Towing with a 2001 Tribute and Cylinder #1 Misfire

So a week or two ago I bought an 18 foot camping trailer with a gross weight of ~3,000 pounds. My 2001 Tribute has a 3L V6 with a towing package and is rated for 3,500 pounds, so I figured the Trib would pull the camper for at least short trips.
On the way home from buying the camper the Mazda bogged a few times but I didn't think much of it. Pushed the "No Overdrive" button on the shift lever to keep it out of top gear and it did OK, even if it still doesn't downshift as early as I'd like when it needs to (does anyone know of any mods to make the tranny more towing-friendly?).
Easy drive home from the seller's house, about twenty miles on secondary streets, no highway time and only one single-block hard climb.
Got home, unhooked, and the next morning as I drive to work the Trib is still bogging and the Check Engine Light is on. Borrowed an OBD-II reader from Schucks (local auto parts chain in Seattle) and found a PO0351, bad ignition coil on cylinder #1. Could feel it missing, pretty much at random, sometimes at idle and sometimes at speed, sometimes while under load and sometimes while pretty much coasting. Code popped up several times daily, I keep stopping back at the parts store to borrow their reader.
Weird that heavy load could cause an ignition problem. For now I'm assuming this is random and unrelated but I'm skeptical.
If you haven't had to dig into the ignition system on these yet, the traditional coil > distributor > wires system has been replaced with a single "brain" (the Engine Control Module or ECM) that's connected by DC wiring to each of six separate coils. Each coil sits directly on top of the spark plug. Better yet, the engine is a sideways V6 with the back three coils/plugs UNDER the intake manifold. Turns out they put in platinum plugs so that they'll only need changing every 100K miles, as you need to remove the intake manifold to do so. Sometimes I really miss my `71 VW.
Trib has 104K miles on it so I bought six new plugs. Took off the manifold, replaced all the plugs, and while I was under there I swapped the #1 coil (rear of the engine on the passenger side) with the #5 (front middle). BTW, if you're ever unsure which cylinder is which (1-2-3 passenger to driver in the rear of the engine, 4-5-6 passenger to driver in the front), there's a label on the coil wire.
So now we have new plugs and the questionable coil on a new cylinder which will be much easier to reach if I need to replace it. The plan is to see if the problem pops back up on cylinder #5.
Another BTW. Those coils are $94 EACH at the local parts store. I shudder to think what they cost at the dealer. I did find them on eBay for $120 shipped for a set of six but it wasn't clear whether those were actually Motorcraft coils or generics. If you order them from eBay you might want to clarify that before you order.
And another other BTW. I've been back to Shucks to borrow that damned reader about a dozen times (you also need it to clear those Diagnostic Trouble Codes or DTCs so you can turn off the CEL and wait for new errors). I have an OBD-II doohickey on the way from eBay that will let me read/clear codes from my laptop. Cost about $30 with shipping ($5 plus $25 shipping as it's coming from Hong Kong).
The problem came back. Still on cylinder #1. This time the OBD reported PO0301, cylinder #1 misfire. In all of my trials since then, this has been the code except for one additional PO0351 (bad coil) but always on #1.
Did a lot of googling and called two dealers with questions and found a few possible problems. Here's a summary of those possibilities and what I've done to rule them out:
* Loose connections: Removed every coil, blew out the boot to the plug and DC connector, checked that connections were tight and that the connectors didn't have a broken lock tab.
* Bad Crankshaft Position Sensor: Seems like if this were bad the thing wouldn't even fire but I removed it, cleaned it and found 374 Ohms across it (should be 290-390).
* Bad supply voltage to the coil: Found steady DC voltage to the DC supply wire. Stuck a pin in the back of the coil #1 "signal" connector and found a regular intermittent voltage as the engine turned (used a DC test light which flickered steadily as I cranked).
* Intermittent connection to coil #1: Connected a continuity tester to each end of the #1 signal wire, at the coil end and at the ECM connector (#1 is wire #26, a light green wire with a white stripe). Yanked and wrestled with the wiring harness from the ECM end to the coil end, including disconnecting and reconnecting the harness connector in between. Nothing made that beep stutter or stumble.
* Dealer said I might have a burned valve on #1 (maybe it is towing related?): Tested compression on all cylinders and got 230-240 pounds on all cylinders. Damn, can this be right? Not even a diesel should have that much pressure. This is with a yard-sale compression tester so maybe the gauge is way off but as all cylinders read the same I'm pretty confident nothing is wrong with the rings/valves/head gasket/etc. That's good news, anyway, as I shudder at the thought of doing the heads myself or of coughing up the funds to pay someone else.
* Bad Fuel Injector: Seems like a serious long shot. These things never really fail. I've run two bottles of injector cleaner through the tank with no change. If I take the manifold off again maybe I'll swap the #injector to another cylinder to see if the problem moves.
Screw it. Put it back together and hoped for the best.
It ran fine for over a day. Then on Friday, I went camping. Backed it up and hooked up the trailer. Started it up and before I even put the sucker in gear, it started lumping and the CEL came on.
Stopped at Schucks to clear the code (301 again) and then drove it to Baker Lake (about a hundred miles, half on the interstate and half on secondary highways, disabled the OD and kept the cruise control at about 50MPH). Thought I felt it missing but the CEL stayed off, never overheated or anything, got about 13MPG).
Hooked it up again Sunday AM and shortly after I was under way the CEL came back on. Ignored it and drove home. Unhooked, hit Schucks and cleared the 301 code. Been driving it for three days now with no codes (it does still seem to miss occasionally, however).
I am fresh out of ideas. I've seen dozens of posts from others with Cylinder #1 misfire problems (none related specifically to towing, however) but no one has said "Hey, I found the problem and it was ____!"
I welcome feedback from anyone with any ideas on how to proceed from here, and especially from anyone who has had and solved this problem.
rrue
Seattle, WA

 

It's been running the same since I last posted. Runs mostly OK, misses for intermittent periods both idling, under load, up hills, cruising at highway speed. If I clear the codes form the OBD the light stays off for no more than 20 miles and then P0301 and P0351 come back. I can usually feel it missing for a mile or five before the CEL comes on.

Took it apart again yesterday. Checked the compression again with a different gauge and got the same numbers, ~230 lbs on all cylinders. So whatever the problem is at least I'm probably not looking at a valve job.

This time we took off the fuel rail and swapped the #1 and #4 injectors. Cleaned up the o-rings, wiped them all off, gave the previous #1 a shot of carb cleaner and put it all back together.

The connector tab on every one of those injectors broke off when we removed them. At first we thought they were a separate piece but couldn't figure out how to get them back together. Finally just pushed them back on an hot-glued the holes where the tabs used to be. A sound connection but here's hoping those injectors never need to come off again.

Cleared the codes and drove it about 25 miles before I felt it missing. Light came back on. Checked it right away and it's a P0351 (bad coil). On #1 again. At least if it came back on #4 I'd know it was the injector.

Again, I'd love to hear from anyone who's solved this.

Got an appointment at the dealer next week for an ABS connector recall. While it's there I'll have them look at this. Will keep you posted...

rrue
Seattle WA
2001 Tribute

 

You are going to love this. Mine did the same thing about a year and half ago. Basically I did the same things as you have and the problem was still there. I took it to a local shop. He worked on it for about a week and could not figure it out either. Tried to get a wiring diagram and was told there are 4 different ones at $150 - $200 each, not sure which one I needed. (He now calls my car "the Mazda from Hell.") He did not charge me, and recommended taking it to a dealer.

I took the car to dealer and they called back and said a wire is broken. Cost to repair, $400.00!! I told them they were crazy and I picked up car. When I asked which wire is broken, they couldn't say without looking into it further. All they knew is a wire is broken.

I took the car to another dealer and they called me and said the same thing. I finally gave up and paid the $400.00 and the car ran great. I thought everything was ok. Then a year later it started acting up again. I went back to the same dealer to see if they would cover this under warranty. No luck. I dropped the car off and went back to my house, (20 minutes away) and they call and say there’s a wire broken. Cost to repair $400.00. I ask which wire and they are not sure, but there is a broken one. So I tell them to go ahead and fix it. They call me back 15 minutes later and tell me it's ready. ($400.00 for 35 minutes work)

I go to pick up the car and the mechanic is out to lunch and he goes on vacation tomorrow. The service writer does not know what wire was broken, but he will ask the tech and call me back. I finally called him back a week later to see what he said and he has forgotten which wire it was. (Go figure)

The car has run great since. I still have no idea what was wrong. I have spoken to others who have had the same problem. I would love to know what was wrong with yours. If you found out it was a wire I would love to find out which wire it was.

 

Venton - are we sure they were talking about a SPARK plug wire and not just another wire in the engine bay? If they replaced ONE spark plug wire, it would be newer and easy to spot (if it was in the front).

 

No this was another wire. I'm guessing it was one going to one of the injectors, but it could have been a wire to the computer or whatever. Just seems strange that wires keep breaking in a harness that has never been work in and they can find and fix it so fast. My guess is this is a common problem and they don't want to say anything about it. If it happens again I will ask to see them make the repair.