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D_E_Bishop's avatar
D_E_Bishop
Explorer
Apr 23, 2014

454 Chevy has low power and high gas usage/some help

My Bounder's engine started running bad a few years ago and at night you could see the leakage from the plug wires. Decided to have full tune up done. Many hundreds later I got it back and it still ran bad. Long story short, at least three years 4 or 5 shops and still running bad. Hesitates when you first step on accelerator, no power, and when you floor it at the time the rear barrels open, even less power. Well last week we were E/B from Fort Smith AR and it suddenly started running like it did several years ago. Ran great up to Russelville and then is went back to same 'O', same 'O' cra--.

I decided that when we got home I would take it to a high performance shop near the house. Well a couple of days later we're in Paducah KY and a bunch of us guys were talking about engine performance and my problem came. Consensus was it didn't make sense. Today I was thinking about the biggest problems I have are with the vacuum system. I also thought back some time ago when the kids were young and we were going over Loveland Pass in our Type 2 VW Bus. No power and high consumption. We also talked about Model A Fords and manual spark advance.

Well I sent the DW off to look at quilts and I pulled the cover off the doghouse. Ultimately what I found was a badly worn and flimsy vacuum hose on the vacuum advance of the distributor that would collapse and seal off and hold the advance at full advance.

All the symptom fell into place considering the vacuum problem.

I need to get a new length of hose and install it but just trimming off the end has made the engine run much better.

There has to be at least 100 feet of various size hoses and I would love to replace them all but I don't think I could and I just don't think I can afford to have it done, so at least I know what to look at when the engine runs crudy.

Improvement in mileage and power. My first tank of gas since Paducah showed a 20% + increase in mileage and a 75% improvement in power. There are still a couple of problems but the improvement is amazing. I was getting 3.5 to 5 MPG and now 6.3 MPG. I will buy 25 feet or so of hose and replace all I can as per darsben's suggestion. I am still going to have the distributer pulled and run on a test stand and have Blair's do a final tune up. With the engine testing as a Gross Polluter and mechanics tweaking it so it woud pas smog last year I am sure it way off.

Thanks for all the suggestions.

18 Replies

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  • Ray___June's avatar
    Ray___June
    Explorer
    Apr 24, 2014
    There's not one mechanic in 10,000 that can make those carbs work correctly nowdays.

    One of the most overlooked problems was a worn secondary air valve cam that controls the metering needles when the secondary opens. If the cam is worn or destroyed (many were plastic, and the first backfire would ruin them) they won't pull the needles up out of the metering jets far enough, and you get a severe stumble, backfire and loss of power.

    Your best bet will be a race shop that is still using carburetors rather than fuel injection. Have them rebuild the carb. In many cases that will cure the lack of power. The other suggestion earlier about the sinking float is also a good idea. It's old enough it should be replaced.

    Good luck.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 23, 2014
    A vacuum advance hose AIN'T going to cause 2% of the problems you've detailed. Plus it off, rip it loose, no way José.

    You've apparently been dealing with idiots masquerading as professionals.

    This is what you need to do with an older Bounder or any other engine.

    FIND A SHOP THAT HAS AND KNOWS HOW TO USE
    A Cylinder-Leak down tester. ALL EIGHT CYLINDERS need to have a leak down test performed.

    Perform an exhaust gas SMOG TEST with certification needed. This test is much cheaper. Use a TEST ONLY station.

    When someone tunes up an engine that has a distributor with mechanical and vacuum advance mechanisms they use an ADVANCE TESTING TIMING LIGHT and an ENGINE TACHOMETER to VERIFY the advance curves in the distributor are not out of whack. They are usually ridiculously broken.

    ROCHESTER QUADRAJET CARBURETORS are notorious for floats that absorb gasoline, get heavier, sink, raise float levels, and engine runs rich as hell. Also these carburetors wear out the steel throttle shaft hole in the aluminum carburetor base. To check, CAREFULLY squirt WD-40 around the shafts when the engine is at idle. The faintest stumble or RPM change and you have a mileage killing leak.

    Your rig is probably so far out of whack as I write this, it isn't funny,
  • mchero's avatar
    mchero
    Explorer
    Apr 23, 2014
    Fred has a VANTASTIC suggestion.
    A properly configured\adjusted distributor can do WONDERS on performance AND mileage! Also, check the exhaust side. Sounds like it "might" be plugged.
  • ScottG's avatar
    ScottG
    Nomad
    Apr 23, 2014
    Lazy 02 sensor - replace even though it passes tests and doesn't light up CEL.
    You won't believe the difference this little $28 part makes.
  • RJsfishin's avatar
    RJsfishin
    Explorer
    Apr 23, 2014
    If your theory of "vacuum advance stuck in full advance" was correct, your 454 would detonated (pinged) itself to destruction.

    If the hose was broke, or not connected, you would barely notice a little difference in mpg during hi maninfold vacumm conditions.

    A malfunctioning centrifugal advance is the only thing that would maybe cause what you describe.
  • Led_67's avatar
    Led_67
    Explorer
    Apr 23, 2014
    You are all correct with the vacum hoses and the mechanical advance on the distrbutor. I would not only have the distributor rebuilt or replaced but also do a full inspection of all hoses and wires to determine wether or not anything elses could be affecting the performance.

    Good luck
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    Apr 23, 2014
    Hi,

    You might want to take the distributor to ClutchesUnlimited in Midway City CA.

    They can rebuild it and give you a setting to correctly time your motorhome at 3,000 RPM, in other words the correct advance for that RPM. Or call them and get a appointment to bring in the whole RV and leave it with them to rebuild the distributor and replace the hoses, you can pick it up with a whole new amount of power added to it. They are only about 40 miles from Eagle Rock. They will probably keep the RV a day or two, in order to have time to rebuild the distributor. Or they might have a 454 distributor they can rebuild, and have it ready to install when you get there, so you will not need a ride home.

    Fred.
  • j-d's avatar
    j-d
    Explorer II
    Apr 23, 2014
    When you go WOT (Wide Open Throttle) and power drops off, it's a good sign of a plugged exhaust. Possibly Catalytic Converter if it has one, but it can be Muffler, crushed/collapsed pipes, or a plugged screen at the end of the tailpipe. Listen to the exhaust at the tailpipe. If it's more of a wheeze than a pulsation, another sign of stoppage.
    If your 454 is old enough to have a distributor vacuum advance, it might also have centrifugal advance under the rotor. Look for stuck, rusted, broken or stretched springs. Check for free movement of the weights.

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