Please educate me RE EGR-FCV-MAF operation

Johnboy · **Posted:** Fri Nov 16, 2007 1:57 pm

She went in for her 3rd or 4th EGR today (turned 30K this week). Time to unplugg.

So:

MAF unplugged = no EGR operation and normal FCV operation?

MAF has no control over the FCV?

From my reading, EGR is bad and FCV is benificial...

Sorry to beat a dead dog, just would like to know a bit more about what I am going to do by unplugging. SEGR does not seem feasible to me. Nuts bolts carburators clutches and the like are ok with me. Computers, wire harness's, and circutry are scary.

Thanks

gmctd · **Posted:** Fri Nov 16, 2007 2:07 pm

http://www.lostjeeps.com/forum/phpBB3/vie ... hp?t=24961

gmctd · **Posted:** Sat Nov 17, 2007 1:37 pm

Ok - now that you've read thru that stuff (you did read thru, right?), it's simple in concept - takes a long time to 'splain, but simple.
So, go get some cookies and milk, kiddies, come back, and settle in fer a long winter's read.....................

Infernal combustion engines - Diesels, and that other kind - convert atmosphere (20% oxygen, 70% nitrogen, 10% junkagen) and fuel to heat which creates pressure which creates thrust on a rotating lever(s) to create torque to move our vehicles - the greater the heat, the more satisfying that push on our backsides as we lay-on the exhiliarator pedal.
As we pour on the fuel in our insatiable quest for more power, combustion chamber temperatures rise satisfyingly, but the nitrogen and oxygen begins to combine to form NOx, which enhances the local smog ambience.

Exhaust Gas Recirculation is used to dilute the fresh air\fuel charge in order to reduce emissions, and to reduce cylinder temps at high-power high-loading which creates those oxides of noxious - bad fer people, good fer power.

Some method of feedback is required so ECM can determine when and how much exhaust gas is necessary, and there are two widely-accepted methods, based on engine type.

1) Gassers (patooie!) use a throttle-plate to regulate air-flow at all rpms, so fuel must be metered at specific ratios to match air flow at any given throttle-angle for complete burn, which produces max power from the fuel charge.

Yer basic O2 sensor, or oxygen sensor, generates a voltage which is precisely dependent upon the amount of oxygen in exhaust gasses, which can be used to determine that the engine is in stoke - the air\fuel mix must be stoichiometric (from the greek word meaning 14), or at 14:1 air to fuel ratio, required for complete combustion of the gasoline fuel - this ratio must be maintained at all times for total burn to produce maximum power with minimal emissions.

O2 sensor output is also used to determine any requirement for EGR at all operating conditions.

But, you don't got one - or two, or four, heated or unheated - in yer 2.8L CRD engine.

2) Air\fuel ratios in Diesel engines cannot fit within any stoichiometrically-metered scheme, as each intake stroke takes in maximum displaced air quantity, at idle or 5000rpm - fuel quantity is mixed in as required for the desired rpm or power output -
small fuel + max air = idle
big fuel + max air = big power
Diesel engines are torque monsters as a result of that scheme.

Thank you, Dr. Rudolph!

A major byproduct resulted from burning oil as fuel is soot, that black stuff in yer shiny new stainless steel exhaust pipe, and in yer engine oil 5 minutes after changing the oil and filter.
Soot will immediately pack any device in the exhaust path, which would quickly render an O2 sensor as usless - but, while exhaust mixtures are all over the map (literally), rpm and power is also dependent on intake air volume, which is always (hopefully) clean.

Enter the Mass Air Flow sensor, which you do got one of - if you measure the volume of air flow into the engine and compare that to the volume of fuel injected (plus some other stuff) you could accurately determine the volume of EGR required to keep the combusted byproducts of Diesel fuel within acceptable standards - that is, if you were foolish enuff to want to stifle yer engine, like that.
Or, were under duress from some government agency to do so.

But, you also got a 'nuther thing which, fortunately or unfortunately, depending on yer perspective, throws the inevitable monkey-wrench into the EGR scheme - that exhaust-gas powered turbine motor that drives the air compressor which gives you that adrenaline-pumping Boost - oh yeah! Power to the people!!!

Thank you, Dr. Bucchi!

The EGR scheme is fairly ineffective any time intake Manifold Air Pressure exceeds Exhaust Gas Pressure - open the EGR valve, and Boosted fresh air would blow into the exhaust system.........suh-weet!!!!

But not even good enuff fer them tree-huggers at EPA.

Enter the Air Flow Control Valve - the AFC - the AFV ( not America's Funniest Home Videos!!!) - the FCV - or, simply, the Throttle Valve - regulate Boost and throttle the intake to reduce MAP below EGP (yep- we're talkin' vacuum in yer Diesel intake, here, kiddies), and EGR is in business.........and yer intake!

If you're still awake, here, the short and sweet of it is: the MAF is strictly for the EGR system, which includes the AFC valve - unplug the MAF and you get no EGR........ever - butcha get the MAF DTC each time you start the engine.

Those other engines - spark-infested girly-man contraptions with their required throttle plates - always shut down with the plate closed - the intake plenum is therefore at high vacuum - vacuum doesn't compress easily, so they shut down smo-o-o-thly - should our beloved Diesel engines also be allowed to do so?

The AFC valve - with two functions: EGR and Shutdown - still functions in the Shutdown mode, by which it throttles the intake plenum at key OFF to prevent that horrendous Diesel shudder, so popular amongst the Dodges with the Cummins 5.9L six-cylinder - a manly man's shutdown!
That bone-jarring shudder is caused by the full volume of intake air entering the hi-compression cylinders with no corresponding fuel to generate combustion to counteract the compressive forces.

The SEGR module disables EGR and AFC while the engine is running, but dupes the ECM into believing the EGR-AFC valves are operational - NOT! - so you get all the advantages of pure clean intake air on each stroke, without the associated DTC.
SEGR then enables AFC in PARK\NEUTRAL to provide smooth shutdown at key OFF.

Unplug the MAF = no EGR, pure clean air + DTC........a-n-n-o-y-i-n-g ! !

Install the SEGR = no EGR, pure clean air + no DTC.

So, whaddayagot? To lose?

the end (finally!)

88888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888

And, there ya have it, kiddies, and let this be a lesson to ya: always be careful as to what you ask for...................

Uffe · **Posted:** Sat Nov 17, 2007 4:52 pm

Thank you kind sir!

That also explains the noises coming from the magnetic vacuum valve operating the EGR valve on my 03 CRD after the engine has been shut off! So at shutdown you want max vacuum to open the EGR valve to let the cylinders run with no pressurized air entering them. Instead the pressurized air is going to the exhaust system directly because the EGR valve is all opened behind the down-spooling turbo.

This makes the darn EGR control valve buzz like a little scooter after shutdown. I've asked the Jeep stealership and they told me it was completely normal. Now there I get the explanation for why it is normal.

Well ... maybe they should've just stopped the darn thing when the engine is at 0rpm but at least I know now why it starts to begin with.

gmctd · **Posted:** Sat Nov 17, 2007 11:00 pm

Ah so - still confused, grasshoppers?

The EGR valve is normally closed until ECM determines EGR is required - it cannot open at shutdown

The normally open AFC valve modulates during EGR requirement, and at shutdown, then reopens.

With the ORM and the SEGR modifications -

the normally closed EGR valve remains closed, blocking exhaust gasses from the intake manifold, forever.

the normally open AFC valve closes at key OFF for smooth shutdown, then reopens ~5 seconds after engine stops

Go, and meditate - your mind must be clear, and your footsteps must be sure on the path to the answers you seek.

And, welcome to the forum, Uffe.............

Johnboy · **Posted:** Mon Nov 19, 2007 12:10 pm

Thanks boss!!

I am not sure if I learn more in grad school, or on the CRD forum...

gmctd's post here should probably go into one of the comprehensive posts about the CRD, no?

alljeep · **Posted:** Mon Nov 19, 2007 1:57 pm

gmctd wrote:

Exhaust Gas Recirculation is used to dilute fresh air\fuel charge in order to reduce emissions, and to reduce cylinder temps at high loading, which creates oxides of noxious - bad fer people, good fer power.

One thing that has always perplexed me bacause I do tow a big-a camper. I want the reduced cylinder temps under high loading right?

gmctd · **Posted:** Mon Nov 19, 2007 3:24 pm

Good question...........

The higher the cylinder temperature the greater the power and efficiency - but the worse the emission of NOx: noxious oxides - high cylinder temperature is not bad - what you don't want is high Exhaust Gas Temperature

Hi EGT's can be caused by
- restricted airflow - most commonly caused by poor maintenance, where the air filter is dirty - less air for same amount of fuel = more unburned fuel = black smoke = high EGT
- restrictive factory exhaust system - designed for EPA-restricted factory power levels, becomes increasingly restrictive as output power levels are increased with aftermarket goodies - even the ORM and SEGR mods will choke up in that factory muffler
- if seldom driven at hiway speeds, the soot trap clogs up, further restricting the exhaust
- increased fuel rates from after-market add-ons, where more fuel than is necessary for demanded power is dumped into the cylinders = unburned fuel = black smoke = high EGT

Black smoke is unburned fuel and increased soot - fuel and soot is much denser than properly combusted exhaust gasses -
-with complete combustion, the entire fuel charge is consumed, cylinder heat quickly dissipates as cylinder pressure drops as piston drops because the gasses have no mass to retain the heat - what little heat remains is absorbed into the block and heads and dissipated thru the coolant in the water jacket, and into the piston, cooled by sprayed engine oil - the next fresh charge-air cooled intake charge further reduces cylinder-head-piston temperatures - life is good
- black smoke is when the fire goes out B4 all the fuel rapidly oxidizes, leaving the dense particulate mass at combustion temperatures, not easily dissipated by the block and cylinder - cylinder-head-piston temperatures remain high, coolant temperature climbs, engine oil temperature climbs - not even the fresh cool intake charge can reduce the climbing temperatures - a veritable formula for disaster

This is why an EGT guage is critically important to Diesel engine operation, particularly when the owner's quest for personal satisfaction and power far exceeds what the government has decided he shall be alloted - e pluribus unum, quid pro quo

You may not even notice the increased heavy particulate emission - black smoke - until it is too late, and the piston siezes in the cylinder from excessively high cylinder temperatures - the exhaust haze may be slight, but the EGT guage can quickly inform the alert driver with indicator needle climbing toward the red zone.

So - high cylinder temps are good for power and efficiency, but high EGT's are indicator of poor efficiency and fuel economy - Boost is good for power and efficiency - charge-cooled Boost helps reduce EGT's

The driver's right foot can also help reduce EGT's..................

widowmaker · **Posted:** Mon Nov 19, 2007 4:59 pm

This grasshopper has a question, but a little ashamed to ask.
I am skilled enough to have done the ORM mod, oil changes, fuel filter, etc.
But that's about it. I did the ORM at 19,000 miles and she has 62,000 on her now. No visits during that time to the dealership, except for pinion seal on real differential.

My question, You said "butcha get the MAF DTC each time you start the engine" with the ORM. Is this a bad thing? What is DTC?

I don't tow with the exception of a utility trailer to the Home Depot store and the rest of the time I'm burning up the highways to the tune of about 65K per year.

Not ready to take the pebbles from your hand, must stay at the monastery a few more years.

gmctd · **Posted:** Mon Nov 19, 2007 5:44 pm

Good sense of humor, my friend, and good question, also -

ECM turns on the Check Engine Light and logs a Diagnostic Trouble Code each time it sees wrong input from a sensor or device - when you disconnect the MAF to disable the EGR valve, ECM senses no input from the MAF, and so logs a P0102 MAF low error DTC, turning on the CEL

There are non-critical errors, such as P0102, and there are critical engine-damaging errors - problem being, they are all displayed on the lone CEL - when it is lit, the codes should be immediately scanned.

Some say this causes no problem, as, having disconnected the MAF, they know what caused the CEL - however, with the CEL always on because of a non-critical error, what happens when a critical engine-damaging error is sensed, such as oil pressure suddenly drops to 0, or engine temperature skyrockets due to total loss of coolant, or similar?

CEL is already on, so the critical error goes unnoticed - a Diesel engine is a terrible thing to waste.

The ScanguageII OBD2 engine monitor can read DTC's and turn the CEL off, so it can be very handy for those with the ORM, clearing the error and turning off the CEL at each startup - since P0102 logs only at startup, that leaves the CEL free for critical errors, which log as they occur, in realtime.

At 43kmi into the game, you seem to have kept ahead of things, but it may be to your advantage to go to autozone and have them read any DTC's in your little mule - if you have only P0102, you're good to go, tho you're living a little vicariously, IMO.

If they see any other codes, write them down B4 they clear them, and post them here for further analysis and diagnosis.

widowmaker · **Posted:** Mon Nov 19, 2007 8:08 pm

I am enlightened, Thank you

I have the scan guage and check things out semi periodically, however I was counting on the other idiot lights to catch potential problems, like the oil pressure, coolant temp., coolant level. etc.

I feel the urge to plug that scan guage in now....thanks again.

gmctd · **Posted:** Mon Nov 19, 2007 9:44 pm

Wow - if you've had only the self-induced MAF DTC in 62kmi, you must own the poster-child for KJ CRD reliability - the Shao Lin must indeed smile on your endeavors, grasshopper.

stump doctor · **Posted:** Mon Nov 19, 2007 9:52 pm

I run off road mod a lot and always have p0102

gmctd · **Posted:** Mon Nov 19, 2007 10:56 pm

P0102 MAF low makes more sense, with the sensor disconnected - I was thinking #2 son said it was P0104, but I'm usually misteaken when it comes to numbers, so my bad - lemme edit the posts for posteriority's sake
Thanks for the correct correction.

Uffe · **Posted:** Tue Nov 20, 2007 7:33 am

Regarding the SCANGAUGE - does it really work on all KJs? I've heard there was some problems using a scangauge for for instance MPG measurements etc. while driving.

I'd be interested in a scangauge if it works properly on my 03 CRD KJ...

Any experience with such a gauge and an 03 KJ??

hatchetman · **Posted:** Wed Nov 28, 2007 9:15 am

I remember some discussion along time ago about the EGR still having some movement even if the MAF is disconnected. So if you pull the plug literally on the EGR, there will be no movement on it. Correct? So, if one were to "pull the the plug" on the EGR, do I do it on a totally cold engine? Also, anyone off-hand know the torque setting for transmission pan bolts and how much fluid I will need to change the tranny filter. I'm also going to install two drain plugs for draining and a trans temp sensor. Thanks. :evil:

gmctd · **Posted:** Wed Nov 28, 2007 11:57 am

The normally-closed EGR valve should not move at any time - exhaust pressure is not high enuff to overcome spring-loaded pressure holding the valve closed without electrical solenoid assistance - without the MAF, ECM has no metering input for solenoid control.

If the EGR valve is opening without solenoid assistance, then you will need to replace the defective assembly - or, remove it, clean the carbonized soot out, see if that helps

The normally-open Air Flow Control valve, on the other hand, does continue to function, but only at each shutdown - that's the ratchety-whirr-clank noise you hear ~5secs after the engine stops - when the AFC stops functioning, the Jeep will give that manly shutdown shudder like the big Dodges - lets ya know that's a Diesel under the hood.

Pan-bolt torque is ~9ftlbs - sealant is oil-resistant black RTV - owners manual gives the various capacities

Please educate me RE EGR-FCV-MAF operation

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