1991 TBI 350, rough idle cold or warm, OPS/FPR? What are these relays?

[RockBottomRacing]

1991 TBI 350, just changed out the ignition module and that got rid of all my codes, but she still stalls out at start, cold or hot, doesn't matter. Curious if its my oil pressure switch. Also, on my firewall, I have the bracket for two relays, one of which is occupied by the fuel pump relay, however, there is no relay in the second slot. Can anyone confirm its where they would have a downshift relay for a truck with a TH400? See image, #14/16.

Thanks!

View attachment 224751

 

[frankin5]

The second relay is for the 4l80 trans, it is not required if you have a 700r4. #14 is the fuel pump relay on all model of TBI.

 

[1-ton]

I do not think any 1991 truck came with a Turbo 400 as original equipment. My 1991 V3500 came with a dual bracket relay set up as well, but only one relay is used.

 

[RockBottomRacing]

That's exactly what I needed to hear. Sounds like we have a similar set up. My 700R4 functions just fine

Now I'm trying to figure out my rough idle issue. I'm not getting any codes currently. I haven't checked my fuel pressure, but previous owner supposedly changed fuel pump and rebuilt the throttle body polished the bowls and put a new fuel pressure regulator in. It has a new IAC. I'm about to change out the Coolant Temp Sensor (the one in the intake for the ECM). Contemplating changing the oil pressure sensor behind the distributor and the fuel pump relay.

Any thoughts? Run's good once I rap the throttle a few times after start up stumble, but if I shut her down, then fire her right back up it does it all over again, even stalls out.

Thanks again!

 

[Overkill6x6]

Have you checked to see if the egr is stuck open? Or carboned up?

 

[RockBottomRacing]

I pulled the vacuum line off the EGR valve with the engine cold, no vacuum in the line, no flow through the valve. That being said, I did have codes 32 and 33 before I changed the ignition module. I drove her around a whole bunch yesterday and no codes popped. I have the dual Windstar fans (to individual toggles) but I'm pretty sure there's no thermostat in the engine. I'm gonna install a 190 degree thermostat, the new coolant temp sensor (in the intake), clean the EGR valve, replace the fuel pump relay, then run her to 210 and turn the fan on and take it for a few passes and see if I pop any codes. If not, I'm gonna unplug the O2 sensor and see if I get any changes, hopefully that will let me know if I'm looking at a problem with sensors or if I should start looking into other problems.

 

[1-ton]

I pulled the vacuum line off the EGR valve with the engine cold, no vacuum in the line, no flow through the valve. That being said, I did have codes 32 and 33 before I changed the ignition module. I drove her around a whole bunch yesterday and no codes popped. I have the dual Windstar fans (to individual toggles) but I'm pretty sure there's no thermostat in the engine. I'm gonna install a 190 degree thermostat, the new coolant temp sensor (in the intake), clean the EGR valve, replace the fuel pump relay, then run her to 210 and turn the fan on and take it for a few passes and see if I pop any codes. If not, I'm gonna unplug the O2 sensor and see if I get any changes, hopefully that will let me know if I'm looking at a problem with sensors or if I should start looking into other problems.

If you think your fuel system is in good working order, then try looking for vacuum leaks. Bad, missing, or disconnected sensors will not stop an OBD-I engine from running because there is a limp mode the ECM will run in if they have to.

 

[black dawg]

What is the fuel pressure, and what does the fuel pressure do when it is running crappy