent no-start condition (ie extended cranking without sounding like it was able to catch at all), 1 in 100 times or less. It would always start on the second try, or once I opened the hood to begin checking for spark etc, it would behave. Then the no-starts ramped up, to the point of several per week, luckily always at home or work. Fuel system relays were good, cam and crank sensors were replaced in the past 16 months, so I was baffled when I checked and found I had a no-spark condition. Despite the recent sensors, I checked them anyways, and they had the correct resistances and voltages, and cam sensor would vary appropriately when cranking. Diving into the forums and wiring diagrams, it seemed like I had low voltage to the DI power stage at the coil (multimeter showed 0.27 volts when the troubleshooting guide says to expect 0.7 to 1.3 volts, but looking back maybe my multimeter was filtering out the spikes?). Based on that, I cleaned up the grounds as best I could (without removing the intake manifold), when that didn't improve anything, I bought another ECU to see if swapping would change anything - it didn't. Swapping a junkyard DI stage / coil also didn't do anything.

I wanted to do one last-ditch check before digging in to replace the starter based on the previous posters' interference comments, so I ran a new ground wire from the ECU ground (labeled 31/33 at the front of the block, just above the starter) to the chassis ground just in front of the battery. Keeping in mind I had previously "checked", ie removed and noted only minimal corrosion, ground 31/33 with no effect... with the new ground jumper wire, it fired up immediately and more eagerly than it ever has. So if anyone else out there needs to hear it... checking and cleaning grounds makes allllll the difference on these cars. In my case, I didn't actually clean ground 31/33 effectively enough the first time around, but a jumper ground to the battery cured my laziness.