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454 Runs Rough

Recently returned from long trip and our 87 Coachmen started running rough under load. Had recently filled up and thought it might be bad gas. Engine skipped occasionally and would pop-pop-pop under heavy acceleration. Within about 50 miles of home topped off (half tank) with 89 octane to see if it would help. Didn't. Still ran fine at 50-55 and even up to 60 on no load, fairly level highway. Replaced coil. No longer POP-POPs but sluggish. RV tech says could be intake gasket or camshaft. One is around $200 ; other is GET RID OF IT. Ideas?

May have a vacuum leak. Probably a failed or cracked hose. Look at the hoses where they push over the connections. They often split up the hoses at the connection. Hook up a vacuum gage and drive it and when it is running rough, check the vacuum. If this problem happened suddenly, there is a good chanch it is a vacuum leak. An intake gasket or camshaft usually gets worse gradually. Good luck.

Had the same problem myself on my 85 Pace Arrow. Hunted high and low and couldn't find out what the problem was. Thing was backfiring so bad under load that I had to replace the carb, as it caught fire and melted the aluminum parts inside. My son, who is a mechanic puzzled over it for a while and took it to a friends placec to check it out. He ended up staying late, and on the way home after dark, he found the problem. He had left the dog house off when they were looking at it, and in the dark he could see the plug wires cross-firing. We replaced the plug wires and never had a problem after. If you have had the plug wires for a while, REPLACE THEM, and your problems will go away.

Hi Bruce Dennis is right on. Every GM truck & motor Home I have owned had to have plug wires right away. This means over a year old. I have a 99 1/2 ton now with all the plug wires only about 8" long for each cyl & coil at each cyl. Now that they will be easy to replace, they will probably last a long time. When you relpace your wires, buy the very best available and route them properly so as not to get to much heat from engine & exaust. Good luck!

Assuming the vehicle was running fine before adding gas. Have you checked your gasline filter? Sluggishness under acceleration can be caused by fuel stravation/ Just a thought!

If you can check your FUEL PRESSURE, fuel pumps can come & go & make it seem like water in the gas. Adding a electric pump in line will also help in vapor locks.... Good Luck!

Hi Bruce, always check the basics first! Air filter, fuel filters, spark plugs etc. It may just be one of these items needs replacing. Be careful with whom you're dealing with as far as repairs go. Believe it or not there are some dishonest folk out there ready to rebuild a perfectly good engine because someone needs a new fuel filter. Remember always start with the simple basics first!!!!
Hope this helps.

Had a 454 for 14 years [2 MH] and problems mentioned in BB always related to sparkplug wires. Once they had just been replaced. Hope this helps.

Thanks so much for the info. I replaced the two fuel filters 3-4 months ago. Will try the new plug wires now and see if that will cure the problem. I really do appreciate this board and all the good responses.

Al C
On two occasions in the last six months on this board, this problem has turned out to be low voltage to the coil. One was a dead alternator the other was a bad ground cable, both caused backfiring and missing under load. Just something else to check-:)

replaced the roto cap on my 454 twice to fix the problem. I need to clean the counter weight on the distributor shaft to fix the cause of the problem.

Wires replaced, plugs too. Still same song and dance....runs fine 55-60 on highway but little to no uphill power to maintain speed . From stop very sluggish and occasional backfire---not pop-pop-pop just skip now. Will continue to consider other alternatives that you guys have been so kind as to input. May let her sit ,til after Jan1. Who knows....Y2K may jump in and fix it or just blow it to _____ and back! Been wanting a newer one with slideout anyway but fighting the urge due to cost factors. Thanks much!

Here is one more that may be worth checking. On my '85,454 the coil is in the dist.cap. The coil must be grounded!! It will run if it isn't grounded but with time the coil arcs from the coil windings to the plates of the core. This will cause the symptoms you describe. You usually can see the carbon tracks on the coil if it is arcing.Take the coil out and see if there is a ground wire and look for any carbon tracks due to arcing. Say, have you gone out in the dark and looked under the hood with it running. You may see the problem. Good luck!

Just a thought-- it sounds like you get the difficulty when you request more power of your engine, am I right. If so it kind of sounds like your distributors vacumm advance is not working properly and if it's not activated by vacumm it's still possible that the electronic component that opperates the advance is bad. Hey if you were here in California I'd check it out for you for free, but since I doubt you are---you may need to take it to a Automotive Tech instead of replacing everything you don't need. All the advice your getting here is great and in some instances a do it yourselfer can benifit but I think in this matter you need to have a specialist hook it up to a scanner to determine the problem and then if after the diagnosis you feel capable of doing the repair yourself go for it. The cost of the diagnosis should be minimal, but could save you tons of hunt and peck aggrivation down the road. I would'nt think the diagnosis should cost more than a 20 spot or less. Good Luck!

I agree with Larry, this is the best advice of all the threads!!! although we are all learning a lot by the posts of others. 3 cheers for Les for keeping this site here.

Hi Bruce,
Did you check your FUEL pressure.??? You may be starving for fuel when you demand power. You can disconnect at the filter & the pump should fill a coke bottle fairly fast when you crank..(pull coil wire)... Of course a pressure guage is the best way... Good luck..Bob

Make shure your timing is set correctly, and check the mechanical advance weights inside the distributor. If the mechanical weights stick and prevent full advance, it could cause your problem.

Also, check for fuel pressure by t'ing a gage into the line and driving. I have seen fuel pump levers wear at the pin and lose stroke and the valves inside the pump are just pressed in and can come loose. And your fuel filter or the filter sock inside the tank could be partially clogged.

Make sure your exhaust is not restricted. Some exhaust pipes use double wall pipes, and when they get hot the inner wall can expand inside the pipe, restricting it. Also check the fuel tank venting, or test drive it with the fuel cap off.

If you are getting popping at high rpm's only, regardless of load, you may have a broken valve spring. Valve springs can break near the end and they will still work but not at high rpm's.

Good luck, don't give up.

Let us know what the outcome is. I am interested to know as I recently have started having the same problems with my 87 Coachmen only it has a Ford 460. I've replaced plugs, plug wires, cap, rotor, and fuel filters to no avail. I am going to check my timing and fuel pump this weekend. I would be very interested to know what the cure for yours is. If I am able to get mine fixed I'll post it here.

Well, tech found problem really by accident. See, he was working with the vac/gasket idea and pulled a wire to check something (see, this has gotten beyond me at this point). Anyway, I happened to be there at the time and he remarked,"that shouldn't kill the engine". Next day he called and she was ready. Turns out that the dist. shaft was 'worn' or something like that. Replaced it and runs fine. Sure was a confusing problem and I'm just glad he was doing whatever it was when the 'puzzling' action caught his attention. There's just too many things in this equation that seem to cause this problem. Hope the solution will help someone else. Thanks again ya'll for the help and suggestions. Catch u later!

Hi Bruce, always check the basics first! Air filter, fuel filters, spark plugs etc. It may just be one of these items needs replacing. Be careful with whom you're dealing with as far as repairs go. Believe it or not there are some dishonest folk out there ready to rebuild a perfectly good engine because someone needs a new fuel filter. Remember always start with the simple basics first!!!!
Hope this helps!

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