1994 Buick Roadmaster wagon. 265,000 miles. Fuel mileage has been lackluster since WFNY in July. Noticed a slight miss cruising at highway speeds now and then last week, Thursday, Friday. Saturday night it didn't want to start, just cranked for 10 seconds or so. then started, like it was flooded, then I smelled fuel once it was running. The next morning (Sunday) the same thing, but once on the highway is had a much more noticeable and consistent miss, or shudder. I drove it about 20 miles and parked it for 5 hours. Went to restart it, and another long crank, started, felt loaded up, and smelled fuel again. Took it home, and pulled the plugs, and checked the wires, grounds, wire connections for the dist., and the vent harness. No check engine light on, and everything looked good. buttoned it back together Sunday night.
Went to work Monday am, and did the same, but worse in every way. longer crank, more loaded up when it did start, fuel smell, and the miss has now turned into a stumble. 8 miles down the expressway it died. No restart, had it towed to the shop I work at. Still didn't start once at the shop, or again in the afternoon. That evening I checked fuel pressure... Okay, a little low at 35 psi, key on engine off. Checked spark... no spark at the coil, or #2, or #4 plug. I have 12 volts at the coil, so I swapped coils with a new AC Delco coil. It fired right up, and ran great... for 2 to 3 minutes, then it started stumbling again. I stared wondering about the low fuel pressure, It should be 41-47 psi, and I was seeing high 20's when it was running, 35 or so when pulling the vacuum from the regulator, so I took a work truck home that Monday night.
FF to Tuesday evening after work, I tested the fuel pump by disconnecting the return fuel line, and closing a valve I rigged up onto the fuel line. The fuel pressure immediately went to 65psi. So I was reasonably sure the pump was fine, and that the regulator was bad. I went out and picked up a new regulator from AutoZone, installed it, and saw no change in fuel pressure. Argh... So, out of desperation I put on a new AC Delco ignition control module on it. It seemed to be okay... I ran the car for a good 30 minutes with no issues. Once I closed up the shop, and went to leave, though, there was a miss again. So I pulled it back into a parking spot, and left it at work again.
So.... Any ideas? Am I missing something stupid? There are no coolant leaks, and there are just minor engine oil leaks.
A little background on the wagon. It was tuned up about 6 years, and 50,000 miles ago with a new Delphi opti, AC plug wire, AC Iridium plugs, a new opti vent harness. 2 years ago I put in a new AC fuel pump, sending unit, and fuel filter.
And before any one asks, yes, it has plenty of fuel, the air filter is fine, and the nut behind the wheel was tightened.
Thanks in advance.
Mike