: 04 STS misfires when idles, goes away when you floor it.



neportlandmv
11-08-06, 03:37 PM
04 sts misfires when idles, but when you floor it runs great. I changed both coilpacks, fuel line with all fuel injectors, put new intake manifold seals, new MAF, spark plugs, no difference.... same crap. PCM code is 0300. misfires all four cylinders on right side (back by firewall). This sts was in street flood, rod on 1st cylinder was bent due to water getting into intake manifold, so it was replaced with new one and engine put back together. Well since then sucker misfires. I am out of ideas what else could be wrong with it?? Also it keeps burning up oxygen sensor on left exaust manifold ( second one i had put in and it works for a while and then goes out). Any ideas what else I could try except for crushing that thing :rant2:

Krashed989
11-08-06, 03:53 PM
Clean out your Throttle Body. :thumbsup:

If that doesn't solve it you can go into diagnostics mode then go into the PCM menu then to PCM OVERRIDE then to PS04 and turn off each cylender one by one using the cooler button to turn it off and the warmer button to cycle to the next one. Whichever one gives you the LEAST amount of change in how the engine is running will be one that is not firing.

nigelb
11-08-06, 04:02 PM
i think that you need to do a compression test and then work from the results.
because you say that all 4 cylinders are misfiring it makes me wonder about cam timing and valves. maybe there was more mechanical damage other than the rod?

Krashed989
11-08-06, 04:11 PM
...because you say that all 4 cylinders are misfiring...

I think he meant 2004 model....

Which I also misread on accident... OBD-II cant do the diagnostics override of the fuel injectors... whoops...

chazglenn3
11-09-06, 01:20 AM
Just out of curiosity, where are you located? I assume not in the USA since the STS wasn't sold here in '04.

neportlandmv
11-09-06, 01:27 AM
compression is same in all cylinders 150psi in all 8. And I know that 4cyl on one head are misfiring, so what could be the reason? As I mentioned enigine has new spark plugs, new coils, new injectors, new maf.... Also if timing is off why is it running good when in higher rpms (2000rpm and up) Thx.

neportlandmv
11-09-06, 01:29 AM
Just out of curiosity, where are you located? I assume not in the USA since the STS wasn't sold here in '04.

No I am in Vancouver, WA and it is us model 06/03 production date

nigelb
11-09-06, 03:56 AM
a valve problem can sometimes cause a misfire at low rpm because at low speed every cylinder is needed to keep the engines momentum going. at higher speeds a slight misfire can be overcome by the rotating force of the crankshaft. many v8 engines run well with one or two weak cylinders.
have you hooked it up to a Tech2 and run through the FSM diagnostic flowcharts?

clarkz71
11-09-06, 05:14 AM
If he's got good (equal) compression in all 8 cyls, there is no valve problem. Sounds electrical, maybe going into camel (limp) mode. If the engine is dropping one bank (4 cyls) at a time. could also be problem in the fuse box. On early models there are 2 fuses for the injection. One for each bank. neportlandmv: You really need to get a factory service manual and follow the diagnotic information.

chazglenn3
11-09-06, 11:59 AM
No I am in Vancouver, WA and it is us model 06/03 production date

Doesn't that make it a 2003 model? I'm pretty sure the STS wasn't sold in the US in 2004...only the SLS that looked exactly like a STS.

eldorado1
11-09-06, 01:06 PM
What did the o2 sensor look like when you pulled it out? Black, or white?