97 Ford Ranger XLT 4.0L Sparkplug/Vacuum Leak Codes

[Cobaltred05]

Hello! Hopefully this has not already been covered. If it has, I apologize. I haven't found anything quite like this yet though. Please see details below and what I've done so far. I will also point out that I am an amateur at this, but have learned a lot so far. It is entirely possible that I messed up during some of this work.

97 Ford Ranger XLT V6 4.0L
I have owned it for 2 years.
VIN: 1FTDR15X1VPA30822

The previous owner converted it over to natural gas with a system that forced a check engine light. The natural gas was fed into the intake hose right before the throttle. I have since removed the natural gas setup as it is not legal in my county with the engine light. I also patched the hole created in the intake hose and smoked it several times to verify that it does not leak at the patch.

Right after buying the Ranger and removing the natural gas system, I changed the intake manifold gasket and cleaned up the fuel injectors. I then smoked it and found that the vacuum lines and EGR valve were leaking too. I replaced the vacuum lines and the EGR valve. A friend of mine helped me to replace the seal and bend/flatten the connection flange between the EGR valve and the pipe leading into the intake manifold. I replaced the heater selector switch in the heater control panel at one point too. We smoked it later and noticed that there were still minor leaks behind the heater control panel and at the firewall connection. My friend informed me that it shouldn't be an issue since we weren't getting the code for bank 1 lean anymore.

Unfortunately, once I finished all of the above vacuum system repairs, a new check engine code came up indicating that my spark plug in cylinder 4 was misfiring. My friend had claimed that he heard a crack when leaning into the engine bay and thought he had broken the spark plug. I replaced it first with a Denso, which didn't work. I then saw several pages here discussing that the motor was largely built around the OEM Motorcraft spark plugs. My local O'Reilley's didn't have that brand, but they did have the Autolite double platinum. I recall seeing somewhere on this forum that those were the only two trustworthy brands for this Ranger. I ended up replacing both the sparkplug and the sparkplug wire that leads to the ignition coil. After doing so, the check engine light did not come back for at least 30 miles and when it did, it came up as P0302 (cylinder 2 misfire if I'm not mistaken). Out of pure laziness, I took a couple of days to ensure I wasn't getting the code as a mistake. It consistently came up, but was also joined by the original P0304 (cylinder 4 misfire) as well as P0300 (overall misfire). It is entirely possible that I did not install the spark plug and the spark plug wire properly as it was the first time I've done this. I did follow the guide on this webpage though.

Changing Spark Plugs and Wires on a SOHC 4.0L - The Ranger Station

Getting ready to change out the spark plugs and wires on your Ford Ranger's 4.0L SOHC Engine? Here's some tips on how to do it.

www.therangerstation.com

At this point I began to wonder if the issue was due to the vacuum still leaking at the heater control switch. My speculations were based off of google's AI, but I figured it was a simple enough fix to try.

The rubber harness that connects to the back of the heater control panel doesn't seal well, so I added heat shrink around the small pins from the heater selector switch to improve the seal. It seems to work most of the time, but I do hear hissing when the truck is on and the switch is set to off. The climate system started working for the first time after that. After testing again though, I got the cylinder 4 code again.

Some more details that may or may not be relevant:
- The vacuum reservoir was full of a slightly red/orange liquid on two separate occasions. I let it drain the first time and blew it out with compressed air the second time.
- The first time I filled up the gas tank, gas spilled onto the ground. Another friend told me it is likely the gasket between the gasoline cap hose and the tank. I have not tried to remove my bed to repair it yet though. I only just recently got the two massive CNG tanks out of the back of the bed.
- I had to replace the bearings, spindle, rotor, and brakes on the driver's side front tire as one of the bearings had ripped apart and welded itself to the spindle. I doubt this had any effect on the error codes above, but figured I'd mention it.

Well, now that I've written out as much detail as I can recall, here's my speculations on what it could be:
- The Ignition coil is bad.
- A coincidence resulting in some of the other spark plugs going bad or I messed up the install.
- The vacuum system is not leaking enough to cause a bank 1 lean code, but it is enough to cause the spark plug codes.
- Google AI claims that the gas tank gasket is possibly to blame?

TLDR; I bought a truck that needed more repairs than I expected, I replaced or fixed many different items, and now I'm wondering where to proceed next.

I would be very grateful if someone had any thoughts on this or could point me in the most likely direction. Thanks!

 

[franklin2]

Google AI is ok, but you have to watch it also. It can give out bad information. One clue is get out of it and then ask the same question again and it will come out with different answers. Logically, the gas tank is common to the whole engine. So I would not think it would foul just one or two cylinders.

I ask google AI the simple stuff. I am going ask it right now, does your engine have a distributor or a coil pack. It's answer, you have a coil pack. I then asked it if it was one coil pack or multiple coil packs, it said it was one large coil pack. I was going to tell you to swap coil packs but I guess you can't.

You might want to put a ohmmeter on the sparkplug wire while you wiggle it around off the engine. If you get rough with these wires, the ends can fray and break.

 

[Cobaltred05]

Thank you! I figured AI might be misleading. It's one of the reasons I'm reaching out here. As far as the coil pack goes, I can confirm it's one part that handles all six cylinders. I think the unit is sold still, but I'll have to check.

I tried to check for continuity on the sparkplug wire (both old and new), but I was never able to confirm that it was continuous. It was difficult getting the leads to touch, so it's possible I never got it right. When you say to put an ohmmeter on the sparkplug wire while wiggling it, are you saying to touch one lead to the sparkplug and the other to the inside of the sparkplug wire? Just wanting to make sure I understand.

 

[97RangerXLT]

what Franklin said above, and the gas tank leak, that is likely the filler neck. these go bad all the time, I am on my 3rd or 4th filler neck on my 97. fairly easy to replace, removing the bed (6 bolts, three screws and unplug the wiring harness) takes two people to lift it over the wheels. you can also get to the rear shocks really easy this way if you are replacing those. another alternative is to remove the bed bolts and three screws and prop the bed up 8 inches.

I would think that unless you are getting a ton of smoke at the leak points, they might not be enough to cause a CEL, and I also think if the wires and plugs do check out, you are on the right track to suspect the coil as a possible suspect. I forget if cyl 2 and 4 are on the same coil, but if they are, that is another nudge in the direction that the individual coil is bad.

AJ