2002 LQ4 excessive exhaust moisture P0300B

[ziptow]

Picked up a 2002 C3500 dually with 88,000 miles and 6.0 LQ4 engine. Going to part it out and use the engine/trans for a street rod project. Noticed that when it's first started it runs a bit rough (not bad) and the exhaust doesn't have moisture out of the exhaust.

 

As it gets up to operating temperature the moisture becomes excessive (in my opinion) but doesn't smell like anti-freeze. The engines seems to run OK but has a slight rough idle. It's not on the road but I've been monitoring the coolant tank level driving it around on my property and it doesn't appear to be loosing any coolant. The oil is clean with no signs of water contamination.

 

As the outside temps warmed up this week (above freezing) the truck began running rough and coded P0300B (random multiple misfires). Figured I might have water in the tanks that was previously ice and melted with the warmer temps mixing water with the fuel.

 

- The truck ran decent in cold weather...but did have excessive moisture out the back only when warm.

 

A couple days ago I dropped in (2) cans of water remover and 5 gallons of fresh fuel, cleaned the filter and did a fuel sample...could not see any moisture...but it did have water remover in it.

 

Like I mentioned - going to remove the engine anyway but it would be nice to isolate the problem before then if possible.

 

One question I had was if it is possible that the coolant could be leaking into the throttle body via the throttle body base coolant lines? If it had a bad head gasket normally one or two cylinders would misfire...this engine has multiple "random" codes. And BTW the P03300B codes take a long time to appear after clearing...it's not a hard code at all. Must be a really small leak.

 

Could check the plugs for water bleaching...but was curious about the throttle body coolant leak potential and if you folks had a similar situation with your LQ4.

 

Thanks

[Jsdirt]

Water pours out both my tailpipes like a faucet if I let it sit and idle in pretty much any temp that isn't summer. The amount depends on the amount of slope that I park on. Nose down, even slightly, builds up quite a bit. Guess it's because the water doesn't pool where the drain holes are in the muffler. Just part of the catalytic conversion of the gasses. Even my '86 Grand Marquis does this - probably even worse than the truck.

 

Even if there's no cat, you'll still get a little moisture - just part of combustion. Not as much as with a cat, however.

 

 

 

Randoms are a pain in the ass to troubleshoot. Normally they result from intake gasket leaks, ignition problems, or any number of failed or dirty sensors. The problems could be many - that's what makes it a royal pain.

[ziptow]

Like I mentioned the codes didn't start until the weather warmed up above freezing, water in the tank will freeze up and lay on the bottom as a solid. Putting in the water eliminator and cleaning the filter did help...it runs good again.

 

Since this is my first LS engine maybe the exhaust moisture is the norm that I'm not familiar with. I may just by-pass the throttle body coolant line since I'm not going to use them in a street rod anyway. Tempted to experiment with some BarsLeak since I have a supply of it and the engine is coming out anyway.

 

With the LQ4 any "specific cylinders" have a history of destroying head gaskets? I know with the old Astro vans with 4.3, the rear two cylinders (4&6) on the passenger side always blew the head gasket.

[Jsdirt]

I hear these LS's are pretty robust. The electronics are hit or miss, but mechanically (except for AFM engines) they're solid. Never heard of anyone blowing head gaskets on these.

 

They did have a crap run of heads for a few years that cracked, though - google "GM Castech" for hours of reading ...

[00Silverado4x4]

Can you get a video of the water run off from the pipe? What one may call excessive the next may say is normal. My truck also has quite a bit of moisture run off while running but I personally don't find it excessive. I'd be more worried if it wasn't there.

[Doug_Scott]

Something that may help in your diagnosing this issue is a better understanding of how water and fuel interact. First is the obvious, they don't mix. Water will always be in the bottom of the tank. The fuel pick up is a solid thing, it always pulls liquid from the same level in the tank, that being near the very bottom. If you have any water in the tank, it will be completely below the fuel within minutes of stopping motion, so over night it will only be at the bottom. If there is enough water in the tank, that is all that will be pumped to the injectors, engine will not run.

 

As others have already stated, water vapour is part of normal combustion, with the more complete combustion producing the most vapour. A well tuned and running engine will put out a good amount of "steam" in colder temps. On very cold days it is sometimes hard to see if you are following one of those cars. Those are also the days that sewers put out "steam".

 

If you are only driving this truck around your property are you actually getting it up to any speed? Short, slow trips are not good on engines. Head gaskets can "blow" in a few ways. One is to blow between two cylinders that only allows combustion gases to cross over to the other cylinder, fouling up combustion on both cylinders, but no coolant is leaked. Another is for the gasket to start leaking from a coolant passage into a cylinder. Typically this means the only time coolant will get into the engine is after it is shutdown hot. The pressurized cooling system will push coolant into the cylinder. While engine is running, combustion pressures will increase coolant pressures and contaminate coolant with combustion gases. The last way is to have the gasket start leaking coolant or oil to the exterior of the engine. There are other combinations as well as some becoming a "flapper valve" where the gasket will leak in one direction only, and will seal when pressure is higher in the other direction.

 

I would begin by pulling the plugs and taking a look at them. Then do a compression test (you should do this before pulling the engine anyways just to save time later). As suggested above, search out the issues with the Castech heads, and double check what you have.

[ziptow]

Thanks guys...going to be busy for a couple of days and can't get to the truck...BUT...

 

If I had a specific cylinder (or two) with bad head gasket wouldn't the PCM detect misfires with those specific cylinders and not be random?

 

Again...I dropped in (2) cans of water remover...more than needed according to the directions...My thought is that any water that was in the tank is now suspended and diluting the raw fuel enough where it runs with occasional misfires and excessive water out the exhaust?

 

The truck didn't code during the freezing weather...just started as it got back in the 40 degree weather.

 

Will do some Castech head research tonight.