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  1. #1

    Default 96 K1500 hard starting when engine cold

    Hi,

    I have a 1996 K1500 (5.7L) that is progressively getting harder to start when it has set for a few hours. I have to crank it multiple times before it finally starts up. It seems to crank just fine, just acts like it isn't getting fuel. Then eventually it'll start to catch and then after a couple more cranks, it finally "catches"...barely. It acts like it's going to sputter out and die and then it starts running. It seems to idle normally and run just fine after that.

    I'm definitely not a mechanic, but I am cheap enough and like to figure things out enough that I don't want to take it somewhere and have someone fix it. So I'm hoping someone(s) on here might be able to help me out with some knowledge here.

    I've done a fair amount of searching online and have read the Haynes manual on the fuel section many times. It looks like it is likely (although not necessarily) one of four potential things:

    1. Fuel pump
    2. Fuel filter or fuel line
    3. Spark plugs
    4. Fuel Pressure Regulator

    I replaced the fuel filter and spark plugs since I haven't done it while I've owned the truck (about 20K miles or so - now at 118K). That didn't help at all.

    I bought a fuel pressure gauge today and hooked it up. After I cycle the key ON and OFF a few times, it has about 58. They Haynes manual says it should be 60-66. This seems pretty close though. If I start the engine (cranking it many times) and let it idle, it has about 54. This is close to what Haynes says it should be. If I let it sit for five minutes, it drops about 3-4. This is within spec according to Haynes.

    The Haynes manual says that I should install a shut off value in the return line and do some tests to help determine if the fuel pressure regulator is bad. The connection in the return line is at the back of the engine and behind a bracket which makes it extremely hard to see, and I have no clue what type and size of fitting I would need to get to hook in a shut off valve and Haynes thinks this ought to be a piece of cake. Perhaps it is for someone who isn't me. So I haven't made much progress on that yet as I need to go buy whatever I need to do this after I somehow figure out what it is I need to buy.

    Searching online though, it looks like a few people who have had a similar type problem and the FPR has been bad have talked about finding fuel in the vacuum tube. I thought this might be an easier check than trying to figure out how to stop the fuel from returning to the tank after the FPR. This is where my stupidity will really show: I'm not sure where the vacuum tube is that folks are talking about. Is this the hose that comes out of the back of the top of the engine under the plastic box with Vortex on top and into the brake booster? Do I need to disconnect it there and check to see if fuel is in it?

    Any help would be greatly appreciated.

    Thanks.

    kcstrom

  2. #2

    Default

    First of all confirm it is in fact a fuel problem.

    While someone is turning the key to start it (1st thing in the morning), spray some starting fluid into the throttle body. If it quickly responds, then it is a fuel problem.

    So far as the pressure regulator and return line, there may be a flexible hose which you can squeeze to test this (as opposed to installing a valve). Squeeze it and this will stop the flow back through the return line. Then pressure should increase.

    Also note there is a check valve as part of the fuel pump. A check valve is a "one way street" for the fuel. This prevents the fuel from draining back into the tank. That check valve could be bad.

    Basically pressure should hold in the fuel lines after shutting off the fuel pump. If it quickly drops, then possibly a fuel pump check valve problem.

    So far as which specific hoses are vacuum, etc. You can order a GM Factory Service Manual set and this will tell you EVERYTHING about the vehicle. These are extremely detailed with instructions for troubleshooting and testing everything. These sets of books cost about $135, but they save in the long run because you can test things and only replace the parts which are faulty. You can order a set from helminc.com or a GM dealer. This is the same information they use at the dealer.

    If you need to replace the fuel pump and have a truck, you can get 4 guys and remove the truck bed instead of lowering the gas tank.
    92 GMC Sierra 2500

  3. #3

    Default

    Searching online though, it looks like a few people who have had a similar type problem and the FPR has been bad have talked about finding fuel in the vacuum tube. I thought this might be an easier check than trying to figure out how to stop the fuel from returning to the tank after the FPR.
    GM threw you a curve ball as far as this goes. On the big blocks, there's a vacuum line hooked up to the FPR. On your small block, they put the FPR inside the intake manifold, where it is exposed to engine vacuum (no need for a line). So, checking for a ruptured diaphragm isn't as easy as pulling a vacuum hose on your engine. Some say you can see any gas from the FPr by sticking an angled mirror (like a dentist's mirror) down the throttle body.

    Hard cold start are often related to the fuel pump check valve as mentioned. As noted, you'll start checking this by seeing whether or not the fuel system can hold pressure when the pump shuts off.
    '98 K1500 Suburban LS 5.7 L 4L60E NV246 ARB
    '92 Ford Explorer XLT 4x4 4.0 L A4LD BW13-54 Trac-loc rear
    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

  4. #4

    Default

    I hadn't driven my truck in a few weeks as I had been riding the motorcycle. When I went to start it last week, it would not start at all anymore. :( I replaced the fuel pump by taking the bed off (this took several hours as all the bolts were very rusty where the threads stuck through on the other side) instead of dropping the tank (which was full of fuel) and fortunately it fixed the problem! It starts right up now.

    I noticed on the fuel pressure gauge that the pressure jumps up to the mid-60s while cranking whereas before it stay in the mid-to-upper 50s.

    kcstrom

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