89 TB stalling/no power
Good day eh,
Working on friends '89 3800 v6 Thunderbird. Symptoms were slightly rough idle, frequent stalling, boggy power occasionally. We replaced plugs, wires, distributor cap, and rotor with no improvement. Also patched a broken vacuum line. Fuel filter, pump and PCV valve were replaced within the last year.
The plugs we pulled had been in about a year, and were covered in carbon. However when he bought the old plugs the register jockey at napa told him they were pregapped. We checked them just now and none were over .050, most were closer to 40. The new plugs also started to carbon up around the threads with about 30 minutes of idling and about 15 miles of driving on them.
Fuel pressure is fine at hold pressure and running, and we couldn't find any more vacuum leaks by listening for a hiss or with carb cleaner shots. Ignition coil tests correctly across primary and primary to secondary, and we have full battery voltage at the coil harness. We tried bending back an old plug electrode to almost vertical, plugging into coil-to-distributor wire, grounding tip and cranking. The arc jumped to the base of the electrode, but it was a fairly weak looking orange spark, not the blue one I'd expected.
At this point I'm say it's between bad O2 sensors and weak ignition. Any suggestions on how to proceed, besides throwing money at new O2 sensors before we're sure that's the problem? Odds are they're not in spectacular shape (car has 137k miles). To be honest, the car is a beater that just has to last one more year while he's in school.
Thanks in advance,