I have been working on swapping a LM7 into my '91 Volvo 240 for ages now. It has basically been sitting since November with a wiring issue. The car has a LM7, PCM and wiring harness (including fuse block) out of a 2001 Silverado. The PCM was reflashed to remove VATS and secondary O2 sensor functionality.

The car will crank but there is no fuel, spark etc. UNLESS I remove the O2A fuse from the fuse panel (circled). When I pull that fuse the car will start. It runs and drives but it throws all of the trans solenoid codes, will not shift through the gears (seems to be only in 2nd or 3rd all the time), and does not charge. I thought maybe it was a ground issue and realised I was missing one of the grounds from the back of the DS cylinder head to the firewall. I added that ground but it didn't make a difference.

Also, on a side note, when I key-crank the car I can hear the solenoid click but it does not turn over most of the time (maybe 1/30 tries) but I can jumper-wire the solenoid to the battery and it fires right up.

Any ideas what it could be? This car has been 95% ready to go for like a year and I'd really like to wrap it up.



Here's a link to a thread I started last year about the trans codes;
https://ls1tech.com/forums/conversio...ans-codes.html

 

I'm guessing that this is a harness you modified yourself, correct??

It sounds to me like you might have more than one thing going on here. Have you measured your voltage at the terminal of the starter? This thread has some good info on troubleshooting that issue. I'm not entirely sure what to suggest on the transmission issue, other than to trace back each wire, probably starting with those connected to the transmission...

 

Thanks! The weird thing is that the fuel pump and ignition does not fire with that 15A fuse in place, but when I remove it, it all works. I did modify the stock truck harness per LT1swap.com's instructions but the trans wiring is all original/un-touched. I'm still thinking it is some battery cable or ground issue - I put a new negative cable on it but it only goes from battery to block (old one went to block & inner fender). I am thinking I should mess around with that some more. The positive cable is also split with one half going to the starter and the other to the distribution block on the inner fender. Both wires are just clamped into a generic battery terminal post which is also probably not great.

None of this explains why the O2A circuit kills everything though.

 

OK, it sure sounds like that 15A fuse is providing a short-to-ground condition, where maybe it's not moving a lot of current, but enough to prevent those two circuits from operating. And until proven otherwise, I'm going to assume that the trans wiring is correct, since it's untouched from the factory configuration. So - what do the fuel pump & ignition have in common??

Also - just to rule out the simple/stupid stuff, perhaps get the body grounded, & confirm positive voltage values at the starter terminal & distribution block. Those won't be the primary causes of the issues you're seeing, but they could be contributing...

 

the area that harness travels to get to trans is notorious for being smashed/pinched while R&R
may even have something to do with neutral safety switch.
Have you unplugged all the connectors on trans and tried it?
will need to fool the neutral safety circuit
is the fuel pump relay engaged when you turn key on?

 

Neutral safety switch makes a lot of sense. When the O2A fuse is in the fuel pump does not cycle at key on. I wonder if it is on the same circuit as NSS. I will look into that, thanks!

 

On second thought, the neutral safety switch does function correctly when the O2A fuse is not in place. So now I'm thinking that is not it.

 

Thinking about it a bit further, I think I have two neutral safety switches hooked up. The original Volvo switch from the shifter and the GM switch on the trans. So the switch could be the issue as it still cranks, just no fuel/spark - which points to the GM switch.