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Need help with 500 idle problem

Started by densie, April 16, 2006, 09:18:59 PM

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densie


  This is really starting to make me feel stupid.

  Last year, I failed emissions testing, and I hired the mechanic next door to the testing place to get it through.  He told me that he did it by raising the idle so much that he could barely hold the brake pedal, and that to fix it properly, I would have to replace the intake gasket.

  So today, I did it.  I used a new valley pan, with a little brush tack sealant around the ports, and I seriously doubt that I have any vacuum leaks there.  There arent any hoses leaking either.  I pulled them off one at a time and plugged the ports.  But, my HC is close to 800!  Idle CO was 1.8, and I raised it to 2 by turning the mixture screws out.  Between that and retarding the timing, I got it down to 700.  Thats still ridiculously high.  It has to be below 350 to pass.

  When I rev the engine, I can get the HC down to 50, and the CO goes down, but as it idles, it slowly creeps back up to 700 or more.  Raising the idle a little doesnt help...it has to really wind up to lower the HC.

   What can I do to get this thing through emissions?  I dont think that I can hold the brake pedal while it runs at 2000 rpm.  I have another engine on the stand that I can put in the car, but Im already working on an engine change, and I have to get this done by the end of April, or the tags expire.  I wont have the new engine done until late in the year, if Im able to do it at all.

   Any ideas, aside from getting rid of the car?

thanks

-denise

Dave MacGregor #18998

In NJ for example, you can keep your older car with current tags if you register it as exempt for inspection.  The guidelines and rules to do this are similar to registering it with the "QQ" historic tags for those who dont want to for whatever reason.  One of the rules are that of how you drive it and how much a year.

Another option is to register it as antique and just get a different set of tags which is easier.

What does your state offer to keep it on the road?

Dave

denise 20352


   There is a new law allowing a car which is insured as a classic and not driven as transportation to be made exempt, provided that the EPA approves it, which may or may not happen.  That would cost extra money, and I drive this car, so I cant really do that.

   There is a one-time exemption, but it can only be done once in the life of a vehicle, and you have to prove that youve spent a bunch of money on it.  The record stays with the car forever, like a restored salvage title.  I dont want to do that.

    I guess I pull the spark plugs out.  Maybe one of them is fouled out and a cylinder is misfiring, although that doesnt explain the low readings at higher RPM.  That reeks of vacuum leak, but I just cant find one.

    Would trying a different carb be worth doing?

thanks

-densie

Johnny #662

Florida has no state inspection on any vehicle.

denise 20352


   I tried a different carb, and the readings got worse.  I got lower CO, but higher HC.  Turning the mixture screws out helped, but I had them turned out almost as far as I could turn them without losing them, and HC was still way too high.  CO was still lower, so I guess this carb doesnt dump in as much fuel.

   This problem still reeks of vacuum leak, right?  I tried closing the choke, and when I got it nearly closed, the CO went up to 4.0 and the HC went down to 350, which is actually passing.  Wow, that reeks even more of vacuum leak.  So I checked vacuum, and it is at 18.  Isnt that about right for stock idle?

   Im going to pull out the plugs and do a compression check, but if I dont find anything, what else could be causing this problem?  If the engine is just worn out, would that cause these readings?  Go ahead and be pedantic, if you want.  I am really weak on auto diagnostics, and I could be missing the simplest thing.

   My tester has been calibrated, by the way, and it shows normal readings on the Mercubox and the Volvo.

Thanks, as always.

-denise

Jim Skelly, CLC #15958

Densie,

Have you checked the PCV system?  Maybe the valve or lines are plugged up with oily gunk.

Is the dashpot solenoid adjusted properly?

Go to a GM dealer and buy a couple cans of top engine cleaner.  I used it on my 71 Eldorado years ago and it cleaned carbon deposits from the engine.  The engine will spew black smoke for probably ten minutes or so after using it.

Jim
68 Eldorado, 77 Biarritz

denise


  Do you pour it into the carburetor?

  PCV valve, good idea.  Ill go pick up a new one when I get the spark plugs.

thanks

-denise

Rhino 21150

If you have too much HC you have too much fuel. Vacuum leak lets in too much air, less fuel, NOx goes up, CO and HC go down.
Crack the throttle plate and restrict fuel at idle?
Do you have a catalytic?

denise 20352


  Yes, it does have a cat.

  What I cant figure out is, why would closing the choke make the HC go down?  This is just really bizarre...the CO goes way up to about 4.0, which means that there is way too much fuel, but the HC goes down near normal.  A little high, but close.

   That means that the engine runs better when it is way too rich, and that doesnt mean anything to me but "vacuum leak".  But its pulling 18" of vacuum, and shouldnt that be enough vacuum?

  Does running really rich help to overcome low compression or something?  Is it possible that just one cylinder might have a vacuum leak, or a bad valve that is keeping it from sucking enough fuel?

-denise

Rhino 21150

Four barrel? Choke is on the primaries only. Closing the choke increases vacuum which pulls the secondaries closed. Secondaries need adjusting. They are opening too soon. Or your timing is off.

Dave MacGregor #18998

NJ has such an exemption on its classics available on both the regular tags and the historic tags.  The difference being that in one you get a sticker stating so and you keep your tags while the other one is inferred with the historic "classic" tags they offer.

Yeah!  Both restrict your driving to that of a historic vehicle so I can see where that would not be good for you.

It was just an idea.

BTW, Sounds like its getting too much fuel or something similar.

Dave

denise


  Would the timing be too far advanced, or retarded?

denise


  I have thought about registering and insuring it that way, but I just love driving it too much.

  I can lean out the idle mixture, and CO will go down as expected, but HC goes way up.  That was why I tried pushing the choke valve shut.  It seems to want a very rich mixture, but with a CO of 4.0?  That is much too rich, and it still wants more.  HC keeps going down until you push the choke shut far enough for the engine to falter.

  Will pull the spark plugs out, and check compression and valve leakdown.  Maybe that will give me a clue.  I was really convinced that resealing the intake would fix it, and the mechanic across the street from the testing center thought so, but it must be something else.

-denise

Mike #19861


 Rhino is right. A lean mixture would mean higher NOX and possibly CO and lower HC. The engine is running too rich.

 The cats wear out on these cars, and the HC and CO will become elevated when that happens. Likeley you will need to replace that to get the HC within reason.
 
 In my experience in getting these carbed cars to pas, I back off the timing, lean out the carb as much as possible. Turn in the idle jets until it barely runs. Another help is to pour in some methyl hydrate. That will surely lower HCs.

 When you get the car to pass, bring it home and return all the settings to spec, and you are good to go until the next test is due.

 Mike

George Woodford clc21025

See my post on the Technical Forum on 1983 SDV Emissions Test Results.  High HC ppm is due to unburnt fuel in the cylinders.  Spark plugs, catalytic converter, and other ignition components could be causing the problem.  It is always good to change the oil and filter before the test.  As stated, make sure timing is correct and fuel mixture is not to rich.  My 1983 is throttle body injection and not carbureted, so this makes it easier to diagnose. My 1976 Eldorado with a the 500 cid engine has a catalytic converter, but no air pump.  I have no idea what the emissions are since it is exempt from the test.

denise


  Unfortunately leaning it wont work, which is what has me confused.  If I lean out the carb, the hydrocarbons go through the roof...1200 or more until they peg out the gauge.  When I richen the mixture, they go down.  When I have richened it up enough to get the CO to 2.0, which is about as rich as I can go without busting the test on CO, the HC are back down to 800.  I need to get them down to 350.  It doesnt make sense, but thats what it is doing.

   Do you know of a source to get the cat?  I can install it myself, but I always have a hard time finding stock exhaust parts.

   Where do you get methyl hydrate, and when do you pour it in?  On the way to the testing center?

thanks

-denise

denise


  Is there anything that could go wrong with the AIR pump and cause problems?

denise 20352


  All of the cylinders had 140-150 compression except for one which was around 110.  I think that it is the same cylinder that had a bent pushrod when I first got the car, so maybe the valve is sticking, or there is something wrong with the rocker or cam.  I HATE these flippitya$$ed rockers that Cadillac used.  Why do that when the Dodge next door has a shaft rocker system?

   Anyway, spark plugs were fouled black, which indicates a rich mixture.  Since I replaced the plugs and set the mixture screws, I have taken the CO from 2.0 down to 0.3, so that problem should be solved.  The hydrocarbons are way up there, and nothing helps with that.

   Perhaps the knock that Im hearing is a valve problem?  I would be thrilled if I could fix the whole thing on the top end, and not have to replace the engine at all.

-denise

Mike #19861


 There are aftermarket cats available at most muffler shops. They usually need to be adapted to fit your car, but that is where these shops come in. They have the pipes and equipment to do so. The prices of them have come down considerably since they dont have to last for 50,000 miles anymore.

 Methyl hydrate is available at most any hardware store. You can find it in the paint section. Pour in a full gallon to about 1/8 of a tank of gas. That should help drop the HCs. Use of premium gas also helps since it uses alcohol as an octane booster.

 Air pumps supply fresh air to the exhaust and are meant to reduce HCs as well. If they are not functioning, then the HCs may be higher. You can check it by removing the rubber hose off the back of the pump, and bring up engine speed. You should feel the ari being pumped. Also, the aspirator valves can malfunction, they ate those round things that the hose goes into on the metal pipe. They are a check valve and at times they will not allow air into the exhaust ports.

 Mike

denise


  Awesome.  I cant believe how much good advice Ive received.  Ill see how close it gets after Ive fixed the bad valve, and if it isnt low enough to be guaranteed to pass, Ill start doing all of this stuff.  Or maybe Ill do all of it, come in with a new cat and a tank full of methyl hydrate and premium gas, my timing retarded, etc., and blow a reading so low that theyll be scratching their heads.

  The main thing is to pass the first time, so that they cant have the satisfaction of telling me that it failed.  I know thats what they live for, otherwise they would be doing telemarketing, or clerking at a convenience store.

-denise