Help with poor mileage
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5th Wheeling
Joined: Jun 2008
Posts: 44
Likes: 3
Help with poor mileage
Here's the story:
1987 f150 4x4 5.0l AOD xcab/lwb
Truck is only getting 10mpg in town and on the highway(65)
Ran error code scans and got:
KOEO
11 - System pass
KOER
45 - Thermactor air upstream
I recently replaced the passenger side exhaust manifold and it has a small leak at the collector. Would this leak throw a code 45? I'm pretty sure my poor mileage is due to the leaky manifold causing artificially lean readings at the O2 sensor.
Thanks
1987 f150 4x4 5.0l AOD xcab/lwb
Truck is only getting 10mpg in town and on the highway(65)
Ran error code scans and got:
KOEO
11 - System pass
KOER
45 - Thermactor air upstream
I recently replaced the passenger side exhaust manifold and it has a small leak at the collector. Would this leak throw a code 45? I'm pretty sure my poor mileage is due to the leaky manifold causing artificially lean readings at the O2 sensor.
Thanks
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
Yes a manifold leak can cause mixture problems but it won't cause that code. When your motor is warmed up and idling is there a steady flow or air out of the exhaust muffler for the air pump? It's over behind the battery and the exhaust muffler is the little cylinder on top of the larger cylinder.. which is the intake air filter for the air pump. If you don't have air coming out this muffler then it's being dumped into the exhaust upstream of the O2 sensor and that will make the engine run extremely rich. The problem is lilely a stuck diverter valve which is down behind the air pump, it's rest position(when no vacuum is applied) is closed which should dump air to atmosphere.
Thread Starter
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5th Wheeling
Joined: Jun 2008
Posts: 44
Likes: 3
I went through the AIR pump and found that the valve connected to the rear of the pump is always open. It is always open because it always has vacuum. If I disconnect the vacuum line to the valve the truck has lots more power and does not die when the AC engages at idle. Where is the red vacuum line for this valve switched. I'm thinking I have a bad vacuum switch somewhere.
Any pictures of this switch or its approx location would be awesome!
Thanks
Any pictures of this switch or its approx location would be awesome!
Thanks
Posting Guru
Joined: Dec 2009
Posts: 1,053
Likes: 0
From: Calverton
It may be that the valve has failed, because I don't think that the vacuum is switched up-stream...there are test's to run that will check the valve out. Do you know if you have a normally open Air bypass Valve, or a normally closed valve? is there a vacuum diagram sticker?
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
This valve is controlled by the TAB solenoid up beside the coil, there are two identical solenoids there side by side and I'm not sure which is but it shouldn't be hard to figure out.
TABTAD1 on Flickr - Photo Sharing!
TABTAD1 on Flickr - Photo Sharing!
Thread Starter
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5th Wheeling
Joined: Jun 2008
Posts: 44
Likes: 3
Ok... Went through everything again today and the valve on the back of the AIR pump is switching... I can fee air blowing out of the bottom of it sometimes. Both TAB and TAD solenoids are switching their respective vacuum lines, and I still have a code 45. If I disconnect the vacuum from the valve on the rear of the AIR pump I get a code for Thermactor Air System Fault.
Where do I go from here? Never worked on one of these smog systems before.
Thanks!
Where do I go from here? Never worked on one of these smog systems before.
Thanks!
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
Is the valve behind the air pump switching to bypass when the engine is warm? It should and if it doesn't then either the vacuum lines are attached to the wrong solenoid or the solenoids are malfunctioning. You definitely do not want air being dumped into the exhaust upstream of the O2 sensor once the engine is at operating temperature, so worse case you could permanently disconnect and plug the vacuum line on the valve behind the pump so that the system is always in bypass mode.
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5th Wheeling
Joined: Jun 2008
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The valve behind the pump does cycle, but only when the PCM is placed in KOER test mode. In test mode the valve cycles, then returns to open. I also noticed another similar valve behind the engine that appears to switch the air flow from the heads to behind the cat... related to this problem?
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Thread Starter
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5th Wheeling
Joined: Jun 2008
Posts: 44
Likes: 3
I think I've narrowed this down to the vacuum switch behind the the smog pump not being told to divert air overboard when the motor is hot. The control solenoid works during the KOER test, but not during normal operation. Is there a sensor that the computer uses to determine when to open and close the smog pump valves?
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
No sensors on this system it's controlled directly by the EEC based on programming. The diverter valve behind the motor is part of the same system, is it switching to direct air downstream(to the cats)when the engine warms up? If not then the TAB and TAD solenoids are your problem, one or both could be shorted electrically or there could be a chaffed wire in the harness that is shorting them out and holding them in 1 position. if you can't find anything like this and replacing them doesn't change the behavior I suggest you permanently remove vacuum from the bypass valve behind the pump.
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5th Wheeling
Joined: Jun 2008
Posts: 44
Likes: 3
Have been through all the wiring and swapped the solenoids, did not change behavior. The strange thing is that the KOER test will switch the AIR diverter, but it will not during normal operation. I am running with the vacuum detached from the switch, but my cold idle is terrible(surging) and I can smell gas at the tailpipe. I did make sure I plugged the vacuum line and have tested for leaks everywhere under the hood, the surging goes away when the AIR switch is reconnected.
Thanks for all the help so far!
Thanks for all the help so far!
