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Showing results for tags '2.5l jeep troubleshooting'.
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T-shooting an intermittent starting problem. About 80% of start-ups are perfect. When failing to start, it will turn over and over, but won't fire up. Sometimes starter fluid will cause it to fire up and then it runs fine, but that's only 50% effective. The rest of the time, only push-starting will work, but push-starting does work every time. Most obvious assumption is fuel problem, but fuel system checks out fine (replaced almost everything over time anyway). Ignition/electrical is fine. Also, the problem seems to be completely independent of outside and engine temperature. I started reading about ECU inputs, and discovered that during startup, an engaged WOT switch causes ECU to cut off fuel because ECU thinks it will flood the engine. The WOT switch is worn, but shouldn't prevent starting if disconnected. Would any other ECU inputs prevent fuel flow during start-up if their signals are outside normal limits? Service manual says during "Ignition On", CTS, MAT and MAP sensors begin providing input to ECU, but doesn't list MAT or MAP sensors during actual start-up. See attached page. So which sensors matter to ECU for start-up fuel supply calculations or decisions? Also, during push-starts, the ignition (key switch) is in the Run position, and not the Start position, which changes the ECU inputs, too. My shop has a DRB II diagnostics reader, but unless they hook it up when it happens to be misbehaving, shouldn't everything check out ok? Unfortunately, I've never been able to get it to fail at the shop. I also tried replacing the fuel relay. I also noticed that it is no longer cycling the ISA motor when it fails to start. It used to, but I can't figure out why it did that anyway. What are my next moves? Might be trying to oversimplify this, but what kind of intermittent problem would occasionally prevent a normal startup, but NEVER prevent a push-start from succeeding?