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87 4.0 NO START

fourplayoffroad

NAXJA Forum User
Location
gresham OR
so I almost have my dovetail project done I plugged my wiring harness back together hooked my grounds up made sure every thing was tight and clean now the POS won't start WTF:gonnablow!!! it turns over everything works but I have no power to my coil or fuel pump. i've checked my fuses and fuseable links it's all good. I'm not the best at electrical so if anyone could help or knows what's going I would greatly appreciate your input thanks! it's an 87 xj with 4.0 and auto
 
if it is not getting power to the coil you should check to see that you plugged in your CPS or make sure that it is still good if it is indeed plugged in....
 
CPS CPS CPS CPS CPS CPS CPS CPS CPS, oh, by the way, did I mention CPS?
 
MAP, IAC, and TPS will make it run like crap, but it will fire up.

CPS is the only sensor that will keep it from running.

Check for spark, check for fuel and pressure. If you have air, fuel, compression, and spark at the right time and the right place it will run.
 
he said that it had no power to the fuel pump too. if the cps had gone bad there would be fuel psi but no spark. it has to be deeper into it.
when you were workin on the truck did you have the battery out or disconected when you were welding?
if not you mighta burned a goin to either part.
 
How did you verify that u have no power to the coil and the fuel pump? Sounds like you may be better at electircal than you think. Start with a wiring diagram, check for other areas without power also. I think you may have just missed something, or meleted a wire somehow... Some of the 87's were known for melted wires.

Also what exactly did you do to the vehcile that made you unplug the wiring harnes? That would help us if we knew.
 
I had to remove the battery and all the wiring from the inner fender wells so I could cut and do the dovetail. I disconnected anything that would prevent me from getting the wiring out of the way of my work area I know that could go alot of different ways but I tag everything that I unplug. The battery was out of the rig the entire process, first I put an inline spark tester and found no spark so then I unplugged both connectors from the coil and tested with a test light nothing at any of the wires same at the fuel pump. I have looked over and over to see if I had missed a connection or a loose connection pinched or burnt wire and found nothing. Im not all that good at wiring diagrams I attempted to read and try to understand it but it's just to confusing to me im excellent at fab work and other areas but for some reason never got into electrical. I hope this helps any other questions feel free to ask and I'll be more than happy to give you as much info as I can or if there is some other ways that I could do more testing at different connections or parts,relays? just let me know and thanks for all your input!!!
 
Not sure if the 87 same as 90 so I will use the Haynes:

Ignition control module has a yellow wire that runs to the ECU, and another yellow wire that runs to the fuel pump relay and on as a org/blk wire to the ECU.

The fuel pump relay has the yellow in from ICM and org/blk out to ECU, and Red in from fusible link (off the starter relay power distribution) and an org to org/blk to the ECU.

Does any of that help?
 
When you are checking for current at the coil and the fuel pump, is that while cranking? Later models (and I think yours too) only get current for 3 seconds in run unless ECM/PCM gets a signal from the CKP (crank pos sensor). While in start, they get current too.
 
thanks for the break down of the wiring I will deffinetly look for those wires and check them out. Is the starter relay that you mentioned silver in color and metal with 1 post and 3 spade terminals that a bunch of fusible links go to? I had some one helping me and I was checking for power both with the key on and while turning over and there was nothing either time should I leave the coil plugged in and probe the wires with a test light instead of checking them while unplugged from the coil? thanks guys!!
 
thanks for the break down of the wiring I will deffinetly look for those wires and check them out. Is the starter relay that you mentioned silver in color and metal with 1 post and 3 spade terminals that a bunch of fusible links go to? I had some one helping me and I was checking for power both with the key on and while turning over and there was nothing either time should I leave the coil plugged in and probe the wires with a test light instead of checking them while unplugged from the coil? thanks guys!!

Yeah, that is the relay and fusible links.
 
ok, so you know that when you disconnected the wiring that something happened. Its better than buying a new coil and a fuel pump.

I wish I had more for you, but you'll find it.
 
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