I have a 94 Jeep Wrangler the motor was smoking and using oil so I bought a used motor (2.5) and installed it I drove it in to the shop put the new motor in I went to start it and before I turned the key on I have the check engine lite, the shift up lite, and the brake lite on with out the key in it. It doesn't not crank I have not fire and no fuel at the rail. This thing has got me pulling my hair out. I took the grounds loose and cleaned them. I checked the battery. I'm lost some help please
94 wrangler electrical
- Thread starter Ddeweese
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greg92jeepxj
Official Supporter
Welcome to jeepz.com . Although I do not have the manual for a 1994 , I went through my '92 FSM YJ section. Knowing that the XJ has a feed from the alternator that powers the PCM , I thought I would confirm that on the YJ . Yes , as you would think , it has the same feed . On the back of the alternator , there is the field connection . It is a black plastic or bakerlite square that is bolted to the rear of the alternator. On the '92 YJ wiring harness it's an 18 gauge wire tan / black tracer that powers the PCM. The '92 has a four wire harness disconnect . Hoping this is relative on the 1994. The ignition coil d alternator along with injector harness , TPS , idle air control motor , temp sensor(s) oil pressure and the like , the alternator would have gotten disconnected in the engine pull . You'll want to confirm there is connection . Do check across all fuses for power . The ignition switch is fed from the PDC from the same fuse as the starter relay. Understanding your feelings on how can this happen on an engine pull when not too much electrical would be disconnected but since this is in fact occurring , these are items that will have to be checked. I believe power is lost to PCM but the starter circuit has lost power as well and the ignition is likely to be why . I'm not suggesting to replace the ignition switch but to confirm if power is present or lost there. BTW , an 8 gauge red wire from the alternator feeds two 50 amp maxi fuses in the PDC. I think those are marked as ignition fuses in the PDC in my XJ , ought to be the same in your '94 YJ ? To me , this seems to point to the alternator wiring which feeds PCM , ignition coil and injector harness ground , all from the field wiring. This is a good place to start since your wrangler is showing signs of power loss in terms of volts. It worked before the pull , try to imagine how the wiring would have been done from disconnect to reconnect . A lot going on in a motor pull , I know . A lot to recall . Went through this last summer on a ford van engine pull ( front subframe drop , actually ) . Although ford and jeep are apples and oranges , the system's aren't worlds apart , just different connections. Anyway , I'd get out the computer safe test light and start probing for power with the key on . The really strange thing is that the dash is lit without the ignition on just by reconnecting the battery ? Before even turning the key to ignition on , go over your connections to confirm them . I'm sure you've got all the right wires in the right place but I'd pay close attention to the alternator field since there is so much responsibility from it to powering the posted items which your having issues with now. No crank , no spark or even power at the positive side of the injectors ? This sounds like the PDC isn't getting power to the 50 amp fuses . I really hope this helps .
greg92jeepxj
Official Supporter
Something I neglected to ask which may or may not be of significance ; does your wrangler have a security system ?
I'm not sure if it does or not where would You find it
Pulled the altanator everything is hooked up properly to the black plug and I have power across both 50 amp fuses and on that note I checked all fuses under the hood and dash none are bad. As far as the alarm I don't see anything. Maybe another clue I have power to the radio and the heat when the key is turned to ac and the check engine lite stays on.
greg92jeepxj
Official Supporter
If there are no fuses or relays pertaining to a factory security system u dear the dash or power distribution center , I would have to say your jeep dosen't have one. Was only asking to rule out the system is armed and preventing the starter circuit from enabling. Since the accessory position shows life , the ignition switch is getting power . Now your question is " where is it going ? " it may involve getting under the steering column to probe wires but that shouldn't be necessary before checking things like the power lead to the ignition coil which is fed from the PCM . Other things to check are power to the injectors . When the key is on , the positive side of each injector plug is live and the ground is live only when the PCM grounds each injector in a sequential order to fire them . This won't happen now since there is no crank. As you know , the priority is to get it to crank. It is also good to see if sensors are receiving power . Techs usually start a check like this at the TPS . Easy to reach . Not concerned at this time for feedback ( signal ) but if the PCM is communicating to sensors. Although this is not what is causing the no crank , we will need to know if this is in order to get the engine to start once it cranks . If voltage is read at the starter from the battery at the big lug with the key on , I'm guessing there is no reading in CRANK position at the solenoid connection on starter ? Your first post mentioned a shift up light . Not very familiar with the wrangler dash . Correct me if I'm wrong , you mean this is a manual trams ( which are on many or all four cylinder ) ? That's usually the light which tells you not to over rev the engine in that gear . If so , then there is no neutral safety switch imvolved . Just wanted to rule that out for the no crank. At this point , pull the starter relay and check if terminal 30 is live with key on . The ignition switch in CRANK is supposed to send volts to terminal 85 to activate starter . If nothing found at terminal 85 when in CRANK but terminal 30 live , jump 30 to terminal 87 to see if starter cranks . My '92 FSM says fuse #4 is for the starter terminal 30 . Terminal 85 will come from ignition switch. The engine light is showing a fault which must be the no crank condition . The auto shut down relay must be picking up maybe a back feed and kicking back to the PCM. Again , realizing that not much in the way of wiring harness gets disconnected that would involve this kind of problem so I understand why your having difficulty . But you obviously have no choice but to check every circuit that pertains to the starter to find the fault. Interested to know what you find when checking the starter relays terminal 30 & 85 key on and in crank .
greg92jeepxj
Official Supporter
You mentioned no fuel . No tone from the fuel pump with key on ? Will need to check if fuel pump relay is active as soon as key is turned on to RUN position when PCM primes pump . You may have to pull,the relay and put jumpers from relay terminals to socket terminals to probe terminal 30 and 85 as soon as key is turned on. This should all be done with a computer safe test light every time you probe a wire which feeds back to the PCM.
greg92jeepxj
Official Supporter
The fact that your starter isn't engaging needs to be diagnosed . A starter will ground upon bolting it on to the engine block or transmission bell. Are all body to chassis and engine to chassis grounds installed ? Is there any reading at the starter lug of battery voltage ? I am assuming that there is no current at the solenoid wire on the starter when the key is held in START position ? If you suspect a ground issue , you can try a battery jumper from the battery negative to the engine block. But I am interested in if any reading is found at the solenoid wire on the starter solenoid . That will tell us if we need to deal with the ignition switch. The thing that has you ( and us ) boggled is that it ran when you drove it in and with no issues other than a sick engine so what happened since ? That is what we're chasing . If we can't get the engine to at least crank , we can't look for spark or injector pulse . The power wires at each injector should be live with the key ON . No fuel pressure is read key ON ? No tone / hum from fuel pump ? You mentioned with the key in the off position the dash lights ? Am I right ? Please recap as I don't want to misunderstand or misdiagnose . I'm not a pro but do have some experience . Would like to help if I can . Hope my factory shop manual can too .
greg92jeepxj
Official Supporter
Just thought I would ask , is the computer and oxygen sensor grounds bolted on where the battery negative grounds to the engine block ?
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