When you don't know exactly what you are looking for, troubleshooting an engine can consume a lot of time. For every knocking sound and symptom affecting overall driving quality, there can be two to three symptom that merit investigation. Ford vehicles come equipped with a tool that can help. All Fords manufactured in 1996 and later include a second generation On-Board Diagnostics system. For Fords 1995 and earlier, there is the fourth version of Electronic Engine Control. Neither system will give you an exact answer, but they will point you in the right direction.
EEC-IV Self Test For 1995 Fords and Earlier
Start the Ford and let the engine run for as long as it takes to warm the engine. To facilitate this, you should leave the air conditioning off. Once running temperature has been reached, shut the engine off and open the engine compartment.2
Connect the Self Test Output and the Self Test Input ports with jumper wire. The STI is a single port on a wire, and the STO is a multi-sided hub with six slots. They will be next to each other and in the rear of the engine. One end of the jumper needs to go into the STI, and the other needs to go into the STO's bottom left grounding slot.3
Turn the Ford engine on, but leave the engine uncranked and off. Wait for the check engine light to start turning on and off. The interval of lights represents a diagnostic code. For instance, EEC-IV code 32 will be three lights followed by two shorter lights. EEC-IV code 48 will be four lights followed eight shorter lights. There will always be a few seconds pause between whole code numbers. Write all the codes down.4
Look up Ford's EEC-IV coding explanations on the web. You will quickly discover that Ford owner's manual does not contain this information. If you are considering a lot of DIY maintenance for your Ford, you should purchase a Haynes Repair Manual for your model and year. This manual will not only have for EEC-IV codes listed, but will also offer detailed repair descriptions. Copy the explanations next to the numbers you jotted down in Step 3.5
Begin at the top of your list and investigate the parts of the engine that correspond with the EEC-IV light codes. Cross off codes once you know they are not part of the problems your Ford is currently experiencing.
OBD-II Diagnostics for 1996 Fords and Later
Connect your OBD-II code reader to your Ford's diagnostic outlet. This Data Link Connector should be uncovered, easy to access, and beneath the dash, within the general area of the steering column, the gas pedal, or the hood release. If you cannot find the DLC outlet, consult your code reader's handbook for specific suggestions.7
Activate your code reader. You may own a code reader that will turn it itself on once it recognizes a connection with your Ford. Code readers also function slightly differently by brand, so always defer to the step by step instructions in the reader's manual.8
Turn the Ford's electrical system on. Some code reader may also require you to start the engine as well. Wait for the code reader to auto-retrieve trouble and pending codes. Some readers will not do this and will require you to enter the command by hand.9
Look up the explanations for the OBD-II codes retrieved. Your manual may have the codes universal to all OBD-II compliant vehicles, but it may not offer Ford's supplemental codes. Your Ford's manual will not have these codes either. Look those up online. Make a list of codes and explanations. Place the trouble codes at the top, and pending codes at the bottom. Trouble codes are responsible for the check engine light going off, so always investigate those first.10
Troubleshoot the Ford's engine with your list of codes as a guide. Work your way down the list until you have checked every code you retrieved from the system.