Here's A brain teaser.

2003 F-250, 5.4, Auto, RWD. 44,000 miles.

There is noticable misfire from idle to about 2,000 RPM. At around 2,000 RPM the apparently dead cylinder(s) can be felt hitting and missing randomly. No MIL!

The truck has generated a few misfire DTCs (apparently pending codes) in the past month. First was #5. Pulled plug and inspected, looked good. Installed plug and moved #5 coil to #1, and vice-versa. Within a week another DTC was stored for #8 (P0308). Pulled all plugs and inspected, all looked good. Moved #8 coil to #7, #7 back to #8. Within another week a DTC was stored for #2 (P0302). Replaced all plugs, gapped correctly. Changed fuel to a different source, brand, and grade just in case it was a fuel problem. This has occured through several tanks of different fuels. Chevron Techron fuel injector cleaner was added just in case (it seems to be one of the safest to use). Additionally, the humidity has been steadily over 70%RH recently, and at night has approached 100%. I've heard the CoPs don't like moisture, but moving them to different cylinders hasn't necessarily moved the apparent problem to that cylinder.

Fast forward about two weeks. Truck is still missing under all conditions up to about a 2,000 RPM cruise, where the "hit and miss" can be felt. The OD indicator lamp on the end of the trans selector lever starts to flash, and the MIL locks on. The only DTC is for an intermittent VSS.

Oddly, the speedo and cruise work fine. All this while the misfire is still going, and never was there a P0300 (Random/Multiple Misfire). The PCM has always identified it as one cylinder, but never the same one, and not apparently related to the movement of the coils. I initially suspected the CKP and CMP due to their input over ignition control, but no problems were reported by the PCM for either sensor.

I am suspecting fuel delivery may be contributing to the misfires. I've read that injectors or even rail contamination may be a factor, and fuel pressure will be tested, along with standing pressure after shutdown. None of this, however, explains the VSS error. After pulling that DTC for the VSS, I'm I'm beginning to suspect the PCM and/or its connections may be a problem. Admittedly, I'm much more familiar with Dephi systems, but the conventions are similar, right?

Any education for the uneducated? Plausible ideas and suggestions would be appreciated.

 

Welcome to the forum

I would check all of the chassis grounds under the hood. Also check the PCM ground which should be at the - battery post.
Also check the wiring harness if it runs down the firewall to under the truck. I have read that some of them rub the frame or exhaust and can short out the PCM.

 

i am having basically the same prob excpt p0300 also, engine runns fine (it seems)up to about 2000 but once under load has little power and u can feel the dead cyl(s) got po300 po306 po308 chged coils and injector on 6 and coil on 8 ....no help any ideas???

 

Thanks for the reinforcement, LX. I'll try to keep the findings posted in hopes of helping someone else with a similar problem.

 

Harness connections and grounds at the engine appear to be intact.

Just for grins, I checked fuel pressure. It was 33 PSIG at idle, and 42/43 PSIG with the pilot vacuum removed from the FPR. Is that normal or within range? That pressure is a bit lower than I'm accustomed to seeing on other vehicles. The fuel filter was just change, just because of the age and mileage, with no obvious difference. Can't hurt anyway.

After another episode last night, the PCM coughed up another code for the VSS circuit and a P0307 (again), even though the plug and CoP were swapped to another hole. That probably doesn't help the diagnosis, but it's more information.

 

Heres my take on this random misfires.
any mileage over 36k change the plugs and boots (boots because of the heat factor they crack then start carbon trackin) use nevesieze on plugs and torque to spec's also chk the spring connection inside the boot for corrosion this also causees misfire.
Use oem plugs because triton engines don't like other brands known fact.
Use dilectric grease on boots beacuse it repells water.
Bad Cops are a known problem (heat breaks them down) with the way summer is going there will be a lot more failing.

Get a known new coil and start replacing them.

Also change the vss on the rear diff it is sending false info to the pcm on shifting and vehicle speed inputs .

There is no cheap way around the misfire problem.

Please don't be disconnecting cops or injectors while enging is running or you may pop the pcm .It doesn't like the surge spikes .

Rich

 

Thanks for the tip on load disconnection while running. Most of the PCMs I work with are fairly immune to that due to suppression. You may have saved me a PCM and more headaches.

The sage continues, and I'll be spending more time on it tomorrow. Since we last conversed, the injectors were replaced with new OEM parts. Pulse widths are now a bit shorter, meaning the fuel is more volatile or the new injectors are flowing better or have a better spray pattern (HINT: The fuel is the same). Unfortunately, the misfire is still there. I'll be pulling, cleaning, and closely inspecting the CoPs, as well as checking primary resistance and secondary connections and insulation.

If I find anything worthwhile I'll post back with results.

 

More info...

I pulled the battery cable and got into the spaghetti. The PCM on a 2003 F-259 HD is on the left side of the passenger compartment. The single connector to the PCM is outside the firewall, and the PCM is mounted so its connector hangs through a grommet in the firewall. Why the harness was not routed through and connected in the clean, dry interior is beyond my comprehension. Regardless, I uncoupled the connector, found dirt and moisture, and cleaned up the tarnished pins. A little further cleaning and application of dielectric grease, and it was back together.

I removed, cleaned, and anti-seize compounded all the ground connections I could locate.

Thjere is a main power node on the LF inner fender. The connetions were corroded, the stud was rusted, and the the copper had more patina than the Statue of Liberty did in 1974. I cleaned, fluxed, soldered, and heat-shrinked all the connections, cleaned up the stud, and bolted it back toigether. the best I could tell is that the node distributes battery power to the main interior BAT circuits. Another potential problem resolved.

I removed the engine wire harness looms and CoP units (fun) and blew out the plug wells. The #3 CoP had the coil connector fused to the spark plug well, so it tore before it would release. I also removed the plugs to discover SINGLE platinum AutoLite POS plugs had been installed. The gaps ranged from 0.060" to 0.080", the electrodes were well worn and ash coated, and there was no evidence of anti seize on any of the threads. One hung on very well, and I was afraid I would get some head thread with the plug - I got lucky. Two of them were barely tight.

I tested the CoP primary and secondary resistances. All the primaries were between 7.1 and 7.6 ohms. All the secondaries were between 5540 to 5580 ohms, except one. The #5 CoP had a secondary resistance of only 5430 ohms. I'm not sure if a hundred ohms is that significant, but most of the epoxy filled coils I've seen are fairly consistent, so I replaced it. I also replaced the coil connector and boot on #3 (torn on removal). EVERYTHING got a liberal dose of anti seize or silicone dielectric grease where appropriate.

 

What I like a man that jumps in with both feet ! How was the sauce????

keep us posted


Rich

 

Ive read in a few post about ford not liking antiseize on the plugs because of the spiting em out problem.

 

Oh - Maybe that wasn't such a brilliant idea? I have been taught and lkearned the hard way that anti seize on plug threase is always a good idea, but your philosphy makes sense. The few aluminum threads holding those plugs in teh head castings probably don't need any help in letting the plugs slide out. I'm going to cross my fingers and hope that it holds together. I was quite particular about installing the new Champions (dual platinum) with the correct torque and not using a universal joint in the drive setup.

Regardless (and at the risk of cursing myself later), it seems that after over 2½ weeks and 2,000 miles, everything is working as Henry intended. There have been plenty of damp mornings, adequate rain, and lots of driving and idle periods to allow a recurrence fo the problems. So far, its been behaving. My suspicion is that a combination of the one weak CoP (only 100 ohms low on the secondary?) the marginally dirty plugs, and the eroding connections at several places contributed to the variety of symptoms.

Sorry if the photos are not as clear as they might be.

The moisture found in the main bulkhead connector for the PCM is evident, even if the corrosion there is not as clear in the picture:




After looking at the location of the connection, it's no great surprise:




The main PCM/engine harness connector, even though hanging out in space, was in very good condition:




The main body power node was a concern, and I spent quite a bit of time making sure it was repaired properly. It migh be worth looking at if you're having some rogue problems:



Thanks again for the encouragement. It's amazing how the little things make such a difference. Working space is actually quite good once the air filter assembly is removed, so don't be afraid to dive in.

 

Blue,excellent post ,we have seen in the past that water intrusion in the connectors has caused alot of strange problems,
Rich