Down Hill Stall Mistery


#1

The following issue has been stumping every mechanic that I have talked too. We have a 1948 Chevy with a 350 ram Jet and 700 R-4 transmission. The water temp while on the road runs about 180, and up to 195 in town. The following is the problem. When coasting down a hill it will periodically quit, like the key was turned off. I have to through it in neutral, start it, and then put in drive while rolling. It never has done it at idle, on straight a ways, or up hill. No, I can’t avoid going down a long hill sometimes. Please help…

Thanks,
Art


#2

Carburetor float bowl adjustment.

Yosemite


#3

This is a fuel injected engine…


#4

“This is a fuel injected engine…”

Doh! There goes all my theories. Can you find a downhill with a wide shoulder where you could coast to the side after the engine stalls, and pull a spark plug or two for a “read”?


#5

What kind of fuel tank and where is the pump assembly located?
What kind of fuel pump assembly and does it do this on a full tank also?


#6

Full tank of gas. Doesn’t happen all the time. 3x on 180 mile trip. Not sure about fuel assembly. Will have to check. Again, never happens at any other time, but coasting down long hill.


#7

I would have your fuel pump pressure checked. If it’s OK then replace your fuel filter since it may be partially clogged. I had a GMC truck that did this and it turned out to be a clogged fuel filter. One other question…do you coast in drive or in neutral? It makes a big difference in keeping the engine running. BTW…I never advise anyone to coast in neutral for a lot of reasons.


#8

@artdoc; we are talking a 1948!!!

Yosemite


#9

@Yosemite … the car may be a 1948 model but the engine and transmission are, at least, 40 years newer.


#10

I was pretty sure they hadn’t come out with the ramjet that early.

I want to hear more about the 1948 car /truck???

Yosemite


#11

Hot rod, baby.


#12

To clarify something he said in his original post " I have to through it in neutral, start it, and then put in drive while rolling " so it appears the car is in drive when it stalls. Not uncommon for “some” automatics that will not keep an engine turning when the engine quits. When the engine quits so does the front transmission pump…Older cars from the 50’s and 60’s with additional rear pumps would prevent this. I had an 87 mercury that had a flaky ignition control module. Was doing 70 when it quit and all the dash lights came on, engine stopped turning, no PS or PB’s.


#13

No, the car is in drive all the time while moving. Correct though that the car is a 48, but ram-jet and transmission are 5 years old. Will check fuel filter, but wouldn’t this happen at other times as well. I will admit that I am not a mechanic. Thanks for every ones input…


#14

Me thinks this '48 looks a lot different than it did when it rolled off the assembly line. Sounds like a quality-built resto-mod. I agree with fuel starvation being put to blame. Check/replace the filter. Is the fuel pump internal to the tank or external on the frame? Does it draw fuel through a draw tube from the bottom if the tank to the top with the sending unit or from a bottom-of-the-tank connection?


#15

Another though. Does this ramjet setup have an oil pressure safety feature to cut power to the fuel pump if the oil pressure drops? I’ve heard of some trucks with certain oil pan configurations may let the oil run from the oil pickup at certain angles. Do you have an oil pressure gauge?


#16

Have an oil pressure gauge, and it maintaining pressure while running. Not sure about fuel pump at this time. Drawing fuel from top of tank, I think. Thanks again from all of you with suggestions. Car is currently being restored, but can at least check filter. Again though, has only happened sporadically and descending a long hill. Quite unnerving, since you lose PS/PB.


#17

Still thinking on this. Just as an additional aid for any thought processes of mine (or lack of…) is the fuel pump mounted externally or is it inside the fuel tank?
Is the fuel injection a TBI set up or multi-port?

When it dies while coasting is your foot not depressing the accelerator pedal at all when it does quit?


#18

Try this for now, when coasting down a hill in “D” try putting the transmission into “2”, this should keep the tranny clutches engaged in the lower gear and should not cause the engine to stop turning whatever the problem may be…I have experimented with auto trannies without rear pumps. Tried this on a 74 and 76 Ford with the C-4 tranny and also worked on my 87 Mercury…Shut the key off during this when locked in 2nd gear and engine came back to life when key was turned back to run. I know this is not a fix for you problem but may eliminate the stalling going down hill and still maintain PB and PS…There is something wrong here with your situation, has to be spark or fuel or an air intake problem. …I know when these things happen on and off are hard to check if the engine starts right back up…What about the IAC, or MAF acting up can cause this…just a suggestion. if you had a fuel pressure problem it would appear when you are heavy on the throttle taking the motor to its max rpm. i wish i had more to suggest.

The only way you are going to find the problem is when the engine totally refuses to restart, then you can check it out. Good Luck.

EDIT: When I did this experiment If the the car was in “D” and was going between 35 and 40 mph, shutting the key off to on the engine it would not restart. Dangerous if going down a mountain pass. Locking it into a lower gear, engine always restarted ( or starting to turn again ) on its own. Now my 59 Thunderbird with the rear pump would always re-start even dropping down to 20 MPH in “D”. For those of you that want to know what a rear pump did was enable push starting an auto, which was driven by the output shaft of the tranny…Get it up to 20-25 mph, turn on ignition and drop it into gear. Most trannys past 1965 the rear pump was eliminated…Just a little education for you all…Take care guys and have a great day.


#19

For starters, I would clean the throttle body and the Idle Air Control pintle. With the throttle lifted the IAC blocks air flow and cuts invector feed i.e. no air and not fuel on decelleration.

At some point the ECU has to recognize that the manifold vacuum and engine rpm needs air and fuel to idle. Therefore, check the setting of the Throttle Position Sensor to make sure that the ECU recognizes that the throttle plates are closed. Then you will have to research the decelleration part of the program to see what sensor is being used to restart fuel flow. Most times it is the Manifold Pressure Sensor but I guess it could be a conbination of the Mass Air Flow sensor and engine RPM. Maybe you can consult with the manufacture of the program installed. A software upgrade/download may be in order if your ECU has that capablity or an upgraded PROM if your ECU runs on that.

You might also look to see if the program is commanding 1st gear in the 700R4 before the idle enrichment has begun. You might be able to get ‘freeze frame’ data ouput on a capable scan device.

Keep us appraised of your progress. Give us ‘eye candy’ pictures of the truck and power plant installation.