1970 Datsun 240Z — catalyst efficiency code but car drives normally

If it were in my driveway, write temp, speed, and in-gear vs coast when the 1970 Datsun 240Z does it — then decide on parts. Don't erase codes until someone who can help has seen them. That's the whole play. I'd sleep better after that step, even if it finds nothing. I'd rather pay for diagnosis than a second guess-repair.

Ask what changed right before it started. Move a coil or plug on the 1970 Datsun 240Z if it's cylinder-specific and see whether the code follows. You'll know quickly if you're on the wrong tree. Stop there until you know. I already checked the easy fluid levels.

I went back under the 1970 Datsun 240Z and it only happens after a heat soak, not on a cold start. Wrote this up on my lunch break.

Intermittent stuff lies if you only catch it once. Capture voltage while the 1970 Datsun 240Z is actually failing — after it restarts you've lost the clue. You'll know quickly if you're on the wrong tree. On “catalyst efficiency code but car drives normally,” that was the fork that mattered for me. This is from a 1970 Datsun 240Z in Salt Lake City with 254,500 miles. Post the numbers (or the code) and people can get more specific. Doing the boring step first on purpose.

Log the conditions before you spend. Two 1970 Datsun 240Zs can feel identical and have different causes, so measure before you copy someone else's repair. Save the big job until that test fails. On “catalyst efficiency code but car drives normally,” that was the fork that mattered for me. Verbal 'we'll take care of it' is not a plan. Cold start is when I can actually reproduce it.

I wouldn't throw parts yet. Two 1970 Datsun 240Zs can feel identical and have different causes, so measure before you copy someone else's repair. If the cheap test changes it, stop and reassess. Have you gotten a second quote in writing? Worth doing even if the car feels fine right now. I'll update if anything new shows up.

Start with the test that can prove you wrong. If a shop can't duplicate it on the 1970 Datsun 240Z, bring a video plus freeze-frame data, not just a story. Save the big job until that test fails. Post the numbers (or the code) and people can get more specific. Your commute and mine probably aren't the same, but the test still applies. Cold start is when I can actually reproduce it.

I'd want a measurement, not a hunch. Two 1970 Datsun 240Zs can feel identical and have different causes, so measure before you copy someone else's repair. Save the big job until that test fails. I'd want that in writing, not as a promise. I'd sleep better after that step, even if it finds nothing. I'd rather look cautious in this thread than stuck later.

If it were in my driveway, capture voltage while the 1970 Datsun 240Z is actually failing — after it restarts you've lost the clue. Save the big job until that test fails. Time, temperature, and whether it's in gear are the notes that actually help a shop. Not trying to scare you — just skip the expensive first guess. This is me being the wet blanket on purpose.

Ask what changed right before it started. Move a coil or plug on the 1970 Datsun 240Z if it's cylinder-specific and see whether the code follows. You'll know quickly if you're on the wrong tree. I'd want that in writing, not as a promise. Make the next action something you can finish this week. If it repeats twice more I'll book time.

Log the conditions before you spend. A pressure test beats staring at a dry driveway if the 1970 Datsun 240Z is losing coolant with no puddle. That's the branch I'd chase this week. On “catalyst efficiency code but car drives normally,” that was the fork that mattered for me. Keep sale price, fees, and rate as three different conversations. Cold start is when I can actually reproduce it.

Intermittent stuff lies if you only catch it once. Get a real battery/charging test on the 1970 Datsun 240Z, not just resting voltage, before blaming a module. You'll know quickly if you're on the wrong tree. On “catalyst efficiency code but car drives normally,” that was the fork that mattered for me. Run the total, not the monthly, before you commit. I'll update if anything new shows up.

Tried a second charger / second scan and the story on the 1970 Datsun 240Z didn't change. Next check is the cheap one I can do in a driveway.