Jeep 1991 yj won't start

[DBodner]

My son's jeep won't start. We checked the fuel at the injection manifold and we have fuel there. The #1 Spark plug fires. We have changed the plugs, wire, distributer cap, rotor button. And still it doesn't start. Any help would be appreciated.

Thanks, David.

 

[greg92jeepxj]

Welcome to jeeps.com . No starts are very involved diagnostically but let's try to get started . Ok , you've got spark but in all cylinders ? And fuel pressure is adequate ? Did you test the fuel injector wiring harness for voltage and ground ? Do not use a 12 volt test light on the injector harness , use a noid light or at least a COMPUTER SAFE TEST LIGHT. The grounds are closed,from the PCM to fire the injectors in a sequential firing order as the ignition system is by the PCM. Sounds like the crank position sensor and cam sensor are ok but we'll hang onto that for a moment. Need to see results of injector harness and if all plugs are firing . Your ignition may be ok bit if the injectors are not firing then even if the electric fuel pump is priming and building pressure , the injectors won't open and fuel won't spray. We don't know the condition of the injectors but we need to know of they're firing. Look,for voltage on the power circuit on each injector harness plug which is fused so check fuses as well. If power is found , all,will light when ignition is ON. Grind is only applied by PCM WHEN the PCM wants the injector to fire in the sequential,order it's supposed to when that cylinder is on compression stroke. So , you see there are two firing orders ( ignition and fuel injection) and a no,start is pretty involved. The crank sensor will find #1 TDC when flywheel reaches correct position to start firing order sequence . The cam sensor will follow to,distribute spark when cylinder position is verified and consistent with with crank sensor and flywheel position . It all sounds very complex , granted , but when it works right , your reward is hitting the trails ! Good move changing secondary ignition components as a tune up,is never a bad thing and rules out problems there providing those parts are working right and aren't defective. You'd be surprised , lots of replacement parts fall into this category. Cam and crank sensors as well. New parts don't always work. Dealer parts are best for jeeps but $$. This will be a good start diagnostically and hopefully it isn't more involved than this. Of all grounds are clean ( battery negative , chassis , engine block, etc) the PCM should work right if there is no faults. PCM faults happen because of many reasons. Improper jump,starting ( short to alternator ) , overcharging condition ( PCM controls alternator output), ignition coil overdraw due to bad spark plugs , wires , cap and rotor over long periods of time. Bad grounds contribute to PCM demise. Let's not worry about PCM health in this thread but let's hope the best for your boy's jeep. Hope this helps .

 

[DBodner]

Welcome to jeeps.com . No starts are very involved diagnostically but let's try to get started . Ok , you've got spark but in all cylinders ? And fuel pressure is adequate ? Did you test the fuel injector wiring harness for voltage and ground ? Do not use a 12 volt test light on the injector harness , use a noid light or at least a COMPUTER SAFE TEST LIGHT. The grounds are closed,from the PCM to fire the injectors in a sequential firing order as the ignition system is by the PCM. Sounds like the crank position sensor and cam sensor are ok but we'll hang onto that for a moment. Need to see results of injector harness and if all plugs are firing . Your ignition may be ok bit if the injectors are not firing then even if the electric fuel pump is priming and building pressure , the injectors won't open and fuel won't spray. We don't know the condition of the injectors but we need to know of they're firing. Look,for voltage on the power circuit on each injector harness plug which is fused so check fuses as well. If power is found , all,will light when ignition is ON. Grind is only applied by PCM WHEN the PCM wants the injector to fire in the sequential,order it's supposed to when that cylinder is on compression stroke. So , you see there are two firing orders ( ignition and fuel injection) and a no,start is pretty involved. The crank sensor will find #1 TDC when flywheel reaches correct position to start firing order sequence . The cam sensor will follow to,distribute spark when cylinder position is verified and consistent with with crank sensor and flywheel position . It all sounds very complex , granted , but when it works right , your reward is hitting the trails ! Good move changing secondary ignition components as a tune up,is never a bad thing and rules out problems there providing those parts are working right and aren't defective. You'd be surprised , lots of replacement parts fall into this category. Cam and crank sensors as well. New parts don't always work. Dealer parts are best for jeeps but $$. This will be a good start diagnostically and hopefully it isn't more involved than this. Of all grounds are clean ( battery negative , chassis , engine block, etc) the PCM should work right if there is no faults. PCM faults happen because of many reasons. Improper jump,starting ( short to alternator ) , overcharging condition ( PCM controls alternator output), ignition coil overdraw due to bad spark plugs , wires , cap and rotor over long periods of time. Bad grounds contribute to PCM demise. Let's not worry about PCM health in this thread but let's hope the best for your boy's jeep. Hope this helps .

My son ended up taking the vehicle to the shop...they put sea foam in the engine and now all is well. Never heard of doing this but then said that the rings were seized. This took care of the problem and his jeep is running great now.

Thanks, for your reply

david.

 

[greg92jeepxj]

Your welcome . Happy your son's jeep is running well . Hope the repair bill wasn't staggering . Guessing a compression test revealed low compression. Happy it all worked out. Thank you for your reply.