Drew Scott

Going down the hwy suddenly oil pressure kinda jumped around a few times then hit 0 had no response from throttle so I put it in neutral and shut her down ... since then I have replaced fuel pump relay and oil sending unit and both were bad now it will start with starting fluid or gas then die no pulse from injectors but i do get 12v on them both ... i think its worth mentioning a few months prior i noticed a broken ground strap the one from firewall to back of motor I was unable to access it and ran the ground up top where the battery ground goes... but have since got it back where it belongs I had an extra battery cable and used that should I swap it for an actual ground strap? And shouldn't there be 2 grounds back there?

Sabino56

It is a good start to make sure your grounds are good/clean. I can’t remember where they all are - one to firewall, one on back engine, one on CTS - but maybe more. Hopefully someone who knows will come along.

It it sounds like a sudden death think so wouldn’t be surprised a fuel relay go bad and kill things, but a bit surprised a oil pressure sending unit go bad at same time. How’d you determine the oil pressure sending unit was bad?

there is also a fuse, I think, for the fuel pump on firewall in a holder - did you check that?

Drew Scott

I did check that fuse and replaced even though it tested good I'm unsure of it's age. As for the sending unit iirc the new one read 1.6 ohms and the old read .2ohms as well as when I try to start it now the oil pressure does climb as before the gauge stayed 0... it may well have only been the wire going to dash that was bad that I'm uncertain of... I also forgot to mention I replaced the temp sensor not that I think it is related in any way, as for grounds I've cleaned what I've found.... battery to block alternator to block firewall to frame and firewall to back of block... I'm sure there's more I've not found

Rednucleus

Change out the ICU in the distributor

Sabino56

actually, seems like I've heard on some years the fuel pump relay was enabled by oil sending switch - or something like that so if that's true perhaps the oil pressure switch going out and killing the car isn't surprising. Doesn't explain why it won't start now however. I also seem to remember there is a test port or way to force fuel relay on for diagnostics - but don't know that for sure either.
I have the schematics for a 93 at home but I won't be able to check until the weekend. Figuring out if you're getting power to fuel pump and if not, why not seems to be the next step. Sorry I can't help more now.

Drew Scott

Fuel filter looked pretty rough so replaced.... I have fuel in the injectors... I pulled them and was easily able to blow the fuel out so they are not clogged and I'm getting fuel up there.... I think pressure test is next maybe weak pump isn't giving the full pressure needed?

Sabino56

Checking fuel pressure is a good idea. Here is link with info on how https://www.chevytalk.org/fusionbb/s...php?tid/253427
I found it easiest to check after fuel filter (frame rail, driver side) as you can release the fuel lines from retainer there and get space for adapter.
Make sure you check that fuel pressure remains good (higher than ~11) even when hitting throttle. I had problem where pressure was marginal - around 10ish and would drop with high throttle. . It would idle OK but a lot of drivability problems. Turns out pump was just cheap. I had bought an autozone pump. Replaced with an ACDelco and had solid 13 all the time and no more drivability problems.

I found the schematics for your truck and it may explain some of what happened.
The fuel pump relay is turned on by PCM pin 6 - pin 465 on fuel pump relay. This comes on when key is turned and primes fuel pressure prior to starting (runs for something like 2 seconds if you turn on key and don't start). Pin 120 on fuel pump relay is 12V to fuel pump. Note that it is tied to pin 120 on oil pressure sender and it also has relay in the oil pressure sender. It looks that the oil pressure sender is backup to the fuel pump relay. If you have good oil pressure, it will also provide power to fuel pump even if fuel pump relay is bad. The opposite isn't true - bad oil pressure won't kill your fuel pump.

So, a possible scenario was that your fuel pump relay was bad and you've been running on your oil pressure sender relay. If so, when your oil pressure sender went - you'd lose your fuel pump power also. I would think relying on the oil pressure sender to power the fuel pump would make it hard to start - you'd have to crank long enough to bring oil pressure up before fuel pump would turn on. Did you have that problem prior ?

Regardless, since you replaced both - that shouldn't be the problem now. If you check your fuel pressure, you'll know if the pump is on or not with key on. However, if you haven't done that yet - you might want to make sure you are getting 12V to the fuel pump. Note that 12 V to fuel pump relay and oil pressure sender is thru a fusable link. This is in addition to the fuse you checked (between the relay and pump). If oil sender shorted when it went bad it could have taken that link out. If it did it would also have taken out power to a line going to the PCM also - E16 and probably other stuff. Should be easy enough to check at fuel pump relay connector. Note you can also jump 440 to 120 and supply power to fuel pump directly if the fusable link is good. The last bit on this is that the normally closed position on relay connects pin G in ALDL connector under dash to 120-power to fuel pump. 12V on pin G will turn on fuel pump. This was the diagnostic thing I couldn't remember w.r.t. the fuel pump. I would imagine some factory testers did this in past. It'd be easier to jump relay connector for manual diagnosis.

I wanted to confirm that engine will start if you put starter fluid or gas down the TBI? So it appears ignition is OK at least in limp home mode.?