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P0307 affects transmission?

jharrypope

By jharrypope
in Ask A GM Technician

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jharrypope Enthusiast

jharrypope

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2003 Silverado, LS1 engine, mostly stock. No catalytic converters. Recently had to replace fuel pump, drove for a week and had no problems. had to take a road trip and 100 miles into the trip i get a flashing CEL. I pull over and use my handy scanner and i get the P0307 code. The only issue at that time was that it wouldnt shift into overdrive. Had plenty of power and I couldnt detect a miss. Anyways, after a little while it shifted into overdrive. This happened several more times, each time i would get a flashing CEL and the P0307 code and the tranny shifting problem and eventually the code and shifting problems went away. I also had the P0300 pop up once. Tried swapping coil packs around and the problem still stayed on cylinder 7. Did not try switching injectors as all of them were replaced about 1 month ago while dealing with another issue. Checked for vacuum leaks and found none. I have read many, many posts on this particular code but have not yet found one with the same symptoms as mine(transmission shifting). Wondering if during fuel pump install that some trash somehow got thru and clogged up injector in #7? Have tried fuel system cleaners and no luck. should i try a fuel injector cleaning kit or shell out some $$$ for a new injector?

Doug_Scott Senior Enthusiast

Doug_Scott

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If you are convinced it must be an injector, why not just swap the injector for one that is not near #7 cylinder? By that I mean look at the intake runners, can you tell what other cylinders are using the same part of the intake manifold? I don't know if the intakes are single or dual plane anymore. Single plane will be like a common plenum for all cylinders, dual plane uses two different plenums. Single plane was more for high rpm. If the intake is single plenum, swap cyl 2 and 7 injectors. If dual plane, swap injector 7 with one from the other plane, and as far from 7 as it can get.

jharrypope Enthusiast

jharrypope

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going to try swapping them around. Would that "misfire" cause the transmission not to shift into overdrive? And if it were a bad injector wouldnt it happen constantly instead of every once in a while?

Doug_Scott Senior Enthusiast

Doug_Scott

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Typically an injector is a go-no/go item. Unless there is a poor connection inside the injector. The injector is basically a solenoid. Fuel injector has voltage applied to one terminal, and the other terminal goes to the PCM. That part of the circuit is the ground side. The PCM controls the ground connection to enable/disable the injector. If the "plunger" inside the injector is sticky, it may cause a misfire. If you think about what the injector manages to do in the length of time it has to do it in, I am surprised it is not always setting the misfire code. This all assumes that the CEL code is not just referring to ignition system.

 

Just noticed something in your original post, no mention of changing spark plugs. If you have not changed them, then do that first, or at least pull number 7 plug and take a look at the tip of it. It should be a clean to tan colour, with no chunks attached. Also verify the gap is correct. Maybe swap with another cylinder or just change the one to see if it fixes the misfire.

jharrypope Enthusiast

jharrypope

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Typically an injector is a go-no/go item. Unless there is a poor connection inside the injector. The injector is basically a solenoid. Fuel injector has voltage applied to one terminal, and the other terminal goes to the PCM. That part of the circuit is the ground side. The PCM controls the ground connection to enable/disable the injector. If the "plunger" inside the injector is sticky, it may cause a misfire. If you think about what the injector manages to do in the length of time it has to do it in, I am surprised it is not always setting the misfire code. This all assumes that the CEL code is not just referring to ignition system.

 

Just noticed something in your original post, no mention of changing spark plugs. If you have not changed them, then do that first, or at least pull number 7 plug and take a look at the tip of it. It should be a clean to tan colour, with no chunks attached. Also verify the gap is correct. Maybe swap with another cylinder or just change the one to see if it fixes the misfire.

Had the plugs checked and they were ok. they have relatively low miles on them about 5000. Just wondering if the fuel pump install stirred up sediment in tank and it made it past fuel filter and is clogging up #7 but that wouldnt explain it happening over and over again. Have a mechanic friend going to swap the injectors this afternoon and we will also check the wiring harness / pigtails. will that code/issue cause the tranny not to shift into overdrive?

Doug_Scott Senior Enthusiast

Doug_Scott

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Does you truck have the fuel filter as part of the pump assembly, or is it an external filter that is in the fuel line on the frame somewhere around the area of the front door?

 

Any sediment in the tank should be caught by the filters. There is a "sock" type pre-filter screen type thing. It will stop coarse dirt, with the second filter be far more efficient. The main filter is made up of a pleated paper-like substance. Very similar to air filter media. The filter(more like screen) at pickup in the tank is just that, a screen. A very fine mesh that will trap anything over "dust " size. The dust gets caught in the mail fuel filter, and will become "mud" eventually.

 

Depending on the code that is thrown, truck may go into limp mode. I would imagine once that happens for a misfire, the PCM/TCM will not allow trans to lock up the convertor. Misfires with the torque convertor locked up will show up in the cab as engine roughness. Just like a car with a manual transmission that has a miss in the engine.

 

I don't recall ever having a vehicle that I owned go into limp mode. I have however experienced the "walk home" mode on more than one occasion.

jharrypope Enthusiast

jharrypope

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Does you truck have the fuel filter as part of the pump assembly, or is it an external filter that is in the fuel line on the frame somewhere around the area of the front door?

 

Any sediment in the tank should be caught by the filters. There is a "sock" type pre-filter screen type thing. It will stop coarse dirt, with the second filter be far more efficient. The main filter is made up of a pleated paper-like substance. Very similar to air filter media. The filter(more like screen) at pickup in the tank is just that, a screen. A very fine mesh that will trap anything over "dust " size. The dust gets caught in the mail fuel filter, and will become "mud" eventually.

 

Depending on the code that is thrown, truck may go into limp mode. I would imagine once that happens for a misfire, the PCM/TCM will not allow trans to lock up the convertor. Misfires with the torque convertor locked up will show up in the cab as engine roughness. Just like a car with a manual transmission that has a miss in the engine.

 

I don't recall ever having a vehicle that I owned go into limp mode. I have however experienced the "walk home" mode on more than one occasion.

The truck has an inline fuel filter on the frame rail and it was replaced a few months ago. The code that was thrown was the P0307. I couldnt tell that it was running on 7 cylinders, only thing odd was the RPM's went from 2000 rpm at 70 mph to 2500 rpm and it not going into overdrive

Doug_Scott Senior Enthusiast

Doug_Scott

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Not sure when GM changed the operation of the transmissions, but, my 2000 GTP would unlock the torque converter when you pressed the brake peddle. Try driving on the highway, set the trans to finish all its shifting, and then without lifting the gas pedal, use your left foot to just turn the brake lights on. See if the rpm goes up, and then after releasing the brake pedal, see if the rpm drops again. Do not brake hard enough to slow the truck.

gmtech4 Senior Enthusiast

gmtech4

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The truck has an inline fuel filter on the frame rail and it was replaced a few months ago. The code that was thrown was the P0307. I couldnt tell that it was running on 7 cylinders, only thing odd was the RPM's went from 2000 rpm at 70 mph to 2500 rpm and it not going into overdrive

look up the code ,,,,there is a heading that says"action taken when dtc is active"or something like that ,,,it will tell you there if the transmission defaults to 3rd gear or any other defaults,,,,limp home mode is an old term,not used anymore ,,its the computers response to a code ,,,,,,just like the stabilitrac and ABS messages come on (and disabled) when a throttle body code trips and turns on the CEL

 

nothing from the tank is reaching the injector,,,,hand this off to a tech ,,,,you're making yourself nuts messing with it

jharrypope Enthusiast

jharrypope

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did a vacuum leak check and on back side of intake near firewall while a scanner was hooked up and found a very slight vacuum leak. so slight that you couldnt hear it but the scan tool showed it on a graph. i have read that can cause the problem but wouldnt it always be there instead of intermittently?

Doug_Scott Senior Enthusiast

Doug_Scott

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did a vacuum leak check and on back side of intake near firewall while a scanner was hooked up and found a very slight vacuum leak. so slight that you couldnt hear it but the scan tool showed it on a graph. i have read that can cause the problem but wouldnt it always be there instead of intermittently?

 

Engine parts expand and contract with changes in temperature. in the winter, the cylinder heads may go from -40 to +200 in 30 minutes, Different materials expand at different rates, so, it is very likely that the issue would be intermittent if the intake gasket is where the leak is. Very slight maybe the baseline leak, and occasionally it gets worse.

Not sure what you mean by couldn't hear it. Are you referring to change in engine rpm?

jharrypope Enthusiast

jharrypope

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Engine parts expand and contract with changes in temperature. in the winter, the cylinder heads may go from -40 to +200 in 30 minutes, Different materials expand at different rates, so, it is very likely that the issue would be intermittent if the intake gasket is where the leak is. Very slight maybe the baseline leak, and occasionally it gets worse.

Not sure what you mean by couldn't hear it. Are you referring to change in engine rpm?

yes, couldnt hear the change in rpm's. I am going to take it to the dealer tomorrow and have them run a diagnostic scan and hope that they can figure out what's wrong.

jharrypope Enthusiast

jharrypope

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Surprise Surprise, the dealer couldnt find anything wrong. couldnt get it to throw the code. I thought that was $95 down the drain for the diagnostic but they didnt charge me.

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