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Old 11-12-2011, 10:23 AM   #76
TheMercenary
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No.
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Old 11-12-2011, 10:38 AM   #77
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But you said your money was on the O2 sensor.
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Old 11-12-2011, 10:49 AM   #78
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Oh, maybe I should have rephrased that.
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Old 11-12-2011, 04:45 PM   #79
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We should all bet on it, and whoever is right gets to pay for the repairs.


Loose wire.

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Old 11-13-2011, 02:05 PM   #80
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I took it to Track Auto or Autozone or one of those places. And they hooked it up to the code reader, and there were no codes found.
I guess that means the oxygen sensor is OK?
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Old 11-13-2011, 05:01 PM   #81
tw
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Originally Posted by glatt View Post
I guess that means the oxygen sensor is OK?
Most likely, yes. But again, described was how to make some code reported. Some codes will not be reported unless a defect is seen in multiple and consecutive restarts.

Most O2 sensor failures I have seen get reported by diagnostics long before it causes engine roughness or lower gasoline mileage. And again, gasoline mileage is an important parameter in locating these intermittent type problems. Some defects will cause mileage reduction. Others will not.
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Old 11-14-2011, 02:48 PM   #82
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Originally Posted by glatt View Post
I took it to Track Auto or Autozone or one of those places. And they hooked it up to the code reader, and there were no codes found.
I guess that means the oxygen sensor is OK?
Was it exhibiting the symptoms at the time the test was taken?
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Old 11-14-2011, 03:01 PM   #83
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Yes and no. It had been rough idling moments before, but it was turned off for the code reading. Key was only turned part way and engine was not running.
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Old 11-14-2011, 05:00 PM   #84
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part one of two

Ok, well then I guess the O2 sensor is not indicating an error.

NO readings means that the problem is coming from some source(s) in the system that don't report back to the computer. Things like ZenGum's "loose wire".

glatt, how much do you know about a 4 cylinder internal combustion engine like the one you've got? I don't want to talk down to you, I'll just think out loud.

When it's running right, two cylinders fire at the same time, like 1 and 4, then two strokes later cylinders 2 and 3 fire (a common firing sequence). Since everything is balanced mass wise and thrust wise, it feels smooth. As soon as something in that little set of sequences doesn't happen (and there's a missing piece, not an extra piece. No phantom fifth cylinder appears to unbalance the weight or the firing. No. Something's NOT happening, like one cylinder not firing unbalancing the engine, manifesting as rough idle). So, what could cause a cylinder to periodically not fire/misfire?

The holy trinity of internal combustion is fuel + air + fire. If you're missing one or more of those you're screwed. And they have to be delivered in precise amounts and precise proportions and at precise times. What could cause an interruption to any of these?

Let's subtract unlikely candidates and see what's left. It's unlikely that you're not getting air to a cylinder. A dirty air filter would restrict airflow to all the cylinders, not just to some, so... I can't think of another likely cause for "missing air" that wouldn't also have some other much more dramatic symptoms. I think your engine's getting the right amount of air.

And, that air is being delivered continuously and at pretty constant pressure and temperature, so it can be treated as a constant, putting the responsibility for fuel/air mixture proportions on the fuel side. You said the engine is fuel injected. Ok, what controls the injection? If it is mechanical injection, it's a masterful clockwork designed to figure out how much fuel to squirt, but your car almost certainly has electronic fuel injection. What electronic fuel injection is about is a system of sensors like throttle position, speed, gear, emissions, etc etc that help the computer decide how much fuel is needed to meet these conditions.

I had an old Buick LeSabre that would sometimes give me grief. It turned out there was a (gah, I hesitate to tell) design weakness that involved the air mass sensor (the MAP sensor in your car). Sometimes the car ran like shit, or wouldn't start at all. I learned to open the hood, and give the plastic intake snorkel a sharp whack, close the hood and carry on, problem solved. It turns out that the sensor was used to determine how much actual air was moving through the engine by putting two different magical detectors very close together, kind of like the rubber hoses you saw in gas stations years ago that rang the bell ding ding when you drove over them? Well the modern version in traffic surveys has a pair of these hoses across the roadway and it can calculate the speed of the cars by measuring the length of time between the tire touches on the two lines. Well this sensor worked like that but the wires were so close together that when a tiny piece of crud was sucked into the airstream, if it caught on the sensor part of the wires (strung directly through the airstream, just like the traffic sensor) it could cause erroneous readings. A smack on the housing usually dislodged the minute particle of junk, the sensor was then able to read the amount of air, and reported back to the main computer and the rest of the calculations would result in the right amount of fuel to be injected; life was good.

Back to your car, something could be interfering with a perfectly good sensor, like some crud on the sensor, and causing it to report bad values, with the downstream effect of a roughness because the cylinder's not getting the right amount of fuel. But which sensor when the computer check says none is ... really tough and expensive.

Maybe you have a tiny piece of dirt in one of the injectors. I have an old house and a very low flow showerhead (2.5 gal / min). Sometimes some rust/crap from the inside of the pipes flakes off and makes it's way to the showerhead. This clogs it and the flow is reduced even further. Not good. I take the showerhead off, clean out the crud, reassemble and carry on. Now, the tub faucet is on the same damn pipes, but I never have this trouble there. The flow/current/pressure (whatever) is just so high that if it even happens, I never notice it. Back to your car. Maybe you have a little piece of dirt in one of the injectors and at idle, low speed, low pressure the dirt can interfere with the squirt of gas, causing a misfire. At road speed, you don't notice because you're pushing a lot more fuel through (like my tub faucet), so problem isn't noticed. To me, this is plausible. Fixing something like this can be pretty hard. The injectors aren't really.... repairable. They're replaceable, but could be bux. The orifice is super tiny, imagine the size of hole that produces a vapor or fine mist, like a perfume mister or spray can. Psssshhhhht. or more like psht psht psht psht psht 800/2 times per minute. You could try commercial injector cleaners that you pour in the gas tank.

What else could cause irregular fuel delivery. It is also plausible that the whole engine is being a little starved for fuel under low pressure situations like this, as might happen if the main fuel filter was moderately dirty. Have you checked your fuel filter? This can be an easy and cheap fix with little downside. Once more, at road speed, this would be less obvious at the higher pressures.

Fuel...fuel... a physical restriction, or bad instructions to cause it to erroneously deliver the wrong amount of fuel... those are all the situations I can think of at this time for fuel. Air, check. Fuel, check. Now fire.

--to be continued--
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Old 11-14-2011, 05:01 PM   #85
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part two of two

--continued--

For fire, you need the spark plug to go zap at precisely the right time. Also you need a big fat spark. Unlike fuel and air, this one is not "quantity" dependent so much, it's really hard to have too big of a spark. You can have too weak of a spark, and no spark is also bad, but there isn't a proportion "rule" unlike fuel and air. But it is definitely timing sensitive. So we're looking for possible faults that could cause a weak spark or a mistimed spark. Ok.

Weak spark could be caused by some deteriorating connection or component working your way backward from the electrodes on the plug to the connector at the top of the plug, to the plug boot, plug wire, other end of the plug wire, to the coil (or whatever is generating the giant pulse of electricity) to the ? and at this point it varies a lot depending on what kind of ignition system you have. This is the same question as what kind of fuel injection, mechanical or electronic. If it is electronic, you only have the ECM (electronic control module(s)) to rely on upstream of the plug wires. There's nothing you can do in there except replace and only on the "instructions" of the code reader (for us shade tree mechanics). You're not getting a code there, so I don't have anything to point to the electronic ignition system, sorry. If you have a mechanical ignition system with a distributor cap (the cap that "distributes" the electrical pulses by rapidly changing which cylinder has a complete electrical circuit) that could be a point of intermittent failure. It also comes with a rotor, same possible fault. There could be other pieces there that are weak at low speed (like points or a condenser). But I don't know if you have a mechanical ignition system. I have a 1996 car (VW Golf) and it has electronic fuel injection and a mechanical ignition system. I have had trouble with the ignition system before.

Trouble's not really fair, it simply needed some regular maintenance which meant replacing some of the components, like the cap and rotor. This was the best $25 I put into the car that whole freakin year. Your car? I can't say. Do you know if you have mechanical or electronic ignition?

Other causes of weak spark could be degraded or damaged plug wires. You could have a bad plug. They operate in severely harsh environments--think Mount Doom--and need to keep performing a very difficult electrical stunt, ionizing air to make a conductive path (fancy ass way of saying spark) a kabillion times. In shitty atmosphere. Sometimes that crud accumulates on the plug and interferes with the spark. Yeah, really. This is an easy thing to check, assuming you can actually get to the plugs and you have a ratchet and an extension and a plug socket. footfootfoot's car doesn't qualify here, since he can't get to all the plugs. He/you certainly could check the ones you can reach though, and if you see one that's bad, replace it. Check them all if you can. There are pics online somewhere I'm sure that show you in living color what the electrode end of a plug in good condition looks like AND what a plug in poor condition looks like. There will be lots of different "bad plug" pictures, since there are lots of reasons why a plug could go bad and be the source of bad symptoms. You can look them up. If you can't find them, report back, we'll find some for you.

So that's weak spark. What about absent spark? That's all the same, just weak to the level of zero. Fine. Oh, just thought that the coil could be weak, that's the part that generates the high voltage needed for a spark. It's like a transformer in your system.

What about mistimed spark? This is less likely, though not exotically rare. You could have a situation where the electricity that would have been your spark is leaking out before it gets to the plug. Like if a plug wire has a fault in the insulation and the spark is grounding out to the engine before it reaches the cylinder. One way to check for this would be to open the hood and look at the engine when it's displaying the symptom of roughness, but do it in a very dark environment. The idea is to have the fugitive spark reveal itself in the darkness. Doable.

Timing... thinking... A car that is mistimed could have a rough idle. What do you know about the car's timing? Have you checked it? Have you changed it? This isn't something likely to change on its own (possible, but pretty unlikely). If *you* have mucked with it or some other mechanic, it is possible that it's been changed from "best" to something less than best. I don't know how else your engine would miss a spark or mistime a spark.

Having thought out loud, it seems the most likely piece is a fuel delivery problem, junk in injector or fuel filter. Next and close behind would be an ignition fault. If it was my car, I'd do these things in this order until I found a likely problem.

1 -- visually check all the ignition wires. disconnect and reseat all these connections. this is free.

2 -- pull the plugs, check them. fouled? cracked? worn? beautiful?

3 -- replace fuel filter.

4 -- run a bottle or three of injector cleaner super duper turbo in a jug or whatever that crap is called through the car a full tank of gas at a time.

5 -- run the car on the TOP HALF of the fuel tank for a while. this probably should be item 1.5 or even item zero.

Tha's a good start. I'm interested to see what happens here glatt. Keep us posted please.
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Old 11-14-2011, 07:11 PM   #86
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Wow, that's a lot of thought you put in there.

We had the timing belt replaced at the urging of a mechanic a few years ago, and after that happened, I was sure to pay attention to the performance of the engine. I don't remember any changes in performance overnight, so I think they did it right. These problems have been gradual, and I've just noticed it recently because it's reached a certain threshold of being annoying.

We also replaced the fuel filter a couple years ago too at the recommendation of a mechanic. Certainly long enough ago that it could be messed up in the meantime.

I'm leaning towards this engine just being old and dirty as being the most likely culprit, but I'm going to follow your ideas. When I get some time and daylight.

Last edited by glatt; 11-14-2011 at 07:16 PM.
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Old 11-14-2011, 07:20 PM   #87
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I learned to open the hood, and give the plastic intake snorkel a sharp whack, close the hood and carry on, problem solved.
I love it when you can fix a machine by thumping it. Very primal. RAWR! Og mad! Og Smash! [thwack ... vroom!!] Bwahahaha!


Oh, and as well as the above ... you are using the recommended grade of gas, aren't you?
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Old 11-14-2011, 11:44 PM   #88
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Originally Posted by ZenGum View Post
I love it when you can fix a machine by thumping it. Very primal. RAWR! Og mad! Og Smash! [thwack ... vroom!!] Bwahahaha!
the technical term is "percussive maintenance". It is very satisfying no matter how effective it is.

Quote:
Originally Posted by ZenGum View Post
Oh, and as well as the above ... you are using the recommended grade of gas, aren't you?
gas grade is a measure of the octane in the fuel. Octane's role is to change the point at which the fuel / air mixture spontaneously combusts due to the heat from compression. You experience this as "knocking". It is most common when the engine is under a heavy load such as hard acceleration or towing or driving hard uphill. The mixture detonates before the piston reaches top dead center and/or the spark ignites an already lit combustion chamber and the result is a hard knocking sound. I've never heard of octane having much if anything to do with idle loads.
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Old 11-15-2011, 12:19 AM   #89
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Good points, but I was thinking in terms of it not burning cleanly and being the source of gunk that could cause the problems you mention.

I've learned to check the very basics first. I've got part way through helping a friend remove the door skin from the back door before asking why he was doing this. The inside door handle wasn't working. Oh, does it have a child safety lock? A what? One of [click] these.

Then there was the friend who's car had broken down. After ten or fifteen minutes of experimenting, then calling the mechanic service, I noticed the fuel guage on E. Done this twice, about ten years apart. Same friend.
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Old 11-15-2011, 07:21 AM   #90
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The car doesn't require high octane fuel.

Our regular corner gas station used to be a Texaco. But then Texaco pulled out of Virginia for some reason. So all the Texaco stations became "Liberty" stations. It's more of a discount gas station, but not significantly cheaper. I assumed it was just as good as Texaco. Around the same time, our grocery store began offering significant discounts on gas at Shell stations when you buy lots of groceries. We have a family of 4 and buy a lot of groceries. So most of our gas has been bought at a Shell, but in the last year or two, we have been buying some of our gas from this Liberty gas station on the corner. Maybe Liberty sells crap gas? I don't know. The dates roughly match the symptom dates.
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