possible misfiring, but no check engine light?

[tpd15]

Hi,

I have a 2002 H4 with 4-speed auto and it has 142,000 miles on the clock. The only major work it has had is the head gaskets replaced a couple of years ago, and an O2 sensor 3 or 4 years ago.

In the last week it has started what I think is misfiring. This happens as I apply throttle from idle, generally when I'm stopped and then pull away, or if I coast into a corner and accelerate out. It is worse the harder I accelerate.

It feels like the engine splutters and stumbles for 2 or 3 seconds, and is then fine. The check-engine light is not on, and has only come on once, yesterday, when I floored it in the snow (gotta have a little fun). Then the check engine light flashed for 3 or 4 seconds and then went out.

A couple of times when it has done it badly under heavy throttle, there's been a 'clunk' sound from the engine. I guess this is a backfire?

I assume because the light isn't on that I can't scan for a code (?).

Any ideas on what's really likely going on, and what I can do to fix it?

Thanks,
Toby
Rochester, NY.

[AWDFTW]

How old are the plugs?
Wires?
Timing belt?
Some scan tools can find pending or recent codes.

[tpd15]

Timing belt was done along with the head gaskets, about 25,000 miles ago. To the best of my knowledge, the plugs and wires are original (unless they were replaced as part of a scheduled maintenance plan by Subaru back during the warranty period).

[AWDFTW]

I'd start with plugs and wires. 142k is a bit outside their expected life.

[tpd15]

I guess I'm having trouble why a misfire wouldn't trigger a code / CEL... Is it normal to not get a code in this situation?

[tpd15]

I had a look over the car just now, and the intake plumbing from the intake vent back to the airbox was pretty loose. I tried to snug it back into place at the different connections, but it's still not ideal. Would a vacuum leak here cause a problem? I'd have figured only vacuum leaks after the airbox would be an issue (and I can't diagnose those).

Also, and a different subject, the coolant in my overflow container is perfectly clear. It's at the correct level (at the uppermost desired mark). The radiator fluid appears green when I dip my pinkie into the radiator. Weird.

[Glennda5id]

1. The flashing CEL tells you that it is experiencing a misfire. You should scan for codes and I suspect there will be one. Just because the light is not go on does not mean that there are not any stored codes. But flashing is bad and is telling you to stop driving the car as you are in danger of damaging the Cat.

2. That being said, your issue does sound like a misfire.

3. If you think the plugs and wires are original then I would replace them. NGK all around.

4. I believe you car has a MAF. A vacuum leak will cause problems especially during acceleration as the rate of air flow is changing and the fuel trim system will not be able to compensate quickly enough.

5. The aftermarket long life coolants tend to be very light in color. This is so they can be mixed with other manufactures coolant and not mess with the color for warranty purposes. You probably have Prestone long life or similar in their.

[tpd15]

I was just out looking at the car with my landlord, he's good with cars. He has a scan tool, and scanned it, but there weren't any codes stored.

He also said not to sweat the clear-looking coolant, his point was that it would have frozen well before now if it was water. True there.

[cardoc]

Originally Posted by tpd15

I had a look over the car just now, and the intake plumbing from the intake vent back to the airbox was pretty loose. I tried to snug it back into place at the different connections, but it's still not ideal. Would a vacuum leak here cause a problem? I'd have figured only vacuum leaks after the airbox would be an issue (and I can't diagnose those).

Also, and a different subject, the coolant in my overflow container is perfectly clear. It's at the correct level (at the uppermost desired mark). The radiator fluid appears green when I dip my pinkie into the radiator. Weird.

Any air intrusion after the MAF sensor mounted at the air filter box is a vacuum leak in a sense. The computer will get incorrect information. When you accelerate, the engine moves. That's why the air tubing is flexible. When you accelerate and the engine moves in such a way to separate a joint in the tube, bucking. Not enough fuel delivery because the computer calculated for air flow reported by the MAF which would be lower than what it actually gets. Running lean.

[tpd15]

Actually the car seems much better today than previously, and all I did was try to put the intake plumbing back in place. This might be it (which would be nice).

How would I go about securing all the joints in the intake plumbing? They're intended to be both flexible and dis-assemblable (is that a word?), so I don't want to interfere with that.