The dread P0307 misfire

[jharry]

I'm having an issue with my 2003 Silverado, current engine is LS1 from a WS6 Trans Am, mostly stock, stainless headers, no cats, stall converter. I replaced fuel pump a few weeks ago and last week i took a road trip and when I hit the interstate the CEL started flashing. I pulled over and used my scanner and saw that it was P0307. I cleared code and continued on. The only noticeable problem was that it was not shifting into overdrive. After a while the light quit flashing and eventually it shifted into OD. THis happened several more times on a 750 mile trip. I had a mechanic friend check it over and he couldnt find anything, wasnt throwing codes at that time. He check sparked plug, swapped the coil to #5 and still had the issue. Didnt get a chance to check the fuel injector. The trip home it did the same thing. IF it were indeed a bad injector, wouldnt the problem be ongoing instead of coming and going? Took to local chevy dealer thinking they could diagnose it but since it didnt throw a code they couldnt find anything (luckily they didnt charge me) Any clues? I have replaced tons of parts and tired of throwing money at it.

[rkvons]

Originally Posted by jharry

I'm having an issue with my 2003 Silverado, current engine is LS1 from a WS6 Trans Am, mostly stock, stainless headers, no cats, stall converter. I replaced fuel pump a few weeks ago and last week i took a road trip and when I hit the interstate the CEL started flashing. I pulled over and used my scanner and saw that it was P0307. I cleared code and continued on. The only noticeable problem was that it was not shifting into overdrive. After a while the light quit flashing and eventually it shifted into OD. THis happened several more times on a 750 mile trip. I had a mechanic friend check it over and he couldnt find anything, wasnt throwing codes at that time. He check sparked plug, swapped the coil to #5 and still had the issue. Didnt get a chance to check the fuel injector. The trip home it did the same thing. IF it were indeed a bad injector, wouldnt the problem be ongoing instead of coming and going? Took to local chevy dealer thinking they could diagnose it but since it didnt throw a code they couldnt find anything (luckily they didnt charge me) Any clues? I have replaced tons of parts and tired of throwing money at it.

I had an intermittent miss on a 3.1. Would come and go. No apparent pattern to it. I changed everything but the injector. Still had it. Then it went to a solid miss. I changed the injector and that fixed it.

[j cAT]

Originally Posted by jharry

I'm having an issue with my 2003 Silverado, current engine is LS1 from a WS6 Trans Am, mostly stock, stainless headers, no cats, stall converter. I replaced fuel pump a few weeks ago and last week i took a road trip and when I hit the interstate the CEL started flashing. I pulled over and used my scanner and saw that it was P0307. I cleared code and continued on. The only noticeable problem was that it was not shifting into overdrive. After a while the light quit flashing and eventually it shifted into OD. THis happened several more times on a 750 mile trip. I had a mechanic friend check it over and he couldnt find anything, wasnt throwing codes at that time. He check sparked plug, swapped the coil to #5 and still had the issue. Didnt get a chance to check the fuel injector. The trip home it did the same thing. IF it were indeed a bad injector, wouldnt the problem be ongoing instead of coming and going? Took to local chevy dealer thinking they could diagnose it but since it didnt throw a code they couldnt find anything (luckily they didnt charge me) Any clues? I have replaced tons of parts and tired of throwing money at it.

the LS1 is a 5.7L engine. this truck is/was not set up for this engine. since it is a different engine I would check that you have the proper fuel pressures. along with the intake manifold leaks and any exhaust leaks.

this can be a tough one to fix since it has been modified. could be the injectors , possibly the wrong injectors or the PCM needs to be programed ..

[jharry]

Yes, I know it's not stock engine. Had it put in back around Christmas. Job was done by a very reputable performance shop. Guess I will be taking it to him fir diagnosis but was hoping to solve it locally as his shop is quite far from me.

[j cAT]

Originally Posted by jharry

Yes, I know it's not stock engine. Had it put in back around Christmas. Job was done by a very reputable performance shop. Guess I will be taking it to him fir diagnosis but was hoping to solve it locally as his shop is quite far from me.

if you had the oem engine you would have little issues getting down to the miss fire.

post back what they say and how they corrected it.

call them find out what the correct fuel pressures should be . the injectors are matched to the engine so you will need the correct pressure for those injectors.

another test check is the compression and also any exhaust leaks ...re check the manifold bolts/gaskets. look at the plug for any difference in color... lets say it looks too clean compared to the others then thats coolant... too much dark color then compression low or a weak spark ...

low compression possible head gasket ..

with the 5.3L we get p0300 code . that can be a tough one to narrow down including the timing re-learn procedure as a fix...

[Tech II]

I would think if fuel fuel pressure was a problem, more than just cylinder #7 would be affected....

You check for spark and compression, if ok, leaning towards an injector.....