CJWessing

Hey guys,

After driving at speed (i.e. highway) and coming to a stop, I depress the clutch and the voltage drops a couple seconds later and then goes back to normal. I can also feel the engine stutter/revs drop a bit. Anyone have any idea what might be causing this? Anything to worry about?

Thanks,
Chris
2002 Targa, 82k miles

Ahsai

Did you feel your a/c compressor or SAI pump kicked in?

CJWessing

I made sure to have the A/C off, but I did hear a faint pump sound come on at the same time and lasted for a few seconds, never noticed it before tonight (probably because I had my radio off for the video). What's an SAI pump?

Ahsai

SAI pump is the secondary air injection pump that's next to the coolant tank for emission. When the engine is not hot enough like after a highway drive, it may come on for a few seconds. It sounds like a handheld vacuum. The pump also comes on durung cold start for 30s to a minute or so.

Btw, do you have a 160F low temp thermostat.

CJWessing

Not sure if I have a 160F low temp thermostat. Temperature seems to be fine, runs stable right around the 180F mark.

Ahsai

Your temp should be fine with or without the low temp thermostat. With the low temp thermostat though, the engine will spend a little more time at the lower temp, say 170 or so hence the SAI pump would turn on a little more frequently.

With a/c and low beam on, if the voltage is 13v or higher, that means your cables and alternator are fine. If the vdrop only happens when the SAI kicks in, the SAI may be drawing too much current, which you can verify with a dc current clamp meter. The SAI draws about 20~30A if Memory serves.

CJWessing

This is the first I've heard of SAI trouble, is it a common fault? If it's drawing too much power, would that mean it needs to be replaced? Or ok to live with it like it is?

Ahsai

Too early to condemn it though. It's just my speculation so far until someone goes to measure the actual current drawn and also confirm the vdrop is indeed due to the pump. I would say just monitor and wait for now if you don't plan to diagnose it further.

The vdrop is not common but a noisy pump is.

CJWessing

Found a DIY page for replacing the SAI, looks like it's fairly involved to take out. Do you know if I can test the current without removing anything? If so, how do I trick the SAI into turning on?

Ahsai

You can activate it using Durametric and put a dc current clamp on the black cable that connects to the "+" jump start terminal in the engine compartment above the a/c compressor. That cable connects the alternator to the starter then to the "+" jump start point then to the battery.

If you don't have Durametric, you can just unplug the SAI pump and supply power to its two pin terminal directly using a jump start cable from the battery. Make sure you get the polarity right though before applying power.

You can also hear if the pump is struggling to start, in which case a big initial current will be drawn.

Ahsai

Btw, removing the SAI pump is very simple. Just two screws and one nut then one hose, not even a hose clamp. Photo in step 4 here http://www.georgeco.org/?p=934

RPMulli

What makes you think it's the SAI? I'd check your voltage regulator on the alternator and make sure your battery has the proper charge.

Is the engine at operating temp when this occurs?

CJWessing

Yup, only happens when I pull off the highway and the engine is up to temp.

Ahsai

I checked my notes, the SAI pump draws ~20A. Next time when it happens again, after the voltage swings back to 14v and the SAI pump has stopped, can you turn on the low beam and rear defroster simultaneously and note any effect on the voltage? low beam + defroster draw about 25A total so that would be similar to the SAI pump load.

If you see a similar dip in voltage, that means you have some probles in the alternator/regulator/cable. If not, the SAI pump is more suspicious.

When cranking in the morning, does the voltage drop BELOW 10v? That will tell us how healthy your battery is.

CJWessing

I get a significant drop (to about 13v) when I turn on the low beams and rear defroster at the same time, and drops a little lower (about 12.5v) when I come off the highway. I think the voltage is fine when I crank it in the morning, will check tomorrow.