Can EXhaust Leak Cause Lean Code?
Lead Driver
Joined: Nov 2002
Posts: 9,556
Likes: 43
From: Concord, NC
If the 542 code comes up from switching tanks, I wouldn't worry about it. The computer monitors the switched, or output side of the fuel pump relay to make sure it switches when the computer tells it to. When switching tanks, the circuit is momentarily open with no ground, which causes that particular code to be set.
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Fleet Mechanic
Joined: Apr 2008
Posts: 1,724
Likes: 2
From: Vancouver BC Canada
Well, had to run some errands yesterday and back came the cel again. Ran a KOEO today and once again the 172 came on (O2 reads always lean). I'm definately going to excelerate plans to finish the exhaust in case there is an exhaust leak. I've just ordered a new egr tube on ebay and am going to order some headers soon. I couldn't see a leak when I looked the other day but that doesn't necessarily mean anything. Couldn't seem to track the source of the ticking.
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Fleet Mechanic
Joined: Apr 2008
Posts: 1,724
Likes: 2
From: Vancouver BC Canada
Still setting 172 code. Changed broken egr tube with a new one and went for a drive. CEL came on again with the 172 again. I've noticed that when it comes on is either when I'm at cruising speed or under light load like going up a short hill at 50kph. Not sure what could be causing this. For those of you who have been following my other truck drama, I've also been having a ticking / tapping problem that was originally diagnosed as a spun bearing but we're now thinking might be a noisy lifter. Could a tapping lifter cause a lean code? Do I need to replace my 9 month old o2 sensor again? Frustration level is growing over here...
I forgot to mention that it seems like the engine is making a sound almost like a diesel when you take your foot of the gas.
I forgot to mention that it seems like the engine is making a sound almost like a diesel when you take your foot of the gas.
New User
Joined: Mar 2009
Posts: 1
Likes: 0
95 F150 V8 302ci w/ same issue
I've been tracking down the same codes in my 95 Flareside for a couple months. Finally getting pushed to fix it before camping season starts.
First I replaced the O2 sensor, which did help. I've replaced the rusted out vacuum canister (tomato can) and cracked vacuum lines.
The EGR tube has a leak right at the converter which I'm working on welding. I don't think that will make much difference, but I'll let you know if it does.
First I replaced the O2 sensor, which did help. I've replaced the rusted out vacuum canister (tomato can) and cracked vacuum lines.
The EGR tube has a leak right at the converter which I'm working on welding. I don't think that will make much difference, but I'll let you know if it does.
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Fleet Mechanic
Joined: Apr 2008
Posts: 1,724
Likes: 2
From: Vancouver BC Canada
Codes finally stopped when I changed the o2 sensor. I think it got all gummed up during a period when the truck ran really rich due to a fuel overpressure situation from a bad fpr.
Of course, the bigger picture is more concerning as the truck definately has a problem in the bottom end.
Of course, the bigger picture is more concerning as the truck definately has a problem in the bottom end.
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