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Sputtering under load

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Mio

Mio

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Yesterday afternoon I was driving happily along on the highway when I suddenly felt a pronounced loss in engine power coupled with sputtering noise upon acceleration. At first I thought I had blown my exhaust as it mimicked the symptoms of an experience in another car. I nursed the car home, put it up on jack stands, and examined the exhaust system and all appears to be fine.

The problem is most noticeable in third gear but will manifest itself if I accelerate hard in any gear. The car starts and idles perfectly (whether hot or cold) and the problem does not appear to be associated with engine temperature (e.g., it displayed the same symptoms after I let it cool down for several hours, changed the plugs, and went for a short drive).

Parts installed within the last year and having less than 600 miles on them include the following:

-Flamethrower Distributor 45D4 w/Pertronix electronic ignition

-Pertronix coil

-Cobalt plug wires

-Weber 45 DCOE w/K&N filter

-fuel filters

I have an in-line fuel pressure regulator next to the carburetor and the pressure is fine (3.5psi). The plugs looked great but I installed a new set of NGKs, just for grins, but this hasn't resolved the issue.

Any thoughts as to what the problem might be?

Mike
 
Fuel delivery prob.
 
Electric fuel pump? If so, I'd pull the fuel line off the carb and run it. I just similar issues and believe it or not it was the pressure regulator (cheap dial type) holding back the flow. Although in my case it was only under high load situations where it couldn't keep up, yours sounds more like a plugged filter?
 
Double check those connections at the coil make sure there tight.loose connections could make for low voltage.
But it does sound more like fuel starvation.
 
jvandyke said:
Electric fuel pump? If so, I'd pull the fuel line off the carb and run it...yours sounds more like a plugged filter?
Click to expand...

Yes, I have a Carter P60504 fuel pump as well as a Holley 12-804 (1 - 4psi) fuel pressure regulator and gauge (all less than a year old) on the car. I'll replace both fuel filters and see if this helps.

Mike

fuelpressureregulator.jpg
 
texas_bugeye said:
Double check those connections at the coil make sure there tight.
Click to expand...

Hi Chris,
Thanks for the pointer. Checking connections was actually one of the first activities that I performed and everything appeared fine. I'm leaning toward it being fuel related and will use the opportunity to purchase one or two Weber carburetor books as I am most assuredly no expert in this domain.

Mike
 
Have you pulled the line off the carb and stuck it in a can and turned on the pump? You'll know pretty quick if everything is fine as far as the carb.
While you're at it, measure how much gas you get and how long it takes, I'm just curious now about pump style, placement and overall fuel flow.
 
jvandyke said:
Have you pulled the line off the carb and stuck it in a can and turned on the pump?
Click to expand...

No, I have yet to try that but will do so, all being well, tomorrow afternoon. The Carter P60504 fuel pump is installed on the passenger-side bulkhead forward of the rear axle. I have a fuel filter between the pump and the gas tank and another one between the fuel pressure regulator and the carburetor.

With respect to flow, the pump should dispense approximately one (1) quart in one (1) minute, correct? As stated previously, the gauge is registering 3.5psi.

Mike

fuelpump.jpg
 
Mio said:
jvandyke said:
Have you pulled the line off the carb and stuck it in a can and turned on the pump?
Click to expand...

No, I have yet to try that but will do so, all being well, tomorrow afternoon. The Carter P60504 fuel pump is installed on the passenger-side bulkhead forward of the rear axle. I have a fuel filter between the pump and the gas tank and another one between the fuel pressure regulator and the carburetor.

With respect to flow, the pump should dispense approximately one (1) quart in one (1) minute, correct? As stated previously, the gauge is registering 3.5psi.

Mike

fuelpump.jpg
Click to expand...

That's about 15 gph if my math's right and that should be plenty I believe. If that's what you're getting.
 
tosoutherncars said:
Sometimes it can be the simplest things!
Click to expand...

Agreed! What makes it challenging, however, is that all possible implicated parts are quite new (less than a year old). I'm therefore tasked with determining which <span style="font-style: italic">very new</span> part should be replaced by a <span style="font-style: italic">brand new </span>part.

Mike
 
I ran the pump for one minute and it put out 32oz of fuel which leads me to suspect that the issue is <span style="font-weight: bold">not</span> with the fuel pump or regulator.

Mike
 
Sounds like ample gas, unless tank filter is plugging and unplugging. Did you check the filter on the Weber inlet? (if your Weber is like mine).
 
When a coil is starting to go bad(wihtout using an oscilloscope to do a definite check); symptoms will be, like you say, loss of power under load. However this will also be accompanied by hard starting cold. What is happening is the internal insulation or windings in the coil are failing. Easy way to check is hold the coil wire away from the distributor cap, with insulated pliers touch the block and have some one crank. You should be able to pull the coil wire away from the block(or other good ground) and see a bright blue white spark, spark should jump(with the high performance ignition you have) at least 1/2"..If this is good, ignition wise, I would check the rotor, and carbon brush in the distributor cap...
 
I was going to opine that it was a failing capacitor until I remembered that he had an electronic ignition. Many times ignition problems can masquerade as fuel problems.
 
jvandyke said:
Did you check the filter on the Weber inlet?
Click to expand...

After removing the K&N filter I could readily see that the bottom of the carburetor was quite wet. In fact, it would drip fuel when I hooked everything back up and turned on the pump. It appears that the fault lays with the soft mount kit as the bushings look quite deteriorated. I have another one on order and hope to receive it by the end of the week. I'll also check the status of needle valve when the kit arrives.

Mike
 
RonMacPherson said:
When a coil is starting to go bad...symptoms will be...by hard starting cold.
Click to expand...

Hi Ron,
Yes, that is my understanding as well but the car starts extremely well (often on the first pull) so I am hopeful that the coil is not implicated. I will, however, perform your test should my addressing of the carburetor issue not prove beneficial.

Thanks,
Mike
 
Did you ever solve this issue? If so, let me know!
 
Please let us know, I am experiencing a similar issue.

When I start the engine, it shutters and loses power when I press on the execrator it sputters. When I pull the plugs 1 (front) is normal, 2 has some carbon, 3 is wet and 'dark' and 4 wet and 'dark' (but after I cleaned 4 it looked normal). The car did sit for a while and I need to use engine start to get the car to fire.
 
Check and see if your points have sliped closed. Don't ask.
 
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