greg92jeepxj
Official Supporter
In addition to COMPUTER SAFE TEST EQUIPMENT , I thought I would write something about this subject of hard start / no start that is a common complaint . From my experience , I've found that with a minimal amount of test equipment , you can still find most or all of what causes this condition . Armed with a fuel pressure gauge , noid light , in line spark tester , computer safe test light and a good multimeter , you can get far in finding the cause . You may even get your engine running . With knowledge in mind for how an engine runs , you've got two basic items to look for ; fuel and spark. Of course it's not that simple and this thread is only meant to point you in the right direction but with the knowledge and test equipment in hand , you might get lucky. Ok , your engine won't start . Not including a no crank condition , let's concentrate on no fuel , no spark . The more common engines found in our jeeps are the 2.5 and 4.0 liter . Older carburetor and ignition systems can be addressed differently but fuel injected and ECM/PCM systems are more complex and more prone to cause folks to mis diagnose and throw parts at due to frustration and hoping for the best and assuming that a diagnostic trouble code is telling us the part included in the description is to be replaced. Before replacing parts , we should be sure they're bad. No starts are not as easy as diagnosing a bad water pump or leaking transmission line . You usually don't see the cause unless it's something like a cut or burned ignition wire , cracked spark plug , cracked ignition coil or a list of other findings on a visual inspection. Further checking is needed. Where to start ? A fully charged battery for one . You'll need it since you'll have to perform cranking tests . The PCM needs a good voltage supply to work proper too. You'll want to have a fuel pressure gauge installed . Multi port has a schrader valve and throttle body injection must have an adapter installed. An in line spark tester should be used at least on the #1 plug , but checking spark on all cylinders is preferred. Check wire from ignition coil to distributor if engine is not DIS (distributor less ignition system ) too. A noid light installed on an injector harness connector should fire once every firing order cycle in a proper firing order for a sequential port fuel system and should confirm all are working and PCM is good to that extent but checking all injector plugs is good insurance. How about the crank and cam position sensors ? We know all too well that a hard start / no start usually includes swapping out these parts. They can cause hiccups in a running engine but that is advanced diagnostics which involves a scan tool or lab scope ( occiloscope) but we've got to get the engine running before we can determine quality . You can check a cam or crank sensor with as little as a computer safe test light and some straight or tee pins. Back probe the weather proof connectors and connect the alligator clip to battery negative. With the engine cranking , check all pins (usually three) . There is a ground , a reference and a signal. You should find a red led light for two wires ; one is PCM supply voltage and the other is return signal. This is for both type sensors , cam and crank. To confirm ground on the third wire( only after confirming which two are supply and reference) , switch alligator clip to positive battery terminal and read the third pin. You should get a green light. These are the results of a good cam or crank sensor. It should be mentioned as well that ALL grounds should be cleaned and tight. No PCM or sensor can work right with bad or broken ground. This thread can help toward self diagnostics for most hard starts / no starts . There are more sensors that contribute to no starts on more advanced systems on later model years . Coolant temp sensors , oxygen sensors , MAP sensors , mass air flow ( if equipped ) are also possible causes. That is when we have to take out the book and especially look for logged DTC's for clues . There are more items that can be added per model , year and system but these are your basic items and are where we usually start. Hope this helps all . Your comments and additions are welcome. Good luck and keep 'em rolling !
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