Fuel delivery (pump or filter?) problem - need advice on how to diagnose

[XH29N0G]

Hi everyone,  I took my charger out for her first trip of 2016 because the temperature is in the 50's and there is no rain and everything went wonderfully until it ran out of gas with a 3/4 full tank.  

I think either the pump failed and then came back (so it is working intermittently) or there was a clog in the filter.  The filter is a year old and the tank was replaced a few years ago so there should not be junk in it.  I do not know what else it could be.

I am writing to ask for thoughts about what to check and in what order to check them, or if there is something else.  


 

What happened:  

(1) I was about 2 miles from home on my way out for the second trip and I noticed the A/F meter rise to 18-19-20.  I thought it was strange and diverted my route to head home, but then it returned to normal so like anyone wanting to drive their car, I returned to my route heading away from home.  

(2) After another two miles, I noticed the A/F rise to 18-19-20 and the engine definitely started to stumble.  It then stalled in traffic on an overpass with exit lanes, but I managed to restart by pumping the gas (accelerator pump) and also to coast across the overpass to a pull off.

(3) I pulled the air filter, and saw no gas in either sight glass.  Both accelerator pumps were empty.  

(4) Two latino workmen stopped to help.  They had some gas that we tried first in the tank (no luck) and then poured into the bowl of the carburetor which allowed the car to start and it also then filled both bowls with gasoline (so the pump worked).

(5) Thinking the gas gauge had failed, I went to the first gas station I saw, but the car only took 6 gallons and went from 3/4 to full on the gauge.  So I think the tank was full  and it has to do with fuel delivery rather than a faulty gauge.

(6) I then drove home from the gas station (about 4 miles)  The fuel was up to 1/2 way on the sight glasses when I returned.  So at least it looks like the fuel system is now delivering fuel.  

[myk]

You're running a mechanical pump, right?

[XH29N0G]

Sorry for not including that detail.  It is a mechanical pump.  It is a few years old.  The engine was rebuilt a few years ago and has about 4000 miles on it - maybe a little more.

If it seems like I will need to change the fuel pump or pump pushrod, a question is whether it will be worth considering an electric pump.

Also, I checked the oil on returning home and smelled no gas in it.

[b5blue]

I've had pumps crap out way too soon. 

[XH29N0G]

I've had pumps crap out way too soon.  

Is this how pumps go?  The only time I had a pump go before it was all at once and filled the crankcase with gasoline (it was a 69 Pontiac so maybe a different design).  Any recommendations?  I do not have a fuel pressure gauge hooked up so I don't have information on the pressure.

[b5blue]

Yes mine just quit pumping, about a year or so old. I've had others last over 15 years? Undo a carb line and crank the motor to see if it's pumping?

[XH29N0G]

That is what is strange.  It must be pumping at some level, because it later filled the fuel bowls.  My guess is that it is not pumping efficiently and maybe a pressure test will be the diagnosis I need.  I think I will first check my fuel filter and then check the pressure.  Did you switch to an electric pump?  Or do you have recommendations on mechanical ones?  I know little about this but provided guidance see no issues fixing it.

[BSB67]

1) Could be tank venting.  Did you open the gas cap after your A/F numbers went up, or after it died?
2) Push rod.  If it is too short, the operating pressure will drop, and vapor lock occurs more easily.  But then it can start and run again
3) Just plain old vapor lock.
4) I've never seen a pump fail and operate like you described.  A sticking pump valve could do that possibly.

Filters are cheap, just replace it, although I've never confirmed one to be a problem.

[XH29N0G]

1) Could be tank venting.  Did you open the gas cap after your A/F numbers went up, or after it died?
2) Push rod.  If it is too short, the operating pressure will drop, and vapor lock occurs more easily.  But then it can start and run again
3) Just plain old vapor lock.
4) I've never seen a pump fail and operate like you described.  A sticking pump valve could do that possibly.

Filters are cheap, just replace it, although I've never confirmed one to be a problem.

Some information/responses:

1) I opened the tank after it died, not after the first time.  I did not notice a vacuum release, but I wasn't looking for it.  This is the first time it has done this so my guess is that tank venting would be something new. 
2) Do the push rods wear?  The car has been running without issue for 4000 miles.  The engine was built by muscle motors  and my guess is they would have installed the correct pushrod.
3) If it is vapor lock it is the first (and second) time it has happened.  It was also only 50 degrees outside today, and the engine does not run hot.  When I pulled the air filter, both float bowls were empty.  Is this how vapor lock works?
4) I need to look up how fuel pumps work to understand the pump valve comment, and appreciate the suggestion.

I'll check the filter.

Thanks.

[A383Wing]

Check the pump push rod, should measure 3.25" when new.....a rod with 1/4" of wear will cause delivery problems

[XH29N0G]

Check the pump push rod, should measure 3.25" when new.....a rod with 1/4" of wear will cause delivery problems

Thank you.  Am I correct in guessing that the pump push rod will drop down and can be coaxed out when I slide the fuel pump out of the block?

(I am also guessing if pump rod wear is the issue, I should check for metal in the oil and it could be a big problem.)

I also saw a series of fuel pump tests (checking to see that the pump establishes sufficient fuel pressure and that the pump can draw sufficient vacuum).

If the pump or push rod is bad, Is there any reason to switch to an electrical pump?

[A383Wing]

to remove rod, first remove pump, then take pipe plug out of block under pump mounting....then rod should fall out. If rod is worn, just get a new one and use grease to install.....I would not worry about any metal in oil, it will be so minor over a long wear period of time. I would not worry about camshaft eccentric either, cam is way harder than pump rod

I'm not a big fan of electric pumps....first they are noisy, and second you will have to mount it back by the tank because they are designed as a pusher pump, not a puller pump

[XH29N0G]

to remove rod, first remove pump, then take pipe plug out of block under pump mounting....then rod should fall out. If rod is worn, just get a new one and use grease to install.....I would not worry about any metal in oil, it will be so minor over a long wear period of time. I would not worry about camshaft eccentric either, cam is way harder than pump rod

I'm not a big fan of electric pumps....first they are noisy, and second you will have to mount it back by the tank because they are designed as a pusher pump, not a puller pump

Thanks.  I forgot about the hex pipe plug.  I am wondering if the order of checks I should pursue are (1) check filter, (2) check pump for pressure and vacuum on engine, If pressure volume are off then (3) check pushrod.  If pushrod is OK, then replace pump otherwise replace pushrod.

If the pump turns out to be bad, are there recommendations on pump brand, type for the appropriate amount and pressure of fuel for an engine making around 500 HP?

[b5blue]

  I get your concern but keep in mind fuel pumps have a valve inside. If the valve fails for any reason even intermittently, it explains what happened. That's what mine did, no leaks just no pumping. After wasting a few days farting around checking other crap I pulled the line and found no pumping. Rockauto will have a Carter pump just look it up. (25.00) Summit gave me an RMA and sent me a new one. (I had a 6BBL then.) I did check my lines to be certain all was well.
  What I learned back then was in an hour I could have gone to Autozone, bought a 15.00 pump slapped it on and tested. Instead I farted around over 2 weekends then waited a week for a new pump. With a 4BBL now I don't even keep a backup pump on hand. 

[BSB67]

Personally, unless you know with 100% certainty that it is not the tank vent, I would test and verify that - it is free, and easy.  Second, the filter.  It is a couple of bucks and easy.  Also, blow back through the fuel line to the tank, this is another ....just in case.... thing.  I agree, at 50° F it seems very unlikely that vapor lock is an issue, but double check the routing of the fuel line around the engine.  Then check the fuel pump push rod.  In my opinion, the only reason the factory original push rods fail is due to longer term storage and lack of lubrication on start up.  I think some of the new or after market rods fail because of the same reason, or because they have a quality problem.  

Finally, in my opinion, there is only one style of mechanical fuel pump anyone on this forum should be buying, it is this, or same thing from others.

http://www.summitracing.com/parts/crt-m6903?seid=srese1&gclid=CP6k2tXB8ssCFQERaQodXQcIGA

I just assumed that this would be the entry level pump everyone would buy.  Guess not.  It seems silly to me to buy $20 junk from AutoZone, or where ever, and a spare, and plan on installing it on the side of the road somewhere, or every couple of years.

[b5blue]

Yup that's a fine pump!  (Wrong for 6BBL.) I see no way a tank vent can fail? My point was for 20.00 he could test today FYI. 

[BSB67]

I've seen it at least twice.  Its the cap.

[myk]

In regards to an electric pump, I've been running one for years now, and the advantages are great: guaranteed start up every time you turn the key.  No more pumping the gas pedal a magical amount of times, clapping your hands, praying it starts, dumping starter fluid/gas down the 'carb, etc.  The car can sit for a day, a week, a month and it will still start up right away.  I don't even have to set the choke and the car will start.  Vapor lock?  My fuel probably boils but with the electric pump forcing the fuel system to work, I don't have trouble starting the car under any temperature conditions. 

BUT...

What I have NOT enjoyed over the years is replacing these crappy electronic, Chinese made fuel pumps (are there any electronical components made in America anymore?).  I had the same mechanical Carter fuel pump on my car for 18 years and it never quit or faltered on me once.  Since I went electric I have replaced 4, FOUR electric fuel pumps that completely failed on me and left me standing there with my hands in my pockets.  Again, the advantages of an electric fuel pump are revolutionary, but I would say that the reliability might be a factor to consider as well.  That Carter posted above or any mechanical you can mount will probably outlast the car.  I'm considering switching back myself.  Definitely something to consider...

[XH29N0G]

Thank you both. 

• I checked the filter and that was clear and clean.
  
• I checked the tank vent tube and can blow air through it.  This is the small tube that starts in the filler neck and drops through the trunk floor into one of the frame rails.  Right?
  

The pump that is presently on the car is not the model/design BSB67 put a link for, but one that looks like the $20-$40 pumps with hose connector outlets.  (I understood the point about just putting on a cheap pump to test so I am not waiting for a part to arrive, and appreciate the pointer - I wouldn't have thought of that.) 

• Since I want to understand whether it is something with the pump or pump pushrod, I am thinking about trying to measure the fuel pressure, and possibly to do the vacuum test with the present pump before swapping one in.  But I suppose the only danger is that it could be an intermittent problem (stuck valve like both of you suggested) and I might not see it.
  

The pump BSB67 suggested looks like a 5.5-7.5 psi high volume pump.  It is on backorder at Summit, but I see it on Rock auto.  Is there a reason for selecting it over the carter m4862? which seems to pop up when I search for big block mopar pumps?

I am running a quick fuel carburetor and see their pump looks similar to the 4862 (slightly higher pressure than the 6903), but I also read somewhere that all that is supposed to be needed is about 6 PSI. 

Myk, thanks for your thoughts/experience with electric pumps.

Thanks.

[b5blue]

Not certain of your build but these worked well for fairly stock: http://www.rockauto.com/en/moreinfo.php?pk=295988&cc=1405088&jsn=12

[BSB67]

The delivery pressure from the 4862 is too high in my opinion.  You might need to run a regulator with it, or it could push through the N/S and change your fuel level.

Check Mancini, they might have it in stock.

Also, the 6903 can be taken apart and inspected, parts replaced. There are like 4 parts inside.  There will never again be the mystery of.... "is working or not?"

[b5blue]

M6903 is what I run now for all the reasons BS listed.  (6BBL needed less pressure.)
http://www.manciniracing.com/cam6bisumefu.html

[XH29N0G]

Thanks again.  

I just measured the fuel pressure and it is between 4 and 5 psi at idle.  It stayed in this range as low as I could set the idle (probably close to 500 RPM) and also up to about 2000 RPM.  The pressure stays at 4 (or 5) psi after the engine is shut off.  I do not know if this is what it should do or if the pump should be higher such as at 6 - 7 psi.  

NOTE added later: two posts below show a second test I did that suggest the pressure is 2-3 PSI and the baseline on the gauge used here is likely off.

The pump is similar to (maybe a step down from) the one b5blue posted the link to.   It has push on hose barbs on both ends.  The engine is more than stock (383 stroked to 450) but not as much as some others have.  

I have not done the vacuum test with this pump, and am thinking I will wait for the fuel pressure to drop.  (the lines were empty this morning after it sat overnight).

After reading your comments and learning more, I am inclined to make the swap to the 6903 (even if the present pump seems OK), but I am not sure it is the fix to the issue I had.  Any advice will be appreciated.

[cdr]

inspect the rubber lines for collapsing & rott, especially the one at the tank.   

[BSB67]

Checking the pressure when the car is idling is probably not a very good test.  It takes almost no gas volume at idle and there for easy to maintain pressure.  Testing it under load, WOT, and/or when it goes lean is when it matters.