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Classic Car Service
Classic Car Service, Dealership Svc. Mgr.
Category: Car
Satisfied Customers: 4911
Experience:  Over 30 years experience in the automotive field
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I bought a 2006 Bentley Arnage with 94,000 miles. I replaced

Customer Question

I bought a 2006 Bentley Arnage with 94,000 miles. I replaced a leaking radiator and engine still misfires. Mechanic claims 2 low compression is now up after adding additive to clean built up carbon. Car still misfires, he claims he will have a Bentley Engine Programmer for Philly come and reprogram engine and 50/50 chance of resolve. Should I trust him? Do Bentley engines need a special programming? I am not sure if I will get result after trial and error expense or get rid of the car I just purchased.
Submitted: 2 years ago.
Category: Car
Expert:  Mike S. replied 2 years ago.

Personally, I have never worked on a Bentley, but I have no idea who told you simply replacing a radiator or fixing a cooling system leak would fix a misfire condition unless of course the coolant leak was a cylinder head gasket. I would assume the carbon he was trying to clean up was on the piston rings and that was the cause of the misfiring, (poor compression). Also, I don't believe programming is going to get rid of a misfire if it was due to carbon on the piston rings in the first place.

Can you give me any specifics on which cylinders were and are now misfiring? Can you tell me any before and after compression readings?

Customer: replied 2 years ago.
Your answer is not satisfactory and I said rad was replaced due to leak and NOT to solve misfires. May I speak to someone who knows Bentley or Rolls Royce.
Expert:  Mike S. replied 2 years ago.

Sure, I'll opt out.

Expert:  Classic Car Service replied 2 years ago.

Hello. Different expert here. I have quite a bit of experience in British cars. I am inclined to agree with my colleague Mike. There is no 'special programming' that can be done to improve misfire conditions. A scan would isolate the number of misfires during a drive cycle, which would then be used to perform specific diagnosis. If you have a low compression situation, there is very little one can do with aftermarket products and additives that claim to restore compression. Compression is created by a positive seal between the piston rings and the interior cylinder walls. If carbon is built up, the can cause the rings to wear the interior surface of the cylinders. Some products will lessen the carbon buildup, yes, to a point, but once the interior walls are worn, you have excessive clearance (we are talking about thousandths of an inch here). If the combustion pressure is low, there is not enough pressure to properly ignite the mixture, ie you get a misfire. A good mechanic should have performed a compression test before doing anything else. Mechanics these days rely too much on computers and scanners. They seem to neglect the basics of automotive diagnosis. In order to have a proper engine cycle (intake/compression/power/exhaust), there needs to be proper engine timing, fuel, spark and compression. Modify any of these, you get misfires. The "Programmer' you mention seems very fishy to me. Once might be able to 'reflash' the computer with an updated engine management program (this is done periodically when the manufacturers improve the computer programming), but would only be viable if you had a cvheck engine light on or something that pertained to something that the computer controls. A carbon issue will never be corrected by a reprogramming or a reflash of the computer. A carbon issue is strictly a mechanical issue. The recommendation here is to have your guy do a compression test. It would be advisable for you to be present and watch. Have him show you the reading on each cylinder. Your readings should be way in excess of 150-160 lbs minimum. If you get reading like this:

150 150 150 150 175 110 150 180

This shows you have very low compression in one cylinder. the 175 and 180 show proper compression. The 150s show that these cylinders have lower than optimal compression. If the reading that he shows you resemble this table of compression pressures, you are looking at a really expensive engine repair.