short term and long term fuel trim outta whack

MMAFIGHTER121

MMAFIGHTER121

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Alrite - this post got lost during a server crash from earlier but let me try again --
I'm getting p0420 and p0430. My Short term fuel is really negative and my long term fuel is really positive. All 4 O2 sensors are relatively new. All 4 were replaced at about the same time a few months ago but one of the downstream were for the wrong vehicle it seemed. The car was driven a little over a month with the wrong O2, but then while underneath I noticed the problem, So both downstream got replaced. I quickly tested the MAF a month or so ago and the voltage did increase with revs.. but thats all I checked on it. I would think any exhaust leaks large enough to cause the errors would be audible, but I couldn't find any underneath. There aren't any intake or vacuum leaks. Generally a bad Cat wouldn't affect Fuel Trims so I don't think the cats are bad. (they're only 4 months old thunderbolts). I'm leaning towards the MAF even though its voltage seemed in range.. any ideas?
 
If one is negative and the other positive, it sounds like you need to disconnect the battery for a while to reset the adaptive and let it start agin.
 
I gave that a shot first thing when I replaced the wrong O2 sensor, and just after I reset the code, it came back after 40 miles or so.
 
Just throwing this out there, as this is well out of my realm of experience, but if I was facing the same thing:
1) Is it really a problem? As long as your gas mileage is OK, it's not pinging, and the plugs don't look rich or lean, then it's working as intended.
2) My best guess is the injectors are kinda-sorta clogged so the computer is swinging wildly trying to get things in spec. Maybe replace the fuel filter, flush the front part of the system, pull the injectors and clean them? Also double check the air assist part of the manifold. Pulling the intake manifold really doesn't take very long.
 
oddball said:
Just throwing this out there, as this is well out of my realm of experience, but if I was facing the same thing:
1) Is it really a problem? As long as your gas mileage is OK, it's not pinging, and the plugs don't look rich or lean, then it's working as intended.
2) My best guess is the injectors are kinda-sorta clogged so the computer is swinging wildly trying to get things in spec. Maybe replace the fuel filter, flush the front part of the system, pull the injectors and clean them? Also double check the air assist part of the manifold. Pulling the intake manifold really doesn't take very long.
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I had all kinds of issues when the hose barb that the air assist hose clips onto broke off on the passenger side of the intake manifold. I was throwing lean and rich codes and the idle was rough at times. Also check that hose that provides the air assist for leaks or maybe a blockage at the IAC. Or maybe your IAC isnt working properly causing the air assist to malfunction.

Did you put your Thunderbolt CATs in the factory location or did you put them on the pipe as it goes horizontal? I will assume you removed the factory CATS either way. I put mine in the factory location, it was tight but they fit. The O2 sensors (pre and post) are very close to the middle part of the CAT. The bungs I welded in the CAT are actually on the angled part of the CAT with the sensor tip about an inch away from the honeycomb inside. So maybe all these issues you have been having lately are due to the location of the O2 sensors on a higher flowing CAT???

I have never tried irridium plugs, Im running factory Motorcrafts. I have no idea if irridium plugs burn the fuel better or worse than platinum.
 
Driveability isn't really affected except for the occassional rough idle, but it usually fights through it after a few seconds. I had the iridiums for a long time. I doubt those are the issue. I did move the cats past the bend, if that's the culprit is there a way to compensate for this with a tune? I could see the filter being clogged-ish.. at 110k I doubt its been replaced.. but I would think more stumbling would result from an injector/fuel delivery issue.. seems to be the next place to hunt through is all those annoying hoses... if you have a few pictures of said hoses, id be eternally grateful.. if not nbd ill hhunt down some diagrams this weekend.
 
The air assited injector hose connects to the intake manifold on both sides of the engine between the 2nd and 3rd injectors. It gets its air from the IAC, its the small hose on the most forward part of the IAC. It runs towards the drivers side of the car to a 'Tee' in the air assisted injector hose. This hose assembly looks like split loom tubing.

I doubt the problem is your fuel filter but you should go ahead and change it anyway. Its cheap and easy.

I dont know if you can/or need to compensate for the location of the CATs with a tune. Did you remove the old CATs or hollow them out? I hope you removed them. Mine work great and they are in the factory location.

You may try tracing the wires from the O2 sensors all the way back to the PCM checking for bad wiring. The possibility of a bad O2 sensor still exists. I would guess it would be the upstream sensor if one was bad.
 
Now that I really think I did replace the fuel filter relatively recently and I doubt the location change is causing it because it ran beautifully for 3 months or so after the install.. upstream could have been burned out by having the wrong downstream in..
 
MMAFIGHTER121 said:
Now that I really think I did replace the fuel filter relatively recently and I doubt the location change is causing it because it ran beautifully for 3 months or so after the install.. upstream could have been burned out by having the wrong downstream in..
Click to expand...

It could have gone bad if the sensors were dumping too much fuel in the cylinders. That could've also ruined your CAT. That's where I would look first, a new upstream sensor 1st. Then maybe use a borescope to look at your CAT thru the O2 sensor hole to see of it is bad.

Do this after you check the air assist hoses of course
 
Alrite, I checked the air-assist hoses, they're straight and clear, then I replaced all 4 O2 sensors (under warranty - actually got $4 back!) And reset the ecu with a 45 minute battery unplug. After 42 miles I got a trouble code, only this time I think it is the actual code I've been hunting for P0136 which is an O2 sensor circuit malfunction.. what could cause this? My battery really is on the last legs.. could that cause it? I've seen low voltage could be the issue. Also it said fuel pump pressure or regulator.. ideas?

Edit: fuel trim is positive, both long and short now.
 
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Only one way to tell about the battery, go ahead and get a new one. I was talking to a local shop on friday and the owner was telling me about a car that had universal cats throwing codes like yours. He moved the downstrean o2 snsors closer to the CAT and no more codes. With my Thunderbolt CATS I have the tip of the o2 sensor about an inch away from the guts of the CAT. No codes.

Change that battery and chase the o2 sensor wire as far as you can looking for damage to the wires. Thats my best guess man
 
New battery is in, we'll see what code returns in 40 miles or so. Oh, the old cats were removed not hollowed out. The iridiums have about 50k on them so I might swap em out just to help, then I'm thinking its on to fuel pressure and injectors..although without getting jumps in throttle or rough spots on partial throttle... i dunno.. the saga will continue if the codes return. Generally -- it seems like there's a lean condition, then the computer overcompensates for too long for some reason and then there's a rich which throws cat efficiency codes. I doubt its the placement of the O2s because, like i said, it ran fine for the first 2 months before these weird issues started cropping up.
 
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I just hope your PCM isnt dumping too much fuel into the cylinders and making your CATS go bad. It might be worth a look with a borescope just to be on the safe side. Good luck
 
same here, although I think it would take a bit longer to make brand new cats go completely kaka and since I've begun getting different codes and weird fuel trims, I don't think its the cats themselves.. when this is all straightened out i'll be picking up one of your heatshields btw!
 
Check engine lit up after about 60 miles this time, because it was mostly thruway miles.. wonder what that means. Pulling code and information after work... *deep sigh*.. at this point I'm more documenting it so if anyone else has these codes they can see my troubleshooting!
 
Ok the STFT and LTFT have steadied but are still unusual. I have a live reader tool of my own now, and the short term fuel trims are right in line with where they should be all the time, but no matter how long I drive it with those correct values my Long term fuel trim never seems to drop below +10%. Wtf? Isn't LTFT determined by STFT?
 
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