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Discussion Starter · #1 ·
Hi all,

I have a 1991 mustang lx..tfs 11r 190s, rpm II, Ed Curtis cam, 24# injectors 306. The car has an auto computer in it but is a 5 speed now (not sure if that matters)....anyway...lately I have had this problem where I am driving the car around at low rpm and under light load (cruising) and the car will lose much of its power and pop through the intake. The problem is intermittent and I notice that cycling the key or going straight to wot will get the car to clear up. I have pulled my maf and cleaned it thoroughly, replaced ect (had code),cleaned and reapplied die electric grease to the tfi module, checked plug gaps, chased plug wires..nothing seems to help. The car will sometimes go down the road for 30+ minutes before acting up..other times it starts almost as soon as you start driving it. Koeo test gives me code 31 and 42, KOER test gives me 31 and 42 as well. Cylinder balance test gave a code 9...has anyone had a problem like this with their car?? Any advise would be much appreciated!
 

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the lack of power, then pop, is called a misfire, and NO, it does not have to run rough all the time if a valve is not closing

why dont address the codes?

one of them is telling you one bank is lean all the time, it could be from a misfire or a true lean condition

its time to diagnose, dont you think?
 

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Discussion Starter · #5 ·
the lack of power, then pop, is called a misfire, and NO, it does not have to run rough all the time if a valve is not closing

why dont address the codes?

one of them is telling you one bank is lean all the time, it could be from a misfire or a true lean condition

its time to diagnose, dont you think?
yessir I do think it’s time to diagnose. I’m going to have the car at my shop in an hour or so to look into this problem. I will definitely pull the valve covers and inspect. I was under the impression code 42 was for the charcoal canister. I tried to check Voltages in pin 24 (rh o2 sensor I believe) and 43 (lh o2 sensor..correct me if I’m wrong) the forum I saw said that I should expect .2-.9v at idle. But my readings were all over the place....truthfully I don’t think Im That good with a multimeter..might just have been operator error...anyways I will have someone who is better with electricity than myself look at it with me today.Any other recommendations on things to test/inspect?
 

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42 is reporting always rich, therefore the ecm has pulled all the fuel it can on that bank, said uncle and stuck a code for you diagnose.

now imagine..........................if the 02 reporting rich is actually lying!!

that should give you a start
 

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Discussion Starter · #9 ·
Alright. Just put an o2 sensor in the car and drove it for a good 45 minutes under varying loads/speeds. The car ran basically perfect the entire time except it idle surged and died while at the gas pump (once, after I restarted the car it ran fine the rest of the drive). After the drive I did another KOER test and code 42 still shows up. The car didn’t pop through the intake one time on the drive and seems to always have power like it should. Could code 42 still be thrown even if the issue is fixed?
 

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Discussion Starter · #11 ·
NOT usually unless the KAM was not erased

you chose parts swapping, i am out

good luck, and open that walllet!!!
I appreciate your advice, the car seems to be getting better as I narrow in on this issue. I don’t really understand how I’m just “throwing parts at it” though. Could a faulty o2 sensor not cause a code 42? That oxygen sensor was old and replacing it greatly improved how the car runs. Maybe I’m wrong but that certainly makes me feel like I am narrowing in on the problem. I’m trying to educate myself on ford fuel injection and how to troubleshoot/diagnose...I am still pretty new to all of this...your passive aggressive comments aren’t helping me fix this car..
 
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