Printable View
5.3 in a 98 chevy truck. It ran great for two weeks, no problems. Now it keeps running when I turn the key off. I disconnected the ignition power wire from the truck to the pcm/harness (wired standalone, so one power wire from teh truck to the 5.3 harness) and it kept running, so it's on the pcm/engine side, not the truck side. Any ideas where it's getting feedback power from after 2 weeks of running properly?
Sounds like a shorted ignition relay. Who's harness did you use?
Speartech. There is no relay on the harness side after where I disconnected power, just the single pink wire that you put ignition switched power to that power everything in the engine harness. When ignition switched power is removed, it doesn't die. My thoughts are that it must be getting feedback power in some way, but I really have no idea.
I finally hooked my brake switch stuff up, I'm thinking since that's "normally closed" maybe it's getting power through that?
The only relay on the harness side is the fuel pump, and I did change that relay to check, and it made no difference. My first thought was a relay somewhere, but I disconnected ignition switched power after all relays and it still ran, so it must be coming from somewhere engine side
Two weeks is slightly misleading, it ran great for months, but then two weeks of DD duty once the exhaust was on, everything was functional, etc. I also wired the harness up myself, then didnt like the look so I sent it off anyways to get cleaned up.
Found out that if I unplug the oil pressure sending unit, everything works fine. It starts, runs, kills like normal. If it's plugged in and doesn't die with teh switch, I can unplug the OPS and it dies. Here's how I have it all set up if it helps someone come up with what's wrong making it do that.
The oil pressure sending unit does NOT go to the 5.3 pcm. It goes into the stock 98 harness like it used to on the stock 4.3 setup. I have no oil pressure going to the 5.3 computer.
The 98 truck fuel ump relay is NOT being used. There is a relay connected to the 5.3 harness that switches it on and off, and it is connected straight to the wire that used to supply the fuel pump coming out of the stock relay/fuse box.
Any ideas?
How many wires on the oil pressure sensor connector? The 98 4.3 used the oil pressure sender in the fuel pump wiring, the GMT800 trucks (that I'm assuming the engine came from) do not. The fuel pump seems to be wired incorrectly but that does not explain why the coils continue to fire.
It's a one wire sensor. I'm assuming it has to be this that's causing it, because if you pull any fuses to kill it (key already off, engine still running) the fuel pump runs for a fuel seconds after the engine dies, assumably till oil pressure is gone.
Whatever it is with the oil pressure sensor setup powers the complete underhood fusebox, not just the fuel pump relay, and that's where my ignition switched power comes from.
But how would a one wire sensor do that? It goes to the gauge? My GM schematic shows 3 wires on a 98 4.3.
Ahhh! Now I see. The 98 had two sensors (actually one sender and one sensor). There is no D&O in GM service information either.
The one wire sender should go to the gauge. It's a tan wire.
The other two wires on the stock 98 go to the other oil sensor. It has one orange wire and one grey wire that are in a parallel circuit to the power circuit for the factory fuel pump relay (bypasses stock relay if relay is stuck OPEN if there is oil pressure).
I'll have to think about it a minute to come up with what could be out of order. Post up the wire colors, where the sensor is on the swap motor, if the oil pressure gauge works when everything is hooked up, and what kind of sensor you have.
yeah, tan wire should be oil pressure. I'm not sure about the orange wire going to the sender if it's switched or not, hopefully it is or GM messed the wire color code up on that one. The grey wire used to go to the 98 fuel pump relay as a safety trigger wire for fuel pump power if I remember correctly and it goes in tandem to the fuel pump. Wiring is tough sometimes.
I am only using one oil sensor of any kind. The stock one from the V6 and it's put into the stock location for the 5.3 sensor. It has the single tan wire going to it.
I took the wire that went out of the stock truck relay out of the box, and wired it to a standalone relay on the 5.3 harness.
It seems they should have been isolated form each other that way, that's why it confuses me.
Then it's what you did with the relay rewire. The stock one wire dealio doesn't care if it's installed in an 8 or a 6...and that would not change a thing.
I've made steps in this swap WAY too complicated over and over. The stock V6 sending unit I'm using has three wires. I cut the two non-tan wires and made it a single wire connector. Gauge works, oil pressure won't keep it running now. Thanks guys!
FWIW, the 5.3 OPS was the one wire, I was confused.
Whew!
Takes some work sometimes but.....it seems fixed.
Good topic, especially since from time to time people recommend checking the OPS when a GMT800 fuel pump won't work (even though the pump is NOT wired through the OPS on the 800). An 800 doesn't need oil pressure to run!
You are correct, I have no oil pressure info going to the 5.3 pcm at all. I only ran the original truck's sending unit, and it's only wired into the old harness.
I didn't realize this truck could bypass the relay in the event of a failure. That's something people should know.