Automotive Diagnostic OBD2 Scanner

OBD II Problem — Engine cranks over but will not start

All internal combustion engines, regardless if they are just simply designed with a mechanical system, or else are OBD II compliant — with full electronic and a mapped management system need to have these 4 vital things functioning in order to start and run.

These four things are: Electrical Spark, Fuel Delivery, Internal Compression and a good Starter. If any one of these are lacking, the engine will NOT start. The OBD II system has more complex electronics technology involved in it the engine than conventional mechanical systems. This means that these four functions have more complex and additional components / circuits involved in them compared with mechanical systems.

The first step is to determine what is causing the main problem in one or more of these four critical areas:

• Spark Problem
• Fuel Problem
• Starter Problem
• Engine Compression Problem

Next logical step is to see what actually caused one or more of the above problems you determined.

It is imperative to start by taking the battery voltage reading across the terminals. This should be no less than 12.5 – 12.6 volts with the engine Off. Electronic circuits found on modern engines do not have any sympathy for low voltages, and will easily stop the vehicle from starting.

Unless it has been noticed previously that the starter is becoming weak, and is just waiting to fail on you (meaning it will need an overhaul or replacement unit) the best way is to start by testing the engine for good spark. If no evident fault is found there, move onto the fuel system. Test the fuel system for any failures and if nothing is found there, check the engine’s compression.

If the starter has been known to suffer when starting, especially first thing in the morning and the battery and charging systems are in optimum condition, have the starer repaired sooner, rather than later.

By eliminated the battery and starter conditions from the equation, three more potential problems are left to diagnose.

Step-by-Step Procedure:

Spark — Testing the Ignition System
Preferably instead of picking a random plug, start from the first plug (no.1) and repeat the test for each plug accordingly. Remove the High Tension (HT) lead from the plug. Remove that particular plug from the engine block and insert it back to its lead. Place that plug somewhere safe and as near to the engine block as possible. DO NOT hold the HT wire barehanded. Use proper high voltage insulated pliers.
Have an assistant crank the engine a few turns and check for strong blue sparks. If no spark occurs replace the spark plug with a piece of high amperage wire or a new plug. Repeat the test again. If there is no spark, test another HT lead by swapping one from another plug.
If possible, also check the continuity and resistance of each HT wire with a multimeter. Repeat test on all pistons.
If still no spark is found on all plugs after the test, and the ignition system utilizes a distributor-less ignition with multi-coil system, you will need to run a diagnostic test run with a proper diagnostic obd2 scanner. The probability is that there might be a faulty Crank Position Sensor. It is nearly impossible for all coils to fail at once.
On OBD II engines equipped with multi-coil spark systems, a failed coil might have the engine misfiring — but will still run. Any Data Trouble Codes (DTC) showing up as P0355 to P0399 are associated with the Crank Position Sensor.

On systems that only use one HT coil and a distributor, the coil should be checked with a multimeter for voltage with the ignition On. The distributor cap and rotor should be visually inspected for any damages. Any cracks or excessive wear on cap points and / or rotor might be causing the starting problem. The only remedy is to replace these damaged items.

Fuel — Testing the Fuel System
If fuel isn’t arriving at each injector the engine will never run. The first step is to loosen the fuel rail and disconnect each injector individually, one after the other. Place the injector in a suitable container and turn the engine on the starter. Fuel should squirt out of the injector as a fine spray. If fuel is being released in droplets there is the probability that this injector is faulty and will need replacement. It can also be that the injector is partially blocked and will need cleaning and calibration.
In this scenario the probability is that the plug tip is being washed through excessive fuel and preventing the correct strength of spark to occur. If this problem is just on one or two plugs, the engine should still start eventually, misfiring badly along the way when running.

If no fuel is arriving at the injectors the problem lies somewhere in the fuel delivery system, mainly the fuel pump. On mechanical fuel pumps check the fuel pump for delivery by removing the outlet pipe and placing it in as suitable container. Turn the engine a few turns on the starter. If no fuel is deposited into the container than the fuel pump is probably faulty. On overhead cam engines with a timing belt it is a wise idea to partially remove the upper timing cover and inspect the belt and its tension before replacing the fuel pump. A loose timing belt can effect the fuel pump’s function, as well as ignition timing problems. If all seems OK, than the pump needs to be replaced.
On fuel injected systems the fuel pump is usually located inside the fuel tank. First task is to trace the fuel pump’s fuse from the vehicle manual and check that it is not blown.

Next step is to check that voltage is arriving at the fuel pump terminals. This can be done by unplugging the electrical connector and taking a voltage reading with the ignition on. If there is a sufficient voltage reading the pump is the culprit. Reconnect the plug back in its original location and with the ignition on try and hear the pump working. Sometimes tapping the pump body gently with a rubber mallet, or a wooden block might reanimate the pump. This can sometimes happen when the engine hasn’t been running for a while. If the vehicle has been used constantly and the pump suddenly stopped working, just replace it. Even if you manage to reactivate it by tapping it, it likely on its last legs and is waiting for the first opportunity to let you down again.

If on the pump is found to be working but there is no fuel delivery to to the injectors the fuel regulator is likely to be faulty. Disconnect the fuel inlet entering the pressure regulator and place it in a suitable container. Turn the engine on the starter a few turns. If fuel is arriving (and should be arriving as pump was tested previously) the regulator is damaged and needs replacement. These are usually the cheapest part from the whole fuel system, excluding the fuel pump fuse.

Alternatively, if a faster approach is being used by applying a scantest through an OBD II scanner, the fuel pump DTC are P0230 to P0233 and the fuel pressure DTC are P0190 to P0194.
The ‘Check Engine’ warning light should trigger under any of these codes.

Note: If bad fuel enters the system the possibility of the engine starting are very slim, and if it eventually starts will quickly “die out” again. This can be through traces of water in entering the fuel, probably after a refill from a leaky Gas Station or entering the wrong type of fuel. In this case the bad fuel needs to be drained out completely and replaced with fresh fuel.

Compression — Testing for Compression
The most common starting problem trait found OBD II engines is when the Crank Position Sensor fails. This most common cause is due to a worn out sensor. The OBD II ‘Check Engine’ light should come on. Any fault codes showing up on a diagnostic obd2 scanner as P0355 to P0399 are associated with this sensor.

The second, and less frequent scenario is when there is a bad timing caused by an old belt loosing its tension through excessive wear and / or a loose or faulty tensioner. This normally occurs when the timing service intervals are ignored completely.
On certain engine designs, the worst case scenario is when the timing belt snaps, leading to destruction on some of valve train parts, together with the accompanying pistons in the process.

Another fault might be a camshaft has sheared along its shaft. This will lead to no drive on the second half of the broken camshaft and potential damage may occur if the engine is turned.

Conclusion:

Finding faults on OBD II engines is more difficult at best. A good diagnostic obd2 scanner, or code reader is an essential aid in OBD II repairs. The engine components might be the same as conventional mechanical engines, but there are more “electronic circuits” involved in these engines. Ultimately the scantool will still be needed to clear the ‘Check Engine’ fault as in most countries it is an offense driving with this warning lamp On. Various diagnostic OBD2 scanners and other diagnostic tools can be found at very competitive prices through the 24 x 7 Online Shop tab.