z24i random cutouts only when temp sensor is connected

[Bludacious]

Put a few hundred miles on my nice freshened Z24i but an old problem has come back to annoy me. When the head gasket started going on the original & it lost enough coolant, the ECU would cut spark (or fuel?) to the motor under light throttle, then turn back on, then cut out again, to the point I'd be bucking down the road at best or stalled at worst. I didn't realize what was happening originally so I unplugged the temp sensor (had given me other issues before) which made it run properly again. Been about 10 or so days of regular driving with temp sensor plugged in, suddenly today trying to get onto the interstate it starts cutting & bucking again. Pull over, check that the coolant's fine, yank the temp sensor, on my merry way again. I changed this sensor due to the old one causing issues when plugged in, but the new one behaves in a very similar way. I had sanded all the grounds when I re-wrapped the harness months ago, and the few that I missed got cleaned when I dropped the new motor in. Really stumped on this one, please enlighten me guru Mike!

[datzenmike]

If new one acts like old one then it would seem that this isn't the cause. Disconnecting the temp sender will convince the ECU that the engine is probably cold. On a cold engine the O² sensor runs in open loop or is ignored so a rich warm up mixture can be used.

 

EFI is too complicated for me. Do a diagnostic test on the ECU and see what codes it's stored.

 

 

[jagman]

When the same conditions apply to my 720 I replace the fuel filter.

[Bludacious]

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When the same conditions apply to my 720 I replace the fuel filter.

The fuel filter was replaced about 4000mi ago.

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On a cold engine the O² sensor runs in open loop or is ignored so a rich warm up mixture can be used.

I figured this, but I've noticed that when I connect the temp sensor the cold RPM's actually drop and the idle is destabilized to a notable degree. I'm pretty sure the O2 sensor is trashed since it is left over from the heavy oil-burning old motor, but I'm confused by the fact it only seems to throw a fit maybe once every few weeks with the temp sensor plugged in. I haven't checked codes yet but last time this happened the only code was for the temp sender & it went away whenever I connected it.

 

A thought occurs, could this be the result of a cavitated fuel pump? The unit in there is the factory pump and the truck was both abused & left sitting by the PO for most of its life from what I can tell.

[datzenmike]

Unlikely. It's intermittent. Check the codes. It saves them even if the problem is intermittent.