Car question

[tw]

If a fuel filter is clogged, the problem is easily identified so that an intermittent no longer exists. Simply remove the filter and blow through it. Flow would be obvious restricted. Or backwash the filter with a solvent. Either means you know if a problem was or was not solved. Since you have a new filter, then blowing through the old and new filter will make any restriction obvious.

Shotgunning did not find the problem. Leaving you unsure if anything was fixed.

Or the entire fuel system could be tested without replacing or buying anything. Shop manuals may state how many pints a fuel pump will pump in a specific time. Then the pump, intake filter (inside the gas tank), pipe, check valves, and in-line filter are all verified as a complete system. IOW a problem is known solved because the problem was first seen before corrected.

Concept was taught in CSI: "Follow the evidence".

[glatt]

If I go through the hassle of taking off the old filter (it's buried behind a lot of stuff) then I'm definitely going to replace it with the new one. The filter is cheap.

This car has 60k miles on it. The manual says filters should be changed every 30k. It should be on its 3rd filter by now. I don't know if it's ever been changed, but I doubt the previous owner changed it just before unloading it.

[Gravdigr]

Glatt, was the vehicle doing that 'surging' thing by itself, or was someone moving the throttle? Assuming it was happening without throttle input, could the throttle position sensor cause such a thing?

[glatt]

It was doing it by itself. It would almost stall, and then the computer would give it more gas to prevent the stall. And then it would stop giving it more gas, and the cycle would repeat.

I just finished installing the fuel filter. And now it's idling a bit fast. Haven't driven it around yet, so that might just be the cold start, fast idle mode. It was a bit of a pain. Had to remove the air cleaner assembly and half a dozen vacuum hoses and sensor cables to get at the thing. Frankly, I'm pretty proud that I got it all back together and working with no leftover parts.

[tw]

Originally Posted by glatt

This car has 60k miles on it. The manual says filters should be changed every 30k.

I would change gas filters, air filters, PCV valve, and spark plugs as recommended. Eventually learned that was mostly unnecessary. But again, if a filter is the problem then blowing through it would make the problem obvious.

Eventually I stopped replacing spark plugs, washed the PCV valve in a solvent, banged the air filter on asphalt to clean it, and never replaced a fuel filter.

Generally, idle is not controlled by the throttle (as that picture shows). An IAV does idle air adjustments (a problem discussed with Cloud? when a Honda that mechanics refused to solve it until another mechanic was used). To say more requires facts from the shop manual.

How to eliminate fuel as a suspect was defined. Air leaks might be found by using vice grips to restrict any hose the manifold. Learning how to examine the EGR valve as a suspect would be useful. Just a few of so many suspects (maybe 50) can create an unstable idle; best identified rather than replacing (shot gunning).

I have long forgotten what is the car, what all symptoms are, what was tried, etc. However you have learned from reading the shop manual how many suspects are on the perp list. A list so long that shotgunning can get expensive.

[glatt]

Pictures are always fun.

This is what it looks like when I start to replace the fuel filter. You can't even see the damn thing, but it's down there.


When I lean in a little closer, you can see the banjo bolt at the top of the guy under there. There is no way I can get my hand in there, even from below, to remove the thing. Well, maybe from below, but the last thing I want is a face full of dripping gasoline when I open the fuel lines.

So here's the filter, and what I need to remove to get to it.

[glatt]

Here it is, with the entire air assembly removed, and half a dozen hoses and cables detached to be able to get to it. Notice I put blue masking tape on everything and numbered them so I could keep track of where it all goes when I put it back.


And look at all the room I have to work with now! I actually had to halfway remove the bracket holding the thing so that I could get the lower (rigid) fuel line to align with the new filter.



It was all pretty straightforward, but took about two hours, including getting all the tools out and putting everything away again.

[Lamplighter]

We're waiting for the denouement.. did you fix it ?

[glatt]

Beats me. I replaced the fuel filter. Didn't take a picture of the new one. The pictures were for reassembly reference and not so much for sharing on the Cellar. That was just a bonus.

It was an intermittent problem that went almost exactly a month between showing up the last two times. We'll see if it happens again between now and Thanksgiving.

[Gravdigr]

Originally Posted by glatt

...that went almost exactly a month between showing up the last two times.

You've neglected to mention, but, uh, ahem - is this car a female, by any chance?

[tw]

Originally Posted by glatt

Beats me. I replaced the fuel filter.

An answer is simple and immediate. Blow through the old filter. Is it restricted? If not, then it did not solve the problem.

[glatt]

Oh, yeah. There was more resistance blowing through the old filter, but it wasn't dramatic.

[tw]

Originally Posted by glatt

Oh, yeah. There was more resistance blowing through the old filter, but it wasn't dramatic.

So a new fuel filter did not solve anything. An original and still 'wet with fuel' filter might explain a slight restriction. It would not explain fuel restrictions during idle.

Imagine what happens when the car was actually demanding much fuel. Idle demands little. Heavy acceleration requires plenty of fuel. The engine would obviously stumble and almost stall on acceleration if that filter had any relevant obstruction (was dirty).

An intermittent problem can be created by many things that exist constantly. For example, if a fuel pump pressure was slightly low, then the car would work normally almost all the time; only have intermittent stumbling.

The EGR valve would not move smoothly. But the car would work normally almost every time - just not in the rare time when the EGR valve intermittently stuck. Move the valve by hand to feel the restriction that only rarely gets stuck. Unfortunately intermittents not reported by the computer can be this difficult to locate.

Distributor vacuum advance and retard motion can also be intermittent. In one case, I discovered that intermittent was created by grease on those moving parts that had become sticky with age. It always existed. And was located by physically moving the part by hand. The sticky grease always existed. But the resulting bad performance only occurred rarely and without any one common action making it happen. Intermittents are that nasty to find when computer diagnostics do not report them.

As you recall, shop manual provides a list of suspects that are numerous.

BTW, the engine is almost two completely different engines when in idle and when moving the car. Many parts do completely different operations in those two modes. Another way to eliminate suspects from that list. That was the case in cloud's IAV failure. Only the 'idle' engine was failing. The 'moving the car' engine worked just fine.

[glatt]

Two months without a problem. Convinced the fuel filter fixed it. Then it was doing the same sputtering today that it was doing before. No time to trouble shoot or look at it. Got to my destination. Shut it off for about 5 minutes, and it's been working fine since then. Such a weird intermittent problem. But it's fine now, so *shrug*.

I guess I know now why the previous owner parted with this used car.

[Gravdigr]

Try writing down all the conditions/details you can come up with each time it happens.

-how long you have been driving it
-distance
-time of day
-amount of fuel
-engine temp
-ambient temp

Maybe you'll see a pattern that hasn't emerged just yet.