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Gremlins in the Thermoquad ? and vacuum circuit, HELP!

C

Charlied

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Just finished a meticulous rebuild on the TQ which turned out very well. Set up the fast idle and curb idle per specs.
Cold start extremely rough and idle drops quickly from 1700 rpm to 1000 ( fast idle cam in correct position) and ready to stall out if I don’t work it. Once warmed up idle steady @ 1000, but still a little rough.
Checked vacuum, it’s steady but low @ 15 (should be 19-20) adjusting mix screws seems to have impact in moving it, strange. Timing is right on the money @ 5 degrees, and has fresh set of plugs.
I replaced all vacuum lines and being a 74 Satellite , it has plenty! Do think their is a vacuum leak somewhere, but @ a loss to find. Would a bad (clogged) EGR be culprit, I’m grasping at straws. I always try to be disciplined in my approach and follow the KISS method (keep it simple,stupid) but quite frustrated at this point that I can’t solve it.

Any advice on what to check and test, would be very appreciated.

Car is a rare bird,74 Satellite Sebring Plus, big block (400) 4 speed , pistol grip. All original I bought it new and never sold it .

Thanks
Charlie
 
How did it run before?
At what idle rpm are you getting 15" hg?
Did you time it with the distributor vacuum advance disconnected?
Did you work on anything else besides the carb?
Will it idle at 750 - 800 rpm when warmed up?
 
BSB67 said:
How did it run before?
At what idle rpm are you getting 15" hg?
Did you time it with the distributor vacuum advance disconnected?
Did you work on anything else besides the carb?
Will it idle at 750 - 800 rpm when warmed up?
Click to expand...


Ran lousy,those internal o rings failed causing super rich condition, reason for rebuild.
Getting 15 hg @ 1000 idle steady no up or down
Can’t recall, but probably not .After initial install and warm up checked timing was dead on 5 degrees (as before)
No other work, did put new plugs in as old were gas fouled. Did notice a slight improvement after replacing all vacuum lines this was done after install of rebuild and initial start up, which makes me lean toward vacuum leak.Will idle @750-800 when warm but not any smoother or worse. Did get a back fire pop when I was adjusting mix screws but only once.
Could clogged EGR be the culprit? It’s original and never been off. Thanks for your help, just want to get right !
 
I don't think the egr opens at idle. If you hook a vacuum source to the egr and open it at idle, the engine should run worse. Maybe the egr is stuck open.
 
Right now you are lighting the fire too late and subsequently sending unburned fuel out of the tail pipe. Today’s fuel makes good power, it just takes a little longer to burn. Therefore we must light the fire earlier to have complete combustion by 10-15 after TDC. You’ll see if you put a vacuum guage to a source below the throttle blades, fire it up and start to slowly advance the timing at idle. You’ll hear it start smooth out and watch the guage rise. That is a more complete combustion and the engine getting happy.
 
Mick56 said:
I don't think the egr opens at idle. If you hook a vacuum source to the egr and open it at idle, the engine should run worse. Maybe the egr is stuck open.
Click to expand...

The EGR valve works via vacuum. The valve is open at idle and cruise since this is where the engine spends most of its time.
The lack of vacuum closes the valve. This way the air fuel mixture is at its best and can take advantage of the timing events from the distributor.

The spent gasses do not harm anything when driving down the road because there inert, which of anything, allows more timing for cruise. Though, it is a air/vacuum leak, it is a controlled vacuum leak, the carb has been compensated for this at the get go.
 
Mick56 said:
I don't think the egr opens at idle. If you hook a vacuum source to the egr and open it at idle, the engine should run worse. Maybe the egr is stuck open.
Click to expand...
Thanks Mick
Need to reset timing first had it @ 5 degrees which I thought was correct. Research on this site and google indicate should be 10-12 , think that should address my vacuum (low) and hopefully smooth things out
Woodruff Carbs said:
Right now you are lighting the fire too late and subsequently sending unburned fuel out of the tail pipe. Today’s fuel makes good power, it just takes a little longer to burn. Therefore we must light the fire earlier to have complete combustion by 10-15 after TDC. You’ll see if you put a vacuum guage to a source below the throttle blades, fire it up and start to slowly advance the timing at idle. You’ll hear it start smooth out and watch the guage rise. That is a more complete combustion and the engine getting happy.
Click to expand...
Hi Dave,
Thanks for the clear sage advice, makes complete sense.When someone who knows can explain it to a person like me who is always guilty of over complicating things it’s a major accomplishment! Really appreciate it.
Thanks
Charlie
 
Wondering if bumping the timing fixed this issue. All I run is thermoquads just seeing if a simple solution worked.
 
72sunroof said:
Wondering if bumping the timing fixed this issue. All I run is thermoquads just seeing if a simple solution worked.
Click to expand...
My timing light ( vintage like me ) died yesterday. Out of town next few days on it next week. Confident that’s the fix.Let you know.
Thanks
 
Mick56 said:
I don't think the egr opens at idle. If you hook a vacuum source to the egr and open it at idle, the engine should run worse. Maybe the egr is stuck open.
Click to expand...
Mick,do you know what proper aftermarket replacement might be ? The original is 3830104, 74 400 bbl 4 speed. P/N 3830105 says for automatic, can’t fiquire what the difference could be.
More challenging, how to remove,the original is on the motor and the nuts I’m afraid frozen, concerned if I use a big breaker bar will snap the stud. Any advice appreciated.
Thanks
 
rumblefish360 said:
The EGR valve works via vacuum. The valve is open at idle and cruise since this is where the engine spends most of its time.
The lack of vacuum closes the valve. This way the air fuel mixture is at its best and can take advantage of the timing events from the distributor.

The spent gasses do not harm anything when driving down the road because there inert, which of anything, allows more timing for cruise. Though, it is a air/vacuum leak, it is a controlled vacuum leak, the carb has been compensated for this at the get go.
Click to expand...

YES...the EGR valve is closed idle and opens when the EGR carb port is exposed to vacuum AND If the EGRs thermal vacuum valve, located in the vacuum line, is above its setpoint value. When this thermal vacuum valve is closed, it inhibits the EGR valve from opening (cold engine conditions - like cold start up). EXHAUST GAS RECIRCULATION (EGR) adds a controlled amount of exhaust gas to the intake fuel charge to REDUCE combustion chamber temps by introducing an inert gas (CO & CO2) to limit or reduce the thermal NOx (oxides of nitrogen) generated IF the combustion chamber temps exceed ~ 1600° F., at the instant of combustion. EGR basically criples the HP produced by the engine at the trade off of cleaner air. The fuel-air-inert gas mix requires more ignition advance to light off the mixture. Chrysler's early EGR systems were fixed orifices, directly under the carb, tapped ihto the exhaust crossover passage in manifold floor.....a horrible example of stop gap engineering.
BOB RENTON
 
rumblefish360 said:
The EGR valve works via vacuum. The valve is open at idle and cruise since this is where the engine spends most of its time.
The lack of vacuum closes the valve. This way the air fuel mixture is at its best and can take advantage of the timing events from the distributor.

The spent gasses do not harm anything when driving down the road because there inert, which of anything, allows more timing for cruise. Though, it is a air/vacuum leak, it is a controlled vacuum leak, the carb has been compensated for this at the get go.
Click to expand...

YES...the EGR valve is closed idle and opens when the EGR carb port is exposed to vacuum AND If the EGRs thermal vacuum valve, located in the vacuum line, is above its setpoint value. When this thermal vacuum valve is closed, it inhibits the EGR valve from opening (cold engine conditions - like cold start up). EXHAUST GAS RECIRCULATION (EGR) adds a controlled amount of exhaust gas to the intake fuel charge to REDUCE combustion chamber temps by introducing an inert gas (CO & CO2) to limit or reduce the thermal NOx (oxides of nitrogen) generated IF the combustion chamber temps exceed ~ 1600° F., at the instant of combustion. EGR basically criples the HP produced by the engine at the trade off of cleaner air. The fuel-air-inert gas mix requires more ignition advance to light off the mixture. Chrysler's early EGR systems were fixed orifices, directly under the carb, tapped ihto the exhaust crossover passage in manifold floor.....a horrible example of stop gap engineering.
BOB RENTON
 
Charlied said:
My timing light ( vintage like me ) died yesterday. Out of town next few days on it next week. Confident that’s the fix.Let you know.
Thanks
Click to expand...
Worked on it yesterday. Here is what I did and how .
Warmed up car to operating temp ,steady idle @ 1000 rpm choke fully open.
Bumped timing to 12, vacuum marginally better (17) idle still slightly rough. Leaned out mix screws best I could. EGR tested works properly. Rechecked all vacuum lines and connections, good no leaks. Puzzled that timing change hasn’t boosted vacuum more and still have that slight roughness @ idle with boosted timing. Guess I have to find the Mopar/thermoquad whisperer here in ATL. Don’t know where to go from here.Frustrated thought I had it.
 
Charlied said:
Mick,do you know what proper aftermarket replacement might be ? The original is 3830104, 74 400 bbl 4 speed. P/N 3830105 says for automatic, can’t fiquire what the difference could be.
More challenging, how to remove,the original is on the motor and the nuts I’m afraid frozen, concerned if I use a big breaker bar will snap the stud. Any advice appreciated.
Thanks
Click to expand...
Hi Mick, ran check on EGR yesterday functions properly, all good there. Did increase timing to 12, but marginal increase of vacuum 17 maybe, leaned out carb best I could, still have that slight roughness @ idle. Rechecked all vacuum lines and connections, tight no leaks. Puzzled, don’t no where to go from here, or just live with it. what do you think?
 
Charlied said:
Thanks Mick
Need to reset timing first had it @ 5 degrees which I thought was correct. Research on this site and google indicate should be 10-12 , think that should address my vacuum (low) and hopefully smooth things out

Hi Dave,
Thanks for the clear sage advice, makes complete sense.When someone who knows can explain it to a person like me who is always guilty of over complicating things it’s a major accomplishment! Really appreciate it.
Thanks
Charlie
Click to expand...
Woodruff Carbs said:
Right now you are lighting the fire too late and subsequently sending unburned fuel out of the tail pipe. Today’s fuel makes good power, it just takes a little longer to burn. Therefore we must light the fire earlier to have complete combustion by 10-15 after TDC. You’ll see if you put a vacuum guage to a source below the throttle blades, fire it up and start to slowly advance the timing at idle. You’ll hear it start smooth out and watch the guage rise. That is a more complete combustion and the engine getting happy.
Click to expand...
Hi Dave, finally had time to work on it yesterday. Increased timing as suggested and saw only marginally improved vacuum (17) and slight roughness still there. Tested EGR, works properly. Rechecked all other vacuum lines and connections, tight no leaks. Puzzled why timing adjustment only marginally boosted vacuum and minimum ( if any) elimination of slight roughness. Did my best to lean out the carb as well. Don’t know where to go from here. Think I need the Mopar/Thermoquad/ignition whisperer here in ATL to work the voodoo. Frustrated.
 
I would get some good rubber gloves.
Pull a plug wire at a time and see what you get.
Do a compression test.
Sounds like a bad cylinder or two.
Maybe something as simple as new plugs.
 
Don Frelier said:
I would get some good rubber gloves.
Pull a plug wire at a time and see what you get.
Do a compression test.
Sounds like a bad cylinder or two.
Maybe something as simple as new plugs.
Click to expand...
Thanks for the advice. FYI pulled and replaced the plugs prior to reinstall rebuilt carb. They all were dry (thankfully) but showed heavy fouling since carb had internal leak ( bad o rings). Will re-check for spark, but think it is ok. Will recheck compression as well, but would think if a cylinder bad the roughness would be more pronounced and some indication of oil consumption seen, none evident.Also when motor @ say 3000 it’s smooth.
The motor was rebuilt long time ago, re bored .30 over, crank cut and balanced, new cam nothing radical ,hardened valves, etc. shop did a great job. I’ve put maybe 5K miles on it since then. Thinking I just don’t have the touch to set mix screws properly or There is a small vacuum leak that I can’t find. Maybe I’m just too critical and comparing it to my 2017 Durango, fuel injected of course which is smooth as glass, not a fair comparison.Just for the hell of it will try to find some no ethanol gas as see what happens. I remember the days of Sunoco 260 and Hi test Amoco which were great fuels.
Thanks for the advice.
Charlie
 
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