Diagnosing an Engine Cutting Out

[alfreema]

Total newb here, but wanting to learn!

BEGIN LONG STORY -- FEEL FREE TO JUMP TO END LONG STORY TO GET TO THE POINT

1976, Chevy Camper Special with a 454.  This baby was purchased by my great uncle who died, passed it to my grandfather who died and passed it to my mom.  She doesn't want to die just yet so she quickly gave it to me. 

Anyhow ... it sat on my grandpa's farm for a looooong time while he was alive and unable to live by himself and it just weathered away.  I decided to go check it out one day and when I flipped open the lid a rodent so large I can only describe it as Ratzilla was standing on the radiator staring me down eye-to-eye.  He was determined that I wouldn't eat him, and I was determined not to poop myself.

After the standoff I was able to inspect and that Godforsaken rat had chewed through every dang hose and copper wire in the joint.

So I decided I wanted to restore this rusty, weathered, rat food back to it's former glory.  I had it towed to an electrical shop to get all the critical wiring redone and then to a mechanic to get it running fairly nicely.  Then I spent way too much on a near cab-off restoration (we did everything EXCEPT take the cab off -- I should have went ahead and done that).  Then I took it down and had a whole new interior put in.

END LONG STORY, BEGIN THE POINT

All was well for a while.  Then several weeks ago my wife was driving (I know, I know, don't say it), and it started "surging" on her badly while she was on a highway.  I had it towed to a Chevy dealer and they were unable to get it to repeat.  So after a while I just went down and rode with a tech and it cut out once early in the ride and that was it.  We just chalked the one slight cut out to "warming up".

Well I dropped off the tech and proceeded to drive home and sure enough at about the 7 mile mark it starts cutting out on me.  My wife described it as a surging but now I know why.  It would cut out, and then suddenly get power again creating a surging sensation.  But really it's just cutting out.

Instead of hauling the thing back to the Chevy dealer, who somehow wasn't able to reproduce what I was able to reproduce after the very first time driving it since we dropped it off, I'd like to troubleshoot this thing myself if at all possible.  That might be a big IF.

Soooooo ... what is the absolute first thing in diagnosing this problem?  I'd like to take a very methodical approach and start with the most obvious things to check and proceed from there.

Where do I begin?  (And please understand I don't know squat about any of this, but I am willing to ask a lot of questions and keep trying).

Thanks!

[zieg85]

First... gas filter  Due to the age, next would be the rubber lines connecting the gas tank to the steel lines.  If both checks out then the fuel pump may be getting weak.  That should get you started..

[VileZambonie]

Sounds like a misfire. Tune it up and check the integrity of the ignition system. Simple test, warm it up and then wet the ignition wires with a squirt bottle.  See if it runs worse.

[alfreema]

Ok, guys!  I'll start with the gas filter tomorrow and see what happens.

[1980c10]

I'm thinking misfire as well. A tune could definatley be in order if it hasn't been done recently. So get some plugs and wires. When you do this inspect your plugs for condition, gap, color and consistancy- this can tell you a lot about how the engine is running, fuel wise. If this doesn't solve it and nothing out order on the spark plug inspection, I would consider replacing the distributor. They have become inexpensive and it would save a lot of trouble shooting and it would all be fresh. You could easily spend double on distributor parts and end up not solving the problem. However do inspect you cap and rotor before-hand(inspect the contacts and the plastic for cracking).

[alfreema]

OK I poked around quite a bit and for the life of me I cannot find the fuel filter.  I managed to find a small fuel filter inside a component that sticks out from and is connected directly to the carburetor, so I will replace it (it didn't look gunky at all or anything but I am not sure if you'd be able to tell if it was bad or not by visual inspection).  But I can't imagine that that is the only fuel filter on this truck?

I started from the fuel tanks (it has two), and worked my way forward and followed the hoses to what looks like is probably a fuel pump bolted to the front-passenger side of the engine.  From there a line comes out and goes into the carburetor, but there just isn't a fuel filter other than the one I described earlier.

Thoughts?

[Donut]

Sounds like your on the right track.  Factory is just the fuel filter in the carb.  Personally I cut in another in the fuel line before the carb, but some old habits are hard to break.  The carb filter is perfectly adequate.
There is also a "sock" on the sender in the tank.  Not something I'd change for the sake of changing, but if the senders have to be pulled for any reason, check them.

Check what Vile posted, that sounds like the likely culprit.  Though what your doing should be done eventually (your not "wasting your time")

[alfreema]

OK I swapped out that filter and the engine isn't running any better (didn't think it would, but like it was said, this needed to be done anyway).  On to Vile's steps now.

[alfreema]

Sounds like a misfire. Tune it up and check the integrity of the ignition system. Simple test, warm it up and then wet the ignition wires with a squirt bottle.  See if it runs worse.

OK, so my father and I replaced the spark plugs last year and gapped them.   And it was running really nicely for quite a while.  But just to be clear on this step, you want me to spray both ends of the ignition wires while the truck is running to see if it starts running rougher, correct?  I mean spray the distributor and then spray the sides of the engine, essentially?

[bake74]

Sounds like a misfire. Tune it up and check the integrity of the ignition system. Simple test, warm it up and then wet the ignition wires with a squirt bottle.  See if it runs worse.

OK, so my father and I replaced the spark plugs last year and gapped them.   And it was running really nicely for quite a while.  But just to be clear on this step, you want me to spray both ends of the ignition wires while the truck is running to see if it starts running rougher, correct?  I mean spray the distributor and then spray the sides of the engine, essentially?

     Your looking for a break in the wires or a short in them, by spraying them like stated, if you do have a wire with the above mentioned problem, the truck will instantly run rougher and you will be able to tell that you have a bad or bad wires.

[Irish_Alley]

hows your engine ground?

[alfreema]

Okay, I decided to hold off on this project until my new carburetor came in from http://www.nationalcarburetors.com/ so that I could swap that out and then begin the ignition tests.  Well it came in yesterday and is wrapped in clear plastic so that I can easily compare it to the older one. 

The old carburetor has a fuel filter in the front going straight in but the replacement carburetor has a 90 degree elbow.  I think there might be enough slack to reroute the fuel line to make the 90 degree bend, but I am wondering if I have the wrong carburetor?   Also my current carburetor has a fairly long arm sticking out on the driver side with two linkages hooked up.  The new carburetor has a connection for only a single linkage (I think I could gang the two linkages on the same one).

I'm just not sure if I have the right carburetor.  Should I open the new one and see if I can make it work, or call 'em up and return it?

[454Man]

I know two people that have had bad experiences with national carbs. If you open it they won't return it. First person said the carb wouldn't idle and this was a tbi. The second had the same problem you have being a diff carb and it also wouldn't idle. One would think that because national carbs does sell there carbs through autozone... the quality would be good. I guess maybe these were mishaps. Idk good luck. But remember if that's not what you paid for once you open it your stuck

[alfreema]

Wulp, that might just be a good enough reason to return it then.  Where's a better bet to get an exact replacement?

[454Man]

What year is your old carb you are compairing to the new one?