99 Sport with induction & EVAP leaks - P0455 | Ford Explorer Forums - Serious Explorations

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99 Sport with induction & EVAP leaks - P0455


Active Member
June 1, 2008
Reaction score
City, State
Memphis, TN
Year, Model & Trim Level
02 Ranger XLT 2WD auto
Today's subject is a 1999 Explorer sport 2WD with auto transmission and 4.0 OHV. It has 190K miles with no known maintenance or history..

I just bought the truck, it had a P0455 large EVAP leak, P0304 Cyl 4 misfire, and a Bank 2 lean code. Both LTFT bank 1 and 2 are right around 25, and the STFTs were in the low teens. The fuel trims indicate a vacuum leak, and the cylinder 4 misfire was a cracked spark plug insulator.

I replaced the spark plug, and also put new DPFE hoses after finding both dry rotted.
Now the codes are cleared (0% occurrences misfire cylinder 4), and the only code to come back is a pending P0455. The scanner says my "Vapor Generation max" failed at -63, and the "Initial tank vacuum reading" failed at 0. I also have a module showing "Not10 front switch ratio bank 2" with a test value of 1024, and a max limit of 0.8 - no idea what that means.
In addition, the STFT and LTFT fuel trims are still too high. ST is low teens, LT is low 20s.

So the misfire is gone (although the cooling system took 1.5 gallons of coolant, so I'm keeping an eye on it and expecting a cracked head at #4) and I'm hunting for
A) An induction leak causing a lean condition on Bank 2, and
B) An EVAP leak, probably multiple leaks if I had to guess based on PIDs and observation of other neglected maintenance.

I've already been through 30+ threads searching for info on troubleshooting, and it SUCKS that people just don't update their threads to tell if they every fixed their issues, or what caused them.

Today's goal is to build a smoke machine to find the leaks. I am a visual learner and the smoke will really help..
Feel free to pitch in with ideas, just keep it on topic please.


Well after driving long enough for the EVAP and fuel/air monitors to test, I got another MIL, with three DTCs.. the same P0455 large evap leak, and two come-backs: P0171 and P0174, system too lean banks 1 and 2.

Awesome! Glad to see it's lean on both banks, that makes troubleshooting a lot easier. I finished my smoke machine and loaded it with mineral oil and A/C system fluorescent dye. The dye didn't show up, but I found several leaks.. the upper and lower intake manifold, the IAC at its black plastic cap, underneath the EGR valve, and the breather tube on the oil filler.

I didn't have enough time to get into the EVAP leaks tonight, so I think I'll try to get a service port adapter whipped up tomorrow.

Also found some coolant leaks at the head gasket :/