2007 Tahoe detonation

[ASJT3]

2007 Tahoe with 5.3L. Under medium to heavy load with light/medium throttle the engine has pretty bad detonation, give it more gas and it goes away.

No codes except for O2 sensor, which I'm pretty sure is because the cat converter has gone bad (replaced both sensors in Bank 1 and watched oxygen trace, cat doesn't appear to be working on driver's side).

I replaced the knock sensor about 7 years ago when it went bad and threw a code. Can't figure out what could be causing the detonation, any ideas?

-Alex

[maxwedge]

Could be the egr valve is not functioning, or the passages are plugged up, under the right conditions this can cause some light detonation.

[ASJT3]

Originally Posted by maxwedge

Could be the egr valve is not functioning, or the passages are plugged up, under the right conditions this can cause some light detonation.

Correct me if I'm wrong, but I don't think the 2007 5.3L has EGR?

[maxwedge]

I was not sure either, but I googled your truck and it listed an egr valve. Check it out.

[Blue Bowtie]

If possible, try running more ethanol in the fuel to see if it masks or band-aids the detonation.

[ASJT3]

Maxwedge, according to my research on the 'net the 2007 5.3L does not have an EGR. Additionally, I cannot find an EGR valve for this engine on the parts websites.

Blue Bowtie, what will this tell me? FYI, I've occasionally run MMO and chevron thru the fuel to treat the system.

[Blue Bowtie]

What that can do is to increase the effective octane to help suppress compression-ignition of the fuel mixture. It also burns cooler, providing a similar philosophy to that of recirculating some exhaust gas (EGR) to hold combuston chamber temperatures down.

Back in the piston engine aircraft days they would run a water/alcohol mixture to suppress detonation in two-stage supercharged engines running many pounds of manifold pressure. That's how a larger air-cooled radial engine making 2,000+ HP for hours on end could intermittently make nearly 3,000 HP until the alcohol mix ran out, all without destroying itself.

[ASJT3]

Originally Posted by Blue Bowtie

What that can do is to increase the effective octane to help suppress compression-ignition of the fuel mixture. It also burns cooler, providing a similar philosophy to that of recirculating some exhaust gas (EGR) to hold combuston chamber temperatures down.

Back in the piston engine aircraft days they would run a water/alcohol mixture to suppress detonation in two-stage supercharged engines running many pounds of manifold pressure. That's how a larger air-cooled radial engine making 2,000+ HP for hours on end could intermittently make nearly 3,000 HP until the alcohol mix ran out, all without destroying itself.

Thanks. Taking this a step further, what will this tell me? Will this indicate that a component may be going awry that causes this detonation? This only started about 2000 miles ago.

[Blue Bowtie]

If increasing the octane and cooling the combustion suppresses the pinging, that could indicate cooling, carbon deposits (hot spots), ignition, or valve timing issues. If it doesn't help reduce detonation, we'll have to focus elsewhere.

FWIW, Marvel probably is doing nothing for the engine. Chevron (Techron) injector cleaner can be beneficial. it's once of the very few injector cleaners in a bottle that can actually work.

If you want better injector pintle and upper cylinder lubrication, move down the aisle from the MMO in the supply store and pick up some two-stroke oil instead. If everything else is working properly, it will have negligible effect on the oxygen sensors and cats. That oil works well enough to completely lubricate an engine, from main journals and rods to rings, so it can certainly get the job done in the fuel system and valves/rings.

[ASJT3]

Originally Posted by Blue Bowtie

If increasing the octane and cooling the combustion suppresses the pinging, that could indicate cooling, carbon deposits (hot spots), ignition, or valve timing issues. If it doesn't help reduce detonation, we'll have to focus elsewhere.

FWIW, Marvel probably is doing nothing for the engine. Chevron (Techron) injector cleaner can be beneficial. it's once of the very few injector cleaners in a bottle that can actually work.

If you want better injector pintle and upper cylinder lubrication, move down the aisle from the MMO in the supply store and pick up some two-stroke oil instead. If everything else is working properly, it will have negligible effect on the oxygen sensors and cats. That oil works well enough to completely lubricate an engine, from main journals and rods to rings, so it can certainly get the job done in the fuel system and valves/rings.

Awesome, thanks. Not sure where to get more ethanol, should I just try using premium fuel?

[Blue Bowtie]

You can try to run the tank fairly low then add about a half tank of premium.

Alternately,if there is a place near you which offers E-85, you can do the math and concentrate up to about 20% ethanol in whatever fuel load you may have. Bear in mind that not everything sold as "E-85" is 85% ethanol, especially in winter blends. You may have to ask the retailer what the present mix is.

And although it has not been mentioned previously, if your Tahoe is a FlexFuel version, you can run E-85 straight up, and see if that reduces the detonation. That alone could be very revealing about the condition of the chambers, fuel sensor, programming, and function.

A quick check online seems to indicate there are only 3 places around Baltimore that sell E-85. Around here about 10% of stations sell it, but this is corn country and the Big Chiefs like ADM and Adkins distill it by the train-load in the region.

[Stealthee]

Be careful with the E85 though. If your Tahoe is not Flex Fuel it would not be wise to use it. High ethanol content will deteriorate lines that are not rated to handle it.

[Blue Bowtie]

Originally Posted by Stealthee

Be careful with the E85 though. If your Tahoe is not Flex Fuel it would not be wise to use it. High ethanol content will deteriorate lines that are not rated to handle it.

Correct, and an important precaution. Thus the advice to limit concentration to 20% if the vehicle is not designed as FlexFuel. The "regular" types are only rated for E22 as is commonly found in Central and South America.

[Stealthee]

Originally Posted by Blue Bowtie

Correct, and an important precaution. Thus the advice to limit concentration to 20% if the vehicle is not designed as FlexFuel. The "regular" types are only rated for E22 as is commonly found in Central and South America.

I personally wouldn't even use E15 in something that isn't Flex Fuel just due to the issues I know ethanol could cause.

[Blue Bowtie]

I have since 1976 without problems, other than one plastic float in a '67 Pontiac 2GC carb dissolving very early on. I even experimented with E85 in a '96 Sonoma for about a year with no problems other than reduce fuel mileage (even with the timing altered in a reflash).

By 2007, materials compatibility should not have been a problem for anything domestic since ethanol had already been around for 40 years in Canada and the U.S.

And even older vehicles can use it if they were built with any kind of robustness. For example, all of these run on blended fuel, just like they were designed before WWII:




And they run about like this on gasoline, kerosene, alcohol, or mixes:

http://www.wwdsltd.com/files/1936DeereB01Running.mp4