Quick Tip Tuesday - Fuel Trim Troubles
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Date: 2025-02-09
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Comments and reviews: 20
miketeeveedub5779
30 years ago I worked one winter as a CAA road-assistant boost tech (Canada's version of AAA. Whenever we had a cold snap (-20C or colder) my supervisor would remind us if you have a no-start situation with a customer, to first check the dipstick. Why To see if there's a fuel line mark on the dipstick. After prolonged starting attempts on many vehicles the fuel injection system would dump so much raw fuel into the engine it would bleed past the rings into the oil pan. It would then collect above the oil level in the pan. You'd see it on the dipstick.
At that point I'd show them the dipstick reading, and inform them that we won't boost the vehicle because it's a potential fire hazard, could cause massive engine damage due to oil dilution, and needed to be towed to a garage for an engine oil change.
The worst culprits at the time Those Ford Tempos and Mercury Topazs with FI. Total garbage in the cold. Funny thing was the carb'ed versions worked great. Had no problem get those started. The easiest to start Any Honda, even at -40C with no block heater. Just boost it and they'd start. Batteries were the culprit and the FI never flood the engines.
Thanks for the memories Eric! Boosting vehicles at -30C was always an interesting time. Cheers!
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30 years ago I worked one winter as a CAA road-assistant boost tech (Canada's version of AAA. Whenever we had a cold snap (-20C or colder) my supervisor would remind us if you have a no-start situation with a customer, to first check the dipstick. Why To see if there's a fuel line mark on the dipstick. After prolonged starting attempts on many vehicles the fuel injection system would dump so much raw fuel into the engine it would bleed past the rings into the oil pan. It would then collect above the oil level in the pan. You'd see it on the dipstick.
At that point I'd show them the dipstick reading, and inform them that we won't boost the vehicle because it's a potential fire hazard, could cause massive engine damage due to oil dilution, and needed to be towed to a garage for an engine oil change.
The worst culprits at the time Those Ford Tempos and Mercury Topazs with FI. Total garbage in the cold. Funny thing was the carb'ed versions worked great. Had no problem get those started. The easiest to start Any Honda, even at -40C with no block heater. Just boost it and they'd start. Batteries were the culprit and the FI never flood the engines.
Thanks for the memories Eric! Boosting vehicles at -30C was always an interesting time. Cheers!
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briq4409
I have a 2023 Honda CRV hybrid At certain points driving usually when the engine is under slight load I could feel stumble I take the car to the dealership after using my scan tool and seeing that I’m getting multiple misfires not enough to cause a check engine light but an awful lot for a car that only had 22, 000 miles on it Fast forward Honda dealer says I need new injectors They actually told me that the misfires were due to not enough fuel being injected They replaced the injectors. I just changed my oil and sent it off to be analyzed and they basically told me that I was in the danger zone for fuel dilution! Leads me to believe the dealership said that to avoid having to do an oil change on top of the injectors being replaced. And at the time I was only at like 30% on the maintenance minder. I’m guessing exactly what you’re talking about in this video is what happened to my car. I didn’t look at fuel trims. I was just looking to see if there were anymore misfires Thanks for posting this! The more you know!
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I have a 2023 Honda CRV hybrid At certain points driving usually when the engine is under slight load I could feel stumble I take the car to the dealership after using my scan tool and seeing that I’m getting multiple misfires not enough to cause a check engine light but an awful lot for a car that only had 22, 000 miles on it Fast forward Honda dealer says I need new injectors They actually told me that the misfires were due to not enough fuel being injected They replaced the injectors. I just changed my oil and sent it off to be analyzed and they basically told me that I was in the danger zone for fuel dilution! Leads me to believe the dealership said that to avoid having to do an oil change on top of the injectors being replaced. And at the time I was only at like 30% on the maintenance minder. I’m guessing exactly what you’re talking about in this video is what happened to my car. I didn’t look at fuel trims. I was just looking to see if there were anymore misfires Thanks for posting this! The more you know!
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ralphwatten2426
Back in the ol' carburetor days you'd flood your car when it was -20 and you'd crank and crank and crank and would not start. You'd pull the plugs and put new ones in and it would start and next day it wouldn't start again and it would crank and crank and crank and would be flooded again. Had to change the oil just about every time it got really cold. Sometimes dumping oil down the carb would help but that was a last ditch attempt. Fuel injected cars are so much better.
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Back in the ol' carburetor days you'd flood your car when it was -20 and you'd crank and crank and crank and would not start. You'd pull the plugs and put new ones in and it would start and next day it wouldn't start again and it would crank and crank and crank and would be flooded again. Had to change the oil just about every time it got really cold. Sometimes dumping oil down the carb would help but that was a last ditch attempt. Fuel injected cars are so much better.
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CedroCron
PCM sensor inputs are so sensitive today that they can see just about everything including too much fuel in the oil giving off too much vapour fed back through the PCV system. This is a good video for folks to see. Also I'd mention about resetting Keep Alive Memory for some brands because even an oil change won't change its mind and either giving it time to right the ship in terms of fuel trim numbers or keep-alive reset is how to get the numbers to change. Good job Eric.
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PCM sensor inputs are so sensitive today that they can see just about everything including too much fuel in the oil giving off too much vapour fed back through the PCV system. This is a good video for folks to see. Also I'd mention about resetting Keep Alive Memory for some brands because even an oil change won't change its mind and either giving it time to right the ship in terms of fuel trim numbers or keep-alive reset is how to get the numbers to change. Good job Eric.
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operator8014
I got burned pretty hard on a F250 6. 2 with a #6 misfire. I got the correct fix on the first try, but it started doing all kinds of weird stuff; bank 2 misfire, injector 5, 7, and 8 insufficient flow, lean conditions, equivalence sensors pegged high with fuel trims pegged negative. Just nonsense.
Had to restart the diagnostic while resetting the keep-alive memory between steps because the adaptive nonsense was trying to break it faster than I was fixing it.
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I got burned pretty hard on a F250 6. 2 with a #6 misfire. I got the correct fix on the first try, but it started doing all kinds of weird stuff; bank 2 misfire, injector 5, 7, and 8 insufficient flow, lean conditions, equivalence sensors pegged high with fuel trims pegged negative. Just nonsense.
Had to restart the diagnostic while resetting the keep-alive memory between steps because the adaptive nonsense was trying to break it faster than I was fixing it.
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bolts5994
Holy smokes. I've been dealing with something like this. 08 Civic 145k. After the car warms up I can feel the engine start to vibrate and the RPM is at about 675. No codes yet but I think it might be coming. I've tried everything. All 3 OEM mounts, cleaned the EGR and MAF, new plugs and coils, new gas cap, 93 gas. Still nothing. Scanned it and still running at -8. Got to get it in and have them scan it and see what they think.
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Holy smokes. I've been dealing with something like this. 08 Civic 145k. After the car warms up I can feel the engine start to vibrate and the RPM is at about 675. No codes yet but I think it might be coming. I've tried everything. All 3 OEM mounts, cleaned the EGR and MAF, new plugs and coils, new gas cap, 93 gas. Still nothing. Scanned it and still running at -8. Got to get it in and have them scan it and see what they think.
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Mag_Aoidh
What infuriates me the most is why can’t an engineer figure out how to place an oil filter that’s not above another piece of the vehicle/frame. My son’s Ford F150 has a molded piece of plastic that is supposed to drain the oil away, but all it does is fill up and run off the back edge. My Chevrolet Z71 I made a little aluminum ramp to help the oil drain off instead of on the frame.
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What infuriates me the most is why can’t an engineer figure out how to place an oil filter that’s not above another piece of the vehicle/frame. My son’s Ford F150 has a molded piece of plastic that is supposed to drain the oil away, but all it does is fill up and run off the back edge. My Chevrolet Z71 I made a little aluminum ramp to help the oil drain off instead of on the frame.
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LouinVB
Now you tell me. I want to hear exactly the same issue with a 2012 Toyota Corolla. It was popping a P0172 CODE even after replacing a known faulty fuel injector that was not closing completely. I thought the code had gone away because I completed a certain number of dry Cycles. Now I realized it must have been the oil change I did a few days after that did.
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Now you tell me. I want to hear exactly the same issue with a 2012 Toyota Corolla. It was popping a P0172 CODE even after replacing a known faulty fuel injector that was not closing completely. I thought the code had gone away because I completed a certain number of dry Cycles. Now I realized it must have been the oil change I did a few days after that did.
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OldManBadly
I am assuming if you ran the car for a while the gas would slowly get sucked out of the oil and used up, and that over time the fuel trims would return to normal. However, I think that when a car has been massively overfueled (like bad injectors, example) that an oil change should be a normal part of the deal. That extra fuel went somewhere! : )
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I am assuming if you ran the car for a while the gas would slowly get sucked out of the oil and used up, and that over time the fuel trims would return to normal. However, I think that when a car has been massively overfueled (like bad injectors, example) that an oil change should be a normal part of the deal. That extra fuel went somewhere! : )
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autorepair
On a slight tangent. I couldn't start my Honda generator. I checked the oil level and it was ok. After a lot of cursing & head scratching I changed the oil which seemed a bit thin. It fired up on the first pull. The float in the Carburettor was letting by and would flood the engine if you didn't turn the valve off when not running.
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On a slight tangent. I couldn't start my Honda generator. I checked the oil level and it was ok. After a lot of cursing & head scratching I changed the oil which seemed a bit thin. It fired up on the first pull. The float in the Carburettor was letting by and would flood the engine if you didn't turn the valve off when not running.
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autorepair
Could have used this a few months ago --- my Lexus had me chasing my tail until I changed the oil, and finally the check eng light stayed off after cleaning the MAF, and changing the bank 2 downstream O2 sensor (stuck high) etc. Short distance driven and 1 year old oil that smelled gassy (yeah - i should have suspected.
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Could have used this a few months ago --- my Lexus had me chasing my tail until I changed the oil, and finally the check eng light stayed off after cleaning the MAF, and changing the bank 2 downstream O2 sensor (stuck high) etc. Short distance driven and 1 year old oil that smelled gassy (yeah - i should have suspected.
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tompetrushka1627
Nice explanation Eric O. Someone will benefit as you said. Back in the days of using a 4 or 5 gas exhaust analyzer, you could see the change in carbon monoxide and hydrocarbon count after a changing oil on an engine that was running filthy rich. Now the fuel trim shows it.
Stay warm up there.
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Nice explanation Eric O. Someone will benefit as you said. Back in the days of using a 4 or 5 gas exhaust analyzer, you could see the change in carbon monoxide and hydrocarbon count after a changing oil on an engine that was running filthy rich. Now the fuel trim shows it.
Stay warm up there.
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justing9902
This is really common on low mileage vehicles, they drive very short distance's with little engine run time so the engine only runs on a rich fuel mixture. Customer only changes oil every 5k miles or so and by the time they need the oil change the p0172 is set from all the gas that's mixed in the oil.
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This is really common on low mileage vehicles, they drive very short distance's with little engine run time so the engine only runs on a rich fuel mixture. Customer only changes oil every 5k miles or so and by the time they need the oil change the p0172 is set from all the gas that's mixed in the oil.
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garyradtke3252
It happens with carbs and diaphragm fuel pumps too. Maybe more often but you don't have fuel trim readings to indicate. Only experience and visual inspections and sometimes the oil doesn't look all that fuel laden but the engine still doesn't run as good as it should. Remember cold weather and chokes
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It happens with carbs and diaphragm fuel pumps too. Maybe more often but you don't have fuel trim readings to indicate. Only experience and visual inspections and sometimes the oil doesn't look all that fuel laden but the engine still doesn't run as good as it should. Remember cold weather and chokes
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autorepair
I don’t want a vehicle that burns oil I don’t want a vehicle that throws gas into the oil. I don’t want a vehicle that leaks oil I want a vehicle when you put the oil in and it’s time to change it. It’s still there and you replace it with clean oil. Is this too much to ask
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I don’t want a vehicle that burns oil I don’t want a vehicle that throws gas into the oil. I don’t want a vehicle that leaks oil I want a vehicle when you put the oil in and it’s time to change it. It’s still there and you replace it with clean oil. Is this too much to ask
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andrewsutton7727
Wow, the algorithm matrix is working OT! Just watched a video on ASE A8 test prep, mentioned a similar scenario with a p0172 and p128. Owner changes the oil and filter and the vehicle won't start. Fuel trim was off the charts.
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Wow, the algorithm matrix is working OT! Just watched a video on ASE A8 test prep, mentioned a similar scenario with a p0172 and p128. Owner changes the oil and filter and the vehicle won't start. Fuel trim was off the charts.
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Fjord_Driver
So instead of regular oil, just add STP Oil Treatment and some Motor Honey in anticipation of fuel dilution. Might be a bit slow cranking at first, but eventually you will hit the right oil weight as you drive and dilute things.
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So instead of regular oil, just add STP Oil Treatment and some Motor Honey in anticipation of fuel dilution. Might be a bit slow cranking at first, but eventually you will hit the right oil weight as you drive and dilute things.
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goptools
It might be obvious to most folks but I for one was not aware of this. I supposed if you think logically what else is involved in the setting the fuel trim level, besides the normal parts, I should have known. Now I do. Good tip!
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It might be obvious to most folks but I for one was not aware of this. I supposed if you think logically what else is involved in the setting the fuel trim level, besides the normal parts, I should have known. Now I do. Good tip!
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jackedwards7420
What I really hate is every single engine I hear running sounds like trash over any device I use (TV, computer, phone all of them) and it doesn't matter the brand or the quality! They all sound like rattles and knocking
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What I really hate is every single engine I hear running sounds like trash over any device I use (TV, computer, phone all of them) and it doesn't matter the brand or the quality! They all sound like rattles and knocking
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autorepair
Good thing my old 1979 Chevy 1 ton with a 350 and the choke stuck on didn’t have O2 sensors they would be - a million. lol. Probably could have put the oil I drained out of in the gas tank and ran on the oil gas mixture.
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Good thing my old 1979 Chevy 1 ton with a 350 and the choke stuck on didn’t have O2 sensors they would be - a million. lol. Probably could have put the oil I drained out of in the gas tank and ran on the oil gas mixture.
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