No voltage at air pump

Okay, I'm attempting my $20 replacement air pump fix on my 1997
850GLT. Basically, I found a surplus all-aluminum 12VDC blower, with
(surprisingly) very close to the right size input/output ports to the
original emissions air pump on the car.

I also bought a new air pump relay, just to be on the safe side. I
did not (yet) replace the SAS valve -- although since the original
motor was rusted out, I assume the valve on the car now is probably
bad.

Question: Upon starting the car cold, shouldn't I immediately be able
to detect voltage on the output side of the air pump relay? I mean,
regardless of whether or not I changed *any* other parts, shouldn't
the controller unit tell the relay to switch 'on'?

I'm not getting anything...so what should I look at next? Is there a
vacuum line that tells the controller to switch the relay on? Is the
bad SAS valve the culprit? Or something else?

Thanks,
Randy

 

On my '98 V70, the air pump doesn't start immediately on cold start - it
starts about 30 sec. later. (My air pump is noisy, and has been for
more than a year, so I can hear it even with the windows closed.)

You're correct in your assumption about the controller turning the relay
on.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Mike...thanks...I'll be more patient and wait 30-60 seconds to see if
any voltage shows up on the output of the relay.

Which assumption was I correct about, for the controller? That it
ought to be switching the relay regardless of the condition of the SAS
valve -- or that there is a vacuum line that tells the controller to
switch the relay?

If I still can't get the pump to run, I next need to figure out if I'm
dealing with a vacuum/mechanical problem - or an electrical problem
(with the controller).

Thanks,
Randy

 

The details on the 850 are a little different than my V70, but the
execution is the same. If the fuel computer decides that the air pump
is necessary, it turns on the air pump relay which applies power to the
pump, and opens a solenoid valve (aka controller) that allows vacuum to
reach the SAS valve. This vacuum opens the valve, allowing a path for
the air from the pump into the exhaust system. So the controller works
in parallel with the relay, it doesn't "control" the relay.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

<snip>

After reading this thread, I've started noticing when my 1997
850GLT runs its air pump. It never seems to turn on until I
start moving down the driveway. Waiting a bit doesn't seem
to matter, and revving the engine a bit doesn't seem to matter.

 

That's an interesting point... I NEVER start my car and just let it
idle. My pump is noisy and has been for about a year, it comes on when
I'm about half way down (in reverse) my 80 foot long driveway.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Well...I finally concluded my experiments with replacing the stock air
pump (which had rusted/seized), with a cheap generic air pump. Here's
what I learned:

1. You guys are right - the air pump isn't called for until the engine
has been running for a few seconds (maybe a minute?). I think it also
depends on outside air temp, humidity, etc. A local tech told me he
also thinks the pump might come on during various driving load
conditions, but I haven't been able to confirm that.

2. You really should replace the SAS valve when doing this job, and you
need to check the control solenoid (easy - just blow through it as you
connect/disconnect it from a 12VDC supply to see that it opens and
closes correctly).

3. You need to check the vacuum line from the control solenoid to the
SAS valve. Mine seemed very brittle and constricted. I couldn't tell
if it had contaminants inside it or not, but it seemed to be hard to
blow through. The end near the SAS valve was very brittle and falling
apart. I replaced it with generic vacuum line. If you do that, you
need to carefully route it so you don't have any sharp bends or kinks.

4. I replaced the relay, which was a waste of money. I should have
tested the original relay first (there should be about 800 to 1000 ohms
of resistance between the small control input and the +12V input). I
guess I have a spare relay now...

I ended up not replacing my SAS valve - instead, I ground the "lid" off
of it, and took out the spring mechanism, which makes the valve's
internal air path permanently open. This is bad, since it allows
exhaust gas (and moisture) to leak back into the new air pump, but I'm
going to experiment with relocating the air pump near (and above) the
valve, to see if it minimizes the amount of moisture which collects in
the hose. This will be tricky, since I don't want it to cook from the
heat of the exhaust, either. The new air pump is all plastic, so
leaking moisture isn't as big a deal as for the stock Volvo pump.

5. If you are going to try this, you need a replacement air pump that
is fairly powerful. First, I had bought a small surplus 12VDC blower
-- it didn't produce nearly enough CFM or velocity. It wasn't even
strong enough to overcome the positive pressure from the exhaust.
Next, I ended up going to K-Mart and buying a $15 air matress inflator.
Problem with that one is it is 6VDC and has rechargable batteries.
So, I had to replace the motor's switch with a small relay. It's kind
of funny, I have to periodically recharge the batteries in my secondary
emissions air pump now! This is silly, of course, so I sent away for
an Intex "quick fill" 12VDC inflator (from www.rei.com). Looks to be a
true 12VDC motor.

Once the new pump arrives, I'll try relocating it closer to the SAS
valve, and see how that all works out. If not, I'll end up replacing
the SAS valve.

So far, I've spent $90 on this project (if I didn't buy the unneeded
relay, would've been $50). Someone else doing this the right way from
the beginning should be able to get away with under $20 just for the
correct pump - assuming that breaking the top off the SAS valve and
leaving the air path permanently open works out okay.

The replacement Piermont original pump motor is something like $275
(probably $425 if you buy it from Volvo).

I had to have the car inspected yesterday (including the OBDC-II
connection for diag codes and emissions check). Passed!

-Randy