1994 Silverado Transmission Problems

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by jdickerson83, Aug 2, 2009.

  1. jdickerson83

    jdickerson83 Member

    Hey all, I just purchased a 1994 Silverado 5.7L Extended Cab. I purchased this truck for mainly hauling purposes. It has 233,000 miles on it and runs better than most trucks with this type of mileage. With that being said, I have a problem. Recently I have noticed the "Service Engine Soon" light appearing approx. 10-15 minutes after it's been running. A couple days ago I was travelling on the interstate doing about 70mph when I approached an incline. In order to maintain my speed I accelerated however, the RPMs did not increase and the speed never increased. After flatting out on the road I attempted to accelerate again however I couldn't get about 45-50 mph. I pulled over and turned the truck off for about 5 minutes. When I started it up again the "Service Engine Soon" light disappeared and I got up to 70 mph again just fine. When I approached the next incline I had the same problem as the first incline. Wouldn't accelerate.

    When I first bought it I noticed the tranny was a big sluggish when shifting from Park to Reverse. I'd have to wait a second or two for Reverse to engage. Also when I got from 1st to 2nd it jerks just a touch. All the other gears work just fine.

    Is this a major problem? Or simply a transmission fluid change? I don't want to have to replace the whole transmission nor do I want to shell out hundreds of dollars to get it fixed. I traded to junkers and paid $1400 for this truck so I don't want to put a bunch of money into it but I love this truck and I just got it! Any suggestions?
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    You need to get it scanned and see which codes are present. There are several codes that can limit the shifting of the trans as well as the engine timing so when the truck goes into failsafe you loose power. Get it scanned and post up the codes.
  3. jdickerson83

    jdickerson83 Member

    Clogged Cat Coverter

    Do you think a clogged cat converter could be the problem? I spoke with the guy who sold me the vehicle (a good family friend and professional wrecker) and he said the cat converter was probably clogged. What do you think?
  4. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Sure the catalytic converter can turn on the Check engine Light, as can 50 other things. :)
  5. jdickerson83

    jdickerson83 Member


    I know about fifty thousand things can set off a check engine light, lol, but do you think that was the performance problem? Not being able to accelerate, etc?

  6. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Very possible Joe but I would hate to see you throw a cat at it without further investigation. I have seen a knock sensor code cause a major lack of power on a Chevy truck and I've even seen a Boom Box cause a knock sensor code.

    A clogged cat is easy to diagnose. Drill a 1/4" hole in the pipe in front of the cat. Tap it out to 1/4" pipe therad and screw in a 1/4' vacuum nipple. Attach a low pressure gauge like most vacuum gauges have built into the gauge. Start the truck and look at the pressure. You do want back pressure but no more than 4 lbs max. A good free flowing exhaust may have one or 2 lbs. A clogged cat may have 10 or more.
  7. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    I forgot to mention you can buy a tool that screws into the O2 Sensor hole but it's expensive and the vacuum fitting works just as well. You won't have to fight removing the O2 sensor. When you're done plug the hole with a 1/4" pipe plug.
  8. jdickerson83

    jdickerson83 Member

    Thanks for the advice. I'll play around with it a little bit and let you know what I come up with.
  9. nathunt1029

    nathunt1029 New Member

    I hallowed mine out and after i did that i saw that i can reach 5 grand way faster. It was a easy thing to do as well. it was easy on mine. I just unbolted it form the headers, and the part behind the cat. took it out and used a metal pipe and a BFH to knock all the stuff out. Iv been having tranny problems lately tho... but i believe thats becuz its at 150,000.

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