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

darsben
Explorer II
Apr 25, 2014
Talk about timely for me. My 454 was having symptoms similar to the ops. Took it to my mechanic. He diagnosed it almost immediately as vacuum line collapse. Says 454's were notorious for that. Having them all replaced as the rig is 25 years old.

Just got it back and took it for a test drive. What a difference 12 feet of hose can make. Runs nice
BrianinMichigan
Explorer
Apr 24, 2014
After headers, 2 carb rebuilds (First one kind of sucked), Then I had the distributor rebuilt and recurved. It runs better than ever. Look up posts by Jim Elliott ( Jim83Itasca ) He has since passed but the man knew his engines.
MEXICOWANDERER
Explorer
Apr 24, 2014
" There's not one mechanic in 10,000 that can make those carbs work correctly nowadays."

When times were simpler I used to de-stake the butterflies from the throttle shafts and bore and install oil lite bushings. That secondary needle life cam was remade from ironwood, a brass float was substituted, and every last damned interconnect hose and choke pull-off was replaced. You're right, this is the era of Plug and Pay.
SilentBob
Explorer
Apr 24, 2014
Gotta love that old school hardware...WTF, could be a million things wrong with it
Norskeman
Explorer
Apr 24, 2014
Had a similar problem (1994 bounder - 454 chevy)- clogged fuel filter. It is located along the frame.
wa8yxm
Explorer III
Apr 24, 2014
A couple of years ago after some non-engine related service my MH started misfiring I could just hear the miss) and performing poorly with reduced MPG.

Finally got to a service center who found Something had nibbled on the ignition primary wire. A bit of splice and solder and 100% again.
BurbMan
Explorer II
Apr 24, 2014
Two things that technology was able to eliminate along with vacuum tubes: the distributor and the carburetor, simple in theory but the source of endless frustration and tinkering. You don't mention how many miles on the ol' Bounder, but at 24 years old, a good rebuild on both the distributor and the carburetor would be beneficial and give you many more trouble free miles.

Re the vacuum hose, first off a leaking hose would have failed to provide any advance, not held the dist in full advance. Rjsfishin is correct when he says, full advance would have had the engine pinging itself to death.. I don't the leak affected the dist per se as much as a vacuum leak in general. Any time you have a vacuum leak like this you will get the symptoms the OP describes, this one just happened to be at the dist advance connection.

Recommended service interval on the O2 sensor is 50k miles, according to this site.
Golden_HVAC
Explorer
Apr 24, 2014
Hi,

Hopefully Blairs will get it all fixed up. I have a friend in Long Beach who might want to dyno his motorhome just for kicks and giggles, and see if it really will put out more than 300 HP that his neighbor's DP puts out.

I will have to let him know about the place. He does have a Clutches unlimited rebuilt distributor, and the 460" engine in his 87 motorhome puts out massive horsepower, enough that he tore the center out of a flexplate on his C6 transmission. He had left the cruise control set at 65 while going up a 5% grade.

Fred.
PaulJ2
Explorer
Apr 24, 2014
All the symptems point to distributor/advance problems. These years had the mechanical advance up top under the rotor. The inner and outer shafts would seize stopping the mechanical advance from working. It needs to be pulled, the shafts removed, freed up, lubed and reassembled. Also check the vacuum advance unit with a vacuum test pump. Vacuum advance unit is an economy device and comes into play at light,cruising throttle conditions.
I repaired many of these in my shop days years ago. You need to find guys that know these older systems meaning probably "OLD" guys.
D_E_Bishop
Explorer
Apr 24, 2014
I changed the hose and the difference is remarkable. There are some problems which I feel were caused by trying to adjust timing and carb to get it to pass smog. I am heading home from Paducah KY on Sunday and I was going to go to Blair's Speed Shop in Pasadena and have them put the scope on it before doing anything else. I will check with Clutches Unlimited if Blair's can't take care of the problems. They have corrected problems for me in the past, don't know why I didn't think of them sooner.

I'm not sure if there is an O2 sensor on a carb engine but I'll ask about it at the shop. I had wondered about the possibility of centrifical weights and will ask about those also. The carb was rebuilt after the problem started and made no difference in performance when installed. The choke did work correctly after rebuild, I didn't know it automatically dropped RPMs after start. Anyway, I think the shop that did the carb is very highly thought of and I think it is working correctly. The guys at Blair's will pull the distributor and put it on the analyzer to map changes they feel will be needed. Blair's has a Dyno that my rig will fit on and I'm sure that will be the first thing they test.

It will be interesting to see what effect the new hose after the first fuel fills are done.

Once again thanks and I report back when we get the rig back from Blair's.