no spark or fuel unless B+ and FP are jumped

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4camSC

New Member
Hi ya'll,
I've got a '97 sc400 that I swapped the engine from a 94 LS400. I swapped the engine to OBDII with the sensors/wire harness/cams etc. from the newer engine. After getting it together I could not start it. Upon closer examination, I found no spark, check engine light on the on position, or fuel. I then tested my FP with 12 V and it worked fine. Before I swapped it, it ran (sort of, due to the previous owners abuse). I thought it was the ECU after checking the cam and crank sensors and the ignitor's ground. Well, after further research I put power to the B+ pin and to the FP and managed to get it to run (roughly).

Any thoughts on why the fuel pump and the ECU won't come on unless jumped?
 
Are the connectors beside the fuse box plugged in tightly? Are the connectors on to the ecu in good condition? I had one the other day where one pin on the ecu plug wasnt tight causing and issue. Fortunately a quick test found it. Do you have connection with the OBD2 port for live data?
 
I have checked the connectors several times, however the wire harness is slightly cooked so that is no guarantee. I believe that the connectors to the ecu are good because I have checked them and the problem happened before I even touched the ecu. The OBDII reader says the there is no communication with the ecu, and the check engine light only comes on intermittently when I crank it with +B jumped. Could the problem be a EFI main relay? When I turn on the ignition switch, power goes to the 40A fuse in the kick panel and then I can hear the EFI relay in the under hood fuse box click, but power does not go to the ecu. Just for grins I replaced the 40A fuse because it was corroded, but nothing changed. By the way, I bought another ecu thinking it was the capacitors at fault, but it changed nothing.

Thanks for helping.
 
After going over the engine very thoroughly, checking the connectors and the sensors, I found that several grounds were faulty, I had not connected one ground for the ecu and the OBDII port on the back of the engine, and the top connector on the fuse box had a couple pins that had worked themselves out. After I fixed those, it started right up, but it bogs down and has an unstable idle. Thanks for pointing out the pin and connector possibility gloverman.
 


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