I have a 1997 F250 light duty with the 4.6L engine, manual transmission, 4WD, and standard cab that is having difficulties with hesistation and stumbling during cold starts. The truck will sometimes have extended cranks but will start right up and idle GREAT no matter how cold it is outside and how long it has been sitting. The problem manifests itself as soon as you put the truck in gear and try to go. It will buck and kick and have NO POWER if you don't rev the RPMs up first before going. If you keep the RPMs up while it is cold, it will run great. You have to be aware of pulling out into traffic for the first 2 minutes or so, especially when it is colder outside and the truck has been sitting overnight or longer.

The truck has 250+ k miles but has a replaced junkyard engine. I haven't checked the compression but the replacement motor uses no oil, doesn't smoke or leak, and seems to run exceptional once warmed up.

Before I go into listing ALL the parts I have replaced, I wanted to let everyone know that this came with an aftermarket cold air intake installed. The first thing I did was replace the junk filter that was allowing dirt through with a LARGE KN cone filter. I have also been told this might be letting in more air than the system is designed to handle, causing my problems. Another part I haven't replaced is the throttle position sensor (TPS) as I tested it with a multimeter and it seemed like it was right on the published specs. The only other issue I can think of after replacing parts is the fuel pump. I have hooked up a pressure gage and taped it to the windshield so I could see it working. The pressure reads between 30-42 psi when driving, depending on the load and seems to come up pretty quick when started. I have been told that this sounds like a fuel delivery problem. I have also not replaced the EGR solenoid. I tested this by removing the vacuum line during a cold start and it still seemed like it was closed.

I got this truck used and have replaced the following parts, either to fix other problems or in an attempt to solve this problem.


-Plugs, wires, and ignition coils. It looked like a lightning show under the hood at night and I had misfire codes.
-Intake Air Temp Sensor (had code)
-Cam and Crank Position Sensors (replaced for good measure as they were cheap)
-Coolant Temp Sensor and sending unit
-Installed known good Mass Air Sensor from same model truck but no luck
-Vehicle speed sensor (the speedometer just quit one day and I had a code)
-Clutch
-Idle air controller motor (had code)
-EGR valve (had code)
-EGR sensor or DPFE (had code)
-Fuel filter (twice - the original one was so DIRTY that a cup or so of black sludge poured out of the backside - the second one was clean after a few hundred miles)
-Manually removed and cleaned/tested injectors
-I have run several cans of Sea Foam and injector cleaner products through the gas as well as some directly into the throttle body
-I also changed the oil, fluid in both differentials, transmission fluid, and transfer case fluid right off the bat.
-Oil filter lines and pressure sending unit (had major leak here)

So, it seems I have replaced everything that would matter during a cold start with a few minor exceptions. I am not getting any codes at this point in time and the truck is running A LOT better with all the parts I replaced except I am having the same problems during and right after a cold start. I hate to just replace things to try to fix this but if anyone has a good idea of where to continue, I would consider it. The problem seems to only occur under load at low RPMs but runs fine cold at higher RPMs under load. This seems to suggest that is isn't the fuel pump but I have had people suggest that this might be the case with the filter being so neglected when I got the truck. I was also reading 40+ psi on my tester gage right after a cold start while I was having the problem so I don't think this is it.

So, I am left with the following possibilities.
1. Intermittently bad EGR solenoid
2. Intermittently bad TPS sensor
3. Issue caused by too much cold air being allowed in by the aftermarket intake system that was installed on the truck and the open loop/cold start controls are not accounting for this.
4. Weak fuel pump (I am not quite ready to rule this out)

I have halfway considered trading out the aftermarket intake for a stock system just to see what happens. Someone would be getting themselves a nice $400 setup with a brand new KN filter.

Let me know what you think or if I have failed to consider something else that might cause this trouble. I really doubt it is the O2 sensors as they are not important during a cold start.

Thanks,

Conor

 

I am going to test to see if the truck runs better with the EGR vacuum line disconnected and plugged in case the EGR solenoid is the cause of my problems. I have disconnected and plugged the vacuum line and will see what happens during the next cold start. I tried starting it after it had been sitting for only a couple hours and might have gotten a suggestion of my past problem. I will see what happens in the morning and I might try it late tonight before I go to bed just in case I get can my problems to return.

Conor