My car has a problem that has stumped my mechanic.
My “check engine” light was coming on every couple of days, then going off after a day or two. The car started and ran beautifully, though. After a couple of weeks of this, I brought it to a shop. The guy said the check engine light was caused by a lean running condition, and found the fuel pressure in the fuel rail to be below spec. The fuel pump checked out OK. He replaced the fuel pressure regulator, and the check engine light stopped coming on.
But the car doesn’t run as well as it used to. It’s fine during the first 20 minutes of running or so. But after making my daily commute of ~20 miles on the freeway, the engine stumbles, hesitates, and feels like it’s about to stall in stop-and-go traffic. (It hasn’t ever actually stalled, though.) Giving it a lot of gas produces a confident surge or power and acceleration, but a saner touch sometimes causes engine RPMs to fall and wander, punctuated by occasional sudden jerks of power. When the engine begins to stumble, I can lift my foot off the gas and let the engine return to idle speed - it idles well - then try a little gas again, and often it will run well for the next 15-30 seconds.
I wonder if perhaps this was some sort of vacuum control problem. The guy who replaced the fuel pressure regulator mentioned a fair number of vacuum-control checks in relation to the fuel pressure regulator, which (I guess?) is vacuum powered or vacuum controlled. Maybe he cracked some vacuum line? I don’t know if engine vacuum is used to advance distributor timing on cars of this era, but could erratic timing cause this sort of thing?
It’s a 1998 Honda Accord, 4 cylinder. It was tuned up less than a year and 10K ago. My mechanic has been unable to duplicate the problem and has offered only vague speculations. Any specific guesses would be much appreciated.
I thought about that as soon as I started experiencing this problem. For a while, I thought this was only happening when the tank was nearing empty. As far as I can tell, the fuel filter is inside the gas tank (and not really intended to be replaced regularly) on this model, so that might make sense if the filter’s bottom edge was blocked. But it has since happened on a full tank also.
Another question might be: why would a plugged-up fuel filter only cause trouble when the engine was good and hot from a run on the freeway?
Oxygen sensor. Now that you have essentially changed the fuel/air mixture, the old oxygen sensor is having trouble reading the blend and sending the wrong signal to the control unit. Are you also experiencing a decline in fuel economy?
I should add that the oxygen sensor only really does anything when it has reached full operating temperature. This is why you don’t see the problem until the engine is warm.
I haven’t noticed a decline in fuel economy, but my driving is overwhelmingly on the highway, and I don’t have the problem there, so perhaps such a drop just isn’t large enough to be obvious. I actually do check the previous week’s fuel economy when I tank up, and it’s been quite steady in the 30-32 MPG range since I bought the car over a year ago.
I would have expected goofy O2 readings to light the “Check Engine” indicator again - is that not the case, or not always the case?
The more I think about it, the more I like the O2 sensor theory.
The car had been running lean for a while. I’m told this causes higher combustion temperatures; presumably that would cause higher exhaust temperatures, too. And the O2 sensor is right there in the exhaust manifold (well, one of them is, anyway). Could high exhaust temperatures damage the O2 sensor?
The people who replaced the fuel pressure regulator also performed an advanced money-ectomy procedure they called a “Fuel System Flush And Cleaning,” or some such nonsense, which I gather involves burning a bunch of solvent-laden fuel while joyriding around in my car. Could weird combustion products from the solvent damage the O2 sensor?
This model appears to have two O2 sensors, one in the exhaust manifold and one after the catalytic converter. I don’t know if it makes sense to replace just one. Parts cost to replace both would be $150+ :eek:, but I might be able to do the labor myself. I think the one in the manifold at least is very easy to get to.
Some cars, my Celica, for example have two O[sub]2[/sub] sensors.
Another thing you might try, is disconecting the battery for 10 minutes, it resets the computer. This worked when nothing else did on mine.
I just thought I’d tell everybody how this worked out, and thus offer a more definite answer to my own original GQ. Maybe it will help someone else.
It was indeed the O2 sensor - in a manner of speaking. Today the shop that originally diagnosed the bad fuel pressure regulator found a bad connection between the O2 sensor and the wiring harness. Cleaning up and re-seating the connector seems to have solved the problem. I think they unhooked the O2 sensor the first time I brought it in, to test it. When they re-connected, they didn’t get a good contact. (Of course they deny that they ever went near the O2 sensor last time…) Apparently my O2 sensor in this case was sturdy enough to survive a little lean-burning for a while.