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Discussion Starter · #1 ·
Hey all,

So this is a bit of a long story but I have been having issues getting my truck to run efficiently and I feel I need to give all the information for the best responses.

Started with a rebuild on my carb which is the holley 6280 lean burn. Ran way better but then a few weeks later found an intake manifold leak ( found by spraying around the mating surfaces ) fixed that, still running crappy, thought it was a fuel problem because it would drop rpm randomly at idle when warm, replaced filter and pump. Then finally picked up one of those vacuum gauges and tested while engine was idling warm ( should have done this in the beginning, novice here :D ). Needle was bouncing quite a bit. I have a video link here

https://www.dropbox.com/s/j2eycm7m1vsepwd/Video.mov?dl=0

Just did cap, rotor, plugs, wires last night, thinking one of the spark plugs was fouled or distributor contact points were too corroded. ( got that from the sporadic needle, Miss-fire? ) Plugs all look good, did compression test as well, even across the board. Was too tired to continue last night so I will be advancing the timing tonight by turning the distributor clockwise. Hopefully that makes things a bit better. I noticed the rotor was pointing to the driver side of the truck, not to the #1 cylinder. ( not sure if this matters )

Furthermore, based on some vacuum reading diagrams I have looked at this bouncing around between 20hg and 15hg could potentially point towards a leaking head gasket? I have no other signs of there being a leak there, no white smoke through exhaust, engine oil looks good, no bubbles in the coolant while running etc. The engine is 34 years old and never rebuilt so I wouldn't be surprised if that was the case. Just doesn't add up though. She also only has 116k on her and has been fairly well taken care of so I would hope to get a few tens of thousands more out of her before rebuild.

I also keep going back to thinking its the lean burn carb, did some reading and found that it only sets the warm idle speed and the actual warming up process is still all mechanical/vacuum. Something could be wrong there? I have never read good things about them and only held onto it because of the people's republic of California smog laws.

This thing has been a pain in my arse! I feel like I am close but if it happens to be a headgasket issue might as well just do a rebuild...

Also keep in mind too that when at wide open throttle or any sort of throttle accelerates fine, maybe a small loss of power but gets up to speed fine, no overheating, etc.

So to summarize:

1. Is adjusting timing here enough? Could it also be the timing chain?
2. Does anyone know if you can put a holley 2280 on instead of the lean burn 6280 in California and still pass emissions?
3. Thoughts on the headgasket leak based on the vacuum readings.

Any help with diagnosing this would be awesome. I am going in circles here... ???
 

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first, I know diddly squat about the lean burn carbs....

but, the way it slowly kinda oscillates like that, would lead me to believe that the carb is the problem. 
The lean burn stuff probably has a bad reputation for a reason. 

I feel you can rule out the head gasket, as you have good compression, no white smoke, and nothing funny about the oil or coolant.

It looks like its running pretty smooth otherwise, so I dont think you have any major issues with ignition or cam. 
 

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Discussion Starter · #3 ·
75whiskey200 said:
first, I know diddly squat about the lean burn carbs....

but, the way it slowly kinda oscillates like that, would lead me to believe that the carb is the problem.
The lean burn stuff probably has a bad reputation for a reason.

I feel you can rule out the head gasket, as you have good compression, no white smoke, and nothing funny about the oil or coolant.

It looks like its running pretty smooth otherwise, so I dont think you have any major issues with ignition or cam.
Based on that, anyone know of the options I have for being in California and needing to pass smog besides leaving the state ;)

I will be doing a timing adjustment tonight and will do another reading with the vacuum gauge and post another video, see how she does.
 

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well, you could find somebody who knows those carbs, to help fix it....or something along those lines.....
get a verified good carb.....
then pull it off and install and tune a nice Holley 1850. 

save the emissions model, and install it for smog checks. 
 

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Discussion Starter · #5 ·
Ok so I am doing some more looking around and comparing things with my FSM. It looks like my ICM is not where it should be and same with the ballast resistor. I don't know where the ICM is but the ballast resistor was bolted underneath the coil on the manifold.




I am not the first owner of this truck. Possibly someone messing with ignition already. The distributor looks stock. No MSD logos or anything. I have no idea where the ICM is.

Sent from my iPhone using Tapatalk
 

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Discussion Starter · #6 ·

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good chance the resistor/s you have in hand are for the electric choke heater , bouncing between 10 - 20 inches of vacume , indicates a problem , remove and plug the pcv valve hose , retest vac ,  same ??? remove the vac hose TO the brake booster, install vac gauge in that hose TO engine ,  same ??? then do a compression test ..... vacume testers use to come with some instruction's to help with diagnosing your readings ...
 

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Discussion Starter · #8 ·
dodge82273 said:
good chance the resistor/s you have in hand are for the electric choke heater , bouncing between 10 - 20 inches of vacume , indicates a problem , remove and plug the pcv valve hose , retest vac , same ??? remove the vac hose TO the brake booster, install vac gauge in that hose TO engine , same ??? then do a compression test ..... vacume testers use to come with some instruction's to help with diagnosing your readings ...
When you say to plug the pcv hose and retest vac, you mean put vac gauge hose onto port to the carb for the pcv? And same with the break booster?
 

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When you said "fixed that" referring to the intake leak, do you mean you pulled it off and put on new gaskets or the spray fixed it? Because an erratic vacuum gauge usually means bad manifold sealing or broken rings or sticky valves. Has it been sitting long? Lots of carbon build-up inside?
 

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Discussion Starter · #10 ·
Canadian country boy said:
When you said "fixed that" referring to the intake leak, do you mean you pulled it off and put on new gaskets or the spray fixed it? Because an erratic vacuum gauge usually means bad manifold sealing or broken rings or sticky valves. Has it been sitting long? Lots of carbon build-up inside?
By fixed I meant I pulled the manifold cleaned it up and put new gaskets in and resealed. Checked for leaks and again and don't get any rpm changes around the mating surface.

No the truck has not been sitting. I would say there's a decent amount of carbon But probably pretty normal for the mileage. Haven't actually looked at the valves though.
 

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Run some Seafoam or something equivalent in it to see if it reduces the erratic vacuum. If it is a carbon issue then the Seafoam or equivalent will hopefully make a difference.
 

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Discussion Starter · #12 ·
Canadian country boy said:
Run some Seafoam or something equivalent in it to see if it reduces the erratic vacuum. If it is a carbon issue then the Seafoam or equivalent will hopefully make a difference.
Yea I'll give that a go tonight and see how the vacuum reading responds. I have a bottle I can just pour down the carb. Is there a specific amount I should be using? 1/2 bottle, whole bottle, etc...
 

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Just do what the instructions on the bottle say to do. I forget. Its not often i use products like that. Plus you may need to repeat the procedure over a second time. Sometimes running just one treatment isnt enough.
 

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thegrid22593 said:
When you say to plug the pcv hose and retest vac, you mean put vac gauge hose onto port to the carb for the pcv? And same with the break booster?
that works , ( one at a time ) it eliminates each as a "problem" and gives actual manifold vacume readings . To ME bouncing vac , says a bad valve OR a worn timing chain flopping , nothing "steady" like a leak ....
 

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Discussion Starter · #15 ·
dodge82273 said:
that works , ( one at a time ) it eliminates each as a "problem" and gives actual manifold vacume readings . To ME bouncing vac , says a bad valve OR a worn timing chain flopping , nothing "steady" like a leak ....
Got it, I'll try that this evening. I originally thought it was some sort of vacuum leak but because its not a consistent like a leak would be I thought otherwise. Either a specific cylinder component having issues or maybe a worn timing chain.
 

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Discussion Starter · #18 ·
thegrid22593 said:
When you say to plug the pcv hose and retest vac, you mean put vac gauge hose onto port to the carb for the pcv? And same with the break booster?
Okay so I think I am getting somewhere...

I did a couple tests:

1. Vacuum Gauge hooked to the PCV: no change

2. Vacuum Gauge hooked to the brake booster. In park idling https://drive.google.com/file/d/1lWGcuaQ0epW-Cam83Z5mfUEwpaom-OfB/view?usp=sharing

3. Vacuum Gauge hooked to the brake booster in Drive idling https://drive.google.com/file/d/1x1KPbXHNpcRTYbvkoTDteoSmaLY9-wrp/view?usp=sharing

Seem like the needle is less sporadic with gauge in the brake booster which makes me think there is a problem with brake booster, any ideas what? Common issues there? And the gauge is telling me late ignition timing.

So... I then loosened the distributor and advanced the timing, no luck sounded even worse and would sometimes die. Tried retarding the timing as well, no luck there either. Possibly timing chain issue?

Also, all of this was done without any punching of the gas to drop the idle down. The second I gave any throttle the truck would die.
 

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O.K. , the amount of gauge fluctuation seen on your videos ( or whatever they are properly called ) is "normal " I did NOT see the needle going from 10 inches to 20 inches as you had written previously in either of the movies of it ...  Know that "blipping" the throttle WILL make the gauge change , also Normal .
 
  how "high" must the idle BE to keep the motor running ?  about like a cold engine choke ?.....  or more ?  what if you very easily / slowly throttle it just a little at a time ? what happens then ?
 

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Discussion Starter · #20 ·
dodge82273 said:
O.K. , the amount of gauge fluctuation seen on your videos ( or whatever they are properly called ) is "normal " I did NOT see the needle going from 10 inches to 20 inches as you had written previously in either of the movies of it ... Know that "blipping" the throttle WILL make the gauge change , also Normal .
Thanks for the help Dodge82273. The amount of gauge fluctuation was actually 15 - 20 inches and you can see that here on the first video I posted. This was with the the vacuum gauge hooked to one of the manifold vacuum tree ports and the PCV and brake booster connected from their components to the carb ports https://www.dropbox.com/s/j2eycm7m1vsepwd/Video.mov?dl=0

dodge82273 said:
how "high" must the idle BE to keep the motor running ? about like a cold engine choke ?..... or more ? what if you very easily / slowly throttle it just a little at a time ? what happens then ?
Definitely a high idle cold engine choke to keep it going. I will try to throttle a little at a time and report back again with how the vacuum gauge reacts. I understand that when the throttle plate is opened there is less vacuum so the needle drops.

As for my carb I have my high idle speed screw on the second to last step when cold and that seems to adjust correctly as the engine warms, the heat coil that pulls the choke open as the engine warms has been replaced as well, carb was rebuilt about 8 months ago.
 
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