sputters on hard acceleration update:loses fuel pressure as it warms up.

[LaOtto70Charger]

Need help. My 318 70 sputters on hard full acceleration. She idles just fine when I first start up. Ran ok for 10 minutes on the highway. Stopped at a stop light with no isssues. Light turns and I floor it. She accelerates about 45 range and starts sputtering. It died just I got to the shoulder. Barely fired up after that. Made it home but kept dieing at idle after that. Same thing happened last year with new spark plugs ngk, new wires, rebuilt distributor, new fuel tank, 3/8 sending unit, 3/8 fuel line to the new fuel pump.  All done over the winter since the issue started. Also replaced the edelbrock 650 due to a stripped mixture screw.  Last time I pulled the plugs when this first happened they were all a nice tan color. No black or severe burnt look. About to go back the autolite. Needs to add some wire separators for spark plugs too. Last week she ran ok and a similar short trip just don't think I got on it quite as quick. Timing is 10 with vacuum advance disconnected.

[XH29N0G]

I don't think I can help, but will respond to keep the discussion moving forward.  Since you have a new tank, pump and carburetor, it is probably not fuel.  Is it something that happens when the car gets fully warmed up and then when you get on it, but then goes away after it cools down?  The reason I ask is because I had something similar (but not as bad) and it was the coil.  I was trying to sort out whether my issue was coil or ecu.  (Do you have points or is your car converted to electronic ignition?)   See what others say.  They will know more than me.

[LaOtto70Charger]

Could be coil. Just replaced that also with an accel one. Does still have points. Original distributor was working fine than tried anew condenser and it acted up. But old condenser in and ran better.  Vacuum advance didnt work so went with a rebuilt one. Does seem to be worse after it warms up. Was running ok with Vacuum advance hooked up but than started acting up. That was last fall. Fired up it with new tank and fuel and it started idling rough so I unhooked vacuum advance and it ran better.

[XH29N0G]

Do the points look OK?  Or are they new, have you checked the dwell? I am no longer running points, but I had a very bad running engine and it was the dwell. Again others will know more than me on this.

[LaOtto70Charger]

Points are new. I will check dwell. Hadn't checked that recently. Now it won't even idle. Have to give it fuel. Than dies when I let off.

[brad mcintyre]

mine was running really rough a mechanic I know said run it out of gas carborator may have dirt in it can you pinch off a line it help me if it is dirt in carb

[LaOtto70Charger]

Now it won't even idle for 10 minutes. Sunday i pulled the cap and found the spring on the rotor broke.  Replaced it, replaced the cap, and found the broke spring end.  Than I put a fuel pressure regulator, and pressure gauge in. It fired right up at 6 psi. I backed it down to 5 and it strated running rough and died.  It would kind of run later in the day.  Couldn't get any change in rpm by placing my hand over it.  Timing starts at a solid 10. When it starts running rough it bounces down.  Not sure if that is because the engine almost dies. Coil has 6 volts when the key is on and not running. I didnt check resistance.  Points look fine. Spark plugs show lean if anything.  Today it fired right up no issue. Ran perfect for a ltitle bit. Throttle movement didn't cause any issues. Than she starts missing a little a bit. Check pressure gauge and still at 5 psi. Starts missing a little bit more.  Give it some throttle and she almost dies and than kind of accelerates, and almost dies again.  I let it drop back to idle and can't get any change in rpm by covering it with both hands. I try turning in the idle air screws half turn. Nothing changes.  I am completely stumped. Saturday I took the top of the carb. Sprayed it out and checked the float. It all looked good.  Any thoughts what to try next?

[RECHRGD]

Has all this been happening with the same tank of gas, or have you run a few tanks full during these troubles?

[LaOtto70Charger]

New gas, and tank.

[BLK 68 R/T]

Vacuum leak on the intake somewhere? take a can of ether and spray around the intake ports and around the base of the carb, see if idle speed changes. Is it a stock iron intake? I have heard of them cracking on the bottom before and as they warm up the crack opens up causing a vacuum leak, would have to pull it though to inspect it.

[LaOtto70Charger]

Edelbrock aluminum 4 barrell intake . If I can get running at idle long enough I can check that.  I went to try and spray some in the carb to see if it would help keep it running, but it died.

[redgum78]

Might still be the condenser? Have you got one from another car that you know works rather than a trying a new one? I had an issue with a car doing similar, turned out it was the condenser but the first replacement I got was faulty as well. Eventually I tried another one I had and fixed the problem.

[LaOtto70Charger]

Updates: I fired the car up and got 7 psi as the rpm settled down.  I backed the pressure regulator down to 5 and locked the jam nut down.  I started checking voltages and timing as it warmed up (more questions on that to follow.) And kept periodically checking the pressure gauge and noticed it slowly bleeding down. It eventually dropped down to around 2 psi as the car finished warming up.  Thermostat was at 170 and oil pressure was at 30 psi and both were holding steady.  I didn't see gas leaking out anywhere around the carb or the lines from the pump to the carb either.  With all the fun trying to get this thing to run right the gas line now runs up the right inner fender to the pressure regulator which is mounted there. Than goes to a pressure gauge and than to the carb.  I have rubber hose from the engine to the fender with the filter in that section.  Up the fender is 3/8 stainless Than I have rubber line again from the regulator to the carb with the gauge mounted in a tee in the middle.  All 3/8 line. Is this just a factor of the rubber line warming up and expanding or do I have a carb or fuel pump issue?

I do plan on finishing regulator to carb with more stainless but wanted to make sure it was running decent again.  That and now I am thinking of moving the coil to the fender and with a/c compressor there I may ending up moving the regulator to make room for that.

On to the other issue. I checked the coil cold and hot but both pimary and secondary resistance was pretty much in specs. I did't right them down though.  So anyway i replaced it since once it got warm it went from running fine with solid timing to missing, dieing with throttle, timing jumping, and dieing at idle. Coil was an accel now a durulast gold. She runs started fine and warmed up ok. Timing is now holding constant. Voltage at coil is 6.6 on negative side and was jumping all the way to 16 on positive side. With this it would bog down if I gave it throttle at the carb.  Checked battery solid 12.5 at idle. Would raise up to 14 range with light throttle.

Base timing was solid at 10 and rpm was 876.  I rechecked coil voltage and was than getting 5.3 on negative (hooked to distributor) and 8.3 on positive.  Throttle responded normally now. Waited a bit noticed a little missing at idle.  Tried increasing rpm and the bogging, was back. Checked the voltage and again found 6.6 on the negative with the positive bouncing all over.

When it was doing this it didn't matter where I ported on the positive side. I checked at the post, the connector and the end of wire sticking through connector. Voltage just kept bouncing.  After a while rechecked voltage and now a steady 8.3. Next I ran the engine speed up to 1700 and voltage at positive went up to 11.  I am assuming this means bad condenisor correct?  I should at that with the key off the voltage is 0.23 on negative,  and 6.2 on the positive side so I think it would pass what I was reading as a typical first test.

Also I did change out the ballast resistor and the voltages at the coil stayed the same.

[XH29N0G]

Updates: I fired the car up and got 7 psi as the rpm settled down.  I backed the pressure regulator down to 5 and locked the jam nut down.  I started checking voltages and timing as it warmed up (more questions on that to follow.) And kept periodically checking the pressure gauge and noticed it slowly bleeding down. It eventually dropped down to around 2 psi as the car finished warming up. 

Can I ask for a clarification on what you have written and how the pressure regulator works in the system?  Even though I am sure it is simple, I do not have a pressure regulator on my fuel system so I don't completely understand how it works.  I am wondering if when you backed it down to 5, it then took a while to reach a stable reading (which was 2) and if you could readjust the pressure regulator to bring it back up to the 5-7 range.  If you cannot, then it seems that there is something with the fuel pump.  I don't think that is the root of your problem, but do not have a good answer.  My guess is that others on here will be able to provide a better assessment from your other tests.

[brad mcintyre]

is your fuel line getting hot causing air lock

[brad mcintyre]

did you maybe move fuel line mine ran along top of motor made fuel to hot

[BLK 68 R/T]

I think your fuel pump might be the issue. I remember reading, on this site I do believe, about todays aftermarket mechanical pumps, once they warm up they start dropping pressure on some of them. What brand/type do you have?

will see if I can find the link to the pump issue....

edit: found the link http://www.dodgecharger.com/forum/index.php/topic,124124.0.html
It is referring to a big block but I would assume the same thing could happen to the small block fuel pumps as well.

[LaOtto70Charger]

XH29NOG My understanding of how the fule pressure regulator works is there a spring with a diaphragm and the bolt increases or decreases spring load to change pressure. Reading some other sites since this one doesn't have a bypass I may need to start at low pressure and go higher.  Sounds like when high to low it act up since there is no pressure relief.  So I will ty the other direction slowly. Since it was over ten minutes there will be a lot idling.

Brad. Right now the fuel line goes to the fender, runs up the fender, and than straight to the carb. So amount close to the engine like original is very little. Got a few 90 degree bends now, and did note the rubber section was getting warm but not hot. How can you check for air?

Blk 6i r/t thank you for the link on that.  If I keep getting these pressure changes I will look into a carter. That I can deal with it. Just hoping it isn't fuel starts blowing past gaskets in the carb I can't see.  Outside it is sealed up fine at least. I sprayed carb cleaner all over the place with no changes in rpm.

[flyinlow]

A few ideas;

Do an ignition test. Pull the coil wire, put a cotter pin in the cap center socket. Use rubber handled pliers with a jumper wire from the metal to the engine to hold the coil wire. (to help prevent shock) With the car in the shade or garage so you can see the spark,hold the coil wire to the cotter pin and have someone start the engine . Slowly pull the coil wire away from the cotter pin and see how far it will jump. Blue spark out to 1/2 inch before the engine quits is good.

Disconnect the vacuum advance for now. The engine will start and run ok. without it for now.

You can hot wire the coil direct from the battery for short periods. The car does this during cranking normally. This will help a weak ignition perform better for a few minutes.

Bad fuel tank vent cap? leave the cap loose with a partial fuel load. (a full tank will slosh out if you accelerate hard.)


High fuel pressure wont hurt the gaskets ,it just overpowers the floats ability to close the needle vales and floods the carb.  My experience is Edey/Carter carbs tolerate up to 6-6.5 psi .