Jump to content

1995 GMC Sierra K1500 5.7 engine misfiring after transmission shifts into second gear.

KenTaz

Recommended Posts

KenTaz Enthusiast

KenTaz

Posted
Posted

Hello, Ken here. I have posted about this issue in another topic which has received only 1 persons reply.

My 95 Sierra 5.7 has been misfiring, backfiring, and almost stalling out, after the automatic transmission shifts into second gear. If I manually shift it back down to 1st the engine then runs fine. I have tested the map sensor, purge valve, and EGR solenoid, which are all ok. I have replaced the EGR valve, TPS, distributor cap and rotor, spark plugs, spark plug wires, ignition control module, and all of the vacuum lines. I have rebuilt the throttle body, including the fuel pressure regulator. I cleaned and tested the injectors which are spraying nicely. I've also checked the timing with the electronic advance wire disconnected and it is fine. The truck is NOT getting a "Check  Engine" light and there are no codes stored. Could this be an ECM issue or a sensor that is throwing the wrong info to the ECM once the transmission has shifted into second? Again, the truck runs great in first gear and at idle. Very frustrated after months of trying to figure this out. Thanks for your help!

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

?,what about testing fuses,both sides for a voltage drop, important ones, ignition?or at coil ,do those tests when it's misbehaving

KenTaz Enthusiast

KenTaz

Posted
  • Author
Posted

I can't test those while it's misbehaving. It's only acting up while driving and after it shifts into second gear. It shifts fine by the way.

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

Yes,takes some wiring,I was just thinking,power is being pulled down,worth pulling electric connection off of tranny for a inspection?

  • 2 weeks later...
KenTaz Enthusiast

KenTaz

Posted
  • Author
Posted

Ok. I pulled the ECM and back probed the connector's battery+ and ignition+ pins. When the truck started to act up both voltages stayed exactly the same. I also did a voltage drop test on both battery and ignition pins. I got a voltage drop of .001v on both pins. I also did a voltage drop test on all of the ECM grounds including the sensor grounds. I got the same .001v drop. So I am not losing power to the ECM and have excellent grounds. 

The truck runs great until after it shifts into second gear. Then the engine starts to hesitate, misfire, and sometimes backfire. If I manually shift it back into first the engine runs great again. I manually put the transmission into the second gear position at a dead stop and I couldn't even pull out without the engine acting up like crazy. I had to shift it into D or 1 for the engine to run right again. 

KenTaz Enthusiast

KenTaz

Posted
  • Author
Posted
9 hours ago, riverbanks said:

Putting it in 2nd gear alone,starts the bad behavior? did you inspect tranny connection?

Sorry, I forgot to mention that I removed and inspected the transmission plug. It was clean with no corrosion. It looked as if it were brand new. The 4l60e has an external neutral safety/backup switch with a 7 pin and a 4 pin plug. The 4 pin plug is for the transmission range switches A, B, C, and P, as seen in the attached picture of the plugs on the right. I cannot find a wiring diagram of the engine harness, which includes the transmission, fuse box, engine components, and sensors leading to the ECM. I need to know where these 4 wires go and how they interact with the transmission solenoids and the ECM.

trans_switch_8604b5d9f025fa1752e6379cd12a674c6a817c1f.jpg

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

The round plug,is to pcm,that neutral safety switch only does 3 things,p,n start, reverse lights and gear selection on instrument cluster

KenTaz Enthusiast

KenTaz

Posted
  • Author
Posted

Oh ok, I see. That makes sense. So what sends info to the ECM from the transmission. Just the transmission range sensor inside the trans? A, B, and C.

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

Google,4l60e in limp mode,many wiring diagrams show up,my only thought with the problem shifting into 2nd gear,sitting or driving is ground control to solenoids from pcm to tranny,so the 12v feed in connection is back feeding a ground to pcm?there is not much else happening at that event,so bad harness or fluid filled connection?

KenTaz Enthusiast

KenTaz

Posted
  • Author
Posted
19 hours ago, riverbanks said:

Google,4l60e in limp mode,many wiring diagrams show up,my only thought with the problem shifting into 2nd gear,sitting or driving is ground control to solenoids from pcm to tranny,so the 12v feed in connection is back feeding a ground to pcm?there is not much else happening at that event,so bad harness or fluid filled connection?

I'm going to check the voltages coming from the ecm to the pressure switch manifold in the tranny. There is no problem with the tranny shifting, so if there was a back feed in the ground circuit of the solenoid(s) the tranny would either not shift or be very sporadic when it tries to shift, correct? I'm also going to try another ecm from my son in laws 95 suburban if it has the same service number as mine. 16197427. Thanks for all your time and suggestions. I really do appreciate it.

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

What about pulling fuse for tranny,put it in limp mode,then start it,shift to 2nd and if motor doesn't misbehave, circuit problem?

KenTaz Enthusiast

KenTaz

Posted
  • Author
Posted

I will give that a try today. I got an ECM from a 95 suburban with the same service number. 16197427. I swapped the prom out and gave it a try. Things were acting goofy when I turned the ignition on. Fuel pump didn't run, all the warning lights that usually come on with just the ignition switch in the on position weren't on, and I heard a clicking noise in the engine compartment around the fuse box. It sounded like a relay. The truck would not even attempt to start. Are these ECM's programmed to each vehicle or is it just the proms that are programmed differently? Shouldn't I be able to buy a new ECM with the same service number and just use the prom from the trucks original ecm?

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

I would say you are correct,but,being the last year of obd1,? maybe v.i.n. is involved also,after fuse pull for tranny test,what else could be isolated?only thing that comes to mind is unplug harness from instrument cluster,what else happens in 2nd gear,that doesn't happen in the others?

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

Did someone in the past,repin ecm for some reason,a fault,still,just thinking out loud,a/c relay was energized, instead of fuel pump?I did go on AutoZone site, halfway decent schematics for your truck

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • marpel
      Travel Trailer 2024 2500 HD 6.6 Gas Engine ?

      By marpel · Posted

      Although there is a "recommended" weight by those who sell trailers, my experience has been that they are way too aggressive in their information, for me at least. My '22 with 6.6 Gas, has a payload of about 3400 lbs and depending on your specs (I don't have 4WD so it has a bit higher Payload than others) yours will likely be different. Payload is one of the most important numbers for towing. Although you "could" tow the max trailer weight for your truck, I, personally, would not go close to that number. Having said that, a lot depends on how/where you will be towing. I live in the LMD of BC and often tow to Denver, Co, along interstates (flat and mountains) and I find I need to keep it in 5th (6spd) for the trip and travel at around 65mph. This is for a trailer dry weight of just under 3500lbs. If you are only doing local, short trips, it would not be that big an issue if you had a heavier unit. You will be surprised how much stuff you load the trailer with, so I would only recognize the trailers "full" GVWR weight rating, then decide on the appropriate trailer from that number. If you are worrying about how much stuff you should be putting in a trailer, you might have too large a rig from the get-go. Once again, depending on what terrain/distance in which you will be pulling. Marv
    • marpel
      Disconnecting Battery

      By marpel · Posted

      davester, Thanks for the response, how ever, I think I am now a bit more confused than I was before I posted - - After I posted, I actually found a YT video of a guy who replaced his Module (above tire) and he only disconnected the ground cable of the battery, but you describe rubbing the two cables together after disconnecting. I presume that is to do as you describe and eliminate any residual energy? - When I picked up the Module (between my posting and reading your response) from the dealer, I specifically asked about any re-programming and he stated it was not necessary as it was simply plug and play. Don't know how knowledgeable he is, though. - The video I watched also showed the Module plug to be difficult to "unlock" and remove, but there was no mention of silicone, although the video did show a bunch of dust/dirt in and around the plug (old truck) during removal. Are you talking about silicone that was applied by the factory, or silicone that you applied prior to plugging in? Thanks again, Marv
    • mandrautomotive
      2022+ GMC Hummer EV 40" Bumper Light Bar PRO: Factory Fit, Maximum Output

      By mandrautomotive · Posted

      Looking for a clean, factory-style lighting upgrade for your 2022+ GMC Hummer EV? M&R Automotive's 40" Bumper Light Bar PRO features a vehicle-specific, bolt-on design with no drilling or cutting required. Choose a bright white or yellow main beam, both paired with an amber DRL backlight for a sleek OEM-inspired look. The kit includes a curved LED light bar, powder-coated brackets, and all necessary mounting hardware.    Learn more or order yours See how it installs and looks on the vehicle:    
    • mandrautomotive
      🔥 2019+ GMC Sierra 1500 40" SLIM Grille Light Bar Kit – OEM-Style Fit, No Cutting or Drilling Required

      By mandrautomotive · Posted

      Looking for a clean way to add serious lighting to your 2019+ GMC Sierra 1500? Our M&R Automotive 40" SLIM Light Bar Kit was engineered to deliver maximum performance while maintaining a factory-inspired appearance.   Features: • Designed specifically for 2019+ GMC Sierra 1500 models • High-output 40" SLIM LED light bar • Clean, integrated grille-mounted design • No cutting or drilling required • Bolt-on installation using vehicle-specific brackets • OEM-style fit and finish   Whether you're hitting the trails, exploring backroads, or need additional visibility off-road, this kit provides powerful illumination without compromising the look of your truck.   For product videos, light output demonstrations, and installation content, check out our YouTube channel:   https://www.youtube.com/channel/UC3lutWP54fkXBl3iFLDJR-A Have questions about fitment or installation? We'd be happy to help.
    • Grumpy Bear
      Gas Prices

      By Grumpy Bear · Posted

      $3.63 today. Inching down. Plenty still over $4.20 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...