What. The. Hell. (Long one)

DamageINC · December 15, 2006

Ok...

I'm not cocky, I don't think I'm the best, or the smartest, or the quickest... but I'll be damned if someone calls me a bad tech.

I have *NEVER* encountered a vehicle that has a concern that cannot be diagnosed. But I'm starting to think that I finally found one...

'00 Explorer, 4.0 SOHC. 51k miles. Customer says that it starts and immediately dies. Verified, figured it was just an IAC (felt just like a bad IAC) but it wasn't after swapping over a known good one. So I decide to actually diagnose this one, haha.

Finally get it running, but it runs *ROUGH*, start monitoring fuel trims, longs showing some severe lean condition signs but oddly enough there were no codes. Grab an aerosol can of brake cleaner and fire around some vacuum lines, until I found a MASSIVE leak at the lower intake gaskets. That's when I looked down and saw that this thing still had the factory Cam tensioner in it!!! (Should have been replaced 6 years ago during the 00M12 recall. Haha it also still has 4 Wilderness A/T's on it.)

So, I sell the 00M12 Recall on it as it not only replaces the Cam tensioner for bank 2 but also replaces the upper and lower intake gaskets. Do the job - start the truck - boom, fires right up and stays running. But it feels rough.

Check oil level and quality - good.

Check power balance - cylinders 1, 2, and 3 are dropping HARD (like -70). Recheck my work for anything I messed up - nothing wrong. Let it idle, doesn't clear up. I notice that if I bring the rpm's up to about 1,300-1,400 rpm, the misfires are COMPLETELY gone, and it's virtually imperceptible at 1,000 rpm.

Check fuel pressure - 65psi running, normal response.

Take off a small vacuum line, and introduce some carb cleaner into the intake while it's running just to see if anything changes - nope. Create a small vacuum leak, just to see what changes - nope. Fuel trims sutprisingly look normal, although I notice that the right (bank 1) 02 voltage is VERY erratic which is likely because the bank is running so rough.

I swap the front 02's from bank to bank - still have cylinder 1, 2, and 3 missing. Now I'm thinking that maybe the right cam chain cassette is busted (although not noisy) and therefore mistimed the right side cam. Check relative compression - perfect. Pull the plugs, and check manual compression - all cylinders at 170-180 psi.

Hmm...

Maybe the right side cat's plugged?? Check exhaust backpressure from the front right 02 bung - less than 1psi MAX on a WOT snap. Perfect.

Decide to replace the plugs, just for grins. No change. Now I'm getting agitated... everythings coming up good and this thing runs like a bucket of crap.

Fuel quality??? - very unlikely, seeing as only 1 bank runs bad. But, I decide to check it - it's fine. I end up running the engine on a canister of known good fuel, and the same problem is still there. Cyl's 1, 2, and 3 looking terrible.

Wiggle test the hell out of everything - no change.

This is when I remove the upper intake, again, and pull the right valve cover to inspect for any damage to the chain or cassette, or any damaged/broken valvesprings as I've seen many fail in these before. Looks mint. Re-inspect the intake manifolds for any weird warpage or cracks or anything, as I'm getting desperate now. Nothing wrong. Pull the fuel rail and inspect the injectors and rail for anything funky - nothing wrong.

Grab all the fun special tools for this lovely engine, and check base engine timing - it's spot on, both banks.

Since the valve covers are off, why not do some leakdown testing?? All of bank 2's cylinders (4, 5, and 6) are at 25% leakdown - good.

All of bank 1's cylinders (1, 2, and 3) are at about 40% leakdown.. which is RIGHT on the borderline of "accetpable" and "raises an eyebrow". I decide to check the intake ports to see if there's any air coming through - nope. I check the exhaust - nope. I check the oil-drain holes in the head - there it is! It's coming from the crankcase!?! What, do I have bad rings on an entire cylinder bank??

I go and re-test bank 2 - it does the same thing. REally, I got nowhere with this test.

This is when I call hotline, and really didn't get anywhere there either. "Base Engine" was all that they could really say, but there are absolutely no signs whatsoever of base engine damage without any intrusive testing. They tell me to put it back together and do a running compression test - ok. I do.

It's mint.

Go drive it around some more - this thing drives *perfect* until you bring it back down to idle.

Perform a relative injector flow test - all good.

Given the strange loop-style ignition system in this truck, I thought *MAYBE*, just maybe, the ignition coil could be the problem. I know that the coils are paired much differently, but whatever, nothing else is getting me anywhere.

And a new coil pack didn't do any good either.

Back in the shop, start wiggle testing again. I get to the PCM, rattle it around, nothing... then I smack it. Good god - something changed!!!! I check power balance, and now cylinders 1 and 4 are misfiring and the rest are strong!! I'm all sorts of excited, thinking I finally found my bug. Talk to a few other guys, chat with the service manager, we decide to order a PCM up for it.

And it came.

And I put it in.

And it still runs like !@#!?$! at idle.

There isn't a whole lot else that can be wrong with this, except that it needs an engine. But I DO NOT want to quote (and replace) a $2,800 engine and then STILL have the same problem later on.

I'm seriously going to light myself on fire tonight. Wish me luck!!

Dave

Jim Warman · December 15, 2006

Dave, I didn't see where your fuel trims are at.. Any clues to be had with them?

I've always been a firm believer in what ignition voltages are trying to tell me, too... at the very least required voltage and spark duration....

pcassidy111 · December 15, 2006

If you disconnect the plug wire on one of the low output cylinders does the rpm pick up slightly? I had a 4.0 with sunken exhaust seats that had low output at idle and the rpm picked up slightly when I disabled one of the offening cylinders. 40% leakdown is probably the cause of the rough idle, are you sure it is past the rings? I have seen rings stuck in the lands when people use 10/40 oil.

Jim Warman · December 16, 2006

Whoooeeee... I missed the part about the leakdown... ("flatrate reading" again).

Change tune to "running compression test"....

DamageINC · December 16, 2006

Haha, well thanks for the input guys but it's all mint now.

The thing that REALLY sucks about it is that it turned out to be one of the very first things I "checked" but disregarded because I was relying on PID data intstead of that 'gut feeling' you get sometimes.

Early on, (don't remember if I mentioned this) I considered a stuck EGR valve because the tube primarily feeds EGR gases into the right side of the intake manifold. So I check my DPFE voltages KOEO and KOER and they were both .96 volts, but the DPFE voltage responded normally when I would command the EVR to open the EGR valve - eliminating the possibility of a stuck DPFE sensor as well. So, I just dismissed the EGR valve as the problem instead of replacing the gasket with a solid piece of cardboard to block off EGR flow completely.

Well.... turns out I should have done that right off the bat.

There's a part of me that wants to kick my own !@#!?$! for not doing it, but "on paper" I really didn't do anything wrong so I don't know how to go about feeling over the whole thing. Win some, lose some, I guess, lol.

Certainly one of those things that I'll never forget though, and I guess as a word of caution to the rest of you - a *SLIGHTLY* stuck open EGR valve on an older 4.0 SOHC can and will cause a misfire across possibly the entire right cylinder bank at LOW rpm.

Even bad experiences are still great ways to learn, sometimes..

Dave

Jim Warman · December 17, 2006

A simple way to check for EGR flow on a gas engine is to feel the valve.... with no flow, the valve should be the same temp as the intake manifold....

DamageINC · December 17, 2006

I've heard that before but for some reason it never did much for me. On the other hand though it's always been very minor flow-thru problems I ended up having so maybe the temp difference would have been much more noticible if I'd been using a laser-temp gun or something more accurate than my bunk-!@#!?$! thumb, haha.

Dave

pcassidy111 · December 18, 2006

A simple way to check for EGR flow on a gas engine is to feel the valve.... with no flow, the valve should be the same temp as the intake manifold....

As long as you feel the tube before the road test.