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Loss of boost if EGR valve is unplugged

37K views 22 replies 9 participants last post by  tom mcgivern 
#1 ·
I have done a lot of reading on different threads about unplugging the EGR valve as a short/ cheap fix to help prevent problems with recirculating exhaust gases back to the intake. In my '05, i didn't have any CEL show, but I did notice that i was not able to get more than 20lbs of boost from the turbo. I plugged in back in after noticing it, and the next time i stood on it i got over 30lbs. anyone know why? thanks..:read
 
#2 ·
With certain stradegies and year trucks, unplugging the EGR valve can set the truck into a limp mode. From my understanding, this is a fairly new find. Othe symptoms that may occur is, the VGT not cycling when at idel, and the clutch fan not reaching full RPM.

As far as what year trucks and stradegies are effected, nobody knows. You noticed less boost, myself and another member noticed that the VGT was not cycling. Without putting the truck on a diagnostic scanner, you wouldn't be able to tell if the clutch fan is reaching full RPM. Now I wonder how may guys have there EGR valve unplugged, and don't realize that there clutch fan is not working properly?!?!?!?
 
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#3 ·
Just to clear things up, did you unplug the valve when the truck was off?
 
#4 ·
It does not matter when you unplug it. The EGR valve is spring load closed and needs a current to keep it open.


If you not not have any issues, you WILL see lower psi from the system because the system is more efficient with its operations.
 
#5 ·
I have my EGR taken out but still plugged in ( got a spool in the opening for the valve) you will have a lower boost pressure, as some have said it can be because it runs more efficiently, some say because your not adding used, burned, usless air back into your cyl it A) dosent need to push as much air (i would think it would still spool up to 30 then back back down to where it would be most efficent B) others say its because your not adding boosted air flow back into the system from exhaust it wont build as much...

At any rate of repeating, I have been running mine plugged at manifold and connected at harness and laying on top of motor for nearly a year with no ill side affect due to it, still runs great! but holds soft codes in computer.
Even with your egr unplugged it can still leak exhaust gas past the valve from what I have read.
 
#6 ·
I did unplug the EGR with the truck off. I plugged it back in after noticing the boost was limited to 20lbs. I'm not a diesel tech, but it seems that the computer is limiting the boost somehow. For now, i'm leaving it plugged in. I have a bypass coolant filter and a bypass oil filter installed to help prevent the problems with the EGR cooler itself. I have seen EGR delete/ bypass kits for sale from $150-400. are they worth it? thanks
 
#7 ·
Let's remember that boost is a measure of "back pressure", how hard the turbo is pushing air into the engine but NOT a measure of how much clean air is entering the engine!

If the turbo is moving 60#/min of clean air, and the EGR is adding 10# of EGR to the intake, where "boost" is measured, what do you think will happen when you remove that 10#/min of EGR but don't alter anything else? Measured boost will go down but clean airflow did not change.

If you want to know if you are getting more air into your engine, look NOT at boost but at the MAF signal in # of Intake air/minute!
 
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#8 ·
John G, how do you measure the MAF? ok, more important, what is MAF?
 
#9 ·
This is what happened on my 05 (no MAF). As John said, boost is a function of backpressure, my truck felt twice as strong at 20lbs as it did at 27lbs. What I did was bolt the valve to the alternator bracket and left it plugged in. No soft codes and boost is normal. My truck doesn't have a MAF so I'm not sure how "MAFFED" truck would react.
 
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#10 ·
It does feel "stronger" at 20 lbs with the EGR unplugged, but i have no way of quantifying that feeling. I assumed that 27-30 is better than 20....
it may seem strange, but i also notice the transmission shifts differently, tends to wind out more with the EGR plugged in...
 
#11 ·
This exact question has been debated for years. Matt from Spartan started a HUGE thread regarding certain maps that couldnt be defeated yet causing bad mileage and some sort of "limp mode" on the newer trucks. Mind you this was a few years ago but nothing ever came of it.

Someone correct me if I'm wrong.
 
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#12 ·
MAF = Mass Air Flow (sensor), measures EXACTLY how much clean air the engine is injesting thru the airbox/turbo.

AMM = Air Mass Mater, same as a MAF sensor, common term for BOSCH equipped vehicles.

Your AFR (Air Fuel Ratio) is lbs of air : lbs of fuel, so 14.7:1 = 14.7 lbs of air to 1 lb of fuel. Fuel is a liquid, so basically incompressable and density changes by temperature comparatively little, so it is considered constant in most systems (although modern EFI systems often measure fuel temperature and correct to density/engergy content accordingly). High temp fuel is less dense, fewer BTUs (in fact molecules) per volume, and less power.

Since you know the fuel quantity very accurately, you also need to know the air quantity very accurately, "speed density" - that is using manifold pressure and temp, is INaccurate where a MAF sensor is extremely accurate.

Without a MAF, you are guessing as to airflow, period.
 
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#14 ·
i have no idea!! lol
 
#15 ·
UPDATE TO MY THREAD

Since I first started this thread, I have gone ahead and installed a complete EGR delete and an updated up-pipe (no scoop) to my truck. The truck runs fine, but I do not have more than 20-22 lbs of boost. before i did the delete, i had boost up to @35lbs. Is this part of the "limp mode" that I have read about with unplugging the EGR valve?
 
#16 ·
Lower boost numbers after the egr modification is apart of having a more efficient air pump!(engine) :)
 
#17 ·
Exactly correct, Smoker. Your engine is no longer ingesting an oxygen depleted inert gas(EGR) that requires higher boost numbers to make up for the depleted oxygen levels. Your getting plenty of oxygen now with only 20-22 lbs of boost. Custom tuning can bring the boost numbers back up, along with added fueling to match, but reliability could be compromised.

Harry
 
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#19 ·
Sounds good... but..

Harry and Smoker,
that sounds good to me. The only thing I worry about is the computer somehow throwing off my fan clutch as part of a modified limp mode...
I don't have a OBD-II reader myself, so I took it to my local advance auto and didn't get any codes or am I throwing any CELs.
just trying to be careful... thanks again!
 
#20 ·
By keeping the egr valve itself plugged in, fan operation should still be normal, its when you leave the egr valve unplugged that the fan clutch operation goes abnormal. But if you are throwing egr system codes due to the no flow, then custom tuning is needed, like with an SCT tuner.

Harry
 
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#21 ·
"But honey, the guys on diesel garage said I NEED a SCT tuner for my truck with custom tunes... and new ARP studs and head gaskets!!!"
 
#22 ·
Custom tuning can vary from stock hp/torque to maximum ranges as I'm sure you well know. Stock factory mapping is designed to work with a functional egr system. Your truck will definitely run much better with good custom tuning to match the changed engine condition of an egr delete, even if power levels are kept close to or at stock settings. A good safe tow tune would probably be your best bet, since you have a 5r setup.

Harry
 
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