oldnavy wrote:
Derek Mc wrote:
Hmm,
How much is an egr valve to buy? or be given might be useful to keep one as a spare guys this seems to be a real issue.
Has anyone contaced DC direct and put the idea of a retrofit Pro-vent to them?
I am sure D/C, VW and who ever else makes intercooled EGR equipped turbo diesels knows about the oil & soot in the intercooler problem, can't be missed. They figure it will not be a problem after ULSD, just the oil in the intercooler tubing. Heck after 10k miles a VW will drain about 3 to 4 oz from intercooler hose just in front of the intercooler coil and probably as much oil and soot has already gone through the intake into the engine. It's not really a big enough of a problem to warrant the mfg's to spend the extra $$$$ for a collector, like MB did on my '83 240D. It had a small oil air seperator mounted on the intake manifold and it worked just great, but a NA diesel didn't have the oil & air flow through the valve cover that new turbo diesels have but for some reason they didn't put it on the turbo powered cars.
The only time a EGR really will cause a drivability problem is if it fails in the open position. On VW's & MB people would just block/disconnect the vacuum for the EGR or remove it completly from the system. On the new VW's you would get a CEL and the old MB's they didn't have an electric or electronic connection to throw a CEL. If I remember correctly in the VW you could clear the CEL and truck on, I'm not sure you can do this in the CRD. I plan on giving it a try sometime when I can catch the Libery in the garage long enough, and I'm in the mood, and have enough time to work on the thing. I may be able to get to it over semester break when the wife doesn't have to be at the college every day. I don't like her driving my car, for several reasons that I won't go into here.
I looked into how the CRD egr controls could set a CEL if you 1. blocked off the egr exhaust into the EGR valve. 2. disconnected the wiring connector to the egr valve. I ran across a project for older VW TDI's called epsilon, that describe how the egr system worked and how to keep the ECM from setting a code if you disconnected it. Based on that description, my best guess (and it is a guess) on how the CRD egr system works is this:
The ECM commands the EGR valve to open and add exhaust into the intake, based on its programming, and other senor input, air intake temperature on the cylinder head, engine load and speed, along with a command to the anti-shudder valve, located in the aluminum air intake inlet, to close slightly to reduce the amount of fresh air and increase the pull of exhaust into the intake. It then measures the flow or pressure drop variance between the masss air flow sensor in the air filter box and the expected amount of exhaust gas. If it doesn't see the expected drop in air flow as measured by the mass air flow sensor, it sets a code. There may also be a hall effect (inductive pickup) position sensor on the egr valve that reports it position back to the ECM as well. This provides both a tamper proof system and a diagnostic that tells the ECM when to set those P0399 codes for insufficient EGR flow.
After looking at what the TDI epsilon project did, it seems their logic was to block off the supply of exhaust gas to the egr valve. Then, knowing about the mass airflow sensor measurments, they built a small electronic device that plugged into the mass air flow sensor, and had a wire input from the egr as well. When the egr command came from the ECM to activate the egr valve, the electronic device they added near the mass air flow sensor received this egr input voltage, and in turn spoofed a "fake" correct electronic response back from the mass air flow sensor to the ECM to tell it that the air flow had dropped a corresponding correct amount,when in fact it had not. This would reportedly avoid setting a CEL and keep the engine free from exhaust soot. While their egr control was a combination of electric/vaccum acuated instead of electical only, the system on the CRD is similar enough that with some measurements of the signal voltage relationships between the mass air flow sensor, while egr command voltages are being sent from the ECM, it would seem possible to do the same on the CRD. If not to eliminate the egr function entirely, it might be possible to reduce the amount of egr gas introduced into the intake, and possibly reduce egt's on the CRD as well.