Jimmy Brooks
Full Access Member
Curious about the supercharge bypass valve. How would I check that?
Anyway to check the MAP sensor as well. The pressure fluctuates with acceleration but I’m not sure that’s enough to tell the integrity of the sensor.
Persistent misfire under load only
- Thread starter greiswig
- Start date
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Curious about the supercharge bypass valve. How would I check that?
Anyway to check the MAP sensor as well. The pressure fluctuates with acceleration but I’m not sure that’s enough to tell the integrity of the sensor.
scapistron
Full Access Member
This is when I start getting the parts canon ready. Just start replacing sensors from easiest and cheapest to the most PITA ones last.
Jimmy Brooks
Full Access Member
Returning with a little bit of insight. Yesterday I tested the the purge valve on the D5 by first comparing the resistance on the purge valve of the D5 compared to my LR4 (both use the same Bosch FoMoCo purge valve.) both red within an Ohm of each other. I never disconnected any lines or moved them in the process of getting this reading so I guess when I was putting the drivers side engine cover back onto my car I upset the evap line running towards the fuel tank because I was greeted with P0442 on the way to work today. Usually this code is linked to the purge valve being stuck open but mine is closed tight and holds vaccum on both ends. The LR4 now runs way wonky, pulling -12% LTFT on both banks and when I try to hold the idle steady at any rpm, fluctuations will occur. Transmission is also shifting harder into gears when accelerating softly and shifting at higher rpms than normal so I’m sure unmetered air is getting into the evaporator line and the ECM and TCM are probably unsure of how to respond to it. I hooked my smoke tester up to it and it wouldn’t show any smoke pouring out despite me opening the fuel door to make sure it was pumping and seeing a bunch of smoke appear.
By observing this behavior that was created with a vacuum leak I want to draw the conclusion that my cheap Amazon smoke tester might not be the best way to check for vacuum leaks. Judging by the similar behavior in RPM fluctuations, the fact that all sensors on the D5 seem to read fine and that the fuel trim behavior on the D5 point directly to a vacuum leak I’m guessing that there probably is a vacuum leak that I am not seeing.
I will most likely be posting a thread tomorrow about my issue with my LR4, I think (hope) that there is a disconnect between the tank and the evaporator line that runs up to the engine (not sure how you drop the fuel tank if there isn’t) so I plan on vacuuming testing that tomorrow to icolate the area of the leak and going from there.
On a side note I feel like I need to contribute to the forum more since I have been asking so much so I will be dropping a step by step walk through on how to replace both rear upper control arms (PITA) Rear sway bar bushings and links, and the rear toe links. My rear upper control arms were in terrible condition at 150k and the biggest issue with them tends to be the rearward bushing rotting out completely, not the big fluid filled bushing in front of it.
Cheers.
By observing this behavior that was created with a vacuum leak I want to draw the conclusion that my cheap Amazon smoke tester might not be the best way to check for vacuum leaks. Judging by the similar behavior in RPM fluctuations, the fact that all sensors on the D5 seem to read fine and that the fuel trim behavior on the D5 point directly to a vacuum leak I’m guessing that there probably is a vacuum leak that I am not seeing.
I will most likely be posting a thread tomorrow about my issue with my LR4, I think (hope) that there is a disconnect between the tank and the evaporator line that runs up to the engine (not sure how you drop the fuel tank if there isn’t) so I plan on vacuuming testing that tomorrow to icolate the area of the leak and going from there.
On a side note I feel like I need to contribute to the forum more since I have been asking so much so I will be dropping a step by step walk through on how to replace both rear upper control arms (PITA) Rear sway bar bushings and links, and the rear toe links. My rear upper control arms were in terrible condition at 150k and the biggest issue with them tends to be the rearward bushing rotting out completely, not the big fluid filled bushing in front of it.
Cheers.
Jimmy Brooks
Full Access Member
so i dropped the spare tire in my LR4 and found that the pipe going up to the engine is vacuum tight when i blow from the charcoal canister towards the engine. at that point i figured that the rich condition was most likely caused by the smoke test i did and was probably the residue from the smoke soaking into the pipes. so i left it and drove it for a while. fuel trims stayed the same, so towards the end of my tank i gave the car an Italian tuneup which im sure allowed the intake to pull all the residue out from the evap lines and my LTFT are back to -3% on both banks and the car runs better than ever.
so with the knowledge that my car has the same evap system as the D5 then they should behave the exact same way. i can blow down the evap pipe, towards the charcoal canister from the disconnect after the purge valve in my LR4 but when i try to do the same in the D5 it wont let me blow down at all. im thinking that the charcoal canister in the D5 is clogged and not letting any fuel vapor into the intake manifold. to test this i unplugged the purge valve so that it would remain closed and in theory if the canister isn't letting the engine suck anything through the evap line then the purge valve being unplugged and sealed off shouldn't change the behavior of the engine running and the fuel trims.
to my surprise the engine behaved exactly the same with the purge valve unplugged. the fuel trims behaved the exact same at idle, at 2000 rpm and at 3000 rpm when the engine was warmed up in park. it also ran the same, misfiring the same ways that it does.
my question to all is, while the car is off can you blow down the pipe towards the charcoal canister at the disconnect right after the purge valve on the SCV6 models? im about to pull the trigger but want to make sure this is normal behavior.
so with the knowledge that my car has the same evap system as the D5 then they should behave the exact same way. i can blow down the evap pipe, towards the charcoal canister from the disconnect after the purge valve in my LR4 but when i try to do the same in the D5 it wont let me blow down at all. im thinking that the charcoal canister in the D5 is clogged and not letting any fuel vapor into the intake manifold. to test this i unplugged the purge valve so that it would remain closed and in theory if the canister isn't letting the engine suck anything through the evap line then the purge valve being unplugged and sealed off shouldn't change the behavior of the engine running and the fuel trims.
to my surprise the engine behaved exactly the same with the purge valve unplugged. the fuel trims behaved the exact same at idle, at 2000 rpm and at 3000 rpm when the engine was warmed up in park. it also ran the same, misfiring the same ways that it does.
my question to all is, while the car is off can you blow down the pipe towards the charcoal canister at the disconnect right after the purge valve on the SCV6 models? im about to pull the trigger but want to make sure this is normal behavior.
Jimmy Brooks
Full Access Member
ok, after a slight bit of more research the charcoal canister on the discovery is different... and oh is it expensive.
but now that i know its different, does anyone know if i should be able to blow down it freely or if it should be sealed off?
but now that i know its different, does anyone know if i should be able to blow down it freely or if it should be sealed off?
jlglr4
Full Access Member
I don’t know the answer to this question. There is more to it than just the canister. Somewhere in the line, there is the dmtl pump that tests for EVAP leaks, and that controls some valves in the lines. I spent some time studying that system years ago, but I no longer remember how it all works.
But, I don’t see how a plugged canister on the D5 would give you a lean condition. If you had open air flow all the time, then you might get a lean condition (or rich depending on the contents of the canister). But a plugged canister would not let air through. It could create pressure problems in the tank though…again, not sure how that would cause the lean conditions.
On the LR4…
But, I don’t see how a plugged canister on the D5 would give you a lean condition. If you had open air flow all the time, then you might get a lean condition (or rich depending on the contents of the canister). But a plugged canister would not let air through. It could create pressure problems in the tank though…again, not sure how that would cause the lean conditions.
On the LR4…
I’m confused about how the smoke testing was done, but it sounds like the purge is stuck open. It’s not unmetered air (like fresh air) because it’s causing a rich condition (negative trims), so it’s tank fumes if anything. Wondering if you somehow got a short in the purge valve wiring that is keeping it open when the engine is on. The purge would still close up when the engine is off.
Jimmy Brooks
Full Access Member
Was about to hang it up and take it into the shop but decided to swap out cylinder 5 coil and plug before I did. To my surprise that was the answer. However the fuel trims still behave the same but the misfire is completely gone.
scapistron
Full Access Member
Might take a little bit for the fuel trims to clean up
