Jim Grant's Tech Tips
‘89 Ford F-150, Hard Start When Cold
Q: My ‘89 Ford F150 with a 5.0 liter engine starts hard when itís cold. It runssmooth after it starts with no smoking. The fuel pressure is over 40 psi whenstarting, after start drops to 32 psi. The spark is very good, timing 10 deg.BTC and steady. The distributor cap and rotor are okay. There is good enginevacuum of 18 in. and it is steady. The coolant temperature sender ohms okay.The Idle Air Control (IAC) doesn't respond as well as I think it should but whoknows.
- Galen Brouse
A: It sounds as if your engine is sound enough with a steady and strong vacuum reading. If youíre having trouble starting with a sound engine then you likely have a fuel delivery or ignition problem. Also your diagnosis should not be based on running or key on testing. All testing for a hard start condition should be performed when the engine is cold and during cranking. You should start with connecting a fuel pressure gauge to the fuel system and briefly run the engine and then turn it off. Allow the vehicle to set long enough for the hard starting condition to occur. Before you turn the key check the fuel pressure. If the system is sound there should be at least 20 psi residual fuel pressure. If there is less than 20psi then there is an internal system leak that has to be addressed. The next step is to watch the fuel pressure as the engine is being cranked over. The fuel pressure should jump in a blink to at least 40 psi while cranking. If the fuel pressure climbs slowly then there may be circuit resistance that is slowing the fuel pump during cranking. If all checks good then inspect the condition of the ignition spark under the same conditions. If the engine is sound and in a good state of tune, you likely have a fuel delivery or ignition problem that is present during cold start.