Author Topic: Runs rough when accelerating  (Read 1799 times)

Offline Rapid Roy

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Runs rough when accelerating
« on: April 03, 2021, 06:45:35 PM »
Engine started running rough this last week on accelerating. Runs normal in Park or Neutral while revving. Runs rough in gear sitting still also. Replaced plugs and the in-carb fuel filter today and no difference. Truck died on the street last weekend and I found a vaccuum hose had split on the end and fell off. Trying to restart I flooded carb and could not start for a while. This flooding may have caused an issue in the carb. The last rebuild was July 2017. Thinking I may need to rebuild again, not sure.

Any help is appreciated.
 
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Online bd

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Re: Runs rough when accelerating
« Reply #1 on: April 03, 2021, 07:28:21 PM »
Check all of the spark plug wires for hard spots, arcing to ground (grayish-tan ash traces on the outside of the wires) and burn-back (carbon soot) inside the boots.  Lift the distributor cap and closely inspect for carbon tracks as well as the condition of the carbon button.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Rapid Roy

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Re: Runs rough when accelerating
« Reply #2 on: April 04, 2021, 05:24:23 PM »
I have rechecked all vacuum lines, plug wires and all seem good. Pulled dist cap and nothing bad found. Checked fuel lines and cannot find anything I can tell that is causing this. Would a bad ignition module cause this or possibly coil? I have had a no start due to the module before.
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline JohnnyPopper

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Re: Runs rough when accelerating
« Reply #3 on: April 04, 2021, 08:24:48 PM »
Welcome to the world of variables!

Trying to understand "rough on accelerating"- is it stumbling while accelerating from 0-30 mph?

Q: Did 73 have an ignition control module? I thought those came about later.

Did  you pull the cap off the coil and inspect for evidences bd described?

Flooding doesn't affect the carb, it just annoys the plugs... ;D

Finally, have you adjusted the carb idle jets?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline TexasRed

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Re: Runs rough when accelerating
« Reply #4 on: April 04, 2021, 08:38:36 PM »
If the module was bad, it's probably the coil too. The coil in my experience can take out the module. Bone stock coil if yours is the internal coil (none of the high "performance/voltage" ones). Unless you find a tester for the coil that gets it hot and puts it in a running simulation, then a simple resistance check will NOT tell if you if it's good or bad.

You may find a tester for the module in autoparts store.

Also, check your grounds.

Offline Rapid Roy

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Re: Runs rough when accelerating
« Reply #5 on: April 04, 2021, 08:43:09 PM »
If the module was bad, it's probably the coil too. The coil in my experience can take out the module. Bone stock coil if yours is the internal coil (none of the high "performance/voltage" ones). Unless you find a tester for the coil that gets it hot and puts it in a running simulation, then a simple resistance check will NOT tell if you if it's good or bad.

You may find a tester for the module in autoparts store.

Also, check your grounds.

I haven't changed module yet. I have a spare and thinking about changing but not sure if it is the problem.
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline TexasRed

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Re: Runs rough when accelerating
« Reply #6 on: April 04, 2021, 08:58:21 PM »
Well, I wouldn't change the module until you verify that the module you have is bad OR get a spare, good coil to swap in at the same time. A bad coil takes a very short time to knock out a module.

Offline JohnnyPopper

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Re: Runs rough when accelerating
« Reply #7 on: April 04, 2021, 09:01:07 PM »
So I guess the question about the 'module' is irrelevant?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline TexasRed

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Re: Runs rough when accelerating
« Reply #8 on: April 04, 2021, 11:09:26 PM »
My post came right after yours so yours may have gotten missed.

I'd assume since he put HEI in the tag, that he may have converted to it. I'd also assume he ran an appropriate gauge wire with a full 12 volts to the distributor as well if it is a conversion.

Seems like the model year 1975 was the first year of HEI as we know it.

Offline JohnnyPopper

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Re: Runs rough when accelerating
« Reply #9 on: April 05, 2021, 02:45:56 AM »
Thanks  8)

I have read here about "modules" that control knock/detonation by affecting the timing etc.

I don't think that's the same as a HEI (high energy ignition?) system.

I think that was introduced in '73. Maybe wrong but close. Replaced the GM adjustable point system.

So, I'm still wondering what he means by 'module'?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Rapid Roy

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Re: Runs rough when accelerating
« Reply #10 on: April 10, 2021, 06:36:34 PM »
UPDATE

I performed all the troubleshooting I could do with only having a carport and limited tools. Finally decided to take it to my tech and said my cam had finally worn down that is causing the rough running. He had discovered the #8 cam lobe was worn a few years ago when replacing the valve stem seals. It was worn and only raising rocker arm a little. He is in the process replacing cam. He is going to put in an Edelbrock Performer cam. He said it is the beefiest he could install without any other upgrades which is more than the stock one. Should be finished by next Friday.
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice