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  1. #1
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    Corvette(s)
    1990 Charcoal Metallic Coupe
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    Default Jackstands & misfire

    This is my second post since I bought my '90 coupe two weeks ago.
    Jackstands;
    I've never owned a corvette before but I've worked on and under many older (mainly 70's or earlier) British sportscars. I always use jackstands when working under cars. At the rear end, I typically position my floor jack under the differential and then place the jackstands under the rear axle shafts or spring mounting points. At the front, I typically position my jack under the front cross member and place the jackstands under the lower A arm mounting points.
    What is the best method for my '90 C4? I'm concerned that by using the jacking points and putting the jackstands under each point, I'll place abnormal stress on the frame.
    Misfire;
    I've read many of the posts on this forum that discuss rough idle and acceleration probems but have not found any that sound specifically like my problem.
    The PO said he only drove the car once a week for several months so I convinced myself that the following problems were related to a lack of use.
    My car starts easily and runs smoothly, under normal acceleration, until it is completely warmed up. Once warmed up, while sitting at idle with the (newly repaired and very effective) airconditioning on, it starts to miss (heavy misfire) sporadically. The misfire becomes more frequent the longer the car idles. If I accelerate normally from rest between misfires the car runs OK. If I accelerate normally from rest during a series of misfires, the car tends to stumble. It almost always stumbles under hard acceleration (we used to call the way the car acts under heavy acceleration "crapping out").
    I've replaced the distributor cap & coil. The ignition module tested OK at AutoZone. The plug wires appear OK. I've added injector cleaner to my fuel , I 'm going to replace the fuel filter (hence the need to place the car on jackstands) and clean the TPI air intake with carb cleaner per the manual.
    The water and oil temperature both stay at about the lower third of their range during the mid 80 degree temperatures we've enjoyed the last couple of weeks.
    I'll appreciate any and all suggestions.

  2. #2
    aussie
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    sounds a lot like my problem turned out to be a faulty plug which would break down when the car got hot

  3. #3
    New Member DaveMach's Avatar
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    85 white/saddle & 06 MS A6
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    I was having a promblem when I idled for more then, let's say 4 or 5 min. she start to hunt 400-700 rpm. What I did is pull of the TB she was brown on the back side, clened it up runs pretty good now. Not sure if that was what you were saying.

  4. #4
    Gone but not forgotten Ken's Avatar
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    Default Re: Jackstands

    Originally posted by cash's90
    What is the best method for my '90 C4?
    I always use the factory jacking points.

    First raise the car with a floor jack at the front crossmember to get that end off the ground, then at the rear differential for those wheels. It's possible to lift the whole side of the vehicle by raising it high enough at one of the side jacking points, but it is not recommended.

    Some people suggest leaving some sort of support at the crossmember and differential as backup for the jackstands. You could crib it up or just leave the floor jack in place. Whatever makes you feel safe.

  5. #5
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    Thank you for your responses. I went ahead and cleaned the TPI intake with carb cleaner (per the manual) and took the car out for a 25 mile spin on our local freeways (amazingly light traffic day).
    On entering the freeway, under heavy acceleration, the 2nd to 3rd upshift produced a "chirp" from my new tires so the power appears to be OK. Please realize that I've always owned older British sportscars so burning rubber during an upshift is new to me (the last time I did it was in a brand new 1957 Pontiac).
    I still noticed some "crapping out" during some short periods of heavy acceleration (as traffic allowed) but not every instance. Maybe the injector cleaner has helped.
    The idle has appeared to improve with fewer hiccups.
    The ambient temperature was in the low 80's and I ran the a/c.
    My water temperature never went above the lower 1/3 of the dial. I extrapolated the temperature to be about 160 degrees based on the needle's distance between the 100 and 260 marks.
    The oil temperature was at about 145 based on the same approach. They both seem low to me.
    I'll replace the fuel filter tomorrow.

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