Reader Question: Water in the Intake?

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Here’s the latest reader question, along with my reply!

Brian asks: When I was a kid, my dad would sometimes dribble a little water into the open throat of the carburetor – engine running – to steam clean the carbon off the valves. Is this still valid with fuel injected cars?

My reply: The question is whether it’s advisable. Adding water to the intake stream could result in problems downstream – O2 sensors, catalytic converters. Anything that upsets the A/F ratio or alters combustion or changes combustion byproducts can have that effect and it can be an expensive effect. O2 sensors – many cars have two or even four – can cost $75 a pop and a new catalytic converter – many cars have two or more – can cost several hundred a pop.

Also, is it necessary? Modern engines burn more cleanly because their EFI systems meter fuel more precisely. Is there reason for suspecting carbon build-up and incomplete sealing of the valves because of it?

Have you done any diagnostic tests to confirm?

Finally, it is much less practicable and may be not possible given the way modern PFI system are set up. They are dry flow – meaning, the intake is for air only. Not liquid – gasoline or water. And the only place to introduce water in a PFI-equipped car is near the air intake tract – as opposed to down the venturis of the carb and a straight shot (along with the vaporized gas) through the intake runners to the intake ports.

I personally wouldn’t mess with this. If you have a carbon build-up issue, try using fuel system detergent (added to the gas). And try using a brand of gas that has a really good detergent package, such as Techron or Shell.

. . .

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  1. What Eric says. As long as the car is driven at least occasionally at highway speeds, it won’t develop carbon build-up, unless there is something seriously wrong with it. A bottle of Chevron Techron in the gas tank can help clean fuel injectors and valves without harming anything- and if for any reason the fuel system should need a good cleaning, some mechanics have pressure cleaners, and will generally service most cars with it for under $150…..but if it ain’t broke…I wouldn’t fix it; and if it is broke…fix it properly.


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