Rich fuel mixture help - Toyota FJ Cruiser Forum
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post #1 of 27 (permalink) Old 09-20-2019, 08:11 PM Thread Starter
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Rich fuel mixture help

Ok Iím at a loss with this one and looking for some help.

So I had the Fj apart and installed a upgraded radiator, transmission cooler, replaced all the water hoses, and thermostat and housing. Put it all back together and pressure washed the underside and engine compartment throughly.

Now here is the problem. Fuel mileage dropped 4 to 5 mpg. I have been monitoring the system via odb2 for several days. No codes!! The A/f ratio seems to be very rich under modest acceleration and the exhausts temps seem to confirm this as well. TPS is within specs, MAF is within specs. O2 sensors seem to be in spec as well.

Anyone got any ideas?




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post #2 of 27 (permalink) Old 09-20-2019, 08:46 PM
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Re: Rich fuel mixture help

Yikes, thatís a huge drop! Following for my own benefit.

What got wet when you pressure washed the engine bay?


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post #3 of 27 (permalink) Old 09-20-2019, 08:54 PM
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Re: Rich fuel mixture help

This same issue happened to me years ago on a ford F350. Performed normal maintenance, flushing the radiator and replacing the thermostat. It was a week of troubling shooting before I discovered that I installed a thermostat with the wrong temperature range. The engine would never reach optimum operating temp and the ECM kept the fuel mixture rich.
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post #4 of 27 (permalink) Old 09-20-2019, 08:54 PM Thread Starter
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Re: Rich fuel mixture help

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Yikes, thatís a huge drop! Following for my own benefit.

What got wet when you pressure washed the engine bay?


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Pretty much everything, but it set for a couple of days before I started it back up, and it started up fine. Seems to run fine ie no skips of mis firing, just crappie mpg compared to before.


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post #5 of 27 (permalink) Old 09-20-2019, 08:56 PM Thread Starter
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Re: Rich fuel mixture help

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olongapo2 previously said: View Post
This same issue happened to me years ago on a ford F350. Performed normal maintenance, flushing the radiator and replacing the thermostat. It was a week of troubling shooting before I discovered that I installed a thermostat with the wrong temperature range. The engine would never reach optimum operating temp and the ECM kept the fuel mixture rich.


Engine temps are at 185 to 190. Isnít that about right?


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post #6 of 27 (permalink) Old 09-20-2019, 09:26 PM
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Re: Rich fuel mixture help

Possibly just water in the MAF sensor or MAF sensor connectors which is erroneously indicating to the ECU that there is more air entering the engine than actually is, and the ECU is commanding excess fuel.

Remove the MAF and clean it carefully, and de-mate the MAF connector and blow out both halves with clean, dry comoressed air.

Also, de-mate the connectors at all four of the exhaust gas sensors and blow out the connectors with compressed air.

But, much more info is needed to perform any kind of useful diagnostics.

1. What year model?
2. Original or aftermarket air cleaner system?
3. Have you verified that the engine air filter(s) are not water saturated?
4. How many miles on the odometer?
5. Have any or all of the exhaust gas sensors been replaced?

NEVER, EVER PRESSURE WASH THE ENGINE CMOARTMENT OR ANY PART OF THE WIRING HARNESS WITH A HIGH PRESSURE WASH SYSTEM

All the electrical connectors are “sealed”, but a 2,000 PSI pressure-washer will force water (or worse, detergent solution) past the seals, where it will stay and immediately cause false readings from sensors, or it will sit there for weeks or months, slowly causing corrosion
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Last edited by FJtest; 09-21-2019 at 06:53 AM.
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post #7 of 27 (permalink) Old 09-20-2019, 09:49 PM Thread Starter
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Re: Rich fuel mixture help

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FJtest previously said: View Post
Possibly just water in the MAF sensor or MAF sensor connectors which iis indicating to the ECU that there is more air entering the engine than actually is, and the ECU is commanding excess fuel.

Remove the MAF and clean it carefully, and de-mate the MAF connector and blow out both halves with clean, dry comoressed air.

Also, de-mate the connectors at all four of the exhaust gas sensors and blow out the connectors with compressed air.

But, much more info is needed to perform any kind of useful diagnostics.

1. What year model?
2. Original or aftermarket air cleaner system?
3. Have you verified that the engine air filter(s) are not water saturated?
4. How many miles on the odometer?
5. Have any or all of the exhaust gas sensors been replaced?

NEVER, EVER PRESSURE WASH THE ENGINE CMOARTMENT OR ANY PART OF THE WIRING HARNESS WITH A HIGH PRESSURE WASH SYSTEM

All the electrical connectors are ďsealedĒ, but a 2,000 PSI pressure-washer will force water (or worse, detergent solution) past the seals, where it will stay and immediately cause false readings from sensors, or it will sit there for weeks or months, slowly causing corrosion


MAF was the first thing I checked and cleaned, no moisture in the connector. I havenít checked the o2 sensors connects but I will tomorrow.



1. 2012
2. TRD intake
3. Filter does not appear to be saturated and MAF reads within specs at idle and at 2,500 rpm per specs.
4 137,000 miles
5. I havenít replaced any of the exhaust sensors but they appear to be reading voltages within factory specs.

Thatís whatís getting me, sensors seem to be reading a rich condition, high exhaust temps seem to confirm this (along with the poor mpg) but itís like the computer is not adjusting accordingly.

TPS sensor is within specs as well....



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post #8 of 27 (permalink) Old 09-20-2019, 10:17 PM
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Re: Rich fuel mixture help

Quote:
cory3122 previously said: View Post
MAF was the first thing I checked and cleaned, no moisture in the connector. I haven’t checked the o2 sensors connects but I will tomorrow.

1. 2012
2. TRD intake
3. Filter does not appear to be saturated and MAF reads within specs at idle and at 2,500 rpm per specs.
4 137,000 miles
5. I haven’t replaced any of the exhaust sensors but they appear to be reading voltages within factory specs.

That’s what’s getting me, sensors seem to be reading a rich condition, high exhaust temps seem to confirm this (along with the poor mpg) but it’s like the computer is not adjusting accordingly.

TPS sensor is within specs as well.... Sent from my iPhone using Tapatalk
How and where are you reading "exhaust gas temps"? The 1GR-FE has no true exhaust gas temperature sensors, only the electrical heater temperatures in the exhaust gas sensors.

At 137K miles, ALL four of your exhaust gas sensors (2 air/fuel, 2 O2) are well past their design life, and are very likely not providing accurate data to the ECU. They air/fuel sensors typically function correctly for 85 to maybe slightly over 100K miles, but are very unlikely to be accurate at 137K miles. It's not just output voltage that's critical, but linearity and response time.

A rich mixture typically LOWERS exhaust gas temperature, while a lean mixture RAISES exhaust gas temp.

Regardless of what else you might find, replace the air/fuel sensors ASAP, using ONLY the OEM Denso sensors.
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post #9 of 27 (permalink) Old 09-20-2019, 10:37 PM Thread Starter
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Re: Rich fuel mixture help

Quote:
FJtest previously said: View Post
How and where are you reading "exhaust gas temps"? The 1GR-FE has no true exhaust gas temperature sensors, only the electrical heater temperatures in the exhaust gas sensors.

At 137K miles, ALL four of your exhaust gas sensors (2 air/fuel, 2 O2) are well past their design life, and are very likely not providing accurate data to the ECU. They air/fuel sensors typically function correctly for 85 to maybe slightly over 100K miles, but are very unlikely to be accurate at 137K miles. It's not just output voltage that's critical, but linearity and response time.

A rich mixture typically LOWERS exhaust gas temperature, while a lean mixture RAISES exhaust gas temp.

Regardless of what else you might find, replace the air/fuel sensors ASAP, using ONLY the OEM Denso sensors.


Yeah the o2 sensors was my original suspect until I plotted them together and watched how they reacted voltage wise. I already had them in my cart to order and then second guessed it after looking at the readings from the computer.

Exhaust temps where pulled via odb2 scan from the exhaust sensors.

It was my understanding that running rich could raise or lower temps depending on the fuel and wasnít always one way or the other.

At the same time Iím also the dump a$& that thought it would be a good idea to take the pressure washer to the engine bay, smh. Lesson learned.




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post #10 of 27 (permalink) Old 09-21-2019, 12:34 AM
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Re: Rich fuel mixture help

Maybe check that the post-MAF intake coupling didn't get slightly bumped off (or cracked) from the pressure washer. Maybe some of the air going past the MAF isn't making it to the engine. The ECU is going to trust the MAF but, if not all of that air is getting there, it would run rich.
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