Hello again everyone! I have a 91 Firebird Formula, LB9 with the 5 speed manual. Here's the issue.
It started with an intermittent fuel pump. Decided to do the hardest part first and replace the fuel pump. I needed to replace the rear arm bushings and shocks anyways so I figured why not. Also did the distributor rotor and wires.
Sure enough, ground was melting at the connection to the fuel pump inside of the tank.
Replaced it AND and sending unit. Pump runs great, sending unit... Might have gotten stuck during install because I only read up to half a tank. The ohm reading is correct for the fuel gauge to read at half so 🤷
THEN the relay went out. Cool, new relay. But still it would die out. Traced the ground for the harness inside of the car, and it was ROUGH. Fixed the ground, and boom. No more issues. UNTIL
I replaced the starter positive cable... One of the old ties came undone and one of the pulleys rubbed through the cable causing it to arc over bumps. Got that fixed and now... I'm absolutely lost and confused. The car WILL NOT activate the relay. I get 7 volts from the computer ok key on and like 1 ish after a few seconds. Cool. But the relay won't switch... Easy enough. Sent ignition voltage into that post of the relay so that my fuel pump kicks on when I key on. But it STILL WONT FIRE OFF!
I got a can of starting fluid, and bam. Fired up, died, and fired off again but this time stayed running.
Drove to work and realized something wild.
The car will not fire off until the oil pressure gauge reads above 10 PSI. During a cold start, I can crank until it builds that pressure, check engine light blinks twice really fast, and she fires right up. But after it gets warm it won't build enough pressure to start. I have to give it a shot of ether.
So... WHY?! I thought that the oil pressure switch only controls the fuel pump? And second, I know I have spark because the starting fluid works.
So since when did the oil pressure switch control injectors?? Or am I missing something??

 

Ops is backup for fp relay. It closes at 4psi. What is the voltage at ops and ecm content powers ?

 

I didn't bother checking voltage since I have the fuel pump relay paralleled into an ignition source. Took the ignition source and spliced it into the "on" signal wire that goes from the ecm into the fuel pump relay. So OPS no longer controls the fuel pump at all.
Fuel pump is working great, spark is working great, but it's acting like the injectors won't kick on until the computer reads enough pressure... Which doesn't make sense to me for this car.

 

why not diagnose the electrical problem instead of reinventing the wheel , smh

the injectors will not pulse until the ecm sees 400 or higher rpm. But you could have several issues. Low voltage at the ecm. Faulty ecm. Possibly a bad ground. A bad iac or pu coil or magnetic pole. Or low resistance /shorted injectors. Just a few things to check

 

Hard to do sitting on the side of the highway. Had to get running as quickly as I could. Tiny jumper from an ignition source did the trick. It's my daily driver as well. Waiting for my days off to REALLY dig into it.
Now, as I said previously, the signal coming from the ECM to the fuel pump relay is there. It's showing 4-7 volts and cycles down to .4 v during its prime sequence. Which is why I went ahead and just bypassed it for the time being.
STILL though... Why would the injectors not pulse until it reads pressure? I thought that only VATS could keep the ECM from sending signal.

 

the 1227730 does not read oil pressure, good luck might make some time to properly diagnose.
It’s not a vats issue. Might buy a fsm and educate yourself.

 

I am not suspecting vats. I was just stating that I couldn't think of another system outside of vats that could keep the computer from sending signal to the injectors.
Everything sensor wise is golden excluding possibly the OPS. The only thing I have not dug into yet is the main harness and ECM connections. It really wouldn't surprise me if I had bad grounds in places. I've had to fix two or three already. I'm doing everything I can to keep things as stock as possible as well. This is a 1 of 2 made going off the RPO codes. Manufactured on the 7th day of production. I just find it really neat. I may get a new wiring harness soon though because this one does have a few spots of corrosion.
If anyone wants a lesson out of this, don't let the positive cable to the starter ground out on the engine. 😅 0/10 do not recommend.

 

Did you check the fuses? Grounding the engine/frame/body with a positive lead will either blow a fuse or melt the wire. Recheck grounds also. Could have lost connection after ark due to carbon build up. Low voltage/melted wires is usually caused by bad grounds. Good luck to you brother 💯

 

That's also what is driving me nuts haha all fuses are good. No obvious wire damage other than the spot on the old cable where it was touching. I appreciate the good luck. Looks like I'll be needing it!

 

UPDATE!
This morning I realized that when I key on, the SES light doesn't come on. I jumped the diag port, and nothing.
Checked voltage at fuse block. 12V.
Got the computer down and checked voltages. Neither of the two constants in the plugs had voltage.
Checked the plug coming from the battery. 12V
Checked the wiring diagram, noticed that the Orange constant from the battery split somewhere in the loom. One goes to the OPS, and two others go into the computer.
Got a little bare wire on both Orange Constants that lives in the harness past the OPS going into the computer. Sure enough, no voltage.
So, my best guess is that ONLY when the OPS sees pressure, it allows voltage into the computer. Not sure why exactly unless the switch itself has a ground fault when opened.. maybe..
I took two new wires and placed one end into the Constant Hot group that comes off of the fused section for the fuel relays. I then simply poked and wrapped those into the constant hots for the computer. I DID NOT cut and splice. Technically, the OPS is still in parallel.
The added constant fixed it! Everything is alive and she starts right up again.
Next I will get a new OPS and take out the added constant to see if that was in fact the issue. More updates to come!

 

It’s wired like this, as I said before the ops has nothing to do with ecm operation. It’s backup for if the fp relay fails. See schematic.

 

 

This is how it is "Kind of". Instead of the fuse&holder, there's a two wire plug coming from the battery. The red from the plug goes to the fuse, turns into Orange from the fuse, and spits off into the constant hots for the relays on the firewall, and the orange from the plug disappears into the harness behind the engine bay where at some point splits into the three hots. One for OPS, Two for computer.
I understand that what you're saying SHOULD be the case. But for some wacky reason, it isn't. Once I added new constants into the harness past the three way split, everything worked as it should.
I would chalk that up to a bad split if it wasn't for the fact that once there's oil pressure, the computer gets power.

 

Nice job diagnosing the problem. I like that you didn't let wiring diagrams dictate your diagnosis and kept a hands-on approach. This isn't the first time I've seen a problem that "shouldn't" exist because of the way the car is wired.

I once had a pretty long argument with a moderator on a Dodge forum after I did something similar and fixed my problem. Moderator told me the problem I had was impossible because the factory wiring diagram didn't show that could ever happen. All the wiring on that truck was original, and he didn't like me suggesting he spent too much time giving advice online and not enough time getting his hands dirty. Haven't been back to that forum since. It was full of idiots. The kind of guys who work for Autozone 30 years stocking parts on shelves and dishing out repair advice based on "30 years in the automotive repair industry".

 

Much appreciated! I am really hoping that a new OPS fixes it. Only time will tell. At this point though, I'm just kind of waiting to see what fails next. 😂

 

Great thread! Good work!