woodstockaz

Any help is appreciated. I'm much more familiar with fuel injection so the carburated 454 is a bit of a mystery as of now.

1990 Motorhome with a chevrolet 454 motor at 70K miles.

Won't pass emissions because of the idle.

When started, it idles up and down at 2-4 second intervals. I'm guessing between 6-700 RPMs and then up to 1000-1200 or so RPMS, then back down and continues to do so.

Is this a choke issue? Possible vacume problem?

Anyone know what this may be?

Terry Neff

Motor homes are known for one thing.That is for them setting of long periods of time unused.That opens a whole host of issues.From mice making nests where they shouldn't and crewing on wires to vac leaks to bad gas plugging up the circuits on carbs.

Take off the dog house and inspect for any rodents nests.Look for crewed on wires.Run the engine after dark and look for any leaks on the spark plug wires or coil.Pull the cap and inspect the cap/rotor for any carbon on the cap or rotor.

With vac leaks you want to run the engine and spray sections of the intake/carb with carb cleaner.If you see any change in the way the engine runs then somewhere near where you sprayed you have a vac leak.Look at all the vac lines closely.

Carb rebuild kits are still available from parts store and it is a common problem with motor homes that don't have gas treated with a stabilizer like the band name "Stabil".(sp)??.The idle circuits get varnished up and the gas flow isn't as it should be.You need to soak a disassembled carb like over night and then apply the purchased carb kit.

The engine is hunting for a idle and sounds more than likely is a fuel issue,but all the other things I am suggesting is more than likely needed also.

Give us a update and let us know what you have found.

in2pro

Terry's advice sounds like a pretty good place to start...
I would also suspect a vacuum leak as well as the less then great fuel..
there is also the possiblity that someone(previous owner) put in a different cam for power in a different RPM range and that can cause a loping at lower RPM's but I'd most likely suspect vacuum leak...

Terry Neff

One thing I forgot to say and wanted to add,is these Motor Homes are geared pretty high and on a GM chassis with a 454 it would likely be rear end gears like 4.56's.It is one main reason why it is suggested not to run the much beyond 55 mph for prolonged periods of time.70,000 miles is alot for a Motor Home and I think you should do a compression check too.80,000 is about a target mileage for rebuilds.Yeah,yeah........I am sure we will hear about guys that have millions of miles on their's,but I am talking about averages and real world experiences with gas engined Motor Homes.

woodstockaz

Much appreciated advice guys. Thank you.
I'm going to take a closer look before buying this week. I would like to know if there is a manual or technical diagram type book for the carburated 454 from 1990 that could help me along the way. I'm usually pretty good at troubleshooting when I have diagrams and chiltons etc...lol
Any online links or sources to carb 454 technical support?

in2pro

With the 454 engine its probably a Rochester quadrajet, there is lots of info on the web about them and for the most part ( at least when I dealt with one on my 73 Grand Prix with a 454 they were fairly simple)
give this link a try

http://www.carburetor.ca/carbs/tech/...jet-index.html

Terry Neff

I am not sure "IF" and that is a big if,you find the carb is the problem,that you would be just be better off to go belly up to a parts counter and buy a Edelbrock carb.90% of the time they are a out of the box turn key replacement.

woodstockaz

Alright. I'm leaning towards the purchase in the next couple days... I've got it figured with the following possibilities:
Loping idle=vacume leak $20, new carb $400, rotor plugs wires $50
Fridge=rebuild kit for $500
Tires=replace $1200
Generator=Prime fuel and oil change $20

The price tag on the RV is $2500 so this puts me at the $4500 mark and it'll be worth at least $6000 when road worthy.

My MAIN concern is why the idle is up and down and it won't pass emissions like that. Worst case scenario is probably the cam and maybe needs a rebuild! At that point I think I'd just cut my losses and sell it for cost.
I'll keep my fingers crossed that I can find a simple vacume leak and repair it.

therewolf

Hi woodstockaz,

Welcome to the Chevy Forums.

In the event that basic troubleshooting fails,before digging too deeply into the interior of the engine, you may want to do some research into acquiring a newer drive train for the vehicle at a recycle yard.( if you can find something which fits)

The primary benefit(if you can find something which will drop in and mount up without too much difficulty) is that while you still get a short warranty, you could probably find a smaller and more economical drivetrain with the same horsepower as the original, for less than the cost of an just an engine elsewhere.

Most of the larger recyclers(Remember when they used to call them junkyards?) have interchange manuals which may help. Furthermore, a lot of them have garage bays,and will drop a system into your vehicle right there, for a fee.

Terry Neff

Not trying to put the horse way before the cart here,but if you are force to do a engine swap,it can be a huge job.Some come out the front with it jacked almost on it's rear bumper,some come out the passenger side door,and the worse ones needs to have the windshield removed to get the engine out.Some you have to strip down to a short block form before you can remove it.Depends on which model RV you have.

Honestly,I think you estimate on the Frig repair is kind of on the light side of the real costs.You can get coil replacements that do work for a short periods of time,but in the end,you end up buying a replacement Frig.Three way ones cost some big bucks for a good one.A easy grand or more.........

When you look at it,look closely for any water stains on the ceiling.Roof leaks are common.Walk the whole floor feeling for any soft spots.Look under the RV and look for rust on haft of the driveshaft or mufflers.that means it has been setting for awhile and that is never good for a RV.Have the seller run water line to it and check the water pump by running the sink,shower.Check the black,gray,clear tanks for leaks.Look for any pluming pipe leaks.Look at the propane tank and controls.Have him fire the propane furnace and hot watter tank.Because you opened the topics of costs for this unit,I wanted to give you some tips as what to look for.

One last thing.454's in RV's generally get from 7mpg to 4mpg.They are not cheap to run.