Car question

[tw]

Originally Posted by plthijinx

i hate not being able to do/complete a job. this one won.

Not necessarily. It may have set a trap. What were consequences of, for example, a partially removed pipe? You would have to replace an entire exhaust manifold and catalytic converter that cannot be removed.

You may have outsmarted a car that had laid a trap.

However, just as fun is getting into that mess. And then discovering how to solve it. Either you outsmarted a car. Or you just missed out on having fun. Either way, you did not lose. Only and maybe did not win.

A simplest ‘shotgun’ solution is replacing an oxygen sensor. Soaking in WD-40 for at least 24 hours may be helpful.

[Clodfobble]

I was thinking I might get a small above-ground pool, fill it with WD-40, and soak the whole car in it. Sure, it would smell funny, but the kids would love sliding off the seats.

[tw]

Originally Posted by Clodfobble

I was thinking I might get a small above-ground pool, fill it with WD-40,

I love the smell of WD-40 - anytime. It also cures bed bug problems.

[classicman]

pssst - UG ... you need new bait? try WD-40 next time.

[Undertoad]

omg don't soak the whole car in wd-40! It just occurred to me that every bolt will loosen simultaneously and the car will fall apart while driving down the highway, like a cartoon!

[Clodfobble]

Like the giant lego ball!

[glatt]

[glatt]

Originally Posted by tw

The difference between crap Liberty gas and Shell gas would (for example) result in maybe an 8% difference without any noticeable change in idle smoothness. If your numbers are as reported, then Liberty gas should have caused a noticeable mileage difference. The fact that you saw no difference is troubling.

In another event, a tank of Mobil destroyed my fuel injectors. I knew something was wrong due to a slight roughness in idle. But the resulting mileage change was from 32 MPG to about 27 MPG in that tank. And 24 MPG in the next tank. (Honda replaced those injectors for free). In that case, diagnostics never reported a problem.

In another case, a problem with an EGR valve kept causing a check engine light. No mileage change. Symptoms that helped me trace the problem to a hard and not easily diagnosed problem. (BTW, EGR valve is not connected to the idle system; so did not affect idle. And that failure was unique so as to not affect gas mileage.)

Examples of different failures that do and do not result in mileage changes. And that isolated the problem quickly to a shorter list of suspects.

Assuming that 5% coincided with road conditions (heavy traffic, summer open road driving, etc), then is we can assume you have a problem traceable to the idle system and that does not affect the other 'normal operation' system.

BTW, remember Cloud's problem. That was also traceable to the idle system and that would not cause mileage changes. That mechanic had one clear advantage. The Civic's diagnostic system pointed exactly to the defect - which that mechanic refused to address. An example of why some people just refuse to learn good diagnostic procedure.

Now, with Shell, what is happening? What are the latest symptoms?

For the last two months we've been putting nothing in it but Shell. No improvement. I put a bottle of fuel injector cleaner into it. No change. Still a rough idle after it warms up.

So I bought a CarChip Pro so I can monitor RPMs and other stuff.

I just started it and let it idle for 8 minutes or so. I didn't touch the accelerator. The first 4 charts I got are below. It started off fine, and the idle got progressively rougher, until at 8 minutes in, the roof liner started vibrating it was so bad. Then it was dinner time, so I turned it off.

Chart 1 is RPM. You can see it gradually slows down. I didn't touch the accelerator ever.


Chart 2 is the throttle position. I had no idea what this would show, but here you go. It shows little when you don't step on te gas.


Chart 3 is the first of several oxygen sensor readings it can take. I ahve no idea what this means, but this is O2 B1, S1


Chart 4 is also an oxygen sensor reading. It's called O2 B1,S2, whatever that is.


I'll have to double check the shop manual, but if I recall correctly, it should read between .1 and .9 volts. It goes a little below .1 volts.

There are a whole bunch of other readings I can have this make, but you can only do 4 at a time, and you have to take it out of the car and hook it up to a PC to change what you are monitoring.

It's a neat little gadget.

[tw]

A car at idle runs completely different from one at normal engine speed. At idle, a car must dump more gas in the engine while making the car work so inefficiently as to run at only 800 RPMs. Most pollution occurs during idle. Also why cars sitting in bumper to bumper traffic consume so much gas (another reason why hybrids are so necessary).

IOW a better test of your O2 Sensor and other factors is to be moving at constant speeds as indicated by little or no throttle movement.

Now, some facts. In the first minute, an O2 sensor must get warm before it reports anything. So newer technology sensors have an internal heater to make them hot (work) sooner. In your case, sensor one got to temperature quickly. Sensor 2 seemed to be doing nothing until engine exhaust finally heated it. Sensor 2 may have a defective heater or for some reason is taking longer to get the temperature. (BTW, I am assuming this is a 6 or eight cylinder since fours only need one O2 sensor. If this is a four, then the second sensor may be after the cat converter making this analysis bogus.)

Sensor 2 appears to be reporting inaccurate voltages. An O2 sensor is typically between .6 and .7 volts when the engine is running optimally. When dumping gas excessively, then the voltage is typically about 1 volt. Your sensor two appears to be reporting numbers that are low. Or one side of the engine is using more gas than the other.

However, how electronics measure those voltages might explain different numbers. Your particular car may measure or report those voltages differently. Normal voltages for an O2 sensor must be confirmed from the shop manual. But something is different on both sides of the engine.

Throttle clearly remained closed the entire time. But after 8 minutes, your idle was not yet at 800 RPM? The car should have been hot and at idle after 8 minutes. You might repeat the test while monitoring engine temperature. Your thermostat might not be fully closed (partially sticking) when the engine is cold. Therefore the engine is taking too long to warm up; wasting gas in the first ten minutes.

What you are looking at? Fuel injection is a switch (much like Cloud's idle adjustment valve) that is turned on and off quickly by a microprocessor. Time of each opening (called fuel trim) determines how much fuel is dumped into each cylinder. An O2 sensor measures how much got burned. Microprocessor reads the O2 sensor to determine whether to lengthen or shorten that opening time (adjusts short term fuel trim).

Graph is each O2 sensor number (maybe) sampled only at 5 second intervals. The actual numbers vary significantly in milliseconds. Actual O2 voltage is varying many times more often and more gently. Your chart simply shows some of the highest and lowest voltages. Therefore the steep changes.

Those variations may be normal for idle. But if you see variations that large for normal RPMs, then that may also be symptoms of a problem. An engine at normal speeds should see O2 sensor voltages varying little between 0.6 and 0.7.

Notice that at seven minutes, the variations decrease to what I am more used to seeing.

Voltage should increase when, for example, when a throttle is pressed. An open throttle means intake manifold has no vacuum. So the computer dumps more fuel into cylinders (short term fuel trim increases). More fuel comes out unburned. The O2 Sensor (that I am used to seeing) reports 'more unburned fuel' at about 1.0 volts.

Again, large variation may be normal for your engine. If it was any of my Hondas, I would be concerned. Approaching eight minutes, the variations decreased. Whereas your seven minute voltages to me are too low, still, the O2 sensor varies more like I am used to seeing it.

Meanwhile, the 'Shell' test implies gasoline was irrelevant to your original problem.

You can view a relationship between short term fuel trim, throttle angle, O2 Sensor voltages, and intake manifold vacuum. To see what the microprocessor sees and responds accordingly.

Another parameter is long term fuel trim. I have never confirmed this by doing it. But a long term number would increase if the gasoline is inferior. If gas (ie WaWa) does not burn as efficiently, then engine software may respond by increasing (over a long time) the amount of fuel it dumps into the engine. Long term trim is how a microprocessor learns and adjusts from engine overall performance. Short term fuel trim is how it responds due to immediate road, throttle, load, and other current variations.

O2 Sensor is not the only input. But it varies according to how much gas remains unburned. Other inputs include a sensor that measures atmospheric pressure (are you one mile up in CO or at the shore?), and one that measures manifold vacuum. When does it know to dump more fuel into the engine? When vacuum decreases (due to an open throttle or a sudden air leak). Ignition timing also changes (advances) when more fuel is dumped. You can also view that relationship.

I don't remember what your car's technology is. However older cars adjusted engine timing mechanically (centrifugal force and manifold vacuum). So a sticky or binding ignition timing could be seen on that chart. I have seen where distributor grease got sticky after ten years causing engine timing to intermittently stop changing. That was also indicated by a slight knock. However some auto companies (ie GM) decided knocking is normal rather than fix an inferior engine designs. Knocking alone might not report a problem. But sticky mechanical ignition timing might be seen on the chart. Unlikely. But an example of what the microprocessor can see. But the failure is not serious enough to report. An example of why many detected problems can remain unreported by engine check lights.

Hopefully this successfully introduces simple operations inside a computerized engine. Computerized engines are simpler than carbureted. But involve fancy nouns (ie short term fuel trim) that at first sound confusing.

[tw]

Originally Posted by Undertoad

It just occurred to me that every bolt will loosen simultaneously

But until then, every squeak and rattle will have been eliminated.

[glatt]

Thanks for your input, tw.

FYI, the car is a 4 cylinder.

I was reading the shop manual as I was drifting off to sleep last night. Boy, what an annoying book. You find one list that talks about rough idle possible causes, and each cause sends you to a separate section of the book, so you go to those separate sections, and they each send you to other separate sections, so you spend all your time just flipping around from section to section. I need to just sit down for a couple hours with a notebook and take my own notes from this manual, since trying to find where I read something is pretty much impossible. I've got almost every page in this one section folded over.

Anyway, for the O2 sensor, the voltage ranges are supposed to remain within .1 to .9 volts during operation. It doesn't send you a code until the voltage drops below .05 volts, and in my idle test on my car, it never did.

I also have a few stop and go trips around town recorded, but they are confusing because there is so much variation in road and engine speed. I'll try to fit in a short trip on the highway this weekend.

One amusing thing is that this CarChip Pro is also marketed as a way to snoop on your teenage driver and tell you if they accelerate too fast or stop too fast. My wife never triggered the thing, but almost every time I stop when driving, I set the damn thing off. So I come to a stop at a stop sign and the damn thing beeps at me. Then I stop at a red light, and it beeps again. I'm not jamming on the brakes. Honest. But my wife thinks it's funny. There's some way to turn it off, but I haven't figured it out, and maybe it will make me into a "better" driver.

[Clodfobble]

There was a review on the Amazon page by a dad who had purchased it to monitor his son's driving habits... and when his son got a ticket for going 90 in a 55, the son swore he wasn't going that fast, and the dad's all, "Yeah yeah, sure son. Let's check the record, shall we?" And it turned out, no, the CarChipPro had recorded a speed of only 62 at that time. Still speeding, of course, but obviously not 90. They presented the data in court and got the ticket thrown out.

[infinite monkey]

Originally Posted by Clodfobble

There was a review on the Amazon page by a dad who had purchased it to monitor his son's driving habits... and when his son got a ticket for going 90 in a 55, the son swore he wasn't going that fast, and the dad's all, "Yeah yeah, sure son. Let's check the record, shall we?" And it turned out, no, the CarChipPro had recorded a speed of only 62 at that time. Still speeding, of course, but obviously not 90. They presented the data in court and got the ticket thrown out.

Nice! I like!

[glatt]

A year and 150 posts ago, I complained in this thread about a rough idle my car has. If you are a glutton for punishment, you can go back and re-read it all, starting at post 55. The problem is still there.

The executive summary is that after driving the car for a while and the engine gets warm, I stop at a light and put the car in neutral or step on the clutch, and it begins to idle. And vibrate. A lot. It's annoying. It's loud. It didn't use to be like that. It used to be smooth and quiet. Now it's rough and loud and vibrating. However, the fuel economy is as good as ever. I got 39.5 mpg on the highway on a trip back from Maine over the summer. Very pleased with that. Normally it's city driving and around 30.

We recently bought a second car, which means I can take a day here and there to work on this one, and the other one is available for use. No pressure to get it fixed in a half hour window before the next soccer game. So I am returning my attention to this problem.

So far, I've tested the engine mounts by putting on the parking brake and trying to drive forward and reverse while watching the engine. The engine barely moves. I think the mounts are good. I ran a few bottles of fuel injection cleaner through the gas tank according to instructions. No change. I paid the corner mechanic to clean the throttle body when they were doing an oil change. No change. But I recently took the air filter off to check the throttle body, and noted that it was clean, so they did the work. I tried to clean the mass airflow sensor, but discovered that this car (1996 Geo Prizm) does not have one. It has a pressure sensor instead and I understand you don't clean those.

Here's the throttle body.

Looks clean to me. The little square-ish hole at the bottom of the throttle leads down to the Idle Air Control valve. It looks like it might be a little dirty down there, so I may try cleaning that next. It's kind of complicated though. I'd need to remove a few hoses, including coolant lines, some data cables, and a throttle cable before I can get the throttle body off, and then take the IAC off of the throttle body and clean it out. Maybe this weekend. Seems like if I'm having idle trouble, the problem might be the idle control valve.

How do you take off a couple of coolant hoses without getting coolant everywhere or bubbles in the coolant system? Do I need to flush or bleed the coolant afterwards? Sounds like a lot to go through to clean something in the hopes it will fix the problem.

[tw]

I would not waste time cleaning things. Cleaning rarely fixes such obvious problems. And might even create more problems if disconnecting the coolant is necessary.

If I remember correctly, we went through a list of suspects from the manual and other suggestions. Eliminating many including fuel and O2 Sensor. Mileage and operation when not in idel mode eliminates most suspects (including motor mounts). Listen to the exhaust pipe both on idle cold and idle hot. Any missing that corresponds to the roughness?

When cold, the idle is probably faster. Might not feel rough. A problem not apparent in cold (faster) idle might still exist and be heard in the exhaust pipe. Missing in the exhaust pipe would eliminate motor mounts and other static reasons for roughness.

Does the roughness appear suddenly or gently become obvious as idle RPMs slowly decrease?

Does this fuel injection system do a fast idle by holding the throttle plate slightly open or by opening a fast idle air valve (not to be confused with the Idle Air Control valve)? IOW is there a relay or vacuum line that partially holds the throttle open for a fast idle?

As noted previously, an idle control system operates different from high speed operation. Parts that are common to both operations (ie spark system) can be eliminated since they work fine in high speed operation. Apparently performance and gas mileage say all high speed subsystems work OK.

Some previous questions I don't recall seeing answered. How does this car perform timing? For example, does the distributor have vacuum and centrifical advance and retard to mechanically adjust when spark plugs fire? Or is engine timing done electronically? Carchip may report timing as the engine gets warmer.

One part that operates only in idle mode (not in high speed mode) is the Idle control valve. A binding valve might explain rough idle. However, if difficult to access, then better is to eliminate other possible suspects first.

EGR valve can be in that suspect list. EGR valve is open during high speed operation. But must fully seal always during idle. That valve leaking exhuast gas during idle means it too would be a part that could only affect low RPM idle. And is often easily tested. Two reasons for that leaking would be vacuum on that EGR valve at idle (when no vacuum should be opening that valve) or the valve does not fully seat (close) at hot idle. The later can only be confirmed by temporary removal and inspection. Former becomes obvious by disconnecting an EGR controlling vacuum line and covering that hose with a finger. No vacuum should exist during idle.

I don't remember the long list of suspects. Don't remember any error codes. And don't remember why we spent so much time eliminating an O2 Sensor and gasoline from the suspect list. But gas mileage and high speed performance also eliminate both from the suspect list.