98 Sonoma Misfire Codes

I have a 98 gmc sonoma king cab truck Automatic, 4.3L, V6. I filled up my gas tank. $50.00 :banghead: . A while later, when I parked it was idling real bad. I scanned my truck and it gave me P0300 Random Misfire, P0305 Cylinder 5 detected, and P0785 Shift Timing Solenoid malfunction. I put some fuel Injector stuff in it also. What do I do first? And Am I in for a lot of work? I need advise. My Old Man out of town and I need to get it fixed. Any suggestions???? Is it maybe bad gasoline?? :disappoin

It's possible you got some bad fuel. Take off the fuel filter and empty it onto a white paper plate to inspect the fuel. Empty it from the tank-side of the filter.

May have water in the tank. Add a couple bottles of "dry gas" or "heat" to the tank. It will say on the label if it removes water. One bottle rarely does it, generally two or three but since you already have injector cleaner in it, you might want to just use two. I wouldn't recommend going back to the same place for gas again. My wife had this problem and after getting it worked out, she went back to the same place for the next tank and I ended up having to pull and clean a no.7 fuel injector on her Trans-Am. A year later I saw that station replacing the underground tanks due to holes.

Thanks for the feedback. I will not get gas their again. That's for sure. I just now got my truck scanned again from a Snap-On scanner and it did reveal #5 cylinder definetly misfiring. The spark plugs need changing. So I will get a tune-up done and go from there. Hopefully this will stop misfiring... Any more suggestions greatly appreciated. The m ore info I get the more I know. Thanks so much.....Lil Kim :rolleyes:

Like so many have pointed out on this site and by finding out the hard way, A/C Delco plugs only. Highly suggest wires, dist cap and rotor also. A/C Delco, although I recommend the Echlin dist cap since an A/C Delco cap left my family and I stranded on the highway after one year. Get your parts from a parts store, not a department store. My brother is a 20+ year mechanic and says he has seen more bad plugs out of the package from places like Walmart, Kmart, etc than he cares to count.

Thanks again. Still waiting for my tune up. I believe someone on this forum told me that sometimes these codes have other meanings as well. If so is their any other meanings? Kim

Well the hubby changed spark plugs and still runs shitty. What to do now??? Fuel filter? Cuz when you first start it , It does smell heavily w/gasoline. I also put 1/2 tank more gas from chevron Super unleaded. I scanned it again agave me the same 0300 code. But it also seems to me that something is going on with the timing?? Need help....

What is the condition of the distributor cap? Rotor? Plug wires? Any of those can cause a misfire DTC - It doesn't necessarily have to be fuel related.

These are sometimes hard to locate. Mine was actually an intermittent crank position sensor and no code ever set the SES light. Also check the vac lines left side engine compartment for leakage/rot as they will lean it out. Then as already stated cap/rotor can cause and many aftermarkets have internal defects so you never see the multiple fires and no way to test - Wells are prone to that.

Here's some suggested reasons I found at ODB-II site:
A code P0300 may mean that one or more of the following has happened.
Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer

Hubby checked cap roter and wired and said they were fine. he is going to pull out the fuel filter and check that as stated previously. I'll keep you posted. Thanks again

Hubby did the Fuel filter, He said some water. We replaced it. And still runs like shit.... I still have the same codes. P0305 & P0785. I bought 2 bottles of the Heet and put it in. While driving it seems from a stop and when you accellerate it gives the misfires and then at about 3 rd gear it runs fine with the occassional misfire. What about the code P0785? Do i need to woory about that too?

It's possible that the misfire is causing the shift timing DTC. Some water is not good. There should be no water. I recommend emptying the fuel tank and adding a good quality fuel. The cheapest fuel isn't always the best.