Hi all I have a 2005 4.0. I have been getting a p0300 code. I have changed my plugs and ignition coils. Still have the code. I am wondering how to use the factory service manual to determine the next steps I need to take to get this resolved. I have had a code for my cats for years now that I have ignored. Any help would be appreciated.
Thanks
How to use FSM
Moderator: volvite
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VStar650CL
- Posts: 601
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Re: How to use FSM
The FSM steps are likely to send you on a lot of unnecessary tail-chasing. First question, do you own a good scanner? If not, you'll probably need one. Streaming parameters like short term fuel trim (STFT), MAF g/s, and cam timing will prevent you barking up a lot of wrong trees.
That said, given the ignored cat codes, there's a pretty good chance one or both of your cats has finally clogged up. The two best ways to confirm that are 1) temporarily remove the A/F (front O2) sensors and see if the misfire goes away, or 2) put a vacuum gauge on the intake plenum and see if the vacuum drops precipitously when you raise and hold the RPM's. Don't use method 1 if you're afraid to wake up the neighbors.
That said, given the ignored cat codes, there's a pretty good chance one or both of your cats has finally clogged up. The two best ways to confirm that are 1) temporarily remove the A/F (front O2) sensors and see if the misfire goes away, or 2) put a vacuum gauge on the intake plenum and see if the vacuum drops precipitously when you raise and hold the RPM's. Don't use method 1 if you're afraid to wake up the neighbors.
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montanacruiser
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Re: How to use FSM
I do own a scanner. Its just a cheap one. What can I look for with it to help figure out what is wrong? Also I was told I could use the live stream on my scanner to see if there are any vacuum leaks. Any one know how to do that?
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VStar650CL
- Posts: 601
- Joined: Wed Dec 09, 2020 6:19 pm
Re: How to use FSM
You can confirm the presence of a vacuum leak with a scan, but it won't help you find it if there is one. Warm up the engine and stream the STFT for both banks. If neither is high (or only one bank) then the problem probably isn't a leak, but if both read higher than about +10% then proceed. Raise the RPM to 2000 or more and see if the STFT drops a lot and steadies out lower. If so, there's a leak.
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montanacruiser
- Posts: 17
- Joined: Wed Dec 17, 2014 2:31 pm
Re: How to use FSM
If the cats are clogged would it more likely be the first or do the secondary's clog as well?
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VStar650CL
- Posts: 601
- Joined: Wed Dec 09, 2020 6:19 pm
Re: How to use FSM
Sometimes the front cats fall apart and the debris clogs the rear, but aside from that, rear cats don't cause many problems. The fronts do the bulk of the work converting CO and breaking down HC, so the rears are usually rhodium types simply there to break down NOx which the fronts are less efficient at handling. Their workload is pretty light compared to the fronts and they rarely self-destruct in the same way.
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