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

 

[franklin2]

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.

I pull the sparkplug wire completely off the truck, then test it with the meter. It's easy to slide the meter lead up between the rubber boot and the inside metal terminal.

 

[Cobaltred05]

Thank you everyone! I was able to check the continuity of the sparkplug wire on the Ohm setting instead of using the continuity setting. It worked that way, which makes sense now that I think about it.

I pulled the coil pack and tested according to the Haynes manual and this video: Test a coil pack

I didn't see any issues in the resistance readings. The primary terminals were always lower than 1 Ohm (usually 0.1 or 0.3) and the secondary terminals were just over 13k Ohms, which the Haynes manual said was within acceptable range. I'm seeing a fairly cheap coil pack on Rock Auto for only $20 (Ultra-power brand). Do you think that would be a good option? Or should I go with the Motorcraft brand OEM part?

 

[97RangerXLT]

My gut says go with OEM. but at a 50 dollar price difference... it might be worth it just to check it out. I have not heard anything good or bad on Ultra-power, so if you do go that route, keep us informed.

The bonus part is that if for some unknown reason you have the same issue, you have only dumped 20 bucks into the parts canon.

my other thoughts are that even though you tested the parts and they are "good", you are getting an intermittent miss, so you tested them when they were not missing, which could mean you still have a possible plug wire/ plug/ coil issue. another thought, are your issues under load or idle or both? might be worth changing a fuel filter and checking fuel pump pressure....

AJ

 

[Cobaltred05]

After a lot of thought last night, I came to the same conclusion. I ended up ordering the part from Ultra-power and it will get here Friday. Here's to hoping that will work. At least it is simple to replace. There are some pull apart lots nearby. If the Ultra-power doesn't work out, would it be a bad idea to pull one from there? I imagine it would only be around $15 based on how much the spindle cost on my axle (that was another fun adventure this truck has given me ). I will definitely report how the Ultra-power brand works out after I get it installed.

Good point about the intermittent miss part. As far as when the issues happen, the majority of the time it is under load, but I have had it happen maybe 10% of the time under idle too. Significantly less often under idle, but always when the engine has been warmed up. It is happening much more often right now as we have been hitting temps over 100 degrees F in Ogden, Utah. Before I fixed the vacuum issues this last winter, it would take quite a lot of driving before the check engine light would come back up and it never happened while idling.

When I tested the wires last night, I didn't pull the new wire out of the truck (it's a pain to thread it through the clips and through the gaps in the intake manifold). I did inspect the old wire as best I could, and didn't find any signs of burns, rubbing, kinking, or melting. I know that probably doesn't mean much, especially since it is the old wire that isn't installed. The spark plug and the wires I bought are in the links below.

Double Platinum Autolite
OmniSpark Spark Plug Wires

I am missing part of one of the clips that protect the wire from directly contacting the engine. I pulled a picture off the internet as I'm not home right now to take one, but hopefully this is helpful. You can't see the clip in the picture, but I have indicated roughly where it is located with an arrow. The last channel on the left of the picture has half of the clip snapped off. I figure more details will help even if it's not relevant.

With respect to the fuel pump and filter, I haven't done that yet, but I can definitely look into it. One thing has worried me for a while now, especially since you've told me to check the fuel pump pressure. With the ghetto CNG system that the previous owner installed, what are the chances that my valves are burnt like with Evilthecat's issue in this link? Since CNG is supposed to burn at a higher temp, would it be enough to cause a similar issue?

 

[franklin2]

If you feel you may have burnt valves, do a compression check. One or more cylinders will be down on compression if you have valve sealing problems.

Missfire under a heavy load also brings to mind sparplug gap. Did you gap the plugs?(if they can be gapped)

 

[Cobaltred05]

I honestly have no idea if I do have burnt valves or not, but it has been in the back of my mind since I read Evilthecat's post. I'll look into what I need to do a compression check. Thank you for the advice.

For the sparkplugs, I did gap them. I was as careful as possible while measuring like Jim Oaks instructed in his sparkplug replacement tutorial on this website. The plugs arrived at the correct gap size, so I did not have to adjust them at all.

Edit: I looked into the compression check. Doesn't seem too hard to do. If I have time, I'll do it one of these next few nights.