Well, usually I refuse to even drive my wife's XLR because it has had so many problems It just puts me in a bad mood.

Her car continues to knock/ping on light acceleration, regardless of the type of fuel used. It is very intermittent, but sometimes it sounds like a friggin rod is going to come out of the block! This is an ongoing problem that GM has given up on (and so have I).

Their brilliant diagnosis a year ago was that there was a carbon build up on the pistons because of cheap gas. I went round and round with them advising that the manual does NOT mandate the use of premium fuel. Sure, it "recommends" premium for optimum performance, but no where does it say you HAVE to use it.

They poured some kind of GM approved cleaner into the combustion chambers and let it sit overnight, then started it up to "burn" out the residual carbon deposits. It seemed to work initially, but soon it started pinging/knocking again......even though she was now using premium.

They then suggested that we run ONLY Shell premium gas because of some type of additive they have to defeat carbon build up. For the last 6 months she has complied, but my drive today shows that it is not doing anything.

GM has refused to do another decarbonizing treatment because they say that the use of low octane gas is the cause. I have told them about the manual and it's acceptance of low octane fuel, but they have flat out denied to pay for fixing this piece of Sh*! car.

I have been in/around the car business for 20 years now and have steered clear of anything GM because of how inferior they are. If this is GM's flagship vehicle it's no wonder they are bankrupt!:mad

What year model of XLR do you have?

I suggested you sell it as soon as possible to relieve your pain.

What year model of XLR do you have?


It's a 2005

Their brilliant diagnosis a year ago was that there was a carbon build up on the pistons because of cheap gas. I went round and round with them advising that the manual does NOT mandate the use of premium fuel. Sure, it "recommends" premium for optimum performance, but no where does it say you HAVE to use it.

:mad

Is there some confusion here? The manual states that fuels with increased levels of detergents are recommended. Fuel quality is not the same as fuel grade, the manual also says to not use MMT (so what is the position in Canada where I thought MMT was standard?).

Does anyone know more about what exactly the manual is getting at with respect to the use of MMT and minimum detergent levels?

(For those unfamiliar with MMT it is an octane booster. Its use in poor quality fuels to achieve the stated octane level is probably not a good recommendation for that fuel, but what is less clear is what effect it has in low concentrations in good quality fuels, which is the situation I guess exists in Canada?)
(See http://en.wikipedia.org/wiki/Gasoline#MMT and http://en.wikipedia.org/wiki/Methylcyclopentadienyl_manganese_tricarbonyl , note how these articles imply it is used in all (around 90% of) Canadian gasoline but the same article suggests that it might be bad for emission control systems.)

The studies seem to suggest that MMT is OKish for older vehicles (pre 1995 or thereabouts), not good for vehicles from 1995-2001 (so called Transitional Low Emission Vehicles (TLEVs)) and bad for vehicles considered to be LEVs which come in around 2001 onwards, with the tougher standards from around 2004 resulting in even worse emission problems. Anyone know more?

So, coming back to the original question, if using cheap gas that has had its octane rating achieved by the use of MMT or has the absolute minimum detergent level, then my reading of the manual is that there is a risk to the XLR N* engine. Thoughts? (I should add that I have no evidence at all that MMT has been used in this way, I am just guessing that it is a possibility.)

If carbon build up on the pistons is a possibility, why not get a boroscope and have a look?

Jonathan

Johathan:

Thanks for sharing your thoughts. I certainly learned something.

I have a XLR-V and I noticed today that there is a sticker inside the gas door stating exactly what fuel you should use. I am assuming that it is the same for standard XLR's.

I believe the V's require premium fuel and the premium was recommended for the regular XLR's, but not required.

I believe the V's require premium fuel and the premium was recommended for the regular XLR's, but not required.

The 2004 XLR manual page 5-6 states: "... However, some gasolines contain only the minimum amount of additive required to meet the U.S. Environmental Protection Agency regulations. General Motors reccommends that you buy gasolines that are advertised to help keep fuel injectors and inlet valves clean. If your vehicle expereinces problems due to dirty injectors or valves, try a different brand of fuel."

It also states in bold , do not use fuels containing methanol; and goes on to not recommend the use of fuels containing MMT.

Only the "do not use methanol" is in bold, but I would suggest that using minimum levels of detergent additives is also a bad idea in an engine as advanced as a N*.

My advice is use gasoline with high levels of detergents, it is worth it! These are premium vehicles and deserve decent gas.


Jonathan

The 2004 XLR manual page 5-6 states: "... However, some gasolines contain only the minimum amount of additive required to meet the U.S. Environmental Protection Agency regulations. General Motors reccommends that you buy gasolines that are advertised to help keep fuel injectors and inlet valves clean. If your vehicle expereinces problems due to dirty injectors or valves, try a different brand of fuel."

It also states in bold , do not use fuels containing methanol; and goes on to not recommend the use of fuels containing MMT.

Only the "do not use methanol" is in bold, but I would suggest that using minimum levels of detergent additives is also a bad idea in an engine as advanced as a N*.

My advice is use gasoline with high levels of detergents, it is worth it! These are premium vehicles and deserve decent gas.


Jonathan
Well said!!!!

Jonathan you peaked my interest with your interesting comments. I am not sure if you are in Canada but I am and was concerned about potential issues with MMT based on your research. I found MMT is not used much if at all in Canada. Many of the major refiners do not use it. Shell, Petrocan, Sunoco, Chevron etc. all commit to "top tier" standards which specifiacally exclude the use of MMT. For those who live or travel frequently in Canada stick to these major retailers and you'll be OK.

Jonathan you peaked my interest with your interesting comments. I am not sure if you are in Canada but I am and was concerned about potential issues with MMT based on your research. I found MMT is not used much if at all in Canada. Many of the major refiners do not use it. Shell, Petrocan, Sunoco, Chevron etc. all commit to "top tier" standards which specifiacally exclude the use of MMT. For those who live or travel frequently in Canada stick to these major retailers and you'll be OK.

That is good to hear. The article (published in 2002) I found is linked from Wikipedia and is (purportedly) published through an official Canadian investigation into MMT, it piqued my interest too. The article claims that some 90% of Canadian pump gas has MMT in it (though they make clear that they did not test _every_ source of gasoline), while in the USA the article reports that MMT is likely to be rare. I don't know the situation in Europe, though MMT is certainly available as an additive.

The front cover of the pdf report I read has the following text:

"
Final Report
Effects of MMT in Gasoline on
Emissions from On-Road Motor Vehicles in Canada
November 11, 2002
For:
Canadian Vehicle Manufacturers’ Association, and
Association of International Automobile Manufacturers of Canada
Air Improvement Resource, Inc.
"

If you could include your references as to the source of data that MMT is not in Canadian gasoline, that would be helpful. It is of course entirely possible that after the report I have quoted, the Canadian suppliers removed MMT. That would make sense!

Regards

Jonathan

That is good to hear. The article (published in 2002) I found is linked from Wikipedia and is (purportedly) published through an official Canadian investigation into MMT, it piqued my interest too. The article claims that some 90% of Canadian pump gas has MMT in it (though they make clear that they did not test _every_ source of gasoline), while in the USA the article reports that MMT is likely to be rare. I don't know the situation in Europe, though MMT is certainly available as an additive.

The front cover of the pdf report I read has the following text:

"
Final Report
Effects of MMT in Gasoline on
Emissions from On-Road Motor Vehicles in Canada
November 11, 2002
For:
Canadian Vehicle Manufacturers’ Association, and
Association of International Automobile Manufacturers of Canada
Air Improvement Resource, Inc.
"

If you could include your references as to the source of data that MMT is not in Canadian gasoline, that would be helpful. It is of course entirely possible that after the report I have quoted, the Canadian suppliers removed MMT. That would make sense!

Regards

Jonathan

MMT importation was banned 1992 in Canada and had to be permitted again as the North American Free Trade Agreement as Chapter 11 prohibits foreign bias and was sued sucessfully by an American oil company Ethyl Corp. in 1997after signing the agreement. I cannot find the exact date but according to one of Canada's well known environmentalists (now Leader of the Green Party) Elizabeth May in 2004 most of the major gasoline retialers in Canada were no longer using MMT.

http://www.aenweb.ca/content/mmt-its-way-out-canada

Here is a link to a website regarding top tier gas and agreement not to use MMT.

http://www.toptiergas.com/deposit_control.html

MMT importation was banned 1992 in Canada and had to be permitted again as the North American Free Trade Agreement as Chapter 11 prohibits foreign bias and was sued successfully by an American oil company Ethyl Corp. in 1997after signing the agreement. I cannot find the exact date but according to one of Canada's well known environmentalists (now Leader of the Green Party) Elizabeth May in 2004 most of the major gasoline retailers in Canada were no longer using MMT.

http://www.aenweb.ca/content/mmt-its-way-out-canada

Here is a link to a website regarding top tier gas and agreement not to use MMT.

http://www.toptiergas.com/deposit_control.html

Thanks for the references. Those pretty well sum it up. I note the first paragraph of the top tier specification specifically naming (and banning!) MMT:

"1.1 Retail Gasoline Performance Standards. The deposit control performance of unleaded gasoline conforming to section 1 of this document shall be met at the retail level in all grades of gasoline sold by a fuel company in all marketing areas of a selected nation. In addition, conformance to the standards shall mean gasoline sold in the selected nation shall not contain metallic additives, including methylcyclopentadienyl manganese tricarbonyl (MMT)."

Well, usually I refuse to even drive my wife's XLR because it has had so many problems It just puts me in a bad mood.

Her car continues to knock/ping on light acceleration, regardless of the type of fuel used. It is very intermittent, but sometimes it sounds like a friggin rod is going to come out of the block! This is an ongoing problem that GM has given up on (and so have I).

Their brilliant diagnosis a year ago was that there was a carbon build up on the pistons because of cheap gas. I went round and round with them advising that the manual does NOT mandate the use of premium fuel. Sure, it "recommends" premium for optimum performance, but no where does it say you HAVE to use it.

They poured some kind of GM approved cleaner into the combustion chambers and let it sit overnight, then started it up to "burn" out the residual carbon deposits. It seemed to work initially, but soon it started pinging/knocking again......even though she was now using premium.

They then suggested that we run ONLY Shell premium gas because of some type of additive they have to defeat carbon build up. For the last 6 months she has complied, but my drive today shows that it is not doing anything.

GM has refused to do another decarbonizing treatment because they say that the use of low octane gas is the cause. I have told them about the manual and it's acceptance of low octane fuel, but they have flat out denied to pay for fixing this piece of Sh*! car.

I have been in/around the car business for 20 years now and have steered clear of anything GM because of how inferior they are. If this is GM's flagship vehicle it's no wonder they are bankrupt!:mad

I'm down in the southwestern desert area and my car has no 'carbon knock issues'. We have all kinds of FUEL being sold here, so even with water not removed and octane levels well below advertized numbers, I have not had any problems. Our summers hover around 115/ 121 F for 3 to 4 months a year. The car adapts to the heat and the 'throttle loads' with 'very little pinging', only on hard runs. I would suggest you take your car to another dealer, and get a second opinion on your problem. As far as "steering clear of anything GM" you just don't know what you speak of. I've had a number of GM vehicles over the past 40 + years and have NEVER been let down. I still have my 1972 Corvette, and my 1979 Chevy Dually that has 497,000 miles on it, along with a 1995 Suburban with 139,000 miles on it. GM must have done something correctly, at one time or another. I have a 2005 Cad ESV that has been in TWO TIMES for warranty work, once for the seat and once for the rear A/C control module. Turn key car every day. GM cars and trucks have never let me down, sorry for your bad luck.

this is well after the fact but for future info. could this be miss diag. as a bad knock sensor??I'm down in the southwestern desert area and my car has no 'carbon knock issues'. We have all kinds of FUEL being sold here, so even with water not removed and octane levels well below advertized numbers, I have not had any problems. Our summers hover around 115/ 121 F for 3 to 4 months a year. The car adapts to the heat and the 'throttle loads' with 'very little pinging', only on hard runs. I would suggest you take your car to another dealer, and get a second opinion on your problem. As far as "steering clear of anything GM" you just don't know what you speak of. I've had a number of GM vehicles over the past 40 + years and have NEVER been let down. I still have my 1972 Corvette, and my 1979 Chevy Dually that has 497,000 miles on it, along with a 1995 Suburban with 139,000 miles on it. GM must have done something correctly, at one time or another. I have a 2005 Cad ESV that has been in TWO TIMES for warranty work, once for the seat and once for the rear A/C control module. Turn key car every day. GM cars and trucks have never let me down, sorry for your bad luck.

My 'engine noise' may be in the valve train and seems to be cured by a motor oil change. However, after I have about 800 + miles on the 'new oil' the noise comes back. I am not a fan of Mobil 1 but I use it when required. I have tried "W5- 30" and "W10-30" and the 'sound' still comes back. I do have a 'cooling problem' when I idle or stop and go with the A/C OFF though.