Hey all, looking for some advice where to go next with my troubleshooting. We were given a 1998 E150 conversion van about a year ago from family. Told it never had issues, we did regular oil change type services and it ran ok until now.

The engine is the 4.6L Triton V8. 200k miles. It started missing recently and it seemed obvious it was either fuel starved or misfiring on a cylinder. Codes P0305 (Cyl5 misfire) and P0401 (EGR valve) showed up. assuming the p0401 was due to the p0305, i started digging online. Seems these tend to have coils that go bad? I'm not a great mechanic so with some advice from one that is i was led to believe that switching the coils on the plug side and on the coil pack side (both sides of wire anyway) would be a good test to see if it was the wire. I have no spark tester.

so with a borrowed code reader i removed air filter, found coil 5 next to cylinder 5 and after some time realized that unlike what i have seen online there are no screws holding these coils on the plug so i simply pulled it off. Traced it back to the coil pack and pulled that side off. Did the same for coil 6 wire. I then swapped them, cleared the code and started. It starts immediately but then dies out if you do not stay on the gas. It was not throwing any codes now but wouldn't stay running. So i put the cables back thinking at least it was running before and maybe time for a true mechanic. Nothing changed when i put them back to normal, it starts and dies out quickly if not on the gas. And of course there is no code. I let it run for about 30 seconds to try and throw a code but no luck. so seems i have made things worse somehow

So any recommendations on what to do next? Not sure with 200k miles how much we're willing to spend on it. Whats the expectation on these engines?

Maybe i have two that are misfiring now? bad plugs? i dont know... hard to get to some of those.

 

Sounds like you knocked the PCV hose loose (it's right there near cylinder #6) and you've now got a massive vacuum leak.

Make certain you inspect that hose all the way from the PCV valve around to the back of the intake. There's a rubber elbow that commonly fails back there, too.

If an engine of that era has a massive vacuum leak, it won't stay running unless you really get on the pedal.

 

Thanks for the advice! Now off to find out where the PCV Valve is located and track the hose down.

 

On thing I have found on my 4.6 in my Crown Vic P71 is a very slight exhaust leak where the exhaust pipe connects to the header will cause CELs & misfires etc. The bolt was loose at the manifold you could hear an exhaust leak when it was cold but went away at warm up. But every so often it would throw a CEL of misfire on a cylinder. After freeze framing it it was a lean bank code. That small leak messes with 02 sensor enough to show a lean condition.
Not sure if this helps you. But I have never seen this sensitive of a lean condition. Makes me wonder what would happen if the pipe fell off.

 

So i finally got back to checking this issue out. Sure enough i didn't get the PCV hose connected again to the intake. Problem 1 fixed. So i drove it and it threw the cylinder 5 P0305 again. Swapped 5 and 6 wires on the plug and at the coil pack, cleared code and drove....again a P0305.

So what next? Cylinder 5 Plug? Should i be brave enough to pull that plug if i have a socket for it? ive heard they break easy and leads to more problems replacing them.

 

Yes, you should replace the #5 plug. After that, swap the coil packs, if needed.

Breaking plugs is not an issue on these engines.

 

any chance you would what size socket it takes?

 

5/8"socket

 

Pulled #5 plug and it was in pretty bad shape. It ended up being the culprit i believe. Thanks to all for the help here.