5.0 EFI engine backfire

[DirtDonk]

It should be fully controlled by the PCM, but it does take vacuum/load into account through the sensors. This is a full Explorer setup with coil packs then? If so it can handle quite a bit of a vacuum leak before it messes things up, but a really big leak might give it some fits.
However, backfiring and stumbling and whatever it's doing is not just minor.

Is this still a roller cammed later block or did you put Explorer stuff on an older block? If a flat-tappet cam, did it get broken in properly for the first half hour?
Since it's not a a distributor setup with a TFI module, there's no issue with power going to the one wire keeping timing retarded, but that used to be a common issue with swaps.

What cam is being used? Stock Explorer, or aftermarket replacement?

What injectors?

Did you ever connect your CAN-P vacuum line?

Paul

 

[EFI Guy]

Can you see specific misfires on your PCM? Might need to use a Windows laptop to see them.

 

[agboy91]

DirtDonk, its all original Explorer set up from a 2000 explorer. EFIGuy did the PCM flash and deleted the rear O2 and EGR. All other is still original explorer. I’ll pull the codes and look as short and long term fuel trim as well. I was told they should be around 10 but if you know what I should be looking at, I’m all ears.

EFI guy, The initial look Was 4&5 were misfiring but I pulled plugs and checked wires and all seemed OK. Thanks

 

[agboy91]

Paul, p-can line is connected.

 

[agboy91]

Sorry CAN-P I’d connected.

 

[needabronco]

I chased a percieved misfire/fuel loading issue for over a year, and found a nipple covering a vacuum port had crac ked and was leaking unmetered air. A 10 cent plug solved the issue. Sometimes it's something simple

 

[agboy91]

Thanks Needabronco. I’ll check them, all again. Are you in Nevada.

 

[EFI Guy]

My reason for asking if you could watch the misfire counter in real time is so that you could spray around looking for vacuum leaks and physically see the change on the screen.
Since you have been over the ignition system and 4&5 have nothing in common I am leaning towards a vacuum leak myself. With 4&5 being on opposite corners, perhaps you have a warped intake.

If you can't watch misfires, you can still diagnose a bit with fuel trims. If you watch short term trims and spray for a leak, you will see short term go negative when you hit a leak.

I personally use carb clean in small amounts that can't pool up and cause a fire. Some people use propane which is probably a little safer. In either case, don't go crazy with it and take safety precautions like having fire extinguishers ready and doing it outside etc...Also, don't use anything that might ruin a painted surface.

FWIW longe term trims should always be within 10% + or -. When you have a vacuum leak, long-term trims will usually be a pretty high positive number at idle but come closer to zero when you're on the throttle.

 

[DirtDonk]

...Since you have been over the ignition system and 4&5 have nothing in common I am leaning towards a vacuum leak myself.

Other than being next to each other in the firing order perhaps?
That's consistent no matter which cam/firing order you use. 154 or 654.
Though I don't immediately see how the two can be effected by something together. Just thought I'd mention that.

Paul

 

[agboy91]

Well, as with most problem resolutions the solution is often found by accident. I found the problem with my engine backfire. I thought all along it was a timing issue however another possibility was a sticking valve so I hooked up the vacuum guage and all came out normal around 45-50 psi at idle. It does pull down to 20-25 while driving in 4th gear. Is that normal or should it recover to 45-50psi? The engine still had a shutter when idling so I looked around the engine. It was getting dark out and found one of the plugs arcing to the block. I tried to pull the plug wire and the inner connector came off on the plug so had to replace the plug wire. I put the wire back one and still was arcing. I pulled the plug and Walla, the plug was cracked at the base. I guess I cracked it when I put them in. New plug in and No more backfire. Happy day and nice go have all the power of my 5.0. My engine does make a howling sound some times at idle. Any ideas what that might be from. Intake volume I suspect as when I throttle up it goes away. Good day to you all.

 

[CA Monkey]

nothing better than fixing long term issues... good job.