CO state emissions test failure
Pro Wrench
Joined: Apr 2021
Posts: 1,411
Likes: 397
From: SE Washington State
Rich, very rich
Negative long term fuel trims indicate the ECU wants to reduce fuel, so the engine is running rich on average. My mechanic says normal long term trims should be between -5 and +5%, closer to zero is ideal. Max allowed is +/-25%. Long term adjusts (ratchets) when the short term trims hit the 25% limit regularly. Reasons for negative LTFT might include leaky injectors (very rare I hear), bad O2s, and others (maybe bad MAF, TPS, Google may help). Maybe running in limp mode?
Short term trim trying to add fuel at idle may indicate a vacuum leak. You didn't show bank 1 short term trim data? Short trims can vary a lot during a drive, but generally, positive at idle, then negative when the throttle opens up (relieves vacuum) indicates a vacuum leak. I had a self inflicted vacuum leak when I forgot to connect the tube for the fuel pressure regulator, the trims swung negative 15 to 25% back towards center when I reconnected it.
Sometimes crud builds up on the tiny MAF sensor elements, that can be sprayed, but a pick can be used to gently pry off the hard crust on the hot wire (I need to use a magnifying glass).
I have taken to leaving my coolant caps a bit loose (per this Forum), so pressure doesn't build up in the D1 cooling systems (and I know that lowers the boiling point of the coolant). Good luck with Indy!
Short term trim trying to add fuel at idle may indicate a vacuum leak. You didn't show bank 1 short term trim data? Short trims can vary a lot during a drive, but generally, positive at idle, then negative when the throttle opens up (relieves vacuum) indicates a vacuum leak. I had a self inflicted vacuum leak when I forgot to connect the tube for the fuel pressure regulator, the trims swung negative 15 to 25% back towards center when I reconnected it.
Sometimes crud builds up on the tiny MAF sensor elements, that can be sprayed, but a pick can be used to gently pry off the hard crust on the hot wire (I need to use a magnifying glass).
I have taken to leaving my coolant caps a bit loose (per this Forum), so pressure doesn't build up in the D1 cooling systems (and I know that lowers the boiling point of the coolant). Good luck with Indy!
Last edited by JohnZo; Jun 21, 2023 at 08:35 PM. Reason: Limp
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Mudding
Joined: Dec 2014
Posts: 232
Likes: 81
From: Erie, CO
I think the issue is finally resolved. I purchased a new Walker MAF which was total crap and caused the stft to stay at +25 and ltft to increase to the -20 range. Luckily Rock Auto provided a refund for that unit. A local LR specialty shop had a used MAF from a Defender that I installed yesterday and the ltft is now -0.8%, and the stft is near zero. I have an appointment with the State Emissions Technical Center tomorrow for a free in-depth analysis to see if it passes.
I replaced the coolant overflow tank, top radiator hose, and thermostat (Stant 45858 180 degree) and a few days later the temps were creeping into the low 200's while the a/c was on. One of the auxiliary fans in front of the radiator was dead, so that has also now been replaced with a VDO/CONTINENTAL PM9115. When it rains, it pours......
I replaced the coolant overflow tank, top radiator hose, and thermostat (Stant 45858 180 degree) and a few days later the temps were creeping into the low 200's while the a/c was on. One of the auxiliary fans in front of the radiator was dead, so that has also now been replaced with a VDO/CONTINENTAL PM9115. When it rains, it pours......
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