P0305: Misfire cylinder #5

Well, it's happened to me: the dreaded misfire fault. I'll use this thread to document my progress in the hopes it'll help others.

Symptoms: noticable misfire. Can't mistake it - the van's running on five cylinders. Happened out of the blue, as well. Took a small trip & ran fine on the way down. Fired up the van to leave, and BAM - there it was.

Plan of attack: Tear down the top side of the intake to get to the injector, coil, plug & wire. Just my luck it had to be the middle of the back cylinder head :(. I'm hoping it's at worst a bad injector. I'm probably going to replace it anyways, even if the problem turns out to be something more obvious.

History: Purchased the van in 2005 w/100K. Did the LIM job in 2006ish & replaced the back three plugs & wires while I had the engine rolled. Van currently has 145K, so I'm hoping & thinking the plugs & wires should be OK

Any tips/advice?

If , (after you fired the van up to leave and the miss was there) it started running on the 6th cylinder within 1 minute then it may be coolant leaking into that cylinder.

In other words, if it misses only after setting A SHORT TIME

534BC, I'm not entirely following you. But the van misfired all the way home on a 60 mile trip.

Update: I've torn everything down; haven't found anything obvious. Injecter OHM'd out OK. Didn't see anything obvious doing a visual inspection of the injector. Pulled the plug; looked ok, but dry. There's no smell of gas in the oil - I would expect there would be if if I was getting fuel but no spark.

Plug wire checks OK. Coil looks OK & DVOM'd out the same at the other two.

Not sure what to do now but throw the new injector in, button everything back up & see what happens...

Do you notice any tapping noise in the valvetrain? If it is a 3.4L engine is is not uncommon for the rocker arm bolt to pull the threads out of the head and leave you without intake or exhaust on that cylinder. Something to keep in mind if your spark and fuel are good. A compression test will usually show high compression if its the exhaust or low if it is the intake. Hopefully that is not your problem but if can't find any other reason for the misfire, you may want to remove the rear valve cover and take a peek. It can be repaired.

On my 99 I had a wire on one of the coil packs that got rusty

Update: Just did compression check on #3. 150 PSI. I think that's good...?

And procaddy, I didn't notice any valvetrain noise...but I didn't really check....

I'm going to put the fuel rail back in & do a fuel pressure test next...

As far as the compression, you would have to compare it to a couple other cylinders. I really hope this is not your problem, I just wanted to mention it in case you did hear a noise and everything else checked out. Paprius has a good point about the coil towers getting corroded.

Update: Well, I got in a hurry & made a rookie mistake. Cross-threaded the fuel feed nut to the fuel rail. Shredded the o-ring; aluminum chips everywhere. It's now scrap. Damn, I hate when I do dumb things. OK - ordered a new one.

As for the compression reading of 150 psi, shop manual says anything above 100 is good. If I'm looking for a mechanical problem, do I really need to test & compare to the other cylinders?

Work is done for the day.

lowest cylinder has to be within 10 percent of the highest cylinder AFAIK. 150 sounds ok, I think mine were in that vicinity 150-160psi.

Swap #5 injector for #4 and see what happens, if your miss moves to #4 then injector is stuck and you can replace the one on #4 now......

Good luck

Sorry to hear about the stripped fuel rail. For future reference, to replace an injector it is not necessary to remove the pipes from the fuel rail. With the upper intake off, the fuel rail unbolted, and injectors loose from intake you can remove the quick connects from the rail and completely remove it with the pipes. Even easier to leave the lines connected and lift the rail out and replace the injector. With everything connected the rail will flip all the way over to the left strut. That aside, are you up and running good or still waiting on parts?

Parts are in, picking them up today. And yes, I know the line doesn't have to be disconnected & the whole assembly can be flipped - that's how I did it when I did the LIM job. But I wanted to remove them so I could take the whole set to the bench & inspect them easier. And after the struggle it was to get the old injector out (takes quite a bit of force to get that o-ring to let go), I feel it was still the right call.

I just got stupid during reassembly....won't happen again...and I'm not swapping the injectors. It's too much work to get to this point & not replace it.

more update later today...

Well, just buttoned it up after 4 more hours of backbreaking work. Lord, these vans are in a pain in the neck.

After correcting a few crossed plug wires, I'm pleased to report it runs like a top!...at least for the initial test-fire in the garage, anyways...lol...

All I replaced was the injector & plug. My bet's on the injector being bad, since the plug looked fine.

Hope this helps someone down the road....

....time for a cold Molson or twelve...!