2000 silverado running bad

[rat454]

My 2000 recently began stumbling off idle up to about 2K rpms. The stumbling varies from almost non-existent to happening every time I take off at a stop light. i checked DTCs and only found P1638 (generator F terminal circuit). This code came up when i checked the dtc codes under the "DTC not Ran" selection on my scan tool. It did not come up when i selected "all dtc codes". ????? When the stumbling occurs frequently it will run real rough (in park and in gear) from 1000-2000 rpms and clear up above 2000. This has been going on for the last couple of weeks.

Today the stumbling progressed to it misfiring at stop lights and having a rough idle in addition to what I described above. I checked DTCs again and a P0300 (misfire detected) code came up with the P1638.

Also, gas mileage has gone down aobut 2mpg in the last tank. Just filled up last night.

Has anyone got any advice where to start looking for the problem?

[Madd Maxx]

Check your fuel pressure.

[WARLOCK]

I agree check the fuel pressure and report back.

[txarkitekt]

Hmmmmm...P1638 makes me wanna think about the alternator. I would check and make sure your wires and connectors to the alternator are good.

Secondly, fueling might be an issue, but the P0300 is so general. It could be anything from bad plug or wire, 02 sensor, faulty coil pack, faulty fuel injector, dirty fuel filter, etc. I would start with the cheap/easy things first (no, not Devin's mom) and go from there.

[rat454]

appreciate the feedback
ill be checking out all of the suggestions this weekend and report back

[WARLOCK]

Tyler and Devin sure are flinging the poo tonight.

[rat454]

Checked fuel pressure. 50psi at idle and the pressure would rise as I gave it gas. i removed the vaccum reference from the regulator and the pressure immediately went to 60psi. So, I don't think its a fuel problem but this doesn't explain the reduced fuel mileage.
Checked the alternator wires and looked fine. The volt gage always reads around 14v. Never seen is fluctuate.
The truck seems to running better but not 100%. Maybe I got a bad tank of gas. The tank it ran the worst on was 93 octane Chevron, where I buy from often. Wonder if since the economy is not so good these days no one is buying 93 and the gas is going sour.
cleared the dtcs and will check later today.

[txarkitekt]

Checked fuel pressure. 50psi at idle and the pressure would rise as I gave it gas. i removed the vaccum reference from the regulator and the pressure immediately went to 60psi. So, I don't think its a fuel problem but this doesn't explain the reduced fuel mileage.
Checked the alternator wires and looked fine. The volt gage always reads around 14v. Never seen is fluctuate.
The truck seems to running better but not 100%. Maybe I got a bad tank of gas. The tank it ran the worst on was 93 octane Chevron, where I buy from often. Wonder if since the economy is not so good these days no one is buying 93 and the gas is going sour.
cleared the dtcs and will check later today.

Ok, fuel psi is fine. FPR is fine. No prob there. How old is the fuel filter? They are cheap and easy to replace.

Alt may be OK. Visual inspection won't cut it. Use a voltmeter to check to see if wires are reading correctly.

Gas could be the problem, but it going sour? Highly doubt it since Chevron is some of the best gas around and is Top Tier Rated.

Change fuel filter, run 93 octane with Chevron Fuel System Cleaner (run it slightly rich..as in one bottle for like 12 gallons of fuel), and drive it like you stole it until that tank is empty. Then report back.

[rat454]

I have run a rich mixture of lucas gas treatment twice and ran it hard with no significant change. I pulled all of the plugs and ohmed each plug wire. All wires measured very close to the same number on my multimeter and all plugs looked the same with no fowling or closed gaps etc. i cleaned the maf with correct cleaner. I took the egr valve off and checked to see if the valve would open freely and it did and visualy inspect it. While I had it off I blew it out with compressed air. The truck seemed to repsond positively to this but I still have a slight hesitation off idle and the truck bucks when applying gas (enough to accelerate but not enough to go into 3rd gear(=) at low rpm in overdrive. Also at wot the truck skips.
I unhooked the egr connection and no difference. I checked live data during my drive to work today. map, iat, maf, tps, knock sensor, spark advance, values seemed ok and would respond accordingly to rpm change and engine load.
Anyone have any ideas?

[txarkitekt]

I would to start to look at the injectors now. Since everything else is checking out, then I would definitely move to having the injectors/fuel rail cleaned.

There are a few ways to do so, but I would recommend taking them off and soaking them in a bath of Seafoam and then a good shot of air with a compressor. Or you could even spray them out with a can of carb cleaner.