Stupid Car Computers

Last Friday I had my truck taken down for a smog test so I could renew the license. I was shocked when it failed the test. First time in my life that has happened. While it is an old truck - 2002 - it has less than 11,000 miles on it and is in excellent condition.

So why did it fail? Several months ago, I had a new battery installed. When the battery is removed, the on-board diagnostics system is reset. Under normal driving conditions, the system will initialize itself and all is fine. Unfortunately, I don't drive the truck very much, and when I do it is short trips, much of which is on low-speed twisty roads. Under these conditions, the OBD will not initialize. I was not aware of this; hence the test failure.

So I had my guy take the truck out and drive down the freeway fifteen miles, then drive back and have the smog check redone. Perfect results.

Seems like they could have a better way to handle this.

I have a similar story.

My 16-y.o. Subaru has some water in the gas tank, I'm guessing, because every time I drop below about 1/8 tank it begins coughing. Last week I ran the tank lower than I usually do, and tried to push through the sputtering by stomping on the throttle. I kept the car running, but my check engine light came on.

This has happened before, and I believe it'll automatically reset after a few hours of successful driving. I have not put enough miles on it yet for the light to go off.

Has this been going on for a while? Because it doesn't sound like water in the tank.

A year or so.

Never happens with a tank 1/4 full or better. Could be the geometry of the siphon, or something with the fuel pump or filter. But since it's easy to avoid I just fill up at 1/4 full.

I don't know the construction of the fuel system in that particular car so I couldn't say for sure, but it sounds like the fuel pick-up. If it's plugged up or coming apart it would exhibit those symptoms. In either of those cases, one of these days it will just quit running. Water in the gas tank is incredibly rare. It has to be either intentionally or accidentally put in the tank.

Of course, there's always the option of a faulty fuel gauge showing 1/8 tank when it's really nearly dry.

That's a problem I would have looked at.

I don't think so, and here's why.

Before this problem started, my fuel gauge was if anything overly generous.  I could show dead empty and still go 40 miles.  I have never (knock on wood) run out of gas in this vehicle.  And I have tried.

Plus, when it coughs, it doesn't cough-and-die.  It hiccups and keeps going.  If I'm accelerating away from a stoplight it can jerk once, twice, three times before catching.  If it was out of gas, or a blocked filter, it wouldn't act like that.

Headed uphill or down doesn't seem to make any difference, except that I rarely step on the throttle headed downhill.

NoCoPilot wrote:

Plus, when it coughs, it doesn't cough-and-die.  It hiccups and keeps going.  If I'm accelerating away from a stoplight it can jerk once, twice, three times before catching.  If it was out of gas, or a blocked filter, it wouldn't act like that.

Headed uphill or down doesn't seem to make any difference, except that I rarely step on the throttle headed downhill.

Actually, a very low fuel level, or a partially blocked filter could cause the jerking you describe on acceleration. In my other post, I wasn't referencing the fuel filter, but the fuel pickup in the tank.

Also, keep in mind that nearly all cars these days have a submerged fuel pump:  it is in the gas tank. These pumps depend on the gasoline for lubrication. If they get water in them, they will fail prematurely for lack of lubrication.

"If it was out of gas, or a blocked filter"
If it's pumping water, then it is out of gas - at least partially - creating a lean condition which causes the jerking, if the jerking is caused by a fuel problem. If you are pumping water, then the fuel filter will become plugged up very quickly.

It's possible that you are correct and you  have water in the gas tank. But if that is the case, you should drain the tank and get rid of the water before it destroys the fuel pump and/or other fuel system components.

Someday I'll do that. The car has another annoying old car symptom, when cold the shifter doesn't work very well. Fine when it warms up.

Neither problem impedes my ability to get around -- and I don't commute anymore -- so it's low priority.

True. But consider the difference in hassle and expense between simply cleaning the tank and replacing the pump and maybe the tank as well.