Guess it's my lucky month. Right before I found my proportioning valve was leaking the car had just about stalled on me. I fixed the brakes and used it mostly locally but I start having problems after about 20 miles.

It seems to happen after I've been driving a while. Sometimes I get 20-40 miles then the car loses power. Like there's no throttle response. I pull over and let it sit 45 minutes or so and I can get another 10 miles or so at a time before it loses power again. Once or twice I could hear it sputter but for the most part it's as though the fuel is cut or restricted. It seems to run better cold or warmed up until I get above 20 miles.

It idles fine, has good power and recently passed smog. I tested my fuel regulator and it was in spec. I recently replaced the fuel filter in hopes it was just a clogged filter but no success. My IAC valve, main relay and distributor are all less than 3 yrs old. I had replaced my distributor with an aftermarket but still have the OEM. My issue there was actually coolant following the harness down to the ECM so I think the OEM dist is still good.

I was leaning toward maybe the fuel pump getting hot or weak but from what I read they either work or don't, there's no "failing" period.

Any thoughts?

 

Swapping back to the old distributor didn't help. Cooling is fine, fans are working. I got the fan to come on before leaving to test the new dist so I knew it was up to operating temp. And at about 10 miles or so is when it started stalling again. I shut it off to rest about 15 minutes or so and I was able to get it back home less than 10 miles away from where it stalled.

 

I pulled my 3 yr old main relay and I see no cracks in the solder.

 

Next time it stalls or sputters, pull over when safe, and pop the gas cap off. See if it is vapor locked. If the car starts right back up, and runs good for another 5 miles, you probably have a clogged vent, or whatever emissions canister you car has.

 

Look at your spark plugs and see if they're all caked up black with carbon.

 

I just did this. Brilliant and thank you! I should have thought of it as a blocked vent tube is common on one of my bikes.

So as it began stalling on me again I pulled over, left it running, and opened the fuel cap. It sounded like it was pulling in quite a bit of air, not that little exhale you get on a hot day. I put the cap back on and tried driving. It got worse for about 1/8 mile then cleared up and was back to normal. AND I finally got a CEL. Never had one for this problem before. It's a code 43, the manual I have only goes up to 41. But what I read online is that it's either a fuel supply issue or O2 sensor.

So next question is how is the fuel tank vented with California Emissions? Would that be the cap or canister? My car is injected, not the carb model.

BTW, the plugs were clean. I had done a pre-smog tune up about 10k miles ago but pulled them this morning to be sure. Tops of my pistons looked clean too.

 

I read up and the fuel cap will only release an excess amount of pressure to avoid spraying fuel when opened. The pressure and vacuum balance in the tank is handled by the two way valve on top of the tank by the pump. This is connected to the canister up front. I can remove the hose to the canister and blow air back to the tank. With the cap on, the tank pressurizes a bit and then blows the air back out the tube. With the cap off I can hear air escaping through the filler neck. I'd say neither my cap nor my two way valve are the problem. I did find a small amount of fuel at the hose to the canister. Maybe just condensed fuel vapor?

Back to square one.

 

Work took me away for a while.

So after I blew out the breather hose to the fuel tank it didn't seem to want to stall anymore but we kept our driving local with short trips. I even hooked up a fuel pressure gauge to see if I could catch a drop in pressure if it stalled again but no stalling.

Today took it out further and it loss power again and I didn't have the pressure gauge this time...figures. I filled it up hoping less of an air gap would cause the stalling to happen sooner if it was due to a blocked two way valve or hose. This time I got farther and even did highway speeds with no issue until about the end of 15 miles. I was on surface streets, pulled over, left it running and was about to get out and see if removing the fuel cap relieved any pressure. But it cleared up before I could get out. I watched the idle drop to about 400-500 then raise again and clear up. Still no CEL.

 

Leave the gauge installed with the hood gently laid on it with the gauge facing you sitting in the drivers seat. Drive around and when it stalls you can see if fuel pressure is dropping off.

 

I got it to act up again with the gauge hooked up. This time it only took a couple miles and the symptoms lasted much longer. I didn't think I'd make it back. Good thing is I got to see what the fuel pressure was doing for a good while. It stayed up around 38 psi under acceleration (or attempted acceleration) while the engine was coughing and sputtering, losing power. And while cruising, with no throttle input, the pressure stayed around 28 psi. Those are the same pressures I was seeing under normal conditions without any loss of power or sputtering. So they are unchanged during my lose of power. And still no CEL.

Once it sat for a while idling in my driveway while I was listening and testing for a vacuum leak, it cleared up.

And for the curious, I had made a fitting using a metric oil drain plug, tapped for 1/8" npt, installed it in the fuel rail test port and then ran a standard high pressure fuel/transmission pressure tester hose and gauge into the cabin through the clutch pedal hole by removing the block off plate. Carefully verifying no leaks of course.

 

Reading back in my own posts I recall having the code 43 but only once. Though it passed smog recently should I change the O2 sensors?

 

Just to wrap this up, it was my oxygen sensor after all. I've had no stalling issues since replacing it shortly after my last post.