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  1. #1
    Fuel Injected!
    Join Date
    Mar 2015
    Posts
    65

    Question Intermittent Rough Running Diagnosis

    I have a 350 chevy small block, TBI motor. In a G-30 van, 1995 model. The engine is a crate GM truck motor, with summit AL heads, roller cam (stock truck cam), rebuilt TBI, upgraded fuel pump, new distributor and all the tune up stuf when it was built. Maybe 20k on the rebuild. It is running a programmed chip from harris. Lots of new stuff on this one, it's been running fairly well for a while, but I recently started having trouble.


    The trouble started in Southern California, after filling up at Costco, I had a lot of stumbles on the highway. Took it easy, switched to Chevron gas. It got better, kept getting smoother after multiple tanks of new gas, as we drove it back to Northern California.

    Then another road trip, to Oregon border, broke down with a power steering pump, took some time to get that fixed, and drove back home. It had the minor stumbles throughout the trip, but nothing to write home about.
    Then it sat parked for 3 weeks or so.

    The next drive, was a 75 mile drive, and it ran like crap the first hour, really shuddering stumbles, and it had no power under WOT. It even struggled to raise the RPms and reach highway speeds on uphill sections. Then after about an hour it ran normally. Drove a bit around for a day or two, then drove the 75 miles back home. Intermittent mild stumbles coming back home. It sat another 3 weeks or so.

    Yesterday I drove it locally, and it was really bad, shaking the van again with the stumbles. Short trips, but it was worrisome.

    Today I got my ALDL cable out, and PC loaded with TunerPro again, and monitored it while it was running, and some short 1 mile drives. It was back to the mild stumbles.

    I was able cause some bad shudders by holding down the gas while parked in drive with my foot on the brake. I recorded that in TunerPro.

    I did see that the system is adding knock retard during that shuddering time.

    Could someone take a look at the file and let me know if they see any possible items to dig into? I am new to this, and am not sure where to look first. And I don't know if the numbers are what they should be anyway! :-0
    Last edited by tony-baroni; 09-30-2019 at 02:10 AM.

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