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Have you checked your Secondary Air Pump Lately?

SilverFoxDan

Member
Joined
Sep 19, 2015
Messages
12
Location
New Hampshire USA
Corvette
1993 Quasar Blue Metallic
Applies to 1992-93 C4's 5.7L Vin 8 that have electric Secondary Air Pimps

Part of the restoration of my '93 included pulling the secondary air pump (in the compartment below the left headlight). Found a corroded fuse... seized motor and a high water mark inside the pump housing. I should mention that the car did not throw a code (don't think there is one on this year) at any time. This pump normally comes on with a cold engine to pump O2 through the exhaust and catalytic systems (heats them up) so the rich mixture at start-up is burned more efficiently. Having a dead one will stress your catalytic converters and expel excess "bad stuff" out the pipes.

I was able to free up the motor (silicone and WD-40 soak) for now and I also drilled a 3/16's hole in the bottom of the pump housing to allow water to get out if any gets in going forward. I also tested the air flow before and after and this hole does not affect the air flow.

Notes:
1.
My pump in its restored state draws 17 Amps when running and puts out about 47 CFM. A Crude method to test air flow is to tape a 30 gallon garbage bag to the output and time how long it takes it to fill. In my case, it took about 6 seconds. To calculate, I used a solar air flow collector formula I picked up sometime before I hit my head and forgot where I found said formula. Anyway, you need two values:

Value1 = bag size * 0.155557
Value2 = 60 / # of seconds to fill bag
cfm = Value1 * Value2

My values:
Value1 = 30gal * 0.155557 = 4.66671
Value2 = 60/6 seconds to fill = 10
So... CFM = 4.66671 * 10 or about 47CFM

2. Pump comes out easily: Two bolts come totally out on the front (headlight) side of the pump bracket and one bolt that you just have to loosen up on motor side (forked bolt hole). Two hose clamps and two electrical connectors later and the pump is out. You can finger-spin the impeller with a good motor or hook it up to a battery watching the polarity of course.

Maybe the same guy who drowned my Opti-Spark also did in the pump. Rest of exhaust system (one way valves.. etc) seem ok.

By the way, I tried to price a pump from O'reilly and they called the company that used to rebuild them. O'reilly was told they would take the broken one in and, for $164.00 would look at it to see if they could fix it. If they could, it would generally be for a price above the 164.00. I tried Autozone and Napa and, even though they listed them as available on their web-sites, calling them got me pretty much the same answer. Since I got mine working for now I stopped looking.

Good luck with yours.
 
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Loubiere

Member
Joined
Nov 18, 2013
Messages
24
Location
Plano
Corvette
1986
Secondary Air Pump

What does this pump do? Which C4's have one?
 
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SilverFoxDan

Member
Joined
Sep 19, 2015
Messages
12
Location
New Hampshire USA
Corvette
1993 Quasar Blue Metallic
What does this pump do? Which C4's have one?

Short answer is: To get oxygen to the catalytic converters so they can balance their chemical reactions and turn very bad stuff into not so bad stuff. Really amazing devices.

Longer answer is: The pump is controlled by the ECM which supplies a ground to the pump relay (pin F). This relay is mounted on the air pump case.

To determine if the pump should be on, the ECM calculates engine/exhaust temp, O2 sensor data in the exhaust stream as well as fuel mixture. It then determines if it needs to get oxygen to the Catalytic converters to start their chemical reactions. Car designers know that the converters are starved for oxygen at startup and the pump supplies this O2.

The pump is normally on for only a few seconds as the system balances itself pretty quickly. The pump then shuts off and stays that way for most of the time, As I say, it is usually a cold engine and a stagnant exhaust system that is the key factor. Catalytic converters can actually bank excess O2 away for later use (banked when the engine runs lean, released when it runs rich).

At least on the '93, this is an electric pump. I don't have the tech. manuals for any of the other C4's so really can't say which ones have this design. Easy to tell though... just pop the hood and look in the forward compartment under the left-drivers side headlight. If you see a black, conical shaped unit aft of the horn that has a square relay on top and there is a 1 inch (toward the engine) and 2.5 inch (toward the radiator) hose setup you have one.

Really easy to take out and test although there are other ways (grounding the relay coil) but I tend not to push my luck in that area unless I am sure and there is no other way. You can also listen to the pump at startup (they do make noise when running) but, because the ECM knows things we don't including the fact that you are trying to hear the pump so it keeps it off on purpose :). The fact that you can't here it does not make it bad.

Best to yank it and give the impeller a spin with your finger. You can even put +12 and ground to it (+ to Black-white and - to black ). It will torque kick-spin a little at start-up so don't let it jump off the bench. Really, REALLY efficient blower as far as amps VS CFM and I have tested many in my day (why it is hard to find a substitute).

Hope this helps. As I say I can't find a check engine code condition for a locked up pump other than a "possible" link to an O2 sensor report on this model-year. Later cars certainly coded this item though. It could be a silent problem but, a problem none the less. Electric motors WILL eventually fail, for sure.
 
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Loubiere

Member
Joined
Nov 18, 2013
Messages
24
Location
Plano
Corvette
1986
Secondary Air Pump

What is confusing me is the term secondary. I know that my 86 has a "primary" belt driven air pump. Is there a secondary pump?
 

SilverFoxDan

Member
Joined
Sep 19, 2015
Messages
12
Location
New Hampshire USA
Corvette
1993 Quasar Blue Metallic
What is confusing me is the term secondary. I know that my 86 has a "primary" belt driven air pump. Is there a secondary pump?

Hi and thanks for the question. Looks like GM decided to use the term "Secondary" meaning an alternate source of O2, Engine being the first and attached air pumps as the second. According to Chilton's 84-96 Corvette repair manual, your belt driven type is also a "secondary" air pump.

My world is confined to the '93 so I tend to think in those terms. Sorry, I'll be more specific in my titles going forward.

You only have one pump. C4's made between 1992 and 1993, 5.7L (VIN8) have the electric pump I am referencing. Chilton's says that C4's either side of these dates are mechanical.
Guess that's why I am finding it hard to locate a replacement since a two year span of Corvettes Ain't much demand for the secondary market. Finding a replacement electric motor with the right AMPs and RPMs + form factor may be a challenge us 92-93's may have to face going forward. But... such is the challenge we all face at some point.
 
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