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  1. #1

    Default Ignition Suggestions

    Ever since I had my unfortunate incident where I lost the transmission in the suburban, it's been running a little rough at idle. I also have not done anything to the motor since I bought the truck other than change the oil. I did do a tune-up when I first bought it. It did get a new set of plug wires after I lost the transmission and discovered it had 2 burnt plug wires. So, it's running rough, and I'm thinking it may need something along the lines of a tune-up. So, I'm going to replace the plugs, wires with a custom, exact fitting set if I can find some, cap/rotor, and hopefully a hotter coil. All parts will be replaced with high-quality parts. On the Bronco forum I'm on, there's an ignition tuneup called the "Sixlitre Tuneup" (http://www.fullsizebronco.com/forum/...ad.php?t=63592). Basically what this is is replacing all the ignition parts with high-quality MSD products or any other high-quality product, gapping the plugs pretty wide, and bumping the timing to something around 12 degrees BTDC. This upgrade will not only increase fuel mileage, but also increase power and response. Sixlitre recommends using el-cheapo autolite copper plugs because that's all you need, and that other plugs such as bosch platinums can actually degrade performance. Tons of people have attested to this. However, that's for the Ford small-block 302 motor. The suburban has a small-block 350 in it. Can anyone recommend what plugs, wires (MUST be custom perfect fitting, I'm tired of "custom" sets that are not the right lengths), cap/rotor, and coil I should go with. Also, how far can/should I bump the timing and what gap should I use? I'm not expecting anyone to have actually done this, but simply to give suggestions so that I can try to piece together a similar upgrade to restore my idle and get a little in the performance and MPG lines while I'm at it.

    Thanks
    (Tim and Mike, this is right up ya'lls alleys ;) )
    Christopher

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 265K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half



    There are 10 kinds of people, those who understand binary, and those who dont...

    Remember kids, the only difference between screwing around and science is writing it down- Adam Savage

  2. #2

    Default

    MSD ignition parts and wires should work good for an ignition tune-up. The "Six Litre Tune-up" works pretty good for most V-8's, V-6's, or 4cyl's.
    I used "Live Wires" and "Accel" ignition parts on the wifes Jeep Wrangler 2.5 last summer and improved the mileage by 8 mpg. With the hotter spark I gapped the plugs as wide as .060 before I started having detonation issues, It's at .047 now and runs good, I bumped the timing up 5 deg to smooth things out, had the injectors cleaned and balanced, and indexed the spark plugs. Dont know the hp improvement but it feels stronger. If you've ever ridden in a Jeep Wrangler 2.5ltr with 32's and 4.10 gears you'll know you can feel every little bit of horsepower improvement, these trucks are weak when it comes to hp.
    Something that bothers me about this is why is your truck running rough? I think before you invest in a tune-up you may want to find the reason for this condition, I'm thinking it may not be an ignition issue, maybe you burned a valve. The reason I suspect this is the situation that led to the problem you now have.
    Have you:
    Done a leak down or compression test on the engine?
    Checked for vacuum leaks or bad gaskets?
    Cleaned the fuel and air intake system?

  3. #3

    Default

    I'm a big fan of MSD ignition products. I bought all MSD for the last tune up I did on both my 87 chevy and my 75 Dodge powerwagon. on the powerwagon, I went with the 8.5mm MSD Helicore wires from summit and the wires actually fit perfect. I also upgraded the coil, Cap & Rotor with MSD parts. Runs great! I also used champion spark plugs.

  4. #4

    Default

    Tim, I have not conducted a compression or leak-down test on the motor, nor do I have the equipment neccesary. However, I do think I can rent the compression gauge from Autozone. I'm not quite familiar with the process to do a leak-down, but I'm sure I can figure it out. As for vacuum leaks, I don't THINK I have any, but I'm not certain. If there is a leak present, I don't think it can be much of one. I did seafoam the motor through pouring some down the throttle-body, but I want to seafoam it again both through the gas tank and through the brake booster line. If I remember correctly, the seafoaming didn't really seem to do much, but I think that was primarily due to the method I used. I don't think I was pouring it in fast enough to do anything, it was just burning it. The motor doesn't idle horribly, in fact, it's almost unnoticable. It shows up a little more when it's idling under load (ie, a/c on with blower on high). I'll see if I can't get some video of it. However, for now, you have given me some things to check out.
    Christopher

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 265K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half



    There are 10 kinds of people, those who understand binary, and those who dont...

    Remember kids, the only difference between screwing around and science is writing it down- Adam Savage

  5. #5

    Default

    Even a small vacuum leak can cause big problems.
    Leak down and compression tests are easy to do, once you get a compression testor you hook up to the cylinder, turn the engine over (but dont start) and check first for compression, the leak down is conducted by leaving the compression on the cylinder and reading it 20 mins later to see where the compression reads. You'll have to get the specs on you engine to see where your readings should be, even different year models but same size engines can sometimes require different readings.

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