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Discussion Starter · #1 ·
I NEED HELP! My car runs horribly and I want to make it perfect again! I changed the cap rotor and the plugs and wires. I have also replace the alternator and voltage regulator. It is up and running very slow on the acceleration. Terrible gas mileage under 10 miles to the gallon. Somebody help!
 

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What about the carburetor? That’s often the source of performance and economy issues on an old car. Does it still have the stock ignition or has someone swapped it? How many miles are on it? It may need a timing set.
 
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Discussion Starter · #5 ·
What about the carburetor? That’s often the source of performance and economy issues on an old car. Does it still have the stock ignition or has someone swapped it? How many miles are on it? It may need a timing set.
I believe the odometer rolled over atleast once so around 140,000 ide say. Stock ignition I believe. I don't know too much about cars unfortunately 😕
 

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I NEED HELP! My car runs horribly and I want to make it perfect again! I changed the cap rotor and the plugs and wires. I have also replace the alternator and voltage regulator. It is up and running very slow on the acceleration. Terrible gas mileage under 10 miles to the gallon. Somebody help!
If it has a 318, possibly a jumped timing chain. If that has happened it needs to be fixed immediately because if that engine loses timing it could suffer severe damage from the valves hitting the pistons necessitating at least a valve job.

There are many other possible causes and unfortunately, diagnosing by posts on a forum just can't be accurate.
 

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One thing I want to point out because everyone's perceptions are different. Despite the fact the car has a V8, it is not a fast car to accelerate. The engine isn't that powerful and the rear end is geared for economy, not performance.
Some other things not yet mentioned are a restricted exhaust (plugged catalytic converter) though I'd have expected the plugs would be black.
There's also a chance the spark control computer is bad or the distributor internals are frozen so you aren't getting any timing advance.

How long have you had the car? Has it ever ran well while you've owned it?
 
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1974 Plymouth Valiant - 2013 Dodge Dart - 2013 Chrysler 300C
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One thing I want to point out because everyone's perceptions are different. Despite the fact the car has a V8, it is not a fast car to accelerate. The engine isn't that powerful and the rear end is geared for economy, not performance.
Some other things not yet mentioned are a restricted exhaust (plugged catalytic converter) though I'd have expected the plugs would be black.
There's also a chance the spark control computer is bad or the distributor internals are frozen so you aren't getting any timing advance.
Same horsepower rating as a Neon in a heavier body... more torque, though.
I was surprised at how slow the Diplomat felt compared with my 1976 Valiant, which already had most of the emissions gear. I don't think it had the economy axle ratio, though (tow package). This was back in the 1980s when I test drove an ex-police-Dip someone was selling.
 

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Same horsepower rating as a Neon in a heavier body... more torque, though.
I was surprised at how slow the Diplomat felt compared with my 1976 Valiant, which already had most of the emissions gear. I don't think it had the economy axle ratio, though (tow package). This was back in the 1980s when I test drove an ex-police-Dip someone was selling.
All civilian and almost all 2 bbl police cars had the 2.2 gearing. it made them sluggish but provided decent, but not great, highway gas mileage. The 4 bbl police versions got 2.9 gears.
A 1976 Valiant could have gears from 2.45 up to 3.21.
 

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I agree that it may be the carburetor, but I have to ask you if you put Champion plugs in the car gapped at .035? If you're not running Champions, that MIGHT be a problem.
 
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All civilian and almost all 2 bbl police cars had the 2.2 gearing. it made them sluggish but provided decent, but not great, highway gas mileage. The 4 bbl police versions got 2.9 gears.
A 1976 Valiant could have gears from 2.45 up to 3.21.
Thanks. If I ever knew the gearing before, it was wiped out by, y'know, chemicals.
That really does explain it. At the time, being an ignorant kid (not that kids are ignorant, but I was), I blamed emissions gear, of course.
I am pretty sure it was a two-barrel. Ironically my Valiant's towing package was, as far as I can tell, sharing just about everything with the police package, including the two-barrel. So I should have known police cars aren't necessarily fast!
 

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Discussion Starter · #12 ·
If it has a 318, possibly a jumped timing chain. If that has happened it needs to be fixed immediately because if that engine loses timing it could suffer severe damage from the valves hitting the pistons necessitating at least a valve job.

There are many other possible causes and unfortunately, diagnosing by posts on a forum just can't be accurate.
I wouldn't know where to go to check the timing. I've only done basic upkeep mechanics so far. Need help from someone experienced with the 318 and car mechanics in general
 

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Discussion Starter · #13 ·
I agree that it may be the carburetor, but I have to ask you if you put Champion plugs in the car gapped at .035? If you're not running Champions, that MIGHT be a problem.
Not sure what champions are but they're gapped there and they were the more expensive plugs at the local napa
 

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Discussion Starter · #14 ·
Same horsepower rating as a Neon in a heavier body... more torque, though.
I was surprised at how slow the Diplomat felt compared with my 1976 Valiant, which already had most of the emissions gear. I don't think it had the economy axle ratio, though (tow package). This was back in the 1980s when I test drove an ex-police-Dip someone was selling.
Honestly it rides like a dream but it's just sluggish on the acceleration. When I step on it I can still pee a little haha I just want to make it perfect if not even better!
 

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Discussion Starter · #15 ·
One thing I want to point out because everyone's perceptions are different. Despite the fact the car has a V8, it is not a fast car to accelerate. The engine isn't that powerful and the rear end is geared for economy, not performance.
Some other things not yet mentioned are a restricted exhaust (plugged catalytic converter) though I'd have expected the plugs would be black.
There's also a chance the spark control computer is bad or the distributor internals are frozen so you aren't getting any timing advance.

How long have you had the car? Has it ever ran well while you've owned it?
The car ran like crap when I got it and got about 67 miles on a tank while sputtering the whole time with no acceleration. I replaced the plugs, wires, cap, rotar, alternator, and the voltage regulator. I also cut off the catalytic converter in the end and got a little better acceleration. Ive only had the car maybe a month.
 

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Not sure what champions are but they're gapped there and they were the more expensive plugs at the local napa
The plugs should not have been expensive. Just the cheapest Champion copper plugs will give you the best spark, If you spent money for platinum plugs, it was a waste and they may foul early. Not likely to be the issue when the plugs are new.
 

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Discussion Starter · #17 ·
The plugs should not have been expensive. Just the cheapest Champion copper plugs will give you the best spark, If you spent money for platinum plugs, it was a waste and they may foul early. Not likely to be the issue when the plugs are new.
Well that's good to know for the future. I would have thought the others were better
 

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Discussion Starter · #20 ·
This is my dream car guys. I want to make it my ultimate muscle car with the 318 in it. These are my baby steps. I'm broke as a joke but open to suggestions on anything. It's also going to be my daily driver though so I want the full header and 4bbl experience but I need to figure out what I'm doing first and get it running perfectly
 
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