1996 F-150 I6
#16
01-04-2007, 07:40 AM
Lead Driver
#17
01-04-2007, 08:21 PM
Alright, after much pressure from my buddy I did replace the TPS.......didn't fix it. I replaced the IAC......didn't fix it. I sprayed some carb cleaner on the vacuum lines and found a leak. I replaced it.....it ran better. I sit and let the truck run, after a cig (about 4-5 mins.) it shuddered and that dang air pump thingy started making that noise again. I did run much better but seemed to be under a load when the air thing is making a noise. I let it run another 10 min. it never stopped. I turned the engine off, and then after a few sec. I started it again ran great wasn't making the noise, let it run a few more mins. and started again. Now overall I'm pleased. It does seem to run better. I haven't really drove it much but I will know more tomorrow.
#19
01-04-2007, 08:51 PM
The air pump does one of three things.
1. On a cold engine, it will dump air into the head or manifolds to help ignite and warm up the "pre-cat", assuming the I6 4.9L is so equipped like the 5.0L V8. On my 5.0, I have one cat where the Y pipe joins, and a second much larger cat behind that. The second has an air tube going to the diverter valve next to the pump. There's also plumbing to the backs of both heads for the air feed to the first cat. But, I don't know if the same was done on the 4.9L I6.
2. After it's warmed up to 180 deg F, the TAD (Thermactor Air Diverter) valve will pickup and divert the air to the main cat.
3. Under heavy throttle, and normally during warm idle, when less air is needed in the primary cat, the TAB (Thermactor Air Bypass) valve will pick up and dump the air to atmosphere.
Condition 3, after the engine warms up, 5 minutes or so, is probably what you're hearing. It could be that the pump is making more noise when dumping to atmosphere because of less restriction than pumping into the exhaust system. It could also be the silencer on the air pump dump line is missing or defective, though I've never heard of the silencer just dying without the internals of the air pump being deposited in it. This usually results in a locked up air pump, which is MUCH easier to detect. (Broken serp belt, starter won't turn engine if serp belt doesn't break, screeching belt.) As far as any effects on the way the engine runs, it should have little or no effect, other than possibly too much air into the exhaust during cold idle periods, which might give you the lean O2 indicator. So, as far as the O2 sensor is concerned, leave in the ones you've replaced. Clear the codes, and see if they come back. It normally takes a few miles of driving to get a lean O2 fault, unless the sensor itself is failed. I think there's a different code for Lean than for failed sensor, though. I have a speed/density system ('92 model), so I may be a little off on how the MAF system works versus Speed Density. I do know, I drove nearly 10 miles before my CEL came on with the HEGO (O2) disconnected (on purpose). It also made VERY little difference in the truck's performance with the HEGO disconnected. But, like I said, it is a speed-density system.
Glad you found the vacuum leak too, btw. Vacuum leaks can be a real bugger to find. Make sure you clear the codes, though, otherwise you may wind up chasing a non-existant problem. On the EEC-IV, to clear the codes, start the diagnostic test, but interrupt it by disconnecting the jumper between STI and ground as soon as the codes start flashing. Another way is to disconnect the battery for at least 15 minutes or so. I'd suggest disconnecting it one night when you know you won't be using the truck that night, then reconnecting when you get up the next day. What this will do, in addition to clearing the codes, is force the EEC to relearn the fuel curves. Anytime you replace ANY sensor, it's best to reset the EEC. New sensors won't have exactly the same characteristics as the ones that were replaced (which is why you probably replaced them). Fuel tables need to be adjusted again.
1. On a cold engine, it will dump air into the head or manifolds to help ignite and warm up the "pre-cat", assuming the I6 4.9L is so equipped like the 5.0L V8. On my 5.0, I have one cat where the Y pipe joins, and a second much larger cat behind that. The second has an air tube going to the diverter valve next to the pump. There's also plumbing to the backs of both heads for the air feed to the first cat. But, I don't know if the same was done on the 4.9L I6.
2. After it's warmed up to 180 deg F, the TAD (Thermactor Air Diverter) valve will pickup and divert the air to the main cat.
3. Under heavy throttle, and normally during warm idle, when less air is needed in the primary cat, the TAB (Thermactor Air Bypass) valve will pick up and dump the air to atmosphere.
Condition 3, after the engine warms up, 5 minutes or so, is probably what you're hearing. It could be that the pump is making more noise when dumping to atmosphere because of less restriction than pumping into the exhaust system. It could also be the silencer on the air pump dump line is missing or defective, though I've never heard of the silencer just dying without the internals of the air pump being deposited in it. This usually results in a locked up air pump, which is MUCH easier to detect. (Broken serp belt, starter won't turn engine if serp belt doesn't break, screeching belt.) As far as any effects on the way the engine runs, it should have little or no effect, other than possibly too much air into the exhaust during cold idle periods, which might give you the lean O2 indicator. So, as far as the O2 sensor is concerned, leave in the ones you've replaced. Clear the codes, and see if they come back. It normally takes a few miles of driving to get a lean O2 fault, unless the sensor itself is failed. I think there's a different code for Lean than for failed sensor, though. I have a speed/density system ('92 model), so I may be a little off on how the MAF system works versus Speed Density. I do know, I drove nearly 10 miles before my CEL came on with the HEGO (O2) disconnected (on purpose). It also made VERY little difference in the truck's performance with the HEGO disconnected. But, like I said, it is a speed-density system.
Glad you found the vacuum leak too, btw. Vacuum leaks can be a real bugger to find. Make sure you clear the codes, though, otherwise you may wind up chasing a non-existant problem. On the EEC-IV, to clear the codes, start the diagnostic test, but interrupt it by disconnecting the jumper between STI and ground as soon as the codes start flashing. Another way is to disconnect the battery for at least 15 minutes or so. I'd suggest disconnecting it one night when you know you won't be using the truck that night, then reconnecting when you get up the next day. What this will do, in addition to clearing the codes, is force the EEC to relearn the fuel curves. Anytime you replace ANY sensor, it's best to reset the EEC. New sensors won't have exactly the same characteristics as the ones that were replaced (which is why you probably replaced them). Fuel tables need to be adjusted again.
#20
01-05-2007, 11:51 AM
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