F250 EEC codes..help
Thread Starter
|
New User
Joined: Apr 2005
Posts: 6
Likes: 0
From: In a house
F250 EEC codes..help
Hi..my 91 F250's CEL came on shortly after the truck started running real rough. I had a buddy retreive the codes for me, heres what came out
171 No EGO switch
173 EGO not switching
327 EGR signal too low
328 EGR voltage below closed limit
Am i right in thinking this means new Oxygen sensor? and, is it possible the first 2 codes are causing the other 2
Thanx in advance for any help
171 No EGO switch
173 EGO not switching
327 EGR signal too low
328 EGR voltage below closed limit
Am i right in thinking this means new Oxygen sensor? and, is it possible the first 2 codes are causing the other 2
Thanx in advance for any help
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
171 = fuel system at adaptive limits. This is a memory code only
173 = HEGO is always indicating rich.
The computer observes the oxygen sensor screaming RICH, and proceeds to lean out the mixture by decreasing injector pulse width. It goes as far as it is willing to go towards the lean side, yet the O2 sensor is still screaming rich. At this point, it sets code 171, to say it is at adaptive limit. It also sets code 173, to let you know between lean limit and rich limit.
An electrical problem with the O2 sensor would cause it to fail towards always lean (code 172). About the only way the O2 sensor can fail towards always rich (code 173) is if the sensor end (in the exhaust stream) has been contaminated by leaded gas, gasket sealant, or too much carbon from a misfiring engine.
So the question is, is the sensor giving a false indication of rich, while the truck is idling normally? Or is the truck actually running too rich, due to a failed or leaking fuel pressure regulator or a leaking injector? In the latter case, nothing is wrong with the O2 sensor. It is merely indicating a problem with fuel control. My money is on this llatter scenario. First thing to do is to check your fuel pressure and the rate it leaks down.
Code 327 = EVP below minimum voltage. Usually this is a failed EVP or a wiring problem
Code 328 = EVP below expected value. This can be the same issue as code 327, or it could be that the EGR is not opening when it should, due to such things as a vacuum line problem, failed Egr Vacuum Regulator, or a failed diaphragm in the EGR valve.
If the EGR valve is open, but the EVP says it isn't, it is possible that you could get codes 171/173 as a consequence pf code 327/328 (The exhaust gas displaces oxygen, causing the mixture to be too rich, but the computer doesn't know the exhaust gas is flowing due to the failed EVP.
The reverse is not true. There is no mechanism by which codes 171/173 can cause codes 327/328.
173 = HEGO is always indicating rich.
The computer observes the oxygen sensor screaming RICH, and proceeds to lean out the mixture by decreasing injector pulse width. It goes as far as it is willing to go towards the lean side, yet the O2 sensor is still screaming rich. At this point, it sets code 171, to say it is at adaptive limit. It also sets code 173, to let you know between lean limit and rich limit.
An electrical problem with the O2 sensor would cause it to fail towards always lean (code 172). About the only way the O2 sensor can fail towards always rich (code 173) is if the sensor end (in the exhaust stream) has been contaminated by leaded gas, gasket sealant, or too much carbon from a misfiring engine.
So the question is, is the sensor giving a false indication of rich, while the truck is idling normally? Or is the truck actually running too rich, due to a failed or leaking fuel pressure regulator or a leaking injector? In the latter case, nothing is wrong with the O2 sensor. It is merely indicating a problem with fuel control. My money is on this llatter scenario. First thing to do is to check your fuel pressure and the rate it leaks down.
Code 327 = EVP below minimum voltage. Usually this is a failed EVP or a wiring problem
Code 328 = EVP below expected value. This can be the same issue as code 327, or it could be that the EGR is not opening when it should, due to such things as a vacuum line problem, failed Egr Vacuum Regulator, or a failed diaphragm in the EGR valve.
If the EGR valve is open, but the EVP says it isn't, it is possible that you could get codes 171/173 as a consequence pf code 327/328 (The exhaust gas displaces oxygen, causing the mixture to be too rich, but the computer doesn't know the exhaust gas is flowing due to the failed EVP.
The reverse is not true. There is no mechanism by which codes 171/173 can cause codes 327/328.
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
Just to clarify, the 171/173 pair mean the computer has commanded the fuel system to the lean limit, but the oxygen sensor is still saying rich. A 171/172 pair would mean the fuel system has run to the rich limit, but the oxygen sensor is still saying "lean"
Rate of leakdown means how fast the fuel pressure bleeds down, once the pump turns off. Hook up an EFI rated guage to the Shrader valve. Cycle the key from off to on to off to on a couple of times. Do not start the engine. Check the pressure. It should be 35-40 PSI with an 8 cylinder, about 55-60 PSI with an I6. Now watch how fast the pressure indication on the guage drops, now that the pump has shut off. It should stay within 5 PSI of the above numbers for at least 30 seconds.
Rate of leakdown means how fast the fuel pressure bleeds down, once the pump turns off. Hook up an EFI rated guage to the Shrader valve. Cycle the key from off to on to off to on a couple of times. Do not start the engine. Check the pressure. It should be 35-40 PSI with an 8 cylinder, about 55-60 PSI with an I6. Now watch how fast the pressure indication on the guage drops, now that the pump has shut off. It should stay within 5 PSI of the above numbers for at least 30 seconds.
Thread
Thread Starter
Forum
Replies
Last Post
Big_Walt
1987 - 1996 F150 & Larger F-Series Trucks
1
Feb 16, 2015 03:57 PM
