Loss of Power Under Load

[Amskeptic]

I am not hearing any abnormal sounds from the fuel pump. I also filled up the gas hoping this could solve the issue (bad gas or dilluting polluted gas). Nada.
The fuel pump is located near the starter AND below the tank levels.

Perhaps this is a stupid question, but how do I check the integrity of the electrical supply?

I have a back-up fuel pump I might consider putting in to see if it is actually the pump.

If your pump ever does give the death-rattle, fill up the gas tank pronto, this can help you get to where you are going so you can deal with it on your own terms. I was not thinking bad gas with the above suggestion, just get a good head of gravity fuel pressure for the pump. Your pump location is near the starter but on the car away from heat soak issues? Fuel lines away from big heat producers?

What I was recommending, was to check the integrity of the electrical supply for the pump only, not the whole car. I had a connection that went bad invisibly and I was dropping dead all over freeway onramps, bridge abutments, the car would just lose power and gas pedal seemed like a brake. Once I was futzing with wires, the pump would come back to life then die at the next inopportune time.
Colin

Yes, the fuel pump is away from major heat sources. Yikes, that would be dangerous.

I rewired the pump last night and made sure it was well insulated. Same issue.

I'm thinking of replacing the fuel pump tonight and see if that makes a difference.

I hate throwing parts to "fix" things. Isn't this what GM does? :)

-dave

Heat is not that "dangerous" it is just annoying. It causes vapor lock and heat-soak flooding. What temperatures do you suppose the fuel pump nestled on top of the engine on a 1973 Lincoln, with the A/C on because it is frying out there on the L.I.E., gets to? More or less than a nice air-cooled VW?

Your symptoms again, are only occurring under a load and demand for fuel, but it runs WELL at slow speeds around the neighborhood, idles well pulls from the light nicely, starts right up, yaah?
Colin

[dhoch14]

I am not hearing any abnormal sounds from the fuel pump. I also filled up the gas hoping this could solve the issue (bad gas or dilluting polluted gas). Nada.
The fuel pump is located near the starter AND below the tank levels.

Perhaps this is a stupid question, but how do I check the integrity of the electrical supply?

I have a back-up fuel pump I might consider putting in to see if it is actually the pump.

If your pump ever does give the death-rattle, fill up the gas tank pronto, this can help you get to where you are going so you can deal with it on your own terms. I was not thinking bad gas with the above suggestion, just get a good head of gravity fuel pressure for the pump. Your pump location is near the starter but on the car away from heat soak issues? Fuel lines away from big heat producers?

What I was recommending, was to check the integrity of the electrical supply for the pump only, not the whole car. I had a connection that went bad invisibly and I was dropping dead all over freeway onramps, bridge abutments, the car would just lose power and gas pedal seemed like a brake. Once I was futzing with wires, the pump would come back to life then die at the next inopportune time.
Colin

Yes, the fuel pump is away from major heat sources. Yikes, that would be dangerous.

I rewired the pump last night and made sure it was well insulated. Same issue.

I'm thinking of replacing the fuel pump tonight and see if that makes a difference.

I hate throwing parts to "fix" things. Isn't this what GM does? :)

-dave

Heat is not that "dangerous" it is just annoying. It causes vapor lock and heat-soak flooding. What temperatures do you suppose the fuel pump nestled on top of the engine on a 1973 Lincoln, with the A/C on because it is frying out there on the L.I.E., gets to? More or less than a nice air-cooled VW?

Your symptoms again, are only occurring under a load and demand for fuel, but it runs WELL at slow speeds around the neighborhood, idles well pulls from the light nicely, starts right up, yaah?
Colin

Correct and it is driving me crazy!

Tonight the backup fuel pump goes in.

-dave

[dhoch14]

Tonight I replaced the Carter Rotary fuel pump with the "economy" spare.

Fired right up and purrrrred on the highway. Then on the way back the symptoms came back. This time in 2nd gear on a long uphill.

Here is a summary of what I have done to try and solve this problem:
- replaced fuel pump
- rerouted and cleaned wires to pump.
- replaced fuel filter
- confirmed tight spark plugs, rotor, & cap.

Sigh. I have no idea where to go from here. blah.


Could something be "clogged" or screwy with my carbs?

-dave

[vdubyah73]

Kink in rubber fuel line, gas tank not venting properly? Fuel pump? How experienced are you at synch'ing carbs? Making same mistake repeatedly?

Next time it happens jump out and pop off the fuel cap quickly. If you hear air hissing , your tank ain't venting properly. if the tank doesn't vent , the pump creates a vacuum in the tank that it can no longer overcome. Did you eliminate the charcoal canister vapor recovery? Does your vent line now exit under the bus? Are the roads icy where you live? If yes to these questions your re-routed vent may be clogged with ice.

Or, maybe debris in tank is blocking the fuel pick up. Check the rubber fuel lines for kinks before resigning yourself to cleaning the tank.

[SlowLane]

These may seem like stupid questions, but:
Have you measured your fuel pump's volumetric output under working pressure? Do you know that it's actually delivering the amount of fuel the engine needs at full load?

Are you using a fuel pressure regulator? Have you measured the pressure being delivered to the carbs under load and compared it to when the engine is running strongly?

Seems to me that a first cut at finding this out would be to get a cheap vacuum/fuel-pressure gauge, tee it into the carb fuel rail somehow (sorry, not very familiar with early type IV systems), then drive around with a friend in the back to watch the fuel pressure under different driving conditions ('73 had the inside access hatch, didn't it?)

[Amskeptic]

These may seem like stupid questions, but:
Have you measured your fuel pump's volumetric output under working pressure? Do you know that it's actually delivering the amount of fuel the engine needs at full load?

Are you using a fuel pressure regulator? Have you measured the pressure being delivered to the carbs under load and compared it to when the engine is running strongly?

Seems to me that a first cut at finding this out would be to get a cheap vacuum/fuel-pressure gauge, tee it into the carb fuel rail somehow (sorry, not very familiar with early type IV systems), then drive around with a friend in the back to watch the fuel pressure under different driving conditions ('73 had the inside access hatch, didn't it?)

Very sensible sane suggestion to help you narrow this down quickly and efficiently.

Now, allow me an exploding variable like a Sambanista:
When it happens again, carefully touch the coil. Is it hot? Replace. Points and condensor too.
Colin !

[dhoch14]

S__T his the fan this morning.

After replacing the fuel pump with the backup, I had a minor hiccup then no issues so I thought, ok, I can drive it. Wellllll, on the way into work today, it crapped out on me right on the highway. I thought, well at least I can get home via backroads. I tried to baby it home and got about 2 miles away, but had to concede to a McDonald's parking lot as it wouldn't even hold idle anymore and was stalling out. Lots of bucking and full pedal doesn't get me over 20 mph.

So, now I'm even more confused. Is it really possible that 2 fuel pumps are bad or that there something fudgy in my fuel taken despite the filter(s) being clean? Perhaps I should just throw parts at the ignition system?!

I tried putting on my backup coil (only takes 1 minute). No dice.

I left the bus there to come home and regroup. I have a backup 009 w/ points that I'm going to throw on there in case my Pertronix or Dual Vac Dizzy is wack.

Crosseyed and Painless

[dhoch14]

Towed her home. I played around for 45 minutes before I called AAA. It looks like my LEFT carb is acting wackadoodle under load. I'm going to confirm that full fuel is getting to the LEFT carb then work by way into the carb as need be (insert guidance here).

Closer yet farther!

[Amskeptic]

Towed her home. I played around for 45 minutes before I called AAA. It looks like my LEFT carb is acting wackadoodle under load. I'm going to confirm that full fuel is getting to the LEFT carb then work by way into the carb as need be (insert guidance here).

Closer yet farther!

Dual carbs can be tricky. While you have to appreciate the redundancy of having two separate carburetors to help you limp down the road, the one can mask the death of the other.

Now tell me what makes you think that the LEFT carb is your problem under load? There are quick basic swaps you can do to see if the problem follows the swap. Swap the cut-off jets. Does the problem move right or stay LEFT?
ColinNotYetConvincedButSorryForYourTroubles

[dhoch14]

Try this one on for size:

Sunday I "started over" on this PAIN-IN-THE-ARSE problem.

I confirmed that gas is pumping to each carb(though I didn't test the pressure). I did not see any rust or debris as I pumped the gas into a clear bucket.

Then I did the following:
- Pulled each carb, open & explored for crap (still clean from my rebuild 4 years ago). Tightened anything that could be tightened. Interesting to note that a LOT had come loose over the years.
- I put in my backup dual vac dizzy with properly gapped points. No more Pertronix!
- Timed the new dizzy and confirmed an acceptable dwell (44).
- Synched the carbs like my life depended on it. With the snail AND the "wow, look at me, I have an awesome air flow measuring device, but I still can't dial in my carbs!"
- Replaced 2 rubber elbows that had cracks in them.

Wala, she runs again and has plenty of power. I drove around for about an hour, but didn't venture on to the highway. I'm still a little nervous about that.

I have no clue what "fixed" the issue and it makes my head hurt.

In all, I ended doing the following.
- Ignition system: replaced coil, dizzy, points, roter, + cap.
- Fuel delivery: replaced fuel filter, fuel pump, & tightened everything on the carbs included cut-off jets.

< begin sarcasm >
So there you have it kids, if you throw enough parts at a problem it will just "magically" go away. < end sarcasm >

[hambone]

I have no idea. Maybe something was wacky with your carbs that needed attention. Maybe this whole site (and internet) is a fever-dream and it's really 1928.
Sometimes when something is invisibly wrong with a part, you have to just go thru and replace likely suspects. If you do it part-by-part until it no longer fails then you can isolate it.

[Amskeptic]

Replaced 2 rubber elbows that had cracks in them.
Wala, she runs again and has plenty of power.

I have no clue what "fixed" the issue and it makes my head hurt.

< begin sarcasm >
So there you have it kids, if you throw enough parts at a problem it will just "magically" go away. < end sarcasm >

Voila! Congratulations! Your bus lives another day and you get to figure it out next time . . .
Colin

[dhoch14]

Drove into work fine this morning. Avoided the highways, but she is chugging along.

Fingers crossed.