Hesitation when accelerating

Justwondering

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Since it is raining buckets outside, I'm inside contemplating my current issue and reading my service manual (that's all kind of exciting!).

Since I installed the a/c compressor, I've noticed that there is a definite lag/hesitation when I push the gas pedal and when the engine responds. It feels like if I push the pedal too fast, that the engine will die. It hasn't yet, but only because I know slowly push the pedal til the engine rpms get higher.

The fuel system diagnosis for engine hesitates when accelerating warm says:
- secondary air valve sticking or binding (4bbl)
- vacuum leaks
- loose carburetor or manifold, leaky gaskets or disconnected hoses
- faulty ignition restricted exhaust
- distributor vacuum advance not operating
- idle transfer system dirty
- idle speed low or incorrect misture

Seems like there are many possible suspects given that I also replaced hoses and some of the vacuum lines.

I haven't driven it without the a/c on since its been so hot, so I don't know if this clears up when the a/c is off.

I also had a packrat chew threw lots of electrical lines which I've butt-spliced and heat shrinked.

It doesn't idle rough, it just has this late response to the gas pedal.

Fuel filter was changed 1 year ago in November.

If it quits raining today, what is the most likely suspect I should check? Or is there something I can try to rule out some of the possible problems?

Running non-ethanol gas in it. Was filled a week ago and have used 1/4 tank so far.
 

lowbudget

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When I look for a vacuum leak I usually use starting fluid and listen to see if the engine revs up. Carb cleaner will do the same. That is where I would start. Also check the carb mounting nuts/bolts as I've had them loosen up on both my 2 bbl slants.
 

Master M

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Well the A/C will drag about 5-7 hp from the engine, although that shouldn't make it hesitate. Does it do it the same amount when cold or hot ? Mine has a slight hesitation cold without any warm up time. Check the accelerator pump by looking down the carb with a flashlight and open the throttle and see if you get a nice steady squirt of gas as you open it quickly. The advance not working properly can give you the hesitation for sure. Put a vacuum gauge on the engine to check for leaks.
 

Justwondering

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Hard to believe, but I am going to have to wait for it to quit raining before I can check the carb and vacuum lines. lol
Just a week ago it was heat index of 110 and no rain for over 2 months.
 

slant6billy

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Hesitation as in delay or pause? Or do you mean it struggles to get up to cruising speed. Which AC compressor do you have? Is it the old big twin cylinder compressor or the newer barrell (Sanden style)? The big old ones provided a great deal of AC cooling, but at a tradeoff to power- noticeable at acceleration times. The Sanden screw type compressors don't have as much parasitic appetite, but don't throw snow flakes out the vents- At least I never saw them on the newer cars. My Dad's 83 5th Ave could use the AC to slow the car down, but freeze out the front seat passengers as well. You might have to do an early morning run without AC to see if the acceleration comes back.
 

BudW

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The rain might be all or part of it.
High voltage ignition wires and water moisture - well, shirt circuits.
Sense the ignition cap is behind the air cleaner, it doesn't dry out back there very well.

Not saying that is the only cause. If I only notice a driveability concern after a nice rain, then I don't get concerned.
 

Jack Meoff

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My Fifth has always stumbled if you stomp the pedal before it's totally warmed up. I've never totally known why.....I've always just known that if I hit the pedal hard when it's cold that's what will happen. Once warmed up it's totally fine.
 

rcmaniac791

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How many miles do you have on it? Is it worse when the motor is cold vs warm?
 

BudW

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My Fifth has always stumbled if you stomp the pedal before it's totally warmed up. I've never totally known why.....I've always just known that if I hit the pedal hard when it's cold that's what will happen. Once warmed up it's totally fine.
Sounds like the bi-metallic clock-spring in the choke thermostat has quit working (actually rust and age is what gets ‘em).
 

Mr C

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Is that the spring on the wheel (not appropriate name) on the exhaust manifold outlet?

I think he means this spring that lives on our intakes:
s-l300.jpg


The thermostat spring on the exhaust is called the heat riser.
 

7T8 Custom

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Replaceable, yes I think they can still be found. Difficulty is nil unless mount bolt is seized in the intake manifold and then its gonna be a little more work. Necessary? Well it is part of your choke assembly which really won`t matter if you don`t want to drive the car until it`s at full operating temperature.
 

Jack Meoff

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Replaceable, yes I think they can still be found. Difficulty is nil unless mount bolt is seized in the intake manifold and then its gonna be a little more work. Necessary? Well it is part of your choke assembly which really won`t matter if you don`t want to drive the car until it`s at full operating temperature.

Bingo!.......and thank you kindly.
I have no issues warming up my Fifth in the colder months and my apologies if I've steered this thread but I was curious.

For the record my Fifth doesn't do it as badly in the summer.
 

BudW

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The bi-metallic spring is designed to close choke when cold and be full open when engine is hot.
The problem is as the part heat cycles for decades and rust, it doesn’t open fully (when hot) or close fully (when cold).

In my opinion, the bi-metallic spring is good for about 15-20 years of normal usage (no facts to substantiate this).

When I’m working on a drivability concern, I first make sure the choke pulloff is working.
If so, then replacing the choke thermostat fixes the problem about 90% of the time.

Choke Pulloff.jpg

BBD carb.jpg

Carburetor Choke Pulloff

Choke Thermostat.jpg

Choke Thermostat (pictures swiped from eBay)

3 ways to test the choke pulloff:
. Remove vacuum hose to choke pulloff and test with vacuum pump.
. Remove vacuum hose to choke pulloff and test by sucking on vacuum hose to make sure of no vacuum leaks.
. Remove vacuum hose to choke pulloff. Push diaphragm in. With another finger, plug vacuum port with finger, to see if diaphragm holds vacuum.
In all three cases, it should maintain vacuum (slight loss is OK) and it should move in/stay in.

I’m not aware of any method to test choke thermostat for its full range of travel – other than replacement fixes most cold, warm and hot drivability concerns I run across.

BudW
 

Justwondering

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Could I get the parts numbers for the choke pulloff and the choke thermostat?

Neither of the lads at Autozone or O'reilly's could figure out what I wanted. They kept going out to ebay and looking things up and asking me if it looked like that part.

If I'm going to do the work for them, I might as well order it from home.

I have an extra 40 dollars left from this month's truck budget, so I'm going to put it toward the chrysler.
 

BudW

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1987 Chrysler 318 2-bbl passenger car
Choke Thermostat 4095339 Dodge MSRP is $64.60 (eBay for $21.32 to $59.99)
Choke Diaphragm w/link 4293895 Dodge MSRP is $43.20 (eBay for $37.00 to $41.44)

AutoZone:
Choke Thermostat (GP Sorensen) 777-681 $29.99
Choke Pulloff (GP Sorensen) 779-180 $24.99

O’Reilly Auto Parts
Choke Thermostat - N/A
Choke Pulloff (Walker) 101-926 $12.99
 
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