P304 is very random - trim questions

[urdrwho]

Last month I picked up a used 97 Subaru Outback with 50,000 miles on the transplanted engine. I knew when I bought the car it had a lumpy engine (idle and under acceleration). From my history with Subbies I thought a new set of wires and plugs would be the fix. The car itself sat for 4 years with a blown engine - reason for 50K transplant.

After having the car for a week it threw a P304. It is a random CEL that won't be thrown in any regular manner. Sometimes I can drive 150 miles, sometimes 130 miles and during idle or slow acceleration (such as parking lot) I'll throw a P304.

I've done a lot to track it down and fix the lumpy engine. New vac lines, cleaned idle control valve, cleaned EGR port, new wires/plugs, new fuel filter, cleaned the MAF (MAF cleaner), Tecron fuel cleaner one fill-up, lucas fuel cleaner another fill-up, probably things I can't remember.

From cold to closed loop temp, I ran live time on my scan tool. Short Term Fuel Trim Bank 1-Sensor is always a negative % number up to a certain point in time.

At this point of the test long term goes lean.

No DTC was thrown during this test and it may go days before it throws a code.

Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 status--
Calculated LOAD Value(%)4.7
Engine Coolant Temperature(¡£C)123
Short Term Fuel Trim -Bank 1(%)-0.8
Long Term Fuel Trim - Bank 1(%)-2.3
Intake Manifold Absolute Pressure(kPa)4.4
Engine RPM(rpm) 987
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)24.0
Air Flow Rate from Mass Air Flow(g/s)0.01
Absolute Throttle Position(%)0.0
Location of Oxygen SensorsB1S12--B2S----
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.160
Short Term Fuel Trim Bank 1-Sensor 1(%)-0.8
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.175
Short Term Fuel Trim Bank 1-Sensor 2(%)0.0
OBD requirements to which vehicle is designedOBDII
----------------------
Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 status--
Calculated LOAD Value(%)4.7
Engine Coolant Temperature(¡£C)125
Short Term Fuel Trim -Bank 1(%)-0.8
Long Term Fuel Trim - Bank 1(%)-2.3
Intake Manifold Absolute Pressure(kPa)4.2
Engine RPM(rpm) 962
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)22.0
Air Flow Rate from Mass Air Flow(g/s)0.01
Absolute Throttle Position(%)0.0
Location of Oxygen SensorsB1S12--B2S----
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.690
Short Term Fuel Trim Bank 1-Sensor 1(%)-2.3
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.060
Short Term Fuel Trim Bank 1-Sensor 2(%)0.0
OBD requirements to which vehicle is designedOBDII
----------------------
Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 status--
Calculated LOAD Value(%)4.7
Engine Coolant Temperature(¡£C)125
Short Term Fuel Trim -Bank 1(%)-1.6
Long Term Fuel Trim - Bank 1(%)-2.3
Intake Manifold Absolute Pressure(kPa)4.2
Engine RPM(rpm) 975
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)23.0
Air Flow Rate from Mass Air Flow(g/s)0.01
Absolute Throttle Position(%)0.0
Location of Oxygen SensorsB1S12--B2S----
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.140
Short Term Fuel Trim Bank 1-Sensor 1(%)-0.8
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.135
Short Term Fuel Trim Bank 1-Sensor 2(%)0.0
OBD requirements to which vehicle is designedOBDII
----------------------
Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 status--
Calculated LOAD Value(%)4.7
Engine Coolant Temperature(¡£C)125
Short Term Fuel Trim -Bank 1(%)0.0
Long Term Fuel Trim - Bank 1(%)-2.3
Intake Manifold Absolute Pressure(kPa)4.2
Engine RPM(rpm) 962
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)22.0
Air Flow Rate from Mass Air Flow(g/s)0.01
Absolute Throttle Position(%)0.0
Location of Oxygen SensorsB1S12--B2S----
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.080
Short Term Fuel Trim Bank 1-Sensor 1(%)-0.8
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.105
Short Term Fuel Trim Bank 1-Sensor 2(%)0.0
OBD requirements to which vehicle is designedOBDII
----------------------
Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 status--
Calculated LOAD Value(%)4.7
Engine Coolant Temperature(¡£C)125
Short Term Fuel Trim -Bank 1(%)-0.8
Long Term Fuel Trim - Bank 1(%)-2.3
Intake Manifold Absolute Pressure(kPa)4.4
Engine RPM(rpm) 950
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)23.0
Air Flow Rate from Mass Air Flow(g/s)0.01
Absolute Throttle Position(%)0.0
Location of Oxygen SensorsB1S12--B2S----
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.380
Short Term Fuel Trim Bank 1-Sensor 1(%)0.0
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.160
Short Term Fuel Trim Bank 1-Sensor 2(%)0.0
OBD requirements to which vehicle is designedOBDII
----------------------
Number of DTCs stored in this ECU 0
Fuel system 1 statusCL
Fuel System 2 status--
Calculated LOAD Value(%)4.3
Engine Coolant Temperature(¡£C)127
Short Term Fuel Trim -Bank 1(%)-3.1
Long Term Fuel Trim - Bank 1(%)-2.3
Intake Manifold Absolute Pressure(kPa)4.2
Engine RPM(rpm) 925
Vehicle Speed Sensor(km/h)0
Ignition Timing Advanece for #1 Cylinder(¡£)22.0
Air Flow Rate from Mass Air Flow(g/s)0.01
Absolute Throttle Position(%)0.0
Location of Oxygen SensorsB1S12--B2S----
Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.070
Short Term Fuel Trim Bank 1-Sensor 1(%)-3.1
Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.330
Short Term Fuel Trim Bank 1-Sensor 2(%)0.0
OBD requirements to which vehicle is designedOBDII
----------------------

 

[SteveSRT8]

First guess is a bad injector, remember that all the wiring up to that is suspect also. Especially after a transplant.

A lot of folks assume a code tells you what to fix. But many times a simple wiring fault is to blame.

Best of luck, as diagnosis is always where the skill lies...

 

[Trav]

Are the red or white top side feed injectors?
If so i have set of reds all cleaned and ready to go i can let you have cheap. They are from a 97 with low miles and run good. PM me if you need them.

 

[urdrwho]

Codes are a funny business. I've read posts of people that changed things like the knock sensor, the O2 , etc. and it fixed a misfire. All done without the knock sensor or 02 sensor throwing a code but it fixed the misfire. So codes or the lack of can be misleading.

The lumpy gets worse as the engine heats up.

I've sprayed all around the engine looking for vac leaks but found none. I could pop for $99 and get a smoke test.

 

[Doog]

Swap the coils from side to side. See if it changes. If not, do a double techron cleaning and see if that helps. If not, time to pull the injectors.

I see you already did the techron. Skip that.

 

[cchase]

-2 to -3% is not enough to cause any issues and is "normal"... you have to be way out beyond 10-20% to be a sign of something amiss.

 

[urdrwho]

One thing I forgot is that when cursing at 55>65 the car feels fine. When coming to a slow stop you can't feel it but as soon as you brake at the light, it is lumpy. Taking off again it is lumpy. There are times you can feel a slight boost as though for that moment things are working well.

 

[urdrwho]

Doing a swap is on my list.

 

[urdrwho]

Well when the car was warming up it did hit
Short Term Fuel Trim -Bank 1(%)-14.1.
Short Term Fuel Trim -Bank 1(%)-15.6

Originally Posted By: cchase
-2 to -3% is not enough to cause any issues and is "normal"... you have to be way out beyond 10-20% to be a sign of something amiss.

 

[LeakySeals]

Your scanner results would be helpful with a P0300 random misfire (all cyls). But your CEL is a random misfire isolated to cyl 4. So its spark, coil, injector, vacuum or combustion related issues for that cyl. IMO that rules out fuel trim. may hide the problem some, but not the reason.

Swap coil(s) with another cyl, see if the CEL follows. If not, get the compression checked, service the injector, and so on.

 

[urdrwho]

My fear has been taking a compression test.

One time and only one time it did throw one P303 --- or was it P302?

I did try a used coil and it didn't make any difference. The car body and leather interior is in very good condition, got it for $1200 so I have room to fix an expensive problem. I don't want to but if it turns out to another transplant, so be it. It just won't be the deal I had hoped for.

Wish I could run the same checking routine as that of my 95 Caddie Concours. On the caddie if I press the right buttons I can shut down one hole to isolate problems. At least I think I did that at one time.

Originally Posted By: LeakySeals
Your scanner results would be helpful with a P0300 random misfire (all cyls). But your CEL is a random misfire isolated to cyl 4. So its spark, coil, injector, vacuum or combustion related issues for that cyl. IMO that rules out fuel trim. may hide the problem some, but not the reason.

Swap coil(s) with another cyl, see if the CEL follows. If not, get the compression checked, service the injector, and so on.

 

[LeakySeals]

You still have things to try. Swap injectors, inspect the rubber o-ring seal closely. They can dry up over time causing a vacuum leak.

 

[Doog]

You can get a new coil on RockAuto for $65. I think I would try one on cyl #4 and see what happens. Plus you can always blast it with a whole bottle of Redline SI1 in the gas. I have had dirty injectors take several cleanings before they come around.

 

[urdrwho]

These aren'[t individual coil packs. It is one coil with four connections. I like Redline products and maybe Ill give it a try.

I just did an experiment with the MAP and fuel pressure regulator. I was surprised.

Just for kicks I disconnected the vac line that is attached to the intake, the one that has a "T" and goes to the FPR and the pressure sensor setup. I expected an immediate CEL for the MAP. Didn't happen, so I went for a short drive. I expected to see a worse running engine. After all the FPR wasn't working and the MAP wasn't working, so something should go wrong.

No worse running engine. Hm? In fact the idle may have been a bit less lumpy but I attributed that to the increased RPM's because the intake had un-metered air entering it and higher idle.

Came home stopped the car, hooked up my code reader, started the car and there was a CEL. Yep it was the MAP.

So I hooked pulled the vac line off the FPR and expected to see some kind of difference but no, not one bit of difference. I pulled a vac on the FPR and it held.

Not sure what it means but that little test didn't change a thing and I wonder if it is working correctly. If #4 is the last cyl to get gas and the FPR is acting wiggy, then maybe it is a fuel problem. Just more Hm???? to the problem.


Originally Posted By: Doog
You can get a new coil on RockAuto for $65. I think I would try one on cyl #4 and see what happens. Plus you can always blast it with a whole bottle of Redline SI1 in the gas. I have had dirty injectors take several cleanings before they come around.

 

[LeakySeals]

Just like the A/F O2, the MAP/MAF is calibrating the entire engine, so I don't think its the cause of a misfire on only 1 cyl unless that cyl is on the edge with some other mechanical issue.

 

[cchase]

Originally Posted By: urdrwho
Well when the car was warming up it did hit
Short Term Fuel Trim -Bank 1(%)-14.1.
Short Term Fuel Trim -Bank 1(%)-15.6

Originally Posted By: cchase
-2 to -3% is not enough to cause any issues and is "normal"... you have to be way out beyond 10-20% to be a sign of something amiss.


You can't put much stock in fuel trim when the car is still open loop (warming up). Some vehicles use whatever the last fuel trim was and stick at that, some apply a random fuel trim for any number of reasons. Either way, the computer is not changing fuel trim in any realistic manner during warm up.

Your running numbers do not indicate an issue with fuel trim.

 

[urdrwho]

True true.

While messing with that area, revving the engine, I did manage to throw the P304.

I read an article that the #4 cyl is last in line for fuel and if there is a fuel problem #4 will show it.

Wish the weather was better so I could swap the injectors.

Originally Posted By: LeakySeals
Just like the A/F O2, the MAP/MAF is calibrating the entire engine, so I don't think its the cause of a misfire on only 1 cyl unless that cyl is on the edge with some other mechanical issue.

 

[LeakySeals]

Interesting. Last on the fuel line. You replaced the filter. Leaves the pump, regulator and injector. Some fuel pressure areas to investigate.

 

[urdrwho]

I was surprised that removing the vac from the FPR, which crippled it, did not make any negligible difference in how it ran. Would a crippled FPR allow more or less gas?

Originally Posted By: LeakySeals
Interesting. Last on the fuel line. You replaced the filter. Leaves the pump, regulator and injector. Some fuel pressure areas to investigate.

 

[LeakySeals]

Anything electronic (sensors) should throw a hard failure code immediately if disconnected while running. As far as vacuum and fuel mix, over time it would make a difference as the ECU learned and attempted to compensate. After a day or a few drive cycles, it may complain with an indirect code (like misfires from being too lean) that could be traced back to a vacuum leak. Other vacuum issues its obvious with immediate impact to idle. So it depends what you disconnect whether you get a symptom or a CEL immediately or a delayed problem that shows up in a day or so.