91 F 150 with 5.0 2wd
The truck isn't running right. It dies on me sometimes and it has a little bit of a looping idle and when I have stopped it would die but I quit driving it on the road. I got it started again by cleaning up the grounds and putting a new battery in it and replacing the fuel relay. So far I have tested and replaced the EGR valve control solenoid it failed so I replaced it but that did not fix my issue but EGR system checks out.
I tested the map sensor because I got codes, koer, 12, 22, 16, 73, 25 but truck died during test. This led me to think map but I tested it, got 5vdc at power in, backprobed 2 signal wires with koeo and got normal hz readings, applied vacuum and everything checked out. I can't afford to hit it with the parts cannon. Truck used half a tank of gas on a 40 mile test drive after I thought it was good. At one point I thought maybe I messed something up with the pcm when I removed it to check the capacitors for leaks. But that was when I discovered the bad fuel relay, was swapping the relays ignorantly leading myself on a pcm failure hunt. Replaced the fuel relay and the new issue of using to much gas and weird running/dieing happened. I had replaced the distributor sometime back but the truck ran fine for a couple months and I parked it because I got a new work van but now that van is crapped out and I need this truck. I don't have a timing light or know how to check the timing but does anyone know if the timing being off slightly would cause this issue or combination of issues?
​​​​Also I replaced the oil pressure sending unit with an adapter and a mechanical oil pump would that affect my fuel usage?
​​

 

It’s cheap to clean the IAC, if you can get throttle body cleaner and a gasket for the iac you can clean it just hold the computer part up above the part you’re cleaning so the cleaner doesnt ruin the computer. Should be $10-12. I cleaned my IAC and it fixed a loping idle when it’s on the high idle at startup. I think there’s more to the issue though. Or unplug the IAC and see how it runs from what I’ve heard that’s a way to tell if it needs cleaning/replaced.
Im no expert so take that with a grain of salt.

 

Half tank in 40 miles? That is what..4mpg? Is your fuel pressure regulator bad? Pull the vacuum like off when and turn the key on and if fuel sprays, then it is leaking fuel straight to the engine.

 

You posted engine running codes but what did you do to repair the engine off codes? KOEO test needs to be done first and any active codes repaired before moving on to the KOER test. It is possible the new/reman distributor has failed but you cannot jump to any conclusions just yet.

I suggest you invest in a timing light to set the timing. If you can, get the truck up to operating temperature, shut it off, remove the SPOUT connector, restart the truck and then set the timing to 10° BTDC. Turn off the engine and reinstall the SPOUT.

 

Also in past the smog pump locked up and I just removed the pulley and put a shorter belt on, anyone think this would have caused issues. I figured out how to clear memory codes and am no longer getting the 22 code. I know I need to do the timing test to properly koer test working on getting a timing light now. But still trying to fix in meantime and now I'm only getting a 44r code, I have no koeo codes, chased the vacuum lines, repaired it, think it was to the idle air control valve, thing in back left that goes the tad solinoid, anyway it didn't fix it truck runs same. Cleared codes again and tested, snill nothing for koeo, koer 44 code still. Will be testing that fuel regulator like mentioned, thanks.

 

Did you test this code.
12 Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too low) - ISC

 

Okay I'm stupid, the vacuum leak wasn't the iacv, it was something on the thermactor system that goes with the smog pump. Anyway I am going to clean the iac as soon as the rain stops, kept thinking the iac was the tps. Any advice on how to test the iacv and the coolant temp sensor. Does anyone know if the pcv could cause this. Tried doing a koer test and can't complete cause truck dies, it keeps saying 9 and I think it is with the cyl like it should say 8 cyl. Oh and I did the vacuum hose off key on, even started it test to the fuel pressure regulator and didn't get fuel so I take it it is functioning normally. Thanks to all who read and offer help.

 

This page includes the ETC Engine temp coolant and the IAB idle air bypass OR Idle air control. The PCV should have no direct effect on the problem but shake it and if it rattles it is OK. Check the PCV grommet it is placed in and make sure it is good and not allowing a vacuum leak.

Fuel Injection Technical Library

 

I just cleaned out the iac/bpa-isc to no effect. I do notice it seems to be idling lower more now, maybe because the vacuum leak repair I dunno. But still dieing. I also checked for voltage between the wires key on and got 12.5v, resistance tested the solinoid half and got 10.5ohm. Thanks for the helpful troubleshooting suggestions. I also blew on the holes on the sliding plunger thingy side interchangeably giving them individual attention and got that one had resistance and the other was open and opposite when plunger open but the side that had resistance did leak some with just mouth pressure????

 

Does anyone have a good video source, or better than Haynes manual written instruction on how to do the general eec-iv power and ground checks located chapter 4 Page 24 of the Haynes manual for this truck? The table is a list of like 10 checks to do but I can't understand how to perform them and don't want to fry anything, I am not a trained mechanic just trying to get back on the road using what I have. Thanks. Also if something on that list wasn't working would it simulate my symptoms or stop it from starting? Code 12 I saw that but not sure what to do about it and it hasn't did it again. Rpm not within self test limit, would I need to adjust the screw to throttle linkage on throttle body?? I thought the pcm adjusted all the fuel/air mixtures using the solinoids and sensors with that iac??

 

That means that the idle air motor is not doing what the computer is commanding it to do. I have not been successful in cleaning one of them. Replacement is what has fixed it for me. Do not adjust the throttle stop screw. That is to keep the butterflies in the throttle body from contacting the sides of the bore and is not meant to be used for adjusting idle speed. Correct. The PCM/ ECM controls idle speed and fuel
mix.

When the truck dies, what are you losing: Fuel or spark?

 

My4Fordtrucks , thank you for your help, you are proving yourself to be quite insightful.
I don't know what I am loosing, spark or fuel? I am also trying to obtain a fuel pressure gauge along with a timing light. Not sure I had mentioned it before but back when I changed out the distributor I also seafomed the intake by pulling the brake booster vacuum line and allowing it to suck up a can of seafoam just trying to clean it up. It was, and still has been starting a little hard after it gets good and warm and has a good drive. I figured the motor was just getting gunked up from being so old and used so I cleaned it that way with the seafoam, I now realize that probably does nothing for the crank case and should probably do a motor flush. However in my research I now blame this symptom of having a hardstart/slow crank to battery cables, which I will be replacing as soon as I get it running right. I have been reading the Haynes manual to try and organize my troubleshooting approach because I have to get to work tomorrow with this truck and am thinking what about the crankcase ventilation?? When I seafoamed a couple months went by then I parked the truck because it wasn't running right and I got another work vehicle that is crapped out now, I found the air filter saturated in oil, it seemed the tube that runs from air filter box to valve cover had sucked a bunch of oil and crap there, I deduced this to the seafoam releasing gunk and intake sucked it up stalling it out. I cleaned the filter box and put new filters in. But I wonder if the hard start issue was because the pcv valve isn't working properly, will try to figure out how to test it today, a long with the throttle position sensor now that I know the difference between it and the iac valve. Also would the throttle body having sucked up some oil/gunk cause my loping idle/dieing symptoms you think. Thanks again.

 

I am confused is the thermactor system a completely separate system from the positive crankcase ventilation? Anyway I'm starting to think that the thermactor system will have nothing to do with my symptoms because chapter 6 section 8 troubleshooting options it says at the number 7 point the proper operation of thermacteor system can be difficult to judge since in some cases that failure can exist with no outward symptoms or signs. So basically it's a useless environmental crap that doesn't affect my fuel efficiency or idle? Anyway moving my focus to the positive crankcase ventilation that is my first test but would it affect the fuel efficiency or idle??

 

This contains all you should need to know about what the PCV does.

The Basics of Positive Crankcase Ventilation (PCV)

 

You could check O2 voltage at idle, see if it is cycling between 0.4-0.7V rapidly.

Also the truck is over 30 years old, consider some fresh fuel injectors. 2V 5.4s are all over the junkyards now and have four pintle injectors. Grab a set, have them serviced, and pop them in the truck. I am not sure if your '91 has four pintle or one pintle injectors.

I have had two vehicles with injectors that are stuck open causing poor idling and fuel economy.