No codes, intermittent rough idle and rare misfire

[Dan]

– 2001 Taurus w/ DOHC V6 24v Duratec, 158,000 miles

– I just bought it and know a little about the maint. history, the original owner tried his best to pass on information. He said it overheated on the road once. Several of the big vac. hoses look relatively new.

– just covering all of the bases, the oil has been changed and I have only put in Mobil or Shell 87 octane gasoline

– MPG has been excellent for this model, 22+ driving mostly in a slow city area with a lot of stop and go

– There is oil leaking into cylinders 4 and 5. I have pulled the plug wires and sopped up the small amount that was pooled on top of the plugs, but after a short trip, the same amount of oil has seeped back in. I have not removed and inspected or replaced the plugs themselves. I do not know when the owner last replaced the plugs. Cylinder 6 appears to be dry, but the wires for 4, 5 and 6 all appear to have carbon tracking(?) damage.

– The car idled rough and misfired intermittently on hills when I first bought it. But I replaced the battery, cleaned up the heavily corroded positive terminal, replaced the engine air filter and cleaned out the clogged housing. My mechanic also replaced the MAF and cleaned out the throttle body at this time. The car drove extremely well for a month (1000 miles) with no rough episodes at all, until, my mechanic fixed the AC system and replaced the PCV valve. The new PVC valve failed, cracked a few days later. He replaced the PCV again with apparently Ford’s newest reinforced version. Since then:

– Rare misfires on hilly roads, right around 40 mph.

– Intermittent rough idling in gear, not park or neutral – I have a code reader with some basic live graphing ability – Fuel trims as well as most (read on) of the other available parameters (including O2 sensors) do not look out way of the ordinary.. I don’t think it’s another vac. leak or a problem with fuel pressure. When the roughness occurs, it feels like a surge. I wonder if this is a knock? I have observed, at the moment of the event, that RPM spikes DOWN from roughly 700 to 650. Spark Advance Cylinder #1 spikes UP from 11 to 17 or as high as 22 and Load % spikes up as well. And like I said, these events are random; it might happen two or three times in a row while idling or just once or not at all. There is no pattern that I can see.

I’ve been able to find just one “case” on the internet, involving an ’03 Sable, that appears extremely to be similar (i.e. spark advance spiking, but fuel trims normal). The vehicle owner was able to fix the problem by replacing the plug wires. I will have to find the source of the oil leak as well. But what I don’t understand is if the oil in the cylinders is the problem, than why was the car running so smoothly for the month after the first wave of maintenance? It most certainly was in there, I’ve sopped it out a couple of times.

– Today I took it to Old Route 1, a hilly highway and reved it real good on big hills, several times (10 miles total), no misfires, no hesitation, great power up to between 40 and 70 MPH (keeping it within reason with a posted 50 MPH).

But I still want to hear some opinions on this. It has not been easy to find relevant information about spark advance and idling in non tunable cars. As I understand it, the MAF calculates (maybe the wrong word) the Load and Load is one of the big factors in spark timing.

One of the other things I’ve looked at with the code reader is the MAF g/s at idle. I’ve read that it should measure roughly 1 gram of air per second per liter of engine size. Sinced it has been running rough, for this car it is usually moving up and down in the range of 4.4 to 4.5, but it’s a 3.0L engine. As I said the MAF is new, but the PCV actually had to be replaced twice. The first new one cracked and I discovered that only after it affected drivability. Is it possible that this short period of driving with a damaged PCV valve contaminated the new MAF? I’ve thought about spray cleaning the MAF. Am I wrong about relying on the usefulness of that particular test of the MAF?

– Except for when the PVC valve failed, there have been no codes and no pending codes. And all of the monitors appear to be running. The only clues that I think that I have are the spikes up and down in SPARK ADV, Load and RPM. I was, just once, able to get the car to misfire on a hill while recording with the reader only SPARK ADV and it spiked precisely at the moment of the miss.

– One of the next orders of business with maintenance will be to replace the fuel filter which probably has not been done in a long time.

Topic

[college man]

It sounds like the place to start is with the oil in the spark
plug wells. The O rings need replacement. The oil will cause the
secondary voltage to leak. When you drive the car is the cel or
yellow light flashing? Are any codes stored? More in this link.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Dan]

[quote=”college man” post=110038]It sounds like the place to start is with the oil in the spark
plug wells. The O rings need replacement. The oil will cause the
secondary voltage to leak. When you drive the car is the cel or
yellow light flashing? Are any codes stored? More in this link.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues%5B/quote%5D

Are these O rings, Spark plug tube seals by another name?

I have not seen the CEL flash and there are no stored codes or pending codes. It seems that whatever is happening is not a true misfire because it does not upset the fuel trims and does not set misfire codes, even if I’m at a red light and it happens five times in a row – bam, bam, bam, bam, bam, but not very loud. I can only sort of hear it in the car, with the radio and air blower turned off.

[Dan]

Well my unreliable POS finally threw a pending code tonight after it misfired as I was accelerating up hill on a highway – P0302.

My trusted mechanic is taking it on Monday.

Hopefully it’s something simply related to the previously failed PCV valve.

I will update with the outcome.

[Dan]

I am almost certain the cause of these problems was once again the positive battery cable.

I cleaned the terminal twice and the second time was just before the first new PCV elbow failed. I think I tightened the clamp too much and the terminal was not seated down enough on the post. The terminal was tight on the post but not entirely seated on it, so there was a lip of a few mms above the post.

Loosening the clamp and re-tightening seems to have made a big difference, which is deja vu all over again.

With the HVAC blower turned off, the car idles perfectly in park and every gear. There have been no further misfires while actually moving, on hills, the highway or otherwise. However there is still some roughness at idle in park or in gear with the HVAC blower turned on. It’s not nearly as bad as before, when I thought the car would stall out for sure.

I wonder if my many manipulations have left it useable but unfixable and the remaining cause of the problem?

[Author]

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