1997 Ford F-350 Symptom: Intermittent Stalling
This case by Cody Gaddie comes from our AccuFix platform, and he highlights his diagnostic approach to this older vehicle. You can view this and more on our AccuFix platform at accufix.….com/home
Step1. Scanned for codes, none found KOEO, KOER. The vehicle starts and runs when testing. Checked fuel pressure. Fuel pressure within specs at this time. Fuel pressure spec 28-45 psi.
Step2. Next, I checked the fuel pump amperage on the passenger side A-pillar at the inertia switch. I used a low amp clamp around a wire at the inertia switch. Fuel pump amperage is 5.8-7.9 amps. This amperage measurement is typical. I noticed the waveform looks uniform and has fairly even humps and valleys.
Step3. I wanted to check fuel pump speed. To do this, we need to know if this is an 8 or 10 commutator pump. This pump uses eight commutators, so we need to measure eight humps to calculate the pump rpm. Zooming in on the pump, we can see the pattern of the eight humps a little better. We then use two rulers in-between eight humps, and we come up with an rpm of 7789. Any fuel pump rpm below 6k rpm can cause drivability issues. If rpm was, for example, 9k along with lower amperage, then it means the truck is out of gas, or there is a leak inside the tank from a rubber hose. Since the amperage, speed, pressure, and waveform look good, I am confident this is not a fuel delivery issue.
Step4. Using the same low amp clamp, I checked the ignition coil. I also used a secondary ignition pickup for a sync. Coil amperage is 6.5 amps; this is correct for this application. Blue: Low amp clamp at either ignition coil wire. Red: Sync on #1.
Step5. Shortly after installing the amp clamp, I noticed the vehicle started running rough and eventually died. While looking at coil amperage, we can see the amperage dropped right before the stall. Upon inspection, I noticed I could wiggle the coil connector to get the vehicle to stall again.
All this vehicle needed was a new ignition coil pigtail. Replaced pigtail and verified no more stalling.