I have owned a 94 Dodge Ram 1500 LST with a 318 and 2wd for 15+ years and have had the following recurring problem (as many others also have had).
I have had to replace the $200 fuel pump 4 times due to the following:
As the fuel level approaches 1/4 tank the engine will begin a gradual decline in performance then rapidly falling off to barely running on 2 or 3 cylinders (occasionally this can start happening just below 1/2 tank). It starts with a barely noticeable roughness and may go for many miles before getting worse. Then suddenly within just a mile or two the misfiring starts, one, two then most of the cylinders misfiring. It has never completely died on me and in a several situations I have had to limp 20 or 30 miles to get to a service station.
Here’s the kicker: Once I put 5 or more gal. of fuel in it I can restart it rev it a little and within a minute or so it will be running fine and I can go on down the road.
I have stopped many times and checked the fuel pressure (always around 40psi), checked for bubbles (none noticeable), checked for water or crap in the fuel - from the check valve (none noticeable).
I have taken the old (replaced) pumps and bench tested them and have found no problems and they have good pressure (they make good pressure washer pumps for washing parts w/diesel or kero).
I examine the contraption that the pump, filter, and float sender are mounted in and cannot find any defects.
No fuel line problems are ever found and always replace the stupid little $20 plastic line that attaches to the h/p feed line.
I have talked to other mechanics that have no clue either but said they bought a lot of beans w/the money from replacing these idiotic devices. (Oh the good old days of spending $20 and 20 minutes once every 10 years replacing a fuel pump out in front of the parts store with a 1/2inch wrench a grease rag and a screwdriver.
My cheap solution is to keep at least a 1/2 tank of gas and a 5 gallon can in the back.
Except for the multiple water pump changes (which are also a lot of fun) I have had an excellent truck over these many years.
Any explanation would help me retain what little sanity I have and a permanent fix for this problem would be greatly appreciated.
Thanks,
bcudamatt
Have you ever checked the fuel pressure and volume while the truck is missfiring?
I have stopped many times and checked the fuel pressure (always around 40psi), checked for bubbles (none noticeable), checked for water or crap in the fuel - from the check valve (none noticeable).
I have taken the old (replaced) pumps and bench tested them and have found no problems and they have good pressure
When you pull over and check the fuel pressure, the engine is idling and under no load so the injector pulse width is minimal = great restriction on the pump. Under those conditions, it is easy for the pump to maintain pressure. I would be curious to know what happens to the rail pressure when you drive off, the pulse width widens, the injectors open more and therefore the restriction goes way down. Can the pump maintain the same pressure as a new one under those conditions? I would rig up a gauge I could see while driving or design a bench test with a variable restriction I could adjust and compare new vs suspect pumps.
It would also be good to know, based on the tank design, where the various components are situated relative to the gas level when the problem begins to occur. For example, is the pump body exposed but the pickup tube completely immersed and so on. This may be a clue as to what could be degrading over time. Pinholes, leaks etc. These pumps are good at making pressure at the outlet but their design makes them poor suction devices. The inlet conditions are important and this design could be very susceptible to changes or variations in operating conditions. Just some thoughts…
Yes, as stated above I have stopped several times and checked the pressure, I would think if pressure is adequate the volume should also be OK. Have yet to rig up a fuel line and run it into the cab so I can test at speed.
Thanks.
You both have a good point. Volume/Pressure at speed would be the critical test. What rags me is that the giganto enourmous tank still has 15 or more gallons in it when the prob occurs. It seems that there should be plenty of fuel to pick up - no cavitating or slosh problems should occur at that level although if a small air leak would occur it should also present some bubbles in the fuel rail. One screwy thing about the oddball geegaw that holds the pump requires a substantial level of fuel before it enters the pump ‘chamber’. There is no pickup tube just this chamber where the pump sumps the fuel up thru a screen. Stupidest design I could imagine. I was told you never want to run one out of fuel.
Now that I think of it though the old pumps would shoot a good full (unrestricted) stream 15-20 feet when testing. As I stated they make a good parts washer pump.
I thought for some time of replacing the entire p.o.s. with an external pump but a mechanic freind told me of the Ford rollover probs in the early days of these high pressure systems when the pump kept running and caused hellish fires. So I changed my mind!
Thanks for the info.
Did you remove the fuel tank, clean it out, and change the fuel pump sock (screen/filter) when you changed the fuel pump?
Wow, that does sound like a lousy design to me too. If some small degradation in performance immediately affects the driveability then I’d be ticked off as well. I had one other thought- it would be good to insure that the power supply to the pump is not only delivering the full bus voltage but that it is also capable of delivering the necessary current for the pump to operate properly. The connections near the pump would be most suspect. I’d go so far as to extract the pins from the housing and inspect the crimps. Measuring the voltage directly across the pump leads might reveal if there are any connection integrity issues along the way. Ideally, this should be done with the pump under maximum load. A struggling pump is not good for longevity.
I don’t like the idea of it requiring so much fuel to begin sumping. They may have done that to insure any particulate settling in the tank would be below the pickup screen but that sounds excessive. You sound like a sharp guy and persistant enough to find a solution. I would certainly be interested in hearing what you find and any fix you devise.
Yes, several times. The same problem has always come back after replacing all.
Thanks.
Just an update on this old post.
Never have found the problem but now I have a clue.
Since it has been so Very Very hot the last couple of months the problem has gone away (temporarily I’m sure).
Now I’m wondering:
- bottom of tank had accumulated water and now its remixed and gone?
- regulator working better in hot weather?
- brain fried in hot weather and im inaginin tings?
Just wondering.
bcudamatt, was anybody ever murdered in the truck? Just a suggestion…
I have a '96 Dodge 2500 Van. At about 100k miles it acted alot like you say your’s is doing. Finally I got a new pump and when we removed the old one we found out that it was like 2 cans, one inside the other with screws in elongated holes. The bottom half seemed to move down as the fuel level went down. However, it was hanging up. When it hung up it wouldn’t pump fuel. Putting in more fuel would solve the problem for a while. The new pump was different and hasn’t failed in the last 39k miles.
Thanks for the response.
(I am Not yet having the sputtering and power loss at speed when tank is low.)
Yes I understand the FP arrangement but may not have recognized the ‘hanging’ problem as I always returned the canister for exchange until the last time whence I tore it apart to test the pump itself. Pump still works fine - I use it to pump diesel to clean parts with. Bad design overall I guess. Still working in Hot weather.
Alas, still having goofy problems. Recently (Aug 1st) replaced the ICM/ICV - worked really well for a couple of days. Went on a 160 mile trip and put in Premium Gas at 2 different gas outlets. After a few days now back to buck/snort chug chug at low speed but still better than before.
Maybe back to the fuel pump prob. Any alternates DIY?
Thanks.
Bcudamatt
I have a 1994 ram 1500 2 wheel drive and have a lot of the same problems you are describing. The truck will run fine for a few miles and then start misfiring badly and backfiring through the intake and ex and a lot of detonation and then clear up, and it repeats over and over. Also checked the fuel pressure while running badly and it is at 40psi. Also have replaced coolant temp sensor cap rotor button plugs and wires and made sure to route the wires the specified way. I am ready to burn this thing. Any suggestions would be helpful. Thank you!!!
Just a thought from a shadetree guy…Any chance of a failure in the evap system? As the fuel level in the tank goes down the tank will be under a vacuum, and the fuel pump may not be able to keep up under those conditions. Then, once you fill up, the vacuum situation is gone and you’re ok until it builds up a vacuum again. Are there air hisses when you unscrew the fuel cap?
On my truck, it does not matter what level the fuel is at when it acts up, and it does not hiss at all when I loosen the cap. I am at a loss!!
Becudamatt, Have you noticed if, or not, the pump was like a large can inside another can that moved up or down as the fuel level changed? As I posted back on July 30, I had one that would hang up and would not move down with the fuel. I replaced it with another design and had no more trouble.
dont know if my pump is like that or not but the fuel level does not affect this prob it acts up full, half, or on E
I would like to see a picture of the pump assembly.
Well, it could hang up at “full”
that is a posibility but the truck never dies it just runs very badly and clears up when the truck sits for a period of time (5 or more hours) i have to let it run for bout 15 to 20 min before it clears up enough for me to drive then it runs great for 5 to 10 miles and starts missfiring badly for some miles then clears up and repeats this over and over