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Discussion Starter · #1 ·
Truck started running rough and won’t idle unless RPM is 1200-1500. Then if I put it in geer to move it dies. I couldn’t find a vacuum leak. Plus mechanic said carb was shot. As I started looking at it, choke didn’t work, secondaries didn’t open, so when I would gat it, I could feel the trans kick down but didn’t go faster and felt like it wasn’t getting fuel (because it wasn’t). Then as smog time approaches I’ve read and been told that the carb want smog compliant.

So got the Edelbrock 1400, 600 cfm. Installed it and only marginally better.

While looking for vacuum leak, replaced a few lines that seemed sound but showing signs of dry and cracking plus sniffed down the manifold bolts.

Started looking around for cheap ways to test. Came across carb cleaner and reluctant due to fire hazard. Shop quality machines are close to a grand. Saw a few folks rig up DJ or Halloween fog machine and read about using cigar smoke to find the leak. Has any one here done this? How much smoke from a cigar will you need to puff in if it is an intake gasket? Do you do this with the car running? Or off? Most YT videos seem to connect to EGR tubing. Won’t smoke just come out carb?

Any advice would be appreciated.
 

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Just use an unlit propane torch.
 

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Before you get to far into it.  Check timing.  We've had a member or two that the hold down didn't hold and the timing backed off a bit.  I like brake cleaner for finding vac leaks.  It's less flammable than carb and choke cleaner and tends to drag the idle down when it hits the leaks.  I'd also take a close look at vac hoses.  In any event, have a CO2 based fire extinguisher close by.  No mess to clean up if you do get a flare.  Your plugs will tell you if you are running lean as well.
 

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2 types of cleaner so BE carefull VERY ...    old "Brakekleen " brand was carbontetracloride ( SP?)  that was also a chemical  used in fire extinguishers , it put fire OUT , so it'd slow the engine if it found the leak  BUT  a health problem when put on a fire ! newer stuff like "shopsolve" ( SP?)  is VERY flammable !!!!!  The unlit propane torch  works ok , as long as your aware propane in heavier than air and will "lay" in valleys and such like water would . but with the motor running , fan going  , not so bad ...  acetylene works too ... a small brazing tip .. 
 

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Discussion Starter · #5 ·
So tried something I found online. Used a cigar and blew smoke looking for a leak with engine off. No leaks, it all came out the carb. Tried a Halloween fog machine. Fog didn’t make it out the carb. I believe it turned back to liquid and didn’t go far.

Really reluctant to use aerosol, propane, or acetylene. But guess that’s where I’m headed next. Sounds like Brakekleen or more likely unlit propane torch with engine running. Right now it won’t idle unless someone is on the gas or it finally warms up and adjust idle up to 1500-2000 rpm.

Question now is, most of the vacuum hoses are new. Didn’t see leaks with half assed tests. Will the propane truck work if there is a leak around the manifold gasket? My guess is that if it is a leak, it’s big because of the way it runs. Would think if it’s vacuum, I would hear the hose, not so much.

Anyway, advice for propane testing?
 

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if its sucking air it will suck the propane , which burns and should increase idle rpm so listen for more rpm or use a tach , try to get it to idle as slow as you can , because the difference will be more noticeable , the closer you come to THE leak the faster it should run ...  have you applied a vacume gauge to it ?
 

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Discussion Starter · #7 ·
I don’t have a vacuum gauge and not sure how to use it if I did.

Poking around after work, although close to dark, looked like someone did a crappy repair on some of the smog equipment. No idea what it is but connected to smog pump, up the front of the engine, then a tube along drivers side valve cover, then 90 degree turn along rear of engine along top of bellhousing but restricted access partially blocked by brake booster, distributor, and wires.

Looks like thin metal and a hole that was patched with tons of silicone.

Like I said I’ll try propane test but concentrate on that area. If it’s leaky, no idea what it’s called how to access. I’ve read about exhaust tape/patch that sticks and hardens with heat. Would this work in this application?
 

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air pump and "smog" tubes from the sounds of it .
 

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Discussion Starter · #9 ·
Found this last night. This is the tube between the diverter/check valve that dumps air into the exhaust manifolds. Looks like someone in the past had trouble because signs of brazing. Found a welder, literally across the street who is going to put it back together. Fingers crossed that this is the source of trouble.
 

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Discussion Starter · #10 ·
Update. I got this piece welded up and reinstalled and couldn't get it to crank. Gave up and took it to the shop. Somehow ballast resistor was bad (already replaced it once), relay bad (also replaced and an extra was in the glovebox when I bought it...hmmm), alternator wasn't charging so rewired, and new battery. Starter was having issues and finally would do nothing not even buzz/click. Got it smogged and it passed!!! Mechanic had it almost 3 weeks and had an electrician over twice. Said come and get it. I came the next day, crank, crank, crank. Turn over but no spark. so new distributor and electronic ignition module. Holy crap. I had replaced the distributor already and upgraded to Protonix ignition.

But finally got to drive it to our new house an hour away on a California freeway, in rush hour, in 100 degree temps. Dont think i got over 50 MPH but no overheating issues. My knuckles were so white by the time I go back, not even funny. Bigger tires make it squirrley over about 35. Oh, and body bushings are pretty much dust and the front pair are off altogether. So flopped and banged like you wouldn't believe.

Next body mount bushings and to the frame and alignment shop.
 
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