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engine won't stay running

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Dogman12

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Easthamptom Ma. 01027
I have an 85 jimmy and swapped in an 89 fi from a blazer, the truck fires and runs but after it gets warm it will stall out if I dont keep my foot on the gas. The fuel pump does not get the 2 second prime and I think it is staring and running off the oil pressure switch. It will start after the second try and run for about 8-10 min before it tries to shut down, it idles smooth after 3-4 min as it warms the oil pressure guage starts to flutter i and out as the truck tries to die, if I plug into the fuel pump relay red bypass wire it will stay running if I keep feathering the gas a bit. If i let it stall it will only start if the relay is in bypass or i pray starting fluid into the throttle body. I am not sure if it a wiring issue a fuel issue or somthing like the cts gone bad. It is 4spd and I have the correct ecm, the fuel pump relay is new and did not help any. I do not have the vss or the aldl wired up yet so i cant check the codes. Im am not sure where to look next any help will be appreciated.

Jesse
 
Make sure the relay is wired correctly, orange should have battery power, tan is out to the pump, green 12v from computer, black is ground.

Check the base timing with the single tan/black wire disconnected, it should be set at 0.
Check to make sure the oxygen is wired correctly and is reading voltage.
If all else fails get the ALDL wired up so you can get some scan data.
 
Thanks for the reply, first thing when it warms up I am going to check the timing and wire the ALDL, I checked the relay over and over one more time wont hurt.


Thanks
 
I had some time and checked the wires to the relay, orange good, tan had power when truck was running, green was dead. no signal from the ecm. I used the bypass on the fuel relay and was able to take the truck for a short drive it stays running as long as it is bypassed, it will start of the oil pressures switch but tries to cut out after 15 min and will not restart unless I bypass. What would cause no 12v from the green wire? and do iol pressure switches go bad?

Thanks
Jesse
 
If you aren't getting a signal from the ECM, it's possible the ECM isn't getting a signal from the ignition module.

Oil pressure switches do go bad, not real common, but everything fails sooner or later. Pump should stay running if the oil pressure switch is working correctly of course, it only takes at most 5PSI of oil pressure to keep the switch closed.
 
When it starts to die the oil pressure gauge flutters and hits zero and this causes the pump to sputter and the truck to stall. I can keep it running if I keep my foot on it a bit, I plan on checking the OP with a mech. gauge, the motor sounds quiet and smooth the whole time no lifter noise at all so I assume it still has oil pressure it is almost like there is a restriction in the switch. I checked the oil when I changed it besides having fuel in it, it was clean. So I have two problems no fuel pump signal and the back up to the relay oil pressure switch flutters and shuts the pump off after it warms up. Dyeager I replaced the distributer with a reman, if it runs then the module should be good? if there is no signal to the ecm it would be a broken wire? I am going to go through the pins for the ecm with my test light and wiring diagrams and see what I find. I hope I dont miss all the snow wheeling.

Thanks for the replies
 
The oil pressure switch and the sender for the gauge....are yours separate?

Later on they were combined (three wires) but earlier were two wires for the oil pressure switch, one for the gauge sender. So if they are separate, and your oil pressure switch AND sender are indicating a lack of oil pressure, something else may be going on.

I posted up some wiring diagrams (my name as thread strater, troubleshooting as the thread title) the "crank no run" chart should help, as I believe it lists the steps to test the module to ECM signal.
 
It is the long cigar shaped unit, I can not picture how the wires run from memory, you have me wondering if i have the wire that should go to the ecm going to the gauge side and vise-versa. I think i have your crank no printed. My truck had the computer controled carb with the early ecm so i used the pink and black wire for hot at crank and run and the orange is off its own fuse panel i wired off the battery. I did run two seperate wires one to the oil pressure switch and one to the main 12volt supply for the harness both from the same fuse panel. I never unhooked the harness from the engine, just took of the cruise wires and the auto tranny wires off. I did take the oil switch off as i ws not going to run it but read it id hurt so I put it back on, mayby backwards? If it more then 10 degrees Sunday maybe I can look it over again.

Thanks Again

Jesse
 
After alot of trouble shooting and time spent out in the cold, it turned out to be a bad ECM. Truck is running pretty good only code I get is from no vss.

Thanks
 
Sorry I didn't follow up on your previous question, I must have missed it. :(

Glad you got it running though, good job troubleshooting. Very rarely is the problem the ECM, but apparently you had one of those instances! :)
 
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