Truck sputters and backfires when hot

Discussion in 'Engine Performance + Maintenance' started by 8thNote, May 29, 2019.

Car Parts
  1. 89_C3500_Larry

    89_C3500_Larry Newbie

    Messages:
    8
    Likes Received:
    0
    Joined:
    Sep 23, 2018
    Location:
    Dothan
    All of the parts I listed were part of the engine overhaul, I wasn't throwing those parts at this issue, most of the parts were 30 year old original, and needed to be replaced anyway.
     
  2. 89_C3500_Larry

    89_C3500_Larry Newbie

    Messages:
    8
    Likes Received:
    0
    Joined:
    Sep 23, 2018
    Location:
    Dothan
    I have had it hooked up to a scanner, directly to the ecm, and the only out of spec reading was the throttle position sensor, and we adjusted that. It fixed the high idle. Also the O2 sensor reading rich/lean. Also checked the fuel pressure, and maintained 10psi, I thought this was low, but was assured that it was acceptable. I also failed to mention that the block was bored .030 over.
     
  3. DerekTheGreat

    DerekTheGreat I'm Awesome

    Messages:
    794
    Likes Received:
    246
    Joined:
    May 23, 2016
    Location:
    Michigan
    I disagree. Short of ICM's, I've found the OEM sensors to be more reliable than aftermarket crap. Matter of fact, I pick them when I go to yards. I have at least two spares of everything.

    10 is too low from what I've read around here. I'd like to see what it was under load.
     
  4. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

    Messages:
    1,280
    Likes Received:
    524
    Joined:
    Jan 3, 2019
    Location:
    Tonopah, AZ
    X2 - 10PSI is marginally too low, you want 11 - 13 on a stock engine. I'd almost be willing to bet you lose pressure under power and you're getting "lean pops". The fuel filter can be partially plugged too.

    A brand new, or almost brand new, after-market distributor can have a failed ICM already. My Spectra Premium distributor's ICM failed in under 3000 miles as did my Pertronix Flame Thrower ignition coil. It would run but had a bad stumble at idle. Use AC Delco or Delphi parts.
     
    DerekTheGreat likes this.
  5. 8thNote

    8thNote Newbie

    Messages:
    6
    Likes Received:
    3
    Joined:
    May 29, 2019
    Location:
    Chattanooga, TN
    After much research on this forum as well as other places, I traced the issue to an over heating Ignition control module. I removed the old one, thouroughly cleaned it, and reinstalled it with a new coating of thermal paste (aka heat sink grease). It immediately cured the problem. I purchased the thermal paste from the computer repair department at BestBuy for about $12.
     
  6. DerekTheGreat

    DerekTheGreat I'm Awesome

    Messages:
    794
    Likes Received:
    246
    Joined:
    May 23, 2016
    Location:
    Michigan
    Thanks for posting back. This is most certainly help others in the future.
     
  7. Erik the Awful

    Erik the Awful Newbie

    Messages:
    27
    Likes Received:
    16
    Joined:
    Aug 9, 2019
    Location:
    Choctaw, OK
    I'm a day late and a dollar short. I'd had the thermal paste problem on my old RX-7, and I was scrolling down to recommend checking that. Glad you found it.
     
  8. 89_C3500_Larry

    89_C3500_Larry Newbie

    Messages:
    8
    Likes Received:
    0
    Joined:
    Sep 23, 2018
    Location:
    Dothan
    Great to hear it was
    The only sensor I have replaced was the temp sensor and it needed to be replaced because its wire terminal was broken.

    I did replace the fuel filter, forgot to mention that.

    Thanks for the info. I'm at work now, but this weekend I'll look into that icm.
     
  9. 89_C3500_Larry

    89_C3500_Larry Newbie

    Messages:
    8
    Likes Received:
    0
    Joined:
    Sep 23, 2018
    Location:
    Dothan
    I checked the icm, it had a small amount of "thermal paste" on it, and it was a "transpo" brand (cheapest Chinese crap on Earth) I found them for less than 10 bucks on alibaba, anyway I decided to put in an AC Delco with a generous amount of thermal compound from best buy, and I can say it made a vast improvement, but did not completely solve the issue. Now it seems to do it randomly instead of only when hot. It will spit and stumble only when accelerating hard and not every time. I'm going to go ahead and replace the throttle position sensor since it was reading high on the voltage and causing high idle, so my fix was to dremel the hole out on the plastic mounting tabs on the tps to more of a slot, and adjusted it down to the right voltage at idle. I'm thinking it may be the cause of it. But I'm no mechanic, and I hate taking it to the shop. I'll be sure to update if that completely solves the issue.
     

Share This Page