Random Fan Whine and Misfire

[Wahugg]

Hello all,

Today after a bowling tournament, I went out to my truck to turn it on, and it took an oddly long time to catch. Once on, there was an extremely bad whine. I varied the RPM and the wine did not change, and it did not change when i put the selector in Neutral or Drive. So I turned the car off and went out side to see if there was any fluid leaking, to see if the whine could be accounted for by something running dry. No leaks were detected and all the fluids were full.

I went back to turn it on and the engine caught like normal, but holy crap it was misfiring! Set misfire codes for Cylinders 2,4,5, plus a random misfire code. I reset them all and went to turn it on again and the same thing happened, but this time I gave it a little gas and wham! Everything smoothed out, whine went away, and no codes were set.

I have not been able to reproduce this. The only thing I can think off is the fan clutch was stuck on due to the cold weather. This might account for the hard cranking, but I have no idea on the misfire.

Any ideas?

Thanks

-Wahugg

 

[The_Roadie]

Fan clutch issues would have varied with engine RPM, as would any other rotating part like an idler pulley, tensioner pulley, PS pump, alternator, water pump, or AC compressor.

Could it have been an airflow whistle, like a stuck closed throttle body butterfly valve? That could explain your exact symptoms. How many miles since your last throttle body cleaning?

 

[Wahugg]

It has been approx. 16k since I have had the throttle body off and cleaned. I'll pull it off after work tonight and take a peak. Just in case this is not the source of my problem, is there anything else I might want to be looking at while I'm in there?

Thank you for the quick and helpful answer roadie

-Wahugg

 

[Wahugg]

Just got in from taking off the TB. Was a little dirty, but nothing bad at all. The same scenario as before did happen on the first start after the TB cleaning. A loud whine was present, well it sounded more like an muffled blower motor or vacuum this time. I pulled the fuse to the blower motor while I had the whine present to see if that was the source, it was not. Still no change with RPM or gear. The noise seemed to be coming from the Rear right of the engine block if you were looking down into the hood from the front.

Could it be the starter is not dis-engaging? I think if this was the scenario there would be a more nasty noise then what I am currently hearing.

Thanks for any help

-Wahugg

 

[The_Roadie]

If it sounded like a shop vac, that's the SAIS turbine air pump under the driver's seat. Should have nothing to do with driveability unless you have hose problems near the solenoid valve on the exhaust manifold.

Does it go away in 30 seconds?

 

[Wahugg]

No Roadie, it would stay on until I gave the engine more throttle, which would get rid of the misfiring totally, even when it revved back down to idle.

I did some research on the SAIS and a common code seems to be PO410, which I have not set. It seems from the general consensus that the one way check valve inside wears out so that water can flow back into the pump from the exhaust. It then could freeze not allowing the pump to move, making it pull excess amperage, causing the fuse or breaker to blow/trip, thus setting a code.

The freezing water that makes the pump inoperable could be plausible because the weather has been in the 20's and 30's all week, but wouldn't that make it so the pump makes no noise at all since it cant move, and set a code?

Also what is the SAIS exactly? Do you have any good diagrams of it or a good link to the description to the operation of it?

From looking over a few websites I gathered that there are multiple hoses going to it. From where or to where they go I have no idea, but could a loose or leaky hose cause a vacuum, or lack of a vacuum so that the engine does not run properly? Then when I rev the engine the engine moves and the leak stops?

I am just stumbling around here trying to think of a cause for these symptoms.

Is there anything I can do to confirm or rule out the SAIS?

Thanks for all the help

-Wahugg

 

[Wooluf1952]

Could it be the starter is not dis-engaging? I think if this was the scenario there would be a more nasty noise then what I am currently hearing.

-Wahugg

If the the starter motor failed to disengage, the pitch of the whine would change with the RPM's.

IIRC, someone on the OS, had a problem with the SAIS block connected to the engine. A bolt broke or loosened, causing a leak. That could cause a whistle.

 

[The_Roadie]

Pull front fuse #56 to disable the turbine pump. I haven't written a theory of operation here, here's a quick summary:

On a cold start, the PCM is in "open loop" mode where it has to predict what to use for an air/fuel ratio to get a clean burn, because the heated O2 sensor in the exhaust manifold isn't hot and getting good data yet. To pass an EPA emission requirement added in 2003, GM had to add the SAIS to blow a bunch of air past the combustion chambers into the exhaust manifold to act as an afterburner to heat up the O2 sensor. A solenoid valve opens on the manifold and allows a lot of air from a powerful turbine blower to get in there and hasten the onset of "closed loop" mode there the PCM sees good O2 sensor data. If you drive off before this process completes, the EPA forced GM to program a diagnostic on the SAIS system for later, when you're driging down the road. The turbine runs three times a few seconds apart, and the 30-40A current drain of the pump ends up dimming the lights if it's after dark, and a lot of folks get concerned about a flaky alternator or battery when it's just the SAIS diagnostic. If the diagnostic fails due to a bad solenoid valve, turbine pump, old O2 sensor, or wiring and a couple of relays, code P0410 sets. To check the system functionally on a cold start, pull the hose off the solenoid valve and listen for exhaust noises coming out of the valve. And a rush of air from the hose, pushed by the pump. The hose does collect a lot of water than can freeze and clog it or damage the pump, and the pump has a relay nearby that's exposed to a lot of under-vehicle gunk and it or its socket get flaky.

 

[Wahugg]

It turned out to be a bad pump/turbine. The motor had multiple dead spots and finally it landed on and just wouldn't turn over at all. It pulled excess amps, blew the fuse, and set an SES light. Replaced the turbine, fuse, and relay for good measure and the problems went away. I went ahead and put dielectric grease and shrink wrapped or electrical taped all connections to try to keep as many of the elements as I can out of there.

Took about and hour and a half total; most of it was sealing up the connections the best I could.

I hope this can help someone in the future.

Thanks for all the help

-Wahugg