2004 4.0 DII w/ 40k km
Lately SAI will sometimes run for few seconds while driving, never before. Is this normal or something I should worry about?

 

Will wait for the answers with you. This wouldn't be "normal" per D&O in manual. Hopefully others with more experience will fill us in.

Timely ? since earlier this evening waited several minutes to make a LH turn and my SAI pump cycled on and off several times. Once back home checked for codes/pending and none found.
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It's not normal, as far as I know. Mine did the same before one of the components in the SAI system gave up the ghost. Now, it's silent at start up (as in: it doesn't work anymore).

 

Thanks, may be something to look forward to. Once ghost left were there any drivability issues, codes or SES warning?
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I think the coolant temp sensor on the outlet of the radiator controls SAI pump operation. Check connection is securely fastened to the sensor input.

I've experienced similar. Truck is completely warmed up and Boom pump kicks on for a few seconds. I can't explain it.

 

Ok, to under what the system is doing, it helps to know the system, its purpose and a little information on how it works.

The Primary purpose of SAI is to get your Catalytic converters up to temperature to burn of the un-burned fuel in the exhaust. This is first and foremost. By-product of that is the car enters closed loop faster. The design of the system may change from car to car, but its still the same principal across the board.

It uses a couple of sensors, takes readings from O2 sensor primarily and temp sensors secondarily. Using those readings, the ECU makes a determination on if you're running Rich and turns on the system to burn the un-burnt fuel from the exhaust. When the O2's start reading the "pre-determined voltage" it shuts the pump down.

So, if the pump kicks on when the truck is warmed up, its probably thinking you are either A - running too rich and needs to burn cats a little more. or B - the cats have cooled down and require a little "zip" to get back to operating temperature.

If you think option A may be your problem, you may want to check spark plugs, air filter, maybe even Mass Air Flow sensor operation.

If you think option B - you can check you O2 sensors for operation, how fast the are switching. The may be getting a little slow.

If your system is silent at startup, you may have a blown fuse or a dead pump.

But this is the information I vaguely remember from tech school 7 years ago, so your results may vary.

 

No drivability issues. SES light is on, though. I forgot what the code was, but had to do with one of the valves in the SAI system.

 

Thanks good to know if it craps out during my watch.
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