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Sonoma misfire and p0305

Discussion in 'Chevy S10 Forum (GMC Sonoma)' started by calicarpenter84, Mar 8, 2014.

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  1. calicarpenter84

    calicarpenter84 New Member

    Hey folks,
    new to the forum but not my first crack at car forums. Having trouble with my recently purchased 2001 gmc sonoma sls 4x4 4.3 liter.
    So to get to the point I just finished up with the intake manifold gasket repair as mine was leaking under my ac compressor. Didn't have the milkshake In the oil thankfully but still ended up with a problem when done. So I did a tune up while I had it apart, PVC valve,air filter,plugs,wires,cap,rotor...and the distributor (broke the plastic holes for the cap hold down). Had it back together and now misfiring in cylinder 5, dropped the P0305 code for me...done a few tests with no real results, sprayed starting fluid around cylinder 5 on the intake, engine had zero response...so no leak in the new gasket. Did a fuel pressure test and came back good 60psi and didn't leak off at all. Also did a compression test on number 5 came back 150 psi dry tested, so not a issue with valves or rings... Really at a loss here help me out guys

    thanks much
  2. edsmagichands

    edsmagichands Member 1 Year 100 Posts


    Did you verify it is cyl#5 misfiring? was there any strange noise on the first start after repairs? did you inspect the spark plug when you ran compression, was it wet from fuel or dry? is the gap correct? very easy on these for debris to fall down the intake ports in the head, then ride the piston up and smack the plug, or worse. did you verify spark at the plug.

    I personally have dropped a plug then put it in without checking, got a miss. when i dropped it, it landed on the electrode closing the gap! now if i drop em, i check em! also verify wires are fully connected at the cap and plug.

    Also, not sure about the 01's, but it seems in the older ones there was a vacuum port in the intake near the cyl 5 intake runner for the power brake booster. might check there for leaks.
  3. calicarpenter84

    calicarpenter84 New Member

    I didn't verify that it was number 5, but that's what the code read. No strange noises really on start up, just the noticeable miss. I did inspect the old plugs when I switched them, they all looked worn uniformly. I had the misfire code both before and after changing, plugs, wires, cap and rotor both. So it isn't that, I haven't checked to see if spark is reaching the number five yet though. The old number five plug was dry as is the new one when I pulled it for the compression test. I looked at my code reader a litter closer tonight and it saved the freeze frame data from the engine when the code dropped....noticed two things, my vacuum seems a little low at only 14... And the other is the STFT for bank 1 is 9.36 and bank 2 was -2.86. Bank two seems normal for idle calling for less fuel but bank 1 is asking for more. Not sure why though
  4. edsmagichands

    edsmagichands Member 1 Year 100 Posts

    Was the misfire there before you changed the gasket? if cylinder is misfiring and has good compression and spark, plug should be wet from fuel not burning. dry plug suggests little or no fuel in that cylinder. possible bad/ clogged/ dirty injector. fuel trim numbers point to this possibility. if cylinder 5 is getting little or no fuel, it will pump straight air to bank1 O2 sensor forcing it lean. PCM will then start adding fuel to that bank to try and compensate for the lean O2 reading. verify this by disabling spark, (unplugging the connector at the coil works,not the coil wire to the cap). crank the engine 10-15 secs, then pull plugs on bank1 including cyl 5. each cylinder and plug should show signs of fuel. wetness and strong smell. by pulling mor than just cyl 5 you will have a comparison.
  5. calicarpenter84

    calicarpenter84 New Member

    The misfire wasn't there before the gasket repair, just some hesitation on takeoff, which I attributed to the dirty throttle body I found. Good call on checking for fuel in number 5, cheap and quick test. Just because I have 60 psi fuel pressure and no leak down doesn't mean number 5 injector is opening at all! Hmm I'll be checking this first thing in the AM. Thanks I'll let you know how it goes. Need an excuse to upgrade to MPI anyway

    - - - Updated - - -

    well it looks like a much more definitive answer to the problem this AM. ran the test and number 5 plug is most certainly dry, whereas number 1 plug had a strong smell of fuel. i didn't bother pulling the number 3 plug because it is kind of a PITA. I'm satisfied enough that i have a fuel problem. So question is what next? Go pick up a noid light to confirm PCM is telling injector to open? And if yes then it is almost a guarantee that number 5 is bad. Which is quite possible considering it looked like the original spider when i had the intake apart, thought i was pretty careful not to disturb it but you never know. Had an issue with the mounting holes for the dizzy cap when i took it apart, they were already cracked, and i finished them off LOL, another 120 out the wallet! Damn old parts
  6. edsmagichands

    edsmagichands Member 1 Year 100 Posts

    Yes, you need to confirm the control circuit first. or cross your fingers and just replace it. it's been awhile,so i cant visualize the connector to tell you which pins to test at and my program with wiring diagrams won't load. i'd have to be there to be of more help right now, sorry. if i have some time later, i will try to get my program up and then i could give you better info. maybe j cat or someone else has done the test recently and will see this.

    Iv'e never tried it but, with the plenum off you should be able to see the injectors spray. good luck, and let us know!
  7. calicarpenter84

    calicarpenter84 New Member

    i rented the noid light kit at autozone. not sure which pins are for number 5 though, started by testing the pins on the side of the harness for number 5. i only got through 4 sets of pins before my battery started running down. but all four that i checked did light up. heading to the movies with kids and the misses. will charge battery this afternoon and hopefully finish testing. battery was already pretty weak from testing for the wet plugs this morning. thanks for all the help i do appreciate it. oh and one more thing to confirm it is the bad injector, if i take off the plenum and then reconnect harness and fuel lines can i pull out the injector for number 5 and try cranking the motor to see if it sprays??

    - - - Updated - - -

    bam!!! problem is solved, bad number 5 injector, replaced it this evening and runs like a champ again. on to the next issue, while snooping around i noticed that my muffler has a leak on the backside of it, and my cat seems to be making a rattling sound inside it, probably on its way out with my luck...well anyways i bid you all ado for now. until the next time..

    thanks to you again Ed for leading me down the right diagnostic pathway!!! much kuddos to you my friend
  8. edsmagichands

    edsmagichands Member 1 Year 100 Posts

    You're more than welcome. I wan't to thank YOU for letting me know the problem is fixed. knowing i was able to help someone solve their problem makes my day!!

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