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SUVs Jeep Liberty and Jeep Liberty Diesel Jeep Liberty Diesel
10699 messages, Last post on Dec 05, 2009 at 4:11 PM
You are in the Jeep Liberty and Jeep Liberty Diesel Forum. Your Hosts are steve_ & tidester
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Replying to: caribou1 (Feb 11, 2007 12:27 am) Your explanation of it was not wasted on me since I've been a student of this Jeep since before I bought one. Running the diverted EGR exhaust back to exhaust (perhaps an auxiliary tail pipe!) would be the only reliable remedy to circumvent the plumbing mess they made. Now I have not had any problems with my CRD; do all service myself. However, the city/ stop-n-go fuel mileage is suspiciously low (17mpg in winter w/ my lug wheels mounted), which really costs me for my relatively short daily commute into the city. Vehicle weight, inertia don't explain that well enough, so I suspect 'foul' play. That technique could also provide benefits of more open exhaust, which diesels are known to like. |
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Replying to: siberia (Feb 11, 2007 5:17 am) 
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Replying to: caribou1 (Feb 11, 2007 9:23 am) I enjoyed you explanation especially, "asking for a post injection to re-establish a better catalyser efficiency by changing it's temperature with a 'cloud' of unburnt fuel that will produce heat once in the catalyser element." I believe this is new information to the forum. Indeed, there is boost pressure when EGR flows its gasses into the intake confirmed by direct observation of boost pressure and air inlet temperature. It is only under certain conditions that there is not.  Under hard acceleration or heavy load there is high boost and the EGR valve is in fact closed or reduced. However, when traveling at 55 mph and 2,400 rpm with overdrive locked out there is high EGR flow and low to moderate boost. As power is applied the AIT drops and the boost climbs, thus EGR flow is reduced. Other than when coasting, there is no time when boost is not observed. As long as the exhaust gas pressure is higher than the boost pressure EGR can flow even to extent that inlet flow is refereed by the EGR flow control valve for enhancement.
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Replying to: siberia (Feb 11, 2007 5:17 am) I should just give up on humor. I meant no insult to your abilities. By the way, my brother's nickname is "Bullhead".
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Replying to: siberia (Feb 11, 2007 4:14 pm) Not a problem. I just appreciated the long answer caribou1 provided, too ! |
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Replying to: siberia (Feb 11, 2007 4:06 pm) The use of the post injection is described in the Bosch training books, the "Yellow Leaflets" if I remember well: - the post injection occurs after the compression cycle of the cylinder and increases the combustion temperature from 200C up to 250C. - this unburnt mixture induces a temperature elevation of more than 100C in the oxydising catalyser to help consume all hydrocarbon compounds and solvable particles. Such conditions are used to rapidly build up the temperature in the catalyser when starting a cold engine. For those who read french, here is the article published by PSA, the leading local diesel engine manufacturer: http://www.psa-peugeot-citroen.com/document/presse_dossier/fap_1999_04_151017847- 928.rtf
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Replying to: caribou1 (Feb 12, 2007 2:30 am) Does the post injection provide any explanation of the black smoke during transition to hard acceleration or is the effect more subtile? I am in new territory here.  I read in a trucker's magazine recently where increasing the exhaust temperature prior to the turbo or retaining more heat in the exhaust gas increases turbo efficiency and fuel economy. A procedure was described to modify the exhaust manifold to do this - ported, polished and coated.
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I explained in earlier posts that after the F37 recall that it seemed that it would shudder and twice stalled when approaching a stop. It felt like when driving a stick, one applied the break without engaging the clutch. In fact, I was right. The tech thought that the tranny fluid level had to be checked while in neautral. Instead it had to be checked while it was in Park. So, I was a quart low. Instead of downshifting, it sucked air. Added a quart of fluid. Runs great. That's my update. Boiler |
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Replying to: siberia (Feb 12, 2007 3:44 am) The black smoke produced during heavy acceleration is usually a previous accumulation of "dry" soot the exhaust blows out because it is not well attached to the pipe or muffler. The post injection is intended to bring unburnt gasses into the oxydising catalyser so they burn inside the catalyser and make it warmer. The exhaust temperature is increased from 200 to 250 Celsius inside the cylinder by post injection, and this is before the turbo. Does this improve turbo efficiency: in principle yes because the higher the temperature, the higher the pressure ... Will the polished inner surface of the exhaust manifold improve something: I could think so, it should reduce the loss of temperature by contact with the outer wall with less turbulences, just like isolating it thermally but without the risk of burning through the gaskets 
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Just FYI, Jeep has finally updated their website (jeep.com) with info about the new Grd Cher CRD if you're interested....mileage is posted as 20 city 25 hwy for 2wd, 20/24 for 4wd. The lowest trim level it's available on is the Limited, and even then it's a $3k option! It looks like sticker prices will be in the upper 30's at a minimum, or about $8k more than a similarly equiped Liberty was. I live in the Dallas/Ft Worth area, and haven't found a dealer that has one yet, though the Patriots are starting to show up now.... Twocycle2
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