Hesitation during acceleration when cold

[NA5KAR]

Thanks in advance for your help/ideas. I've got a 2001 F250 7.3 2 wheel drive, auto trans. I'm in South Florida, so the temp is not lower than 70. Truck has 250k miles. I've owned it for 2 years. I'm not a great mechanic, but I can tinker and do most repairs. I also converted the truck to run on Veggie Oil. I have a separate fuel pump/filter and I tapped into the two unused ports on the intake manifold for the oil lines. (Check valves all around). I run oil by throwing a switch on the dash which turns off the diesel fuel pump and turns on the oil fuel pump. Ok, enough about me. For the last couple of weeks, there is a sputtering or hesitation when the engine is cold and I accelerate through the gears. I'm not heavy footed, so it is moderate acceleration. If I back off the pedal, the sputtering/jerking stops. Accel again and it might be smooth. When it warms up, the jerking kind of goes away, but I can 'feel' that the engine is running a little rough. Most people would not notice it, but I do. If the engine is warmed up and I go to the store, when I start it up again, the starter sounds fine but the force of the start is weak. Like it didnt get enough fuel. When cold in the morning, it starts fine. It does the same thing when I'm on diesel or veg oil. Any thoughts or ideas. Thanks again.

[RT]

When you are running any alternative fuel, a fuel pressure gauge is mandatory. You'll need to plumb it somewhere such that you get the actual pressure in the head with your setup. If one or more of your one way check valves is not 100%, then you're bleeding off pressure into the other tank. Are you heating the vegetable oil in any way? The guys that do this say that coking is a serious problem if you don't. You might post a thread in the alternative fuel section with regards to your unique setup.

[NA5KAR]

Thank you RT. That sounds like good advice regardless of the issue I'm having now. Yes, I do heat the oil. I interrupted the coolant at the heater core and send it through the veg oil tank in the bed. I also have a 'line-in-line' system to heat the oil. I dont switch it from diesel to oil until the temp reaches about 150. I do have a pressure gauge on the instrument cluster (on the column). It reads the pressure after the oil leaves the filter and before it goes to the check valve prior to the hoses that enter the intake manifold. It holds well at 65 - 70 and when I switch back to diesel, the pressure is zero. I would be happy to share my setup with anyone interested. It is clean and efficient. As I mentioned, the hesitation happens on both diesel and veg oil. I have been running only diesel for the past 2 weeks now and it still has the issue. Thanks again. Please keep the ideas coming.

[PreservedSwine]

Does it miss at all at idle?

[NA5KAR]

As I mentioned, it does run 'less smooth' compared to before this hesitation started. At idle, I do notice a reduction in smoothness but it does not 'miss' like it does during acceleration. I am working on a theory and testing it today. For my veg oil conversion, I mounted a switch on the dashboard. It is a $5 switch from Pep Boys which has two 'on' positions and a center 'off' position. For my veg conversion, I cut into the hot feed wire to the diesel fuel pump and brought those two wires to the switch. I also brought the power wire from the veggie fuel pump to the switch. The hot wire went to the center switch terminal and the feed wires went to the two outside terminals. So, when I have the switch in one (on) position, the diesel pump comes on and the other (on) position powers the veggie pump. Since this is a rather cheap switch, it burns out every other month and I have to replace it. My theory is that the switch may not be working properly and is intermittently cutting off the fuel pump(s). So, last night, I hard wired the diesel pump wires together to see if that stops the hesitation. This morning, I took my son to school and it did not hesitate. I'm letting the engine cool down before I take it for another drive. Want to do several trips to confirm this theory. I'll keep you posted.

[RT]

Might need to run the switch to control a relay that delivers the power to the pump. That's too much current through a simple switch.

[NA5KAR]

Thanks RT. I agree with you and I will make the upgrade very soon. Well, this morning, I took my son to school with the fuel pump power wire connected, and it still had the hesitation. It ran like crap all day. Back to square one.