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Engine losing power, stalls

 
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relmers



Joined: 24 Aug 2010
Posts: 8
Location: Stillwater, MN

1966 GTO

PostPosted: Wed Aug 24, 2011 9:40 am    Post subject: Engine losing power, stalls Reply with quote

Returning from Detroit's Woodward Dream Cruise driving my '66 GTO, mostly stock 389, we made back to Madison Wisconsin and the car began stalling out.

First, while heading to Detroit at Interstate cruising speed, the engine developed a very short momentary loss of power which I and my wife as the passenger could feel, such as a hiccup, and then continued along fine then several hundred miles later, it happened again. Once in Detroit, while driving on side streets, again I felt it but no further issues until our return trip.

Heading home through Wisconsin, I filled the tank gas tank and about 60 miles later, I felt a similar hiccup but this time I began losing power. The car continued to slow and if I tried to push on the gas, it wanted to stall. I coasted to a stop along the shoulder and the car roughly idled then stopped. Several attempts to restart and it sounded as if it was starving for gas. Hanging over the hood, I could see gas pumping into the carb when I hit the accelerator.

I ordered a tow and while waiting I was able to get the car to start and it was almost like something all of a sudden passed through and cleared, it had it's power back and idled smoothly.Since it was late at night, I still had it towed and we took a room. The next morning, the mechanic took it for a drive and it happened again. He eventually got the car to run and then it ran normally. During the several hours of trying to get it to happen again, we took several fuel pump pressure tests and it was a constant 4.75 lbs PSI.

Finally we decided to continue home and I picked my wife up we again had the same issue. I was eventually able to drive the car to another town about 35 miles away, rented a truck/trailer. Arriving at the rental, the car quit running and we rolled into the lot, eventually pushing it up onto the trailer and returned home.

When we arrived at home, I was able to get the car started, running real rough but was able to limp it into the garage where it is now safely sitting.

-4.75 lbs PSI fuel pump
-car cranked tried to start but felt as if starving
-twice while trying to start, it back fired when the accelerator was pushed near the floor board ( didn't do that a third time) however, once while on the Interstate and it was loosing power, I had my foot off the foot feed and still had a back fire.
-timing is correct
-no visible gas line leaks
-gas in the fuel filter (new this year)
-gas pumps into the carb
-gas in tank
-gas tank 2 years old

-bad gas? don't think so, it did run fine on the gas at times
-fuel pump, new last year on engine rebuild
-not heat related as it did it when it was cold

Any suggestions or ideas on where I should start?
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Larry
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Joined: 01 Jun 2006
Posts: 4768




PostPosted: Wed Aug 24, 2011 3:46 pm    Post subject: GTO Problem Reply with quote

I had a very similar problem with a '65 Coupe deVille years ago when vacationing in Florida (was stationed in Ohio in the Air Force). The car started to stall with just a wiggle of the gas pedal. The only difference was after coasting to the side of the road, it would immediately restart, only to stall again. You had to drive with a feather-touch on the pedal.

We drained out a full tank of new gas- actually in a field next to a gas station. All 25 gallons! I hope nobody lit a match near there for the next week!

We refilled the tank... same problem. We limped to another gas station where I gave the gas to the two young guys working there in exchange for using the hoist to drop the tank. I pulled out the float unit and removed the filter on the end of the pipe (sometimes they can clog up and the fuel pump suction collapses them).- I later learned you can easily blow the filter off with a short blast from an air hose into the gas line going into the tank. That didn't help either.

We limped into Savannah, GA and after "fighting" with the dudes at a Cadillac garage who insisted on changing all the valve springs, we got about two miles away and the same thing happened again. They succeeded in using up our last traveling funds too! That was before we had credit cards.

I had all but begged them to at least try a different carb, as I suspected a fuel problem in the carb. They said their billions of dollars of test equipment didn't lie- it needed new valve springs. It didn't do any good to tell them the engine was all newly rebuilt- including any needed springs- before our trip.

We spit and sputtered along the interstate until we needed more gas- which was soon the way it was running. Out of despiration, I put in two cans of STP gas treatment and after about 10 miles it smoothed out, ran like a top, quit stalling, and we drove straight through back to Ohio.

We must have had a small piece of crud that was getting onto a needle valve or something that broke up and flushed through. I rebuilt the carb just to be sure later at home.

The way you describe what is happening sure doesn't sound like a major "mechanical" problem, especially when all else checks out so good. Before digging much deeper I would try a diferent carb or a good glug of carb cleaner like the STP.

This would at least rule out the carb internals. I doubt any other fuel line/filter problems as they seldom become catostrophic as you describe. An ignition problem is usually more on-and-off without all the inbetween symptoms. Try the easiest things first and work your way to the "once-in-a-million" sort of problem.

Please let us know what you discover and how you fix it.

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relmers



Joined: 24 Aug 2010
Posts: 8
Location: Stillwater, MN

1966 GTO

PostPosted: Thu Aug 25, 2011 4:41 pm    Post subject: Reply with quote

Today, I replaced the fuel tank sending unit, all the rubber fuel lines, the fuel pump and the fuel filter even though I didn't visually see anything wrong with these parts. I took the car out and drove for about an hour. I started to think that maybe I had replaced a unknowingly bad part.

While driving down the road, I decided to pull over and take a look at all my handy work to make sure nothing was leaking. As I slowed, suddenly, I could feel a loss of power. The car again acted up, stalling. Several starting attempts, and I was able to get going again. Thankfully, I was close to home, and when I slowed to turn into my neighborhood, once more, loss of power and the engine stopped.

When trying to start it, the engine tries to run, shakes and sputters, several times some black smoke out of the tailpipes. Finally, it started, sounded and ran normal and finished by pulling into my garage.

Larry, I agree the problem is probably in the carb. I will pull it off tomorrow and open it up.

If not that, then I'll start with the electrical, R&R points, coil, distributor cap and wires. I agree, it's not a major problem, just one of those that is intermittent and could cause real havoc if I'm to far from home.

I'll keep this post updated..................
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Larry
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PostPosted: Thu Aug 25, 2011 5:58 pm    Post subject: Fuel Problem Reply with quote

It's sounding more and more like the carb.

An electrical problem (points, etc.) doesn't get better, go bad, and then get better again (over and over).

That being said, weird things do happen sometimes... but rarely.

If you have a carb to switch with, even not a real good one, it should (hopefully) make a difference that would prove that as the culprit. If not, do a good rebuild and especially a real good cleaning. I'm darn near sure it is a sediment problem of some sort.

The good news is, if that is the problem, it probably came from somewhere-- and now you have all the other stuff replaced. I'm trying to find the silver lining for you in all of this. I sure know how frusterating it can be. Not to mention inconvenient when you're away from home.

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relmers



Joined: 24 Aug 2010
Posts: 8
Location: Stillwater, MN

1966 GTO

PostPosted: Thu Aug 25, 2011 6:57 pm    Post subject: Reply with quote

Larry, I truly appreciate you taking the time to post.

Tonight, I removed the fuel line to the carb wondering if maybe there was a copper colored internal filter inside the carb ( there isn't in the 4bbl). When I pulled the hose off, there was gasoline in the hose, but it seemed that when the gasoline was released that there was a lot of air in the line and not as much gas as usual (this is the pressurized side of the fuel pump, between the pump and the carburetor) .

In my mind, this would make sense that a line of air could cause this loss of power and stalling. However, I don't know where the air would be coming from, especially now since I've replaced nearly all the fuel line system. The only piece not replaced is the stainless steel line going through the underneath portion of the frame. All my connections are tight, no gas leaks visible.

What are the thoughts on this, could it be possible that the metal gas line may be sucking in air even though its not leaking gas? Does this scenario sound plausible?

I'm grasping at straws.....
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Larry
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PostPosted: Thu Aug 25, 2011 9:10 pm    Post subject: Fuel Problem Reply with quote

You reported a good fuel pump pressure, so I doubt there are any leaks. At least in the diaphram, and if there was you would have fuel coming out of the relief hole externally on the fuel pump. And a leak of this sort doesn't pump in air either.

I don't really know how much fuel should come out of the line when removed. Perhaps tipping the line allowed air in, to mix and push out gas...??? I think you are just seeing something that you (or anyone) never paid any attention to before... and are now wondering about it.

Without causing any danger, perhaps putting a hose on the line, and running it away from the car into a container, turn the engine over and see if it gives good strong pulses of fuel.

Air in a line would cause symptoms very much like vapor lock. That sounds like it is sort of problem what you are having. However, unlike vapor lock which quits when it cools down, yours persists under all conditions.

I do not believe (as you) that a system that does not leak under pressure nor at rest would be able to suck air in from somewhere.

Going back to something else you mentioned... the black smoke sometimes when trying to restart. Black smoke is only one thing, and that is too much gas. That still puts me back to some metering problem, probably caused by some debris in the carb.

At this point I think I would be grasping at beers! But, check the carb internals before much more component replacing... if there is anything left. See my favorite cartoon below.

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relmers



Joined: 24 Aug 2010
Posts: 8
Location: Stillwater, MN

1966 GTO

PostPosted: Mon Aug 29, 2011 3:01 pm    Post subject: Reply with quote

To update: The black smoke got me to thinking that the car was getting gas, almost as if too much. I also thought that it may be getting the correct amunt of gas, but not but not burning it properly. Since my problem was intermittent, as a group, I removed and replaced the distributor cap and rotor, points/condensor and coil. Upon inspection of the points, they were pitted and the coil looked rusted in the hole for the wiire to the distributor. I've been driving it now for two days and it is running as smooth as my newer cars. If it is actually fixed, I unfortunately won't know the exact cause but it appears that it was in the ignition system.
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Larry
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PostPosted: Mon Aug 29, 2011 5:15 pm    Post subject: Fuel Problem Reply with quote

The good news is that it is working well... and hopefully will continue to.

If this was all due to bad ignition components... and they were bad enough to cause all this trouble... they must have REALLY been bad. I'm surprised you were running at all. Usually any electrical items that bad are not intermittent. You would be spitting and sputtering most all the time.

However, if it was an intermittent coil, that could explain spark breakdown and bad fuel burning. Be sure to pull your plugs and see if they are black too.

This sounds too much like the new computer repair guys who say "I don't know what the problem was, but it's working fine now." GACK!

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rexs73gto



Joined: 17 Sep 2015
Posts: 94
Location: Niles MI

1973 GTO

PostPosted: Thu Sep 17, 2015 2:29 am    Post subject: Reply with quote

I would still pull the carb & rebuild it. But when you do get a clean WHITE towel so when you turn the carb over & take the carb top off dump it out so you can see what comes out. I will bet your going to see some type of debris I think your going to find that even though it seems to be ok now please rebuild the carb so it doesn't act up again. The ign. may have been a problem in some form & I would say get rid of it & put in a pertronix unit & get rid of the points & then you won't have that problem ever again. I've had mine in for over 30 years with no problems yet.
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I have a 73 GTO that I bought new, well it was a demo because the car I ordered was an SD car which never came in & i had to take what was left because I was in the Navy & had to talk to the dealer when I could.
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