Hi All,

Been having fuel trim issues for a while now need advice. I originally had a no start which was corrected by replacing clogged fuel injectors. However, my STFT was hovering between 10-25% and eventually check engine comes on steady and lately it flashes with severe acceleration/run issue. So, I replaced the fuel filter and original fuel pump which seemed to correct my issue but the problem returned with a system too lean bank 1 P0171 with car running fine but got worse over time as explained above. Finally, it started to shot off at full stop. I restarted it and limped home, barely. For some reason I also got a P0339 code (CRANK SHAFT POSITION SENSOR A CIRCUIT INTERMITTENT). Not sure if this is a cause or a symptom. The next day the car started fine with the usual STFT between 10—25% at idle. There is no change in fuel trim when RPM’s are increased so a vacuum leak can be ruled out. I suspect a fuel delivery problem, AGAIN, but why would the check engine flash one day (long road trip) and car runs decent the next day albeit very lean? Also, what about the Cran Shaft Pos Sensor, could it cuase my performance/run issue simulating a fuel delivery problem?

 

What is the reading of your downstream O2 sensor? (B1S2)
This should be the first step before changing injectors and gas pump!

 

B1s2=0.75v.

 

It's still less than 0.90 volt so it is safe to assume that A/F ratio sensor is not misreading normal mixture for lean. Vacuum leaks do not affect fuel mixture on the MAP controlled engine at least according to the book.
What is the fuel trim reading on cruising vs idle?
In some rare cases the fuel pressure regulator in the tank can bypass dumping too much fuel back into the tank.
Applying external 10 to 20 PSI pressure to the fuel tank unit fuel line outlet can find internal leaks (it should hold it for at least 10 minutes)

 

This data is for a 20-mile trip.

CRUISING (2000 rpm) STFT=21 TO 30%
IDLE (750 rpm) STFT= 16 TO 18% and towards the end went up to 27%
The LTFT varied from -1% to 3%

Not sure if this is relevant but I also have a pending P057 code “check fuel cap.” My fuel cap is okay however.



Thank you for your input & help!

 

Because LTFT is not increasing to correct STFT (it does it there is a fuel delivery problem) and of the flashing CEL (even one episode), I would ask to pull the coils and make sure that spark plugs are nice and tight (ignition misfire cause B1S2 voltage to be on high normal) .
If no issue with spark plugs, next will be reading of the MAP sensor (A/T, metric units):
idle in park , A/C off : 26..27
drive+brake, A/C off: 33...36
Coolant temperature sensor must read ambient temperature with engine off and about 95 to 99C when fans kick in.

 

What is used to read MAP sensor and and at what location? What unit of measure? Thanks.

 

OBD II Scanner with life data, reading is in kPa

 

I had a feeling you would say this. My scanner is not a high end one, does not have the MAP sensor readings. Any other way to do this or do I need a better scanner? Thanks.

 

Okay, I was able to get the MAP data:

IDLE=27 kPa
RUN/DRIVE 2100 RPM=48-99kPa, hovering around 65-75kPa during drive
COOLANT TEMP was 86C at end of 11 mile drive.

Seems like my run MAP data is higher than what you indicated. What say you?

 

Second number is for car with A/ET held with brake in drive.
During acceleration I have 75 kPa as well.
Next step to remove coils and check for the spark plug leaks. Flashing CEL is the thing concerning me the most!

 

Doctor,
I think we can rule out spark plug leaks for these reasons. Last Feb 2022 I had cylinder 2 misfire which led to a no start condition. Because of that, I replaced many items that needed to be replaced anyway do to age and mileage 177,000, etc.: I personally replaced spark plugs, coils, fuel filter, egr valve and performed a valve lash adjustment. Car still would not start. Finally, I replaced the fuel injectors and car started. However, fuel trim was not sat. I then purchased a new denso fuel pump and things improved a little and fuel trim was still off. There was no oil on my spark plugs at that time, they actually looked good for their mileage. This time, and I failed to mention, I had cylinder misfires in ALL cylinders with the flashing CEL along with the lean code. Cylinder misfire in all cylinders implies a condition that is central to all cylinders, i.e., a fuel delivery issue, perhaps the fuel injectors again or I am suspecting a dirty fuel tank. I definitely feeling it hesitating during my drives as if fuel is obstructed for a fraction of time. Baffled again.

What say you doc?

 

On gas pump did you replace entire unit assembly or pump itself? The only thi9ng left is fuel pressure check to make sure pump gives enough pressure (to rule out leaking regulator)
Not a long ago a set of good used injectors fixed an issue with +40% LTFT (and P0171) on 2005 Rav-4 which had been sitting for 3 years; I was lucky enough to diagnose this without fuel pressure gauge by priming the line for 3 seconds, then unplugging the gas pump. The engine run for more than 10 seconds, ruling out internal pressure leaks.

 

I replaced the whole unit (fuel filter, primp, regulator). Things did improve, a little. Unfortunately I don't have the special connectors for the fuel pressure check. Because the vehicle is running with random hesitation/stuttering, I am going to assume fuel pressure is okay. I 'm going to clean my tank, though if this was/is the problem, a little to late. Having a hard time believing my fuel injectors are the problem again so soon, a lot has to be removed to get to them ;( Even though I don't believe there is a vacuum leak, I'm going to blow smote just to see. I am stumped and frustrated on this one.

 

Have you done a valve clearance (lash) adjustment? Misfire, lean code and hesitation are all symptoms that I have experienced due to the valve clearance being out of spec.

 

Mike, Yes I did. It needed it, but it was/is not the cause. Thanks for the reply.

 

sorry, missed that you had done a valve clearance adjustment. Wondering about the P0339 code. The CKP sensor is located below the egr valve (from what I can see in the shop manual. Do not have access to our 08 Fit at the moment. So cannot check. But it is likely fed from the same wiring harness that is connected to the injectors that you replaced. Wondering if replacing the injectors lead to damage of the wiring to the CKP sensor or at the connector itself. Sometimes the break in the circuit is so rapid that it does not set a code always but you experience hesitation. See if you can access the connector and look for any obvious signs of damage. Sometimes tug test works and is enough to break the wire if it is weak.

 

CKP sensor is located on the left, behind the crank pulley. So you can access it from underneath and should be able to access the connector. This connector is an area that is prone to damage from corrosion from road salt.

 

That explains why I never could find the CKP, LOL. . The diagram in the manual ( showing below the EGR ) does not help. I'll check underneath in the morning. If by chance you should happen to have a pic of its location, I'll be much obliged. I could not find one anywhere. Thank you!