I went at it with a vac gauge and pump today, there's no leak. Period. There may have been before I poked and prodded around the PCV valve and hose, though, as the clamp I had put on that wasn't quite over the nipple... the whistle is much less pronounced now and only happens as I'm pressing the gas (e.g. as my foot is actively moving downward), whereas there was previously a position at which I could hold the throttle in certain gears and at certain speeds to make it whistle. Either way, no change in LTFT after 50 miles of mixed driving.
Plugged directly into the manifold, I get a slight but rapid fluctuation in vacuum, like 3 or 4 in/hg. According to this guide:
https://www.onallcylinders.com/2015/05/0...ngine-problems/ that indicates worn valve guides, which is entirely possible with this engine. The fluctuation disappears when I connect the gauge to a vac line; it's possible that my gauge is overly sensitive.
I wish I had easy access to a smoke tester to finally put that to bed, but I don't. I'd take it to a shop for that if I wasn't currently between jobs. I have also pressure tested each and every line individually, as well as the EGR valve and fuel pressure regulator, and they all hold perfect vacuum. So, for now, let's stop considering a vac leak. There, quite simply, isn't one.
I ruled out a cracked, damaged, or improperly sealing valve with a compression test. The engine was already warm, so I don't have cold test numbers (maybe tomorrow afternoon), but I've got 191-195-190-196 hot. Everything's good there, though a leakdown test might show differently. I don't have any gas smell to my oil, so I don't think I have a ring issue.
Coming back around to valve guides, this engine did have oil issues when I bought it, leading to lifter failure, so I wouldn't be surprised if that caused valve guide wear. I am also wondering, though, if dirty/varnished valve stems slamming into the guides could cause them to give a little. That would explain why it sometimes corrects (as it did the other day) and would potentially be fixed with Kreen (which gets here Tuesday).
Going way back in the thread to where I mention an occasional shimmy/shudder, that came about after replacing the lifters, my working theory was that the replacement of the collapsed lifters was pushing the valves open farther. Given that at least two lifters were collapsed for the 10k I put on the truck since I've owned it (and likely much longer than that) my thought is that part of the stems of those valves that would normally pass through the guides (but wasn't because the lifters were collapsed) gummed up and is sticking intermittently now that the lifters have been replaced. I'm leaning more and more toward that theory for the shimmy/shudder, as well as the (now gone) stalling issue because:
- It never happened just idling
- It rarely happened after light acceleration or revving
- It often happened after heavy acceleration followed by depressing the clutch or shifting to neutral
- It almost always happened after revving to higher RPMs while stationary
- Stalling happened about half the time, shimmy/shudder the other half, which makes sense if one or both valves could be sticking -- 1 = shimmy/shudder, 2 = stall
- It has become less common and less pronounced slowly over time, no repair that I've done seemed to have a measurable impact on it
- The duration of the shimmy/shudder, when it happens, has been getting shorter and shorter
- The shimmy/shudder doesn't fade away, it just stops, as though something has IMMEDIATELY corrected, rather than being slowly adjusted/corrected for by the ECU, which is what would happen if a sticking valve suddenly unstuck
If I really hammer on it, I can get it to shimmy/shudder about 5% of the time. Used to be I could consistently make it shimmy/shudder or stall. As listed above, no repair I've done seemed to contribute greatly to that, it's just gotten better over time. There was a whole week where I drove a few hundred miles but did no work on it whatsoever and it improved the most during that week. It's improved about as much in the past week, and I've driven it about as many miles.
At this point I'm just gonna Kreen it and see where that goes. If it's worn valve guides I expect Kreen to make the fuel trims worse as it cleans away crud that's helping them seal; but, then, I'd expect to be burning some oil if it were worn valve guides, and I'm not. Not a drop. Kreen was planned for this engine regardless of these issues, simply given the prior oil issue when I bought it; I'm not expecting it to fix anything or have a measurable effect other than making the oil super dark as it dissolves varnish and deposits.
Back on fuel injectors, though, I would expect to see a hit in fuel economy if my fuel trims were due to a vac leak or other improper metering of air flow, or a faulty O2 sensor, or EGR issue, or whatever else have you. I see a solid 23MPG mixed, which is better than I should be seeing for this truck. Clogged, failing, intermittent, or slow-responding (that's the one I'm leaning toward, reasons later) injectors would *actually* inject less fuel, so a positive trim would put it back where it should be (or close but maybe a little low) which would either not affect fuel economy, or would improve it slightly as the engine could still be running a bit lean. That's what I'm seeing here.
As for why I think I have one or more slow-responding injectors, rather than clogged, failing or intermittent: I have, thus far, run three Lucas fuel system treatments, two bottles of Cataclean, two bottles of Techron, a bottle of Royal Purple Max-Clean, MMO, and an acetone/MMO blend through this engine. That's 10 treatments in 4 months. Mind you, the trip between here and the bay area used almost two full tanks and I made the trip 7 times, so that's 14 tanks right there. I've filled up total of 30 times, though. Literally 1/3 of the gas that's run through this engine since I've owned it has had some sort of treatment in it to clean the injectors. If they *were* dirty, they shouldn't be now.
Failing injectors, I would expect, would remain lean through the entire power band, likely getting worse under load. This engine does the opposite.
Intermittent injectors could explain the shimmy/shudder and stalling, but that problem as been going away. I would expect that problem to be more persistent if it were related to my fuel trims.
That leaves slow-responding injectors, which would self-correct under load as the delay before activation would become a smaller and smaller fraction of the activation pulse as more fuel was requested. It could even be something as silly as a loose plug or corroded connector increasing the resistance to one or more injectors, causing the slow response. I wouldn't be able to answer to that with regard to cylinder 3 or 4 because those simply are not accessible without removing the intake plenum, which I'm not doing unless I have to. I do know that cylinder 1 and 2 are clipped in firmly and the connectors are clean and dry.
My DPFE sensor is also the original aluminum-bodied part that is known to corrode and fail, though mode 6 seems to indicate it is within spec, so it's not really suspect at the moment.
Is it possible that a faulty DOWNSTREAM O2 sensor could do this? I know a faulty UPSTREAM sensor could, but I also know my upstream sensor is functioning well; the downstream sensor doesn't seem to kick on until the truck has been driven a bit, never really kicks on if I just let it idle, and kicks off if I let it idle for a while after driving. Not sure if that's normal for this truck or not, but also not sure if it would cause this issue; if not I intend to leave it alone whether it's normal or not, as my emissions DTCs all report COMPLETED.
In summary: valve guides, fuel injectors, the DPFE sensor, and the downstream O2 sensor are the last 4 things this could really be. The DPFE and O2 are the least suspect, but easiest to address. Any further guidance on this is greatly appreciated; at this point, moving forward without further confirmation would simply be firing the parts cannon at the problem, and I don't have funding for that at the moment; unless a part tests bad, I really can't replace it right now.
EDIT: Another point against worn valve guides: My exhaust is CLEAN CLEAN CLEAN. No smoke, black or white, when starting, when idling, or under load. None whatsoever, even after sitting over night or for several days. Of course, lack of white smoke is expected in an engine that is *not burning any oil*, which is what I've got.
EDIT 2: I found this most useful manual:
http://www.pittauto.com/customer/piauel/pdf/ford/194-287 LRG423.pdf
It confirms what the earlier linked article states re: valve guides and also adds that the flutter will fade with RPMs if it's valve guides or get worse with RPMs if it's valve springs. It also mentions adjusting the gauge damper, which my gauge does not have, but running through a vac line rather than direct to manifold should (and appears to) have the same effect. While I did rev the engine while connected direct to manifold, I didn't note whether there was any change in the needle bounce; I'll do that again tomorrow afternoon. Now I know: no change = gauge sensitivity, increase = springs, decrease = guides. If there's an increase or decrease, I have a definitive answer; if not, I can at least cross a possibility off my list.
