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Its possible that the readings dropped as the engine warmed up and had nothing to do with the brake vacuum lines.
George
I thought about this too. Are readings always high before the engine is completely warmed up? I've checked it several times when it was at full temp and got the high readings.
I downloaded an app called Car Scanner that was recommended for my cheapie dongle. Looks promising with all the fuel trims available. Wish the app pro would chime in. 😁
No, fuel trims starting high and dropping as you warm up is not normal. Given that you’ve gotten high readings after the engine is warm multiple times says that is probably not the explanation. So we still need to find out where your likely vacuum leak is coming from and confirm with proper fuel trim readings. You got a rapid change in readings while you were messing around with vacuum line to check valves and brake booster so it’s probably in here somewhere
I forgot to mention, when I pulled the hose off the booster, it was wet inside. Not water dripping out, just moisture on the surface. That seemed suspicious to me, or is that typical?
Some brake boosters can get water intrusion, BMW for instance has this problem. I don't know the set up on these trucks and how likley water intrusion is (vents, drain pans, etc). Was it water or brake fluid? If anyone else has a perspective on this for the OP please jump in.
Just got back to working on my beast. These are the readings using a different app called Car Scanner. First is at idle. Second is at 2500 rpm. I tried again blocking the brake booster off and the hvac/4x4/reservoir. That didn't seem to change anything. I also swapped out the maf sensor with a new one because, why not, and that didn't make any difference. As before, trims did drop some after engine was warmed up. I am stumped. I already changed the grommet at the pcv valve. I wonder if the grommet at the other end of the pcv line could be leaking.
With the HVAC acting up (and have you noticed any issues with it not actually shifting into 4wd HI as well?) it's almost certainly a vacuum leak. I had a similar issue with the HVAC and and 4WD and found a burned through vacuum line on the driver's side down at the exhaust manifold and again next to the actual exhaust pipe. I know you're probably trying to find an exact answer before getting dirty, but sometimes it's a good idea to do a quick visual double check of the lines near any of the exhaust and making sure that there aren't any 'easy' answers before digging into the electronic signal side of things. It just takes a touch to melt through them so it's worth another look. The other thing that comes to mind is the vacuum line that runs to your transfer case. That guy has a tendency to crack and break so you might want to try capping off that hose to see if it makes a difference with the answer being replacement if it's the culprit leaking of vacuum (and it'll restore your 4wd too).
I don't believe I have the vacuum to transfer case. Mine is the one with the vacuum lines that go into a solenoid on the firewall. The 4x4 actuator only has the incoming vacuum line and the line that goes to the front axle (?). So my vacuum lines all seem to be up top, and in the dash for hvac.
Two things I need to check. The air hose that plugs into the back of the hat on throttle body, is it common for that line to crack and not be obvious, maybe at the end that goes into the valve cover or grommet? Same for the pcv valve cover, wondering about that being brittle from age.
Big discovery yesterday. The base of my EGR valve is cracked as shown. The one "ear" is completely separated so it's definitely not sealed tight anymore. This could be causing my lean codes/vacuum leak, right?
FYI....It's a cheap EGR I installed as a test part, which did clear my EGR code that I'd had for a long time. There are several reviews where others broke just the same. Got what I paid for. Does have a 1 year warranty and I'm requesting a refund. Don't want a replacement that's just going to break again!
03-02-2023, 01:26 PM
