2004 3.8L Struggling W/ P0175 Code For Months

SVT232V6

Member
I have been struggling with a P0175 Bank 2 System Too Rich code for months now. Car usually runs ok on start up, then gets worse after it warms up. Fuel pressure starts off around 30-40 psi then goes up to 67 psi after it warms. Is that normal? So far I have replaced the following:

-Spark plugs
-Plug wires gapped at .054
-Plenum gasket
-Cleaned fuel injectors
-MAF Sensor
-DPFE sensor
-Fuel filter

I had a code for the MAF sensor(intermittent signal/low voltage) so I replaced it. DPFE sensor had cracked off during my changing of the spark plugs and wires(plugs were rusty) so that’s new. Fuel filter was replaced when I changed the engine oil, transmission fluid and filters. I have been trying to chase this issue down with no luck. I thought I had it figured out last night when I discovered my IMRC rod bushings were missing from the IMRC Control Unit arm so the passenger side wasn’t even operating. Replaced the bushings, reconnected the rod and put everything back together. Took it for a ride and it ran better, but after I got home it started idling off again and threw P0175 again. There was also a Misfire Cylinder 4 code but I cleaned the plug and it’s gone. I’m stuck and need some help. I did have a code for the upstream B2/S1 O2 sensor and replaced that with a Denso sensor from RockAuto if that has anything to do with it. Below is a screenshot of some values I was looking at on my BlueDriver.
 

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fasterthanyou

Active Member
67psi isnt normal. Are you using a mechanical gauge or is it reading that from the scanner data?

Those upstream o2's look to be switching back and forth normally. Rear o2's are insignificant. They only monitor cat deficiency and have no affect on engine performance.

Also, what do the o2's show when you hold the engine rpm at 2,000 rpm for 10 seconds in neutral? They should switch back and forth from ~100mV to ~800mV very rapidly. Multiple times per second. If one is "lazy", and not switching rapidly that could be your problem.

What are your short term fuel trim percentages for bank 1 and bank 2?
 

SVT232V6

Member
67psi isnt normal. Are you using a mechanical gauge or is it reading that from the scanner data?

Those upstream o2's look to be switching back and forth normally. Rear o2's are insignificant. They only monitor cat deficiency and have no affect on engine performance.

Also, what do the o2's show when you hold the engine rpm at 2,000 rpm for 10 seconds in neutral? They should switch back and forth from ~100mV to ~800mV very rapidly. Multiple times per second. If one is "lazy", and not switching rapidly that could be your problem.

What are your short term fuel trim percentages for bank 1 and bank 2?

The psi reading is from the scanner. I can’t find a test port anywhere on the fuel rail to verify fuel pressure with a mechanical gauge.. Am I missing something?

The O2s appear to be cycling back and forth similarly to each other. Is this what you’re referring to?

Edit: I also switched fuel injector positions between banks, just in case the problem moves with the switch.
 

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Sauceja

Member
could fuel pump controller not be backing off when it reads a higher psi?

Not much experience with returnless system.
 

SVT232V6

Member
Drove the car 26 miles to a friend’s exhaust shop in Hilo. Car ran perfectly all the way to town. Parked the car, turned it off, went to sign in. Came back and started it up, now it’s idling kind of weird. I will hold the idle at 2000 RPM and report back when I pick it up tomorrow. Here are some screenshots I took during the drive. Also code P2196 came up as a new code.
 

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Sauceja

Member
Wouldn't be that .That would affect both banks.

But if your fuel psi at the rail is high something isn't right.
 

6 Shooter

Well-Known Member
Fuel pump controller?? Where is it and how can I check or test its operation?

On the driver's side fuel rail, there is a Schrader valve just below the location where the fuel rail pressure sensor is located. The solution you look for is a little pricey and a challenge to install, but you can install an electric fuel rail pressure sensor at this location and run the wires inside the car to a fuel pressure gauge which will also require a plastic dash bezel or a plastic door rail pod. The result will be a gauge that constantly shows fuel rail pressure.
 

fasterthanyou

Active Member
The screen shots you posted showed everything to be good. O2's were switching like they should and short term fuel trims were within/around 3% which is normal. ....weird.

The only way those rich codes will set is if the o2 sensors are bad or if the fuel pressure is too high. And since you're saying the fuel pressure is reading in the 60s then it has to be the FPDM.

If the fuel rail sensor alone was defective and reading 60psi when in reality its 40psi then your o2's would read lean instead of rich because the ecu would be reducing the injector duty cycle to try and compensate for the increase in pressure that the fuel rail sensor is reading.

I dont think a defective fuel pump would create more pressure, if anything a failing fuel pump would create less pressure.

So the only thing left is the fpdm.

Thoughts anyone?
 

6 Shooter

Well-Known Member
The fuel rail pressure sensors do fail when the fuel pressures hit above 80+ psi. I have blown 2-3 of them in the past. Replacing the sensor may bring some better control to the pressures in the fuel rail. A permanent fix is to replace the stock returnless fuel value files with improved new ones.
 

SVT232V6

Member
Wouldn't be that .That would affect both banks.

But if your fuel psi at the rail is high something isn't right.

On the driver's side fuel rail, there is a Schrader valve just below the location where the fuel rail pressure sensor is located. The solution you look for is a little pricey and a challenge to install, but you can install an electric fuel rail pressure sensor at this location and run the wires inside the car to a fuel pressure gauge which will also require a plastic dash bezel or a plastic door rail pod. The result will be a gauge that constantly shows fuel rail pressure.

I just got the car back yesterday afternoon. I will check it tomorrow afternoon. Had planned on doing that today, but then got offered OT

The screen shots you posted showed everything to be good. O2's were switching like they should and short term fuel trims were within/around 3% which is normal. ....weird.

The only way those rich codes will set is if the o2 sensors are bad or if the fuel pressure is too high. And since you're saying the fuel pressure is reading in the 60s then it has to be the FPDM.

If the fuel rail sensor alone was defective and reading 60psi when in reality its 40psi then your o2's would read lean instead of rich because the ecu would be reducing the injector duty cycle to try and compensate for the increase in pressure that the fuel rail sensor is reading.

I dont think a defective fuel pump would create more pressure, if anything a failing fuel pump would create less pressure.

So the only thing left is the fpdm.

Thoughts anyone?

That’s the Fuel Pump Drive Module, correct? Little box in the trunk, driver’s side?

The fuel rail pressure sensors do fail when the fuel pressures hit above 80+ psi. I have blown 2-3 of them in the past. Replacing the sensor may bring some better control to the pressures in the fuel rail. A permanent fix is to replace the stock returnless fuel value files with improved new ones.

Is that possible without a tool like an SCT XF4?
 

6 Shooter

Well-Known Member
That’s the Fuel Pump Drive Module, correct? Little box in the trunk, driver’s side?

No. It is the little black box on the driver's side fuel rail. There is also a vacuum line connected to it. BTW, I have no way of testing one. But, when the pressures get too high, they get out of calibration and cause large fuel rail pressure swings.
 

SVT232V6

Member
So it’s my day off and I have been working on the car. I mentioned I switched injectors from one bank to the other but the P0175 code is still there. Fuel pressure is still ~67 psi. The car runs good on the highway, but has a quick lope at idle. I tried swapping the Fuel Rail Pressure Sensor over from my Mach1, no change. Guess I could try the Fuel Pump Drive Module also and see if that changes anything.

On the driver's side fuel rail, there is a Schrader valve just below the location where the fuel rail pressure sensor is located. The solution you look for is a little pricey and a challenge to install, but you can install an electric fuel rail pressure sensor at this location and run the wires inside the car to a fuel pressure gauge which will also require a plastic dash bezel or a plastic door rail pod. The result will be a gauge that constantly shows fuel rail pressure.

I still can’t find a test port on my fuel rail. The bottom corner has the FRPS with the vacuum port, but no valve to connect my pressure gauge. Am I doing something wrong or missing something here? There is a port on my Mach that it connects to just fine.
 

SVT232V6

Member
might be a time for a picture of the top of your engine showing the fuel rails.

10-4. Don’t see any port on the top, bottom or the side.
 

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SVT232V6

Member
The screen shots you posted showed everything to be good. O2's were switching like they should and short term fuel trims were within/around 3% which is normal. ....weird.

The only way those rich codes will set is if the o2 sensors are bad or if the fuel pressure is too high. And since you're saying the fuel pressure is reading in the 60s then it has to be the FPDM.

If the fuel rail sensor alone was defective and reading 60psi when in reality its 40psi then your o2's would read lean instead of rich because the ecu would be reducing the injector duty cycle to try and compensate for the increase in pressure that the fuel rail sensor is reading.

I dont think a defective fuel pump would create more pressure, if anything a failing fuel pump would create less pressure.

So the only thing left is the fpdm.

Thoughts anyone?

You mentioned the short term fuel trims were supposed to be around 3% of each other? I noticed a larger difference today while looking at the data while the car was idling in the garage. Also looked at the B2S1 O2 Sensor Voltage reading at I saw what looks like a flat spot? Does that point out a clue?
 

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fasterthanyou

Active Member
Looks like b2s1 is starting to fail. One free but tedious way to test the sensor is by swapping it from bank 2 to bank 1 and see if it follows the sensor or not.

The weird thing about your fuel pressure reading is that if you really had 69psi at the rail, bank 1 sensor would be reading rich and would be pulling 20-30% fuel instead of adding 11% fuel Since more fuel pressure with the same injector pulse width would cause a richer mixture.

There are fuel pressure gauge adapters that connect in line with the fuel rail. It is an adaptor that the fuel feed line connects into and then the adaptor connects to the rail where the feed line normally goes into.
 

SVT232V6

Member
Looks like b2s1 is starting to fail. One free but tedious way to test the sensor is by swapping it from bank 2 to bank 1 and see if it follows the sensor or not.

The weird thing about your fuel pressure reading is that if you really had 69psi at the rail, bank 1 sensor would be reading rich and would be pulling 20-30% fuel instead of adding 11% fuel Since more fuel pressure with the same injector pulse width would cause a richer mixture.

There are fuel pressure gauge adapters that connect in line with the fuel rail. It is an adaptor that the fuel feed line connects into and then the adaptor connects to the rail where the feed line normally goes into.

I may have to try that. Weird because Bank 2 has new upstream and downstream sensors. Bank 1 still has the factory oem sensors.
 
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