QuestionQUESTION: Hi Mike!
I have a '79 Blazer K5, 350, 4x4. Put in new plugs, wires, roter, dist cap. Also put in a new Edelbrock 4bbl carb. (guess I shouldda gone with an OEM) Anyway, I lose all power now going up hills, and on the straight away changing gears. Going up hills in traffic or neighborhoods, it tops out at 15mph with my foot to the floor!! My mech cousin and a pro shop can't find what's wrong with it. New fuel pump, too. They have the vacuum hoses bypassing the catylitic conv, but not sure what else to try. My cousin thought it might be the "trans vacuum modulator" or some such thing. Can you help me somehow? I'm on a fixed income and this is the only vehicle I have. Thanks a ton!
Scott
ANSWER: I doubt if the carb is the problem, especially if it's a new one. It sounds to me like a timing problem. I assume that you are still using the HEI distributor that came with the truck. From the message I am guessing that you didn't have this problem before the tune-up. Before doing any analysis, make sure that you put the plug wires back in the correct firing order. The order is cast into the manifold. If you got two wires, or more, mixed up it could easily cause this problem. If you are sure they are on in the right order, then proceed with the other stuff I've suggested. Here's what you need to do: Get a timing light and check the timing at idle. Make sure that you disconnect the vacuum advance from the vacuum hose, and plug the hose with a golf tee or similar item. The correct timing number should be on the under-hood sticker but, if it isn't, look for something around 8 degrees before top dead center. If you've never looked at the timing, the marks may be hard to see. Clean off the damper and mark the Top Dead Center line with a streak of white-out or any other white paint. Keep the stripe narrow and right on the mark. Also clean the pointers on the cover so that you can read which is which. Usually the ) degree mark is a little taller than the others, and each mark represents two degrees. Hook the light up to the #1 plug wire (the one closest to the front on the driver's side, in this case) and look at the mark. if it's off the mark, loosen the distributor hold-down clamp and slowly turn the distributor while the engine's running until the mark is where it belongs. Don't grab the top of the cap to turn the distributor--the spark will go right down your arm (they don't call it High Energy Ignition for nothing). Now hook the vacuum advance up and see what happens to the timing when you rev the engine. It should move pretty far, about twenty-five degrees or so. If it does, then we have to assume that that mechanism is working. If the engine stumbles or cuts off during this part of the test, then you probably have a bad ignition pickup. The pickup is what the advance moves to change the timing, it is under the metal plate in the distributor. The two little wires that hook to the end of the module lead to it. Constantly moving back and forth over the years causes the metal wire inside the insulation to fail. It will make contact at idle, then cut off as the advance moves it. The shaft has to come out of the distributor to change it. You can buy a rebuilt distributor instead, but it is not super cheap, around $100 exchange. Given the age of the truck, though, it might not be a bad idea. If you decide to do that, you should be able to re-use the cap, rotor, and wires that you just bought, they don't usually come with the distributor. Also, if you use a cheap rotor, it will fail quickly. The rotor is the weak link in the system. Look at the underside, if you see any black discoloration on the plastic then it is bad.
Before you condemn the ignition, though, check for vacuum leaks. Since you replaced the carb, they could be there if it isn't sealed properly. An old trick to see if there was a leak was to try to smother the carb with a rag held in the hand. If there are no leaks, the engine will shut off, if there are it will keep running. Chevy V8s are prone to developing vacuum leaks on the underside of the intake ports. Fixing that will mean removing and re-sealing the manifold with a new set of gaskets. If you have to do that, let me know and I will give you the tips for that installation. I honestly think that a vacuum leak is your most likely problem, but the fact that you gave it a partial tune-up before this happened makes it hard to judge. Good rule of thumb: test drive the car after every step of a tune-up. Doing a bunch of stuff at the same time makes it hard to track down the problem.
---------- FOLLOW-UP ----------
QUESTION: Hi Mike-
Thank-you sooo much for your great and fast reply!! I'm going to show my cousin your answer and see if he can better understand how to do what you've suggested. We haven't changed the distributor- just the cap, roter, condensor, plugs and wires. He also checked the timing and adjusted the distributor cap in idle. Wierd- it idles fine, but one in gear, just loses so much power. Not sure if I was clear about asking you what you thought about the transmission vacuum modulator that screws into the transmission itself?
I wish I could send you photos of this truck. I'm going to sell it here and try to get another used vehicle. It has 179k miles, and a 4x4, removable hardtop, rear bench seat, white and brown in color, new hearliner and carpet and the body and bumpers are in very very good condition. The a/c and heat work, but not very cold or hot. Do you have any idea what I could get for it? Sorry to keep pestering you here, I know you're a busy man, just not sure where to turn to. Thanks again so much, Mike! Scott
Answer It's very hard to place a value on an older vehicle, there are so few comparables. Keep in mind that you are unlikely to get a better vehicle for the money you get. But, if you're bored with this one, then move on. That's the main reason I usually get rid of cars. The more I think about it the more I think that the wires must be in the wrong order. I've found that it's always best to change the wires one at a time, then change the cap by transferring them to the new cap one at a time. It's extra work, but it prevents mistakes. I sold a set of wires to a guy once, and he went out into the parking lot and proceeded to rip all of the wires off of the car. Then he took out the new wires, looked at them, and came back in to ask where they went. I looked up the firing order and sent out one of my guys to straighten him out. Otherwise he would have been there all day. Even when you are very deliberate and careful it is easy to make this mistake, it happened to me last time I did wires on an old Mercedes V8. But, I knew what I had done the instant I test drove it and had it purring like a kitten in no time. Made me cry when I cracked one of the towers on the $100 distributor cap, though.
