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Old January 12th, 2010, 12:20   #13
Veteran Member
Join Date: Feb 2008
Location: Maryland
TDI(s): 2001 Jetta
Default Your Worst Enemy, EGR

Your worst enemy, EGR

So the most important part to take away from this lesson is hot oil that has not reached its flash/fire point that comes into contact with relatively cool surfaces will start to form carbon (polymerization). EGR is your worst enemy!!! Exhaust gas recirculation involves combustion gases that did not combust (un-combusted tiny WVO particle matter) to be re-circulated through the intake tract (relatively cool surface of the engine) and then to be combusted again. So in the process of this emissions device, the tiny molecules of WVO are being subject to the cooler surface temperatures of the intake manifold and intake valves. Intake temperatures on an engine that has reached operating temperature range anywhere from 120 to 200 deg. None of these temperatures are close to the flash point of vegetable oil and thus, creates the perfect environment for coking, polymerization, clogged up intake manifolds and intake valves. Go back to the example, hot oil on cool surfaces… recipe for disaster.
An interesting theory to note, older IDI engines are more prone to success. None of these are equipped with EGR systems.
EGR is the culprit to many WVO engine failures. It becomes a slippery slope. The more clogged your intake becomes, the less power you have available and the less fresh air you have coming into the combustion chamber. Air flow and boost pressures operate primarily on MAF input and load only. Intake restrictions cannot be compensated for with less fueling. It will continue to burn the same amount of fuel in which the fuel map specifies for (requested/actual injected quantity). So look at the scenario we have. We have a clogging intake which is more susceptible to more clogging due to the process already being started and we have continued decreases in combustion efficiency. The engine is receiving less and less air (being choked) and is still injecting the same amount of fuel. This will eventually cause decreases in performance, fuel economy and excessive smoking. All of which will exacerbate the intake clogging problem.

Primary problem #1 Coking of intake manifolds, and intake valves with polymerized vegetable oil.

Primary Solve- Reduce the EGR duty cycle through use of VAG COM or eliminate it all together (my recommendation). EGR causes way too many problems on a diesel engine that burns vegetable oil. Elimination of the EGR will cause a check engine light; however, I think it is very evident to see that the benefits of eliminating the EGR exceed the drawbacks of a yellow light. A CEL can also be eliminated through tuning.

Primary considerations- If you delete your EGR, your check engine light will be on all the time and will not go away unless you get your car chipped. Also if your state requires emission testing for diesels, there may be a problem in eliminating the system all together. Your best bet would be to reduce the EGR duty cycle to its minimum and then change it back to stock before testing. I do not have to worry about this as Maryland does not require emission testing for diesels. If you reduce the duty cycle and do not eliminate it all together, you probably should check your intake every so often, maybe every year to year and a half. This is why eliminating it all together makes everything much simpler and easier.

Here is an example of EGR at its best while running WVO. This is what will happen if combustion efficiency is poor and EGR is fully functional.

Scrolling down to picture 4, 5, and 6, you see the signs of a car with poor combustion efficiency while running on WVO and having EGR fully functional. Observe the buildup behind the intake valves (valve stem). Remember the thread about polymerization and relatively cool surfaces?

Observe the polymerization on the bottom of the exhaust valve (the flat surface, not the stem). The exhaust valve is the one without the polymerization buildup on the stem of the valve. Un-combusted WVO gases were coming into contact with relative cool surface temperatures in the combustion chamber. Also note, any type of carbon deposit in the form of polymerization on an exhaust valve is proof that combustion efficiency was quite poor to say the least. If that isn’t enough proof, the intake valve stems show exactly what happens when polymerization occurs in a diesel engine due to burning WVO with EGR.

So if you want to run your EGR while burning WVO, you better be absolutely certain that combustion efficiency is at its peak in all instances. If you’re cars air to fuel ratio while burning WVO is leaning towards rich, this is what very well can occur. I did myself the favor and avoided this in its entirety.

2001 Jetta TDI- 190K
17/22, T4 764's, KermaTUNE, Euroject SMIC, Southbend Stg2 Endurance Clutch, LSD, .681 5th

WVO no More 187k
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