Troubleshooting P0300 and other P030X codes (a more systematic approach)

[scottfab]

I have read over the last year or so many threads on various codes being set having to do with “missing”. These range from combinations of non P030x codes with P030x codes as well as, P030x only, codes. This tread will deal with P030x only codes. These tend to me intermittent and therefore difficult to isolate. Most posted solutions have to with shot-gunning a wide set of solutions in the interest of saving time toward getting the vehicle up and running. This thread will attempt to set a series of “isolation” steps toward finding the most prevalent solution and then the lesser.

I will be purchasing a “Data Logger” for ODB II.
I have a scanner for ODB II and an old data logger but it will not work on ODB II. Scanners are fine for some failures. A data logger will be indispensable for this thread. Whether it becomes a necessary device in the isolation of these failures is TBD. (to be decided)

Anyone out there have a favorite data logger they want to recommend? I see several,
The Autoxray, DynoScan, etc.

The Goal here is to not only find the SOB intermittent P030x codes on my 03 4.6L Explorer but to document the process and finally to list a more complete troubleshooting tree toward finding these POS failures. The various parts stores seem to recommend the widest possible set of components to replace. Eventually they know you’ll find it but if they sell you a few extra parts, whose to know right? This is not acceptable.

 

[scottfab]

Data shows all

I was seeing codes
P0300, 301, 302, 304 and 308 (and sometimes 316)
I have my data logger device now. (Auturra A-302).
I took all day to install it. (long stroy but not Auturra's fault).
Then it took just 20min to set up the graphs and capture data
from only the O2 sensors (all four O2 sensors). I could see bank 1 sensors moving normally
but the second sensor on bank 2 was not moving. It is the one on
the down hill side of the cat.
Beats the hell out of bulk replacing the plugs, injectors, coil etc.
Looks like I need just one O2 sensor.
I can live with that.

The only disappointing thing about the device so far is that you have
to pay more to get the "extended" features from each car vendor.
For Ford you get ABS, Air bags, drive train and dash lights. I will pass on
that for now.

 

[matt0248]

A failed downstream O2 sensor will not cause misfires, it is only there to monito emissions. Bank 2 is for cylinders 5-8 anyways, not 1-4. It is possible that the cat is plugged, this can cause too high backpressure and misfires. Or it may just need plugs or coils. I would swap the coils from cyls 1 and 2 with cyls 5 and 6 to see if the misfire follows the coils. If the misfire stays it could be a injector or plug problem.

 

[scottfab]

A failed downstream O2 sensor will not cause misfires, it is only there to monito emissions. Bank 2 is for cylinders 5-8 anyways, not 1-4. It is possible that the cat is plugged, this can cause too high backpressure and misfires. Or it may just need plugs or coils. I would swap the coils from cyls 1 and 2 with cyls 5 and 6 to see if the misfire follows the coils. If the misfire stays it could be a injector or plug problem.

Your sure about that? I swapped the two downhill O2 sensors and the slow moving one moved to the other side. Since #8 is misfiring and it is on the left side (Bank 2) I'd say that both sides are involved. As for swapping things. That had already been tried before I got serious and got the datalogger. I swapped #5 coil and plug with #8. No effect. As for injectors? Yah that is another easy swap. I'll do it with #5 and #8. That is, if a code get's set and the miss does not change.
In the mean time I need to study the fuel parameters I am seeing in the data.
Long term fuel B1
Long term fuel B2
Short term fuel trim B1
Short term fuel trim B2
Short fuel trim B1 S1
Short fuel trim B1 S2
Short fuel trim B2 S1
Short fuel trim B2 S2

I am curious about the Bs and Ss in the fuel trim. Almost as if the ECM listens to both O2 sensors on both banks for adjusting fuel . hmmmmm
More to come........

 

[matt0248]

In my experience, 10 years as a tech. I had never seen a bad O2 cause a misfire. Yes the sensor can get lazy/slow, but it should not effect fuel trim enough to cause a misfire. You'd get rich or lean codes first. Do an exhaust back pressure test too. You can get a back pressure gauge that screws into one of the bungs that the 02 comes out of. too much exhaust back pressure from a plugged cat will cause misfire under load.

 

[scottfab]

In my experience, 10 years as a tech. I had never seen a bad O2 cause a misfire. Yes the sensor can get lazy/slow, but it should not effect fuel trim enough to cause a misfire. You'd get rich or lean codes first. Do an exhaust back pressure test too. You can get a back pressure gauge that screws into one of the bungs that the 02 comes out of. too much exhaust back pressure from a plugged cat will cause misfire under load.

Well based on what you've said then it's not likely a blocked cat. There is no lack of power at all and the missing event only happens upon deceleration and then only after it's very warmed up and driven for 20min or so.

I would think this could be something similar to what I've seen before where an O2 sensor reports that the mixture is rich when it's not. The ECM would respond by going leaner. If it goes too lean... bingo. Misfire.
In my 20yrs of working on 02 sensor controlled engines I've see both too rich and too lean conditions but codes indicating that.
If one or just a few injectors are lean then maybe that's it. An overall lean code would not be set since the other injectors keep the level of fuel up.

First I need to see it set a code again after the swap of O2 sensors. (down side ones) If it sets codes I will look to see if the combo of codes is the same.
From there I think if they are the same I'll go for injector swaps.
It could very well be I have a lazy O2 sensor AND and injector problem. What I'd really like to do is find data evidence instead of just guessing per the code troubleshooting recommendations in the manual.

I just remembered a technique I've used before. And that is to force an OPEN LOOP condition then watch the O2 sensors. In OPEN LOOP things should go rich and the sensors should report so.
I will still keep the cat blocking issue in mind since it maybe marginal. With time if it got worse then power loss would follow. I do remember working on a vett that had that issue. Power loss was the main symptom.
The adventure continues....

 

[scottfab]

I have an update. After swapping the O2 sensors I note the "slowness" of the O2 response had move to the otherside but... that did not fix the 30x codes. Then I tried swapping the fuel injector from #8 to #5 becase #5 had never set a code. Result was #8 still fails. From before I started this tread I had already swapped the plug and coil from #8 so that out too.
Sooo right now I am getting consistent misses from #8 and less so but predictable misses on #2 and sometimes #1 and #4.
This is certainly strange.
If there is blockage at the CAT it would have to be both sides. But then why would the other cylinders not miss? weird. Unless maybe there are some burnt valves?
Maybe a compression test is next. Ether that or I pull the cat assembly and inspect for blockage. Does not seem that difficult to get out.

 

[OGHARDBODY]

Any updates? Was it the cat?

 

[scottfab]

Any updates? Was it the cat?

Nope not cats.
Apparently it's and extremely slow coolant leak into the intake somewhere.
I say extremely slow because there was no initial observable loss of coolant nor excessive vapor in the exhaust. After warm up the leak seals itself.
After an extended time I now see loss of fluid.
The plan now is to pull the intake plenum off and possibly a head.
Probably this weekend
Do you have a similar problem?

 

[OGHARDBODY]

Yeah i installed an engine in 2000 explorer no codes at first then i got p0171 and p0174 changed plenum gaskets fixed the problem,two weeks later i got p0304 and 305 exchanged wireset autozone since i had put new wihen i installed engine cleared code then i got p0300 so i got new motorcraft wires at dealer and new plugs motorcraft again so i will see what happens from here? I still have warranty on engine so if no solution soon i will just pull motor and install new one this is frustrating....

 

[scottfab]

Yeah i installed an engine in 2000 explorer no codes at first then i got p0171 and p0174 changed plenum gaskets fixed the problem,two weeks later i got p0304 and 305 exchanged wireset autozone since i had put new wihen i installed engine cleared code then i got p0300 so i got new motorcraft wires at dealer and new plugs motorcraft again so i will see what happens from here? I still have warranty on engine so if no solution soon i will just pull motor and install new one this is frustrating....

Sounds like the engine from a 2000 is quite a bit different than a 2003.
On a 2003 the ignition there is a separate coil for each cylinder.

 

[rhaynes]

good info here - http://easyautodiagnostics.com/index_ford/index_of_articles_1.php

 

[scottfab]

The problem on mine ended up being the intake manifold. It had developed cracks in multiple places.
Symptoms were failure codes varying between P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308 and P0316