My 07 Express van with the 6.0 liter has started acting up. I went to pick up a car yesterday and while the van was idling while loading the car on the trailer is started running very rough. It has always idled slightly rough but not this bad. A couple restarts and the check engine came on for a P0300 random misfire. It idles very rough and off idle is rough/jerky getting going from a stop. It seems to run fine otherwise but gas mileage seems down.
It also has a code for gross evap system leak that pops up occasionally.
Two questions:
My first thoughts are that I need to take off the doghouse and replace the intake manifold gasket and spark plugs. It has 255k miles and I don't have any service history for it.
Second question, am I correct in thinking I shouldn't tow 800 miles through the mountains with it next weekend?
Ya the 800 mike trip with out resolution may be pushing it a bit.
Do these have the same evap canisters the the early 2000s trucks have that crack and fail? That could be part of your problem.
Random misfire usually means time for plugs, in my experience. I haven't heard of LS engines needing intake gaskets, but I'm not as familiar with the truck/van versions as the car versions.
Purge valves will stick open on those quite regularly, make for some goofy idle. Usually combined with evap codes and fuel trim limits at idle.. Plugs can certainly get old, but modern arc welder coils will usually fire the worst of them. Bad wires or porcelain carbon tracks are more likely to show up under load, at least until they have been ignored for far too long. Squished intake gaskets tend to cause more trouble with a cold engine. They seem to soften up and seal better with some heat.
Not a whole lot else ever goes wrong on those.
Purge valve is easy enough to check, at least. Take the hose off of it, unplug the electrical connector, and with the engine running there should be no vacuum at all.
For some reason, there's a 50/50 chance it will set a code for incorrect purge flow, the rest of the time it just runs like crap, either with a vacuum leak, or flooding/running rich on a cold start after the intake manifold fills with fuel vapor. Or both.
Spark plugs are fairly easy through the wheelwell with a long extension and a swivel socket. although I can't remember if there are one or two younneed to get from inside. At higher mileage the plug wire usually becomes one with its plug and you break one or both in the process of removal.
My car throws a gross evap code after just about every fill up because of the gas cap not sealing right anymore or something like that. I don't think that is much help with the main problem you're having though.
In reply to Pete. (l33t FS) :
I checked the purge valve like that and there doesn't seem to be any vacuum putting my finger over it.
Intake gaskets are a fairly common failure, typically shown with a rough idle at cold start, that goes goes away when the engine warms up. Was it doing that before the it became this more prevalent misfire?
In reply to gearheadmb :
Before it was a slightly rough idle at all times. Now it's even rougher at all times, it started getting really bad when it was hot after about 2 hours of driving.
This is one of the plugs, I pulled the most accessable one. Gap is around 0.050 but there is the deposit on the ground strap.
I would toss plugs and wires at it as it probably needs it at that mileage. One of mine was cured with that and the other ended up needing a fuel injector.
Check which cylinders are misfiring to narrow down if it is still misfiring after the plug and wire change. Remember that a bad enough misfire on one cylinder can effect multiple cylinders to set off misfire codes the those nearby.
EvanB said:
In reply to gearheadmb :
Before it was a slightly rough idle at all times. Now it's even rougher at all times, it started getting really bad when it was hot after about 2 hours of driving.
This is one of the plugs, I pulled the most accessable one. Gap is around 0.050 but there is the deposit on the ground strap.
That's not where you get a problem on modern engines. Turn it over and look for black lines on the ceramic.
The parts inside the engine cause very little trouble these days.
In reply to Streetwiseguy :
That said, the ground strap on that plug is worn the heck out.
No lines in the ceramic, just a band toward the base which is where the boot fused to the plug I assume.
STFT looks normal, varying from 0 to -3% at idle. It doesn't start running really rough at idle until it warms up.
In reply to EvanB :
That points away from an intake gasket issue (they're just O rings, IIRC) because those usually leak when cold and seal when hot.
Besides, you have a smoke tester now, right? This is a good opportunity for it.
What do the fuel trims do when it is running poor? Short term and long term.
In reply to Pete. (l33t FS) :
My OBD adapter disconnected when it started running really poor, not sure if related or just cheap adapter issues. I had to get back to work but I'll check some more things over lunch. Smoke tester is a good idea.
Edit: Checked again and when it is warmed up and idleing poorly the STFT is between 0 and -3.9, normally hovering around -2.3 or so.
Smoke testing didn't reveal anything other than leaks in the airbox pre-MAF.
fuel pressure is good @ 60 psi at idle.
I've been reading a lot of people claiming that a crank sensor relearn fixed their similar issues. I would have to get a new scanner capable of doing that to test it out.
Crank sensor relearn is generally only required after you replace the PCM or the crankshaft.
You also don't want to do it with a rough running engine.
It's also a bit of a pain in the ass, you have to run it at WOT until it bounces the rev limiter and then let off, and your timing has to be just right.
Plugs and wires fixed it. Just got back from a weekend trip to Virginia towing the miata with no issues. This should be a lesson to me to not over think things and try the simple stuff first.
