I have a 1990 F-150(4X2), 4.9L in-line 6 cylinder engine, manual trans. Can anyone tell me how to diagnose the air pump for a potential fault. Mine is noisey, and I have a stumble or stalling condition when the engine is under load after warm up. The engine vacuum is steady at approximatey 18 in. Hg. No fault codes flashing or recorded.

I am also looking at the EGR and EGR position sensor, however Haynes manual indicates that these components are functioning properly.

I have replaced; plugs, wires, cap, rotor, EVR valve, Air by-pass valve, fuel filter, air filter, PCV valve, and crankcase breather filter. The largest noticeable improvement was when I replaced the air by-pass valve; that by the way the diagnostic procedures in the Haynes manual indicated that the by-pass was OK. I also cleaned the by-pass valve prior to replacing it, without a noticable change.

 

Air pumps that rattle could lst a long time or seize up the next day. You may want to look into a replacement. I have seen pumps that rattle and are ready to seize put a nasty load on an engine. Your belt could burn off. Check your exhaust system for any blockage also.

Jakegypsum // Ford fleet, soup to nuts.

 

 

I've been having a stutter-surge problem at moderate throttle settings when the engine is hot as well, on an '89 4.9 EFI 4x2. I had the engine computer and my air pump replaced several months ago to correct a seized air pump and dead computer (caused by sitting on a sea wall for 4 months). Since then, all I can figure out is that either the new computer or air pump can be at fault. The truck checks out OK on a computer test thing when cold.

What does the air pump do? Anyone have similar "stutter" problems at 2,000-2,700 rpm?

Thanks

 

the air pump basically add air (O2) directly to the catalytic converter so that the oxygen (O2) can combine with the exaust gases ( HC + CO ) and the pellets. this produces h20(water) and co2(carbon dioxide). yes that it why water sometimes comes out of you exaust. So it goes air pump produces air (o2) it is routed to a diverter and bypass valve then it is routed to the catalytic converter.
thing that could be wrong with your air injected system
(1) bad bypass valve or diverter valve
(2) simply a vaccuum line attached to the bypass is disconnected (3) simply a vaccuum line attached to the diverter is disconnected
(4) bad air pump (to check air pump disconnect the hose and turn engine on if it pump air it is working)

 

it could be the diverter valve not good. the diverter works the following way. first air enters the diverter valve and it has to outlet openings if the engine is warm then it diverts the air to the catalitic converter outlet opening. 2nd if the engine is cold it sends the air coming in out to the enviroment via small muffler like valve. If air is not being injected to the catalytic converter via the diverter valve then the engine will backfire or will have no power just like the same sysmtons as having a bad catalytic converter.

 

there are 2 kinds of air by pass valves
(1) first there is the air by pass line in the air(smog)pump line
next to the diverter valve. I THINK THE BYPASS VALVE IN QUESTION HERE IS THIS BYPASS VALVE ON THE AIR PUMP ROUTE.
(2) the second air by pass is the (by pass air idle control)solenoid (bpa-isc). this valve or solenoid is located in the trottle body assembly. THIS VALVE CONTROL THE IDLE SPEED ONLY.
I DON'T THINK THIS VALVE HAS NOTHING TO DO WITH YOUR PROBLEMS.SINCE IT ONLY CONTROL THE IDLE SPEED AND THAT IT BASICALLY.