I need to replace my fuel pump... I see them with secondary air and without secondary air. My question is... what is secondary air, and how do I know if I have it? Thanks for any help.

 

Secondary Air Injection







1 Engine Control Module
2 Secondary air injection pump relay
3 Secondary air injection valve control, Bank 1 and 2
4 Multi valve, Bank 1
5 Oxygen sensor, pre-cat, Bank 1
6 Secondary air injection pump
7 Multi valve, Bank 2
8 Oxygen sensor, pre-cat, Bank 2

A secondary air injection system was offered as an emissions control device in later revisions of cars with the MMS411A ECU (starting in late 1997).

General theory

The engine requires a relatively rich mixture for smooth operation on cold start. For this reason, the ECU operates in open loop mode with a fixed fuel map for the first 20 to 120 seconds of engine operation until the oxygen sensors have heated to operating temperature. Because of this, exhaust gases contain high levels of carbon monoxide and hydrocarbons after cold starts. The unburned hydrocarbons could be further oxidized, except there is no oxygen left after combustion. By feeding air into the exhaust manifold (secondary air), CO and HC are oxidized through afterburning at temperatures over 600°C to form water and carbon dioxide. The exothermal reaction also increases the exhaust gas temperature, which warms the catalyist more quickly.

To achieve efficient warmup operation, a high secondary air flow rate must be achieved within the first few seconds of engine startup, and the air flow rate must be maintained until oxygen sensor control is in operation. Air flow is maintained by an electric air pump (6). Once the oxygen sensors and catalytic converters have reached their operating temperatures, valves (4, 7) cut off the secondary air flow.

What the ECU monitors

An activated secondary air injection system leads to an increase in oxygen content in the exhaust (air flow from the secondary air pump). This increase is noted by the ECU by reduced pre-cat oxygen sensor voltage. If the engine management system gives the opening signal to the secondary air injection vaolve and switches on the pump, an extremely lean mixture should be found at the pre-cat sensors if the secondary air system is operating correctly.

















Secondary air injection valve control

The multi valves are controlled via a vacuum line and activated directly via the ECU. If the unit fails to receive the timing signal from the ECU, it can no longer provide accurate control of the secondary air injection process, so the system is disabled and a Diagnostic Trouble Code is stored.








Secondary air injection pump

Operation of the secondary air injection pump is controlled by the ECU via relay J299. The pump furnishes the mass air flow for the secondary air injection system.

Secondary air injection system diagnosis consists of a flow test and a leak test. For the leak test, the secondary air injection pump is switched on with the engine warm and idling, but the multi valves left closed. If the system has no leaks, then oxygen sensor control will not register any

 

Not a bad answer for that post.

By the way, what year is your truck and how many miles on it, that pump may be covered by your extended state or federal warranty.

 

Leads me to believe my other replies aren't to your liking Mike ;-)

Thanks.

 

The additional answer to that is it is another government and car makers way to enforce another costly system that in no way reduces emissions to any significant degree. I wish I could take mine off, but we have emissions laws here that say i can't. All it really is - another thing to go wrong and have to fix...oh and it makes working on your disco and doing things like changing out plug wires that much harder. Okay, my rant is complete...
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Can you remove it without any repercussions?

 

Very good answer to what it is... How do I know if I have it. It is a 2000 Disco II, we do not have emissions testing in my state, so I really don't care if it is working properly(unless it will cause damage or bad performance by the disco).

 

if you have it there will be two stainless tubes with big nuts on the ends
going in the heads near the spark plugs making it hard to change the sparkplugs.
no pipes, no 2ndary injection. CA discovery you prob have it.