1987 2.9 erratic idle and drivability issues

[Zapper]

So i have a 1987 ford ranger stx 2.9, truck is new to me and only has 139k on it, just about everything is original on it. Ive been stumped by this issue because it has a very large surge at idle, randomly while cruising it seems to be cutting spark and if i give it full throttle the issue stops, ive replaced the 02 sensor thinking that it was that causing it but it had no effect, the map sensor i replaced with a known good one, has a new fuel filter, both pumps are new, brand new fuel tank because it had sat for awhile. The fuel pressure regulator is not leaking at it is sitting at spec for pressure. no vacuum leaks and the egr i blocked off to see if it was leaking and it isnt the tfi module i swapped with a test one that i have and had no effecti haven't pulled the ecm yet to check for water damage or blown capacitors yet but i will soon

 

[I support common sense]

Have you bothered to check what makes the spark? Start with the spark plugs by pulling them out and looking at them, then work your way back through the spark plug boots, wires, coil pack, etc… sounds like it could be fuel though too, considering the fact that throttle speed makes a difference.

 

[Zapper]

Have you bothered to check what makes the spark? Start with the spark plugs by pulling them out and looking at them, then work your way back through the spark plug boots, wires, coil pack, etc… sounds like it could be fuel though too, considering the fact that throttle speed makes a difference.

Spark plugs are good, wires ohm out properly, and it isnt cutting fuel because it smells quite rich when it does it, and it will be a consistent "gallop" when i i give it less than WOT when i give it WOT it runs smooth, it randomly will do this going down the road and ive found the easiest way to temporarily resolve it is by flicking the key off and back on real quick and it runs fine for a bit , which is why im considering an ecm issue

 

[Zapper]

Spark plugs are good, wires ohm out properly, and it isnt cutting fuel because it smells quite rich when it does it, and it will be a consistent "gallop" when i i give it less than WOT when i give it WOT it runs smooth, it randomly will do this going down the road and ive found the easiest way to temporarily resolve it is by flicking the key off and back on real quick and it runs fine for a bit , which is why im considering an ecm issue

Well i swapped ecms with one of my test ones and no change, still having the issue, i guess ill order a tfi module to see if that does anything, because im not throwing my cheapie one thats for emergencies on it

 

[Brain75]

...isn't erratic idle most usually a vaccum leak?

 

[I support common sense]

Erratic idle can be a vacuum leak, so good to check there. If your engine is running rich then that is for sure the problem. This can be determined by pulling the spark plugs. So, if you could pull the spark plugs and send photos of each that would be great, or at least describe them. They should have a nice tan color to them, if they are oily or coated in carbon you or burning oil, if they are very dark you’re running rich. You can tell a lot about an engine by looking at the spark plugs. If your “lightning hoses” (Vice grip garage) are still oem it’s probably worth changing them out because they can develop cracks and short through to any metal surface. While pulling the plugs it may be worth while to do a compression test if your engine is high mileage.

 

[Zapper]

Erratic idle can be a vacuum leak, so good to check there. If your engine is running rich then that is for sure the problem. This can be determined by pulling the spark plugs. So, if you could pull the spark plugs and send photos of each that would be great, or at least describe them. They should have a nice tan color to them, if they are oily or coated in carbon you or burning oil, if they are very dark you’re running rich. You can tell a lot about an engine by looking at the spark plugs. If your “lightning hoses” (Vice grip garage) are still oem it’s probably worth changing them out because they can develop cracks and short through to any metal surface. While pulling the plugs it may be worth while to do a compression test if your engine is high mileage.

i dont have the time to pull the plugs for a few days, but they are fairly new, ive smoke tested the intake and couldnt find any leaks and the engine has about 139k on it, i normally dont struggle with diaging drivability issues on most new vehicles hell i normally dont come to fourms for help but here i am

 

[Zapper]

Well was able to scan the codes and the brand new bosch o2 sensor wasnt switching, warrantied it out and its running smoother now

 

[Zapper]

Well was able to scan the codes and the brand new bosch o2 sensor wasnt switching, warrantied it out and its running smoother now

Nevermind... looks like i get to chase wires

 

[Zapper]

Nevermind... looks like i get to chase wires

Coming back to this i decided to just take a break from trying to fix this and ive come back with some knowledge, it seems it has code 42, "(M) System was rich for 15 seconds or more (no HO2S switching) – Fuel control" the regulator isn't leaking fuel into the vacuum line and i know the pumps, filter, and fuel tank are new due to it sitting for a long time, would it be possible that I have fuel injectors that are slobbering causing my issue? Look i know HEUI systems on diesels so gas powered things aren't my forte

 

[89longbed]

Yes, if it sat for a while it could have one or more dirty injector that won’t close property and that’s causing it to be very rich, especially at idle. You can check if the fuel manifold holds pressure for several days or if it loses it much sooner. If it’s not holding pressure an ejector is probably not closing. I think that’s more common than an ejector getting plugged, but this could also happen. You can clean them out with a 9v battery and a contraption to push a cleaner through them. You can buy kits with seals and screens.
You didn’t mention if you tested or changed the TPS. You can check those with a multimeter.

 

[Terrys87]

Not much to add but would suggest cleaning your water temp sensors above the thermostat, and IAC valve. I've had great luck with Seafoam getting fuel system cleaned out. It can take a while to get it flushed that way. Like @89longbed mentioned you can test injectors with a 9 volt battery, hose and a large syringe you might find at cattle or horse store. I have done the same thing. When you clean/test that way, you can put the hose on the spray side of injector and reverse flush the injector as well.

 

[rusty ol ranger]

First thing i would do is check the wiring to and from the O2. They have been subject to 38 years of heat at this point.

If you had a hanging injector it would show up on a KOEO pressure test, as it would prime to 40 or so then dump right off.

Also....make sure your EGR is working properly. If youre getting a rich code that usually means the O2 seen lean at some point and had to richen the mix, the ECM leans the mix when it calls for EGR. The passage into the intake is small and kinda curved. they block up easy. My rangers was so plugged i literally had to chisel it out.

 

[Zapper]

Not much to add but would suggest cleaning your water temp sensors above the thermostat, and IAC valve. I've had great luck with Seafoam getting fuel system cleaned out. It can take a while to get it flushed that way. Like @89longbed mentioned you can test injectors with a 9 volt battery, hose and a large syringe you might find at cattle or horse store. I have done the same thing. When you clean/test that way, you can put the hose on the spray side of injector and reverse flush the injector as well.

i used some BG 44K fuel system cleaner and it helped a little bit, i already bit the bullet and bought injectors though and ive cleaned those sensors, the sensor for the gauge is bad but the ecm one is fine, and the IAC i replaced with a cleaned working one

First thing i would do is check the wiring to and from the O2. They have been subject to 38 years of heat at this point.

If you had a hanging injector it would show up on a KOEO pressure test, as it would prime to 40 or so then dump right off.

Also....make sure your EGR is working properly. If youre getting a rich code that usually means the O2 seen lean at some point and had to richen the mix, the ECM leans the mix when it calls for EGR. The passage into the intake is small and kinda curved. they block up easy. My rangers was so plugged i literally had to chisel it out.

the egr is clean and working properly, i pulled upper and lower intakes to replace the factory gaskets, and the o2 wiring is not bad, no broken wires

Yes, if it sat for a while it could have one or more dirty injector that won’t close property and that’s causing it to be very rich, especially at idle. You can check if the fuel manifold holds pressure for several days or if it loses it much sooner. If it’s not holding pressure an ejector is probably not closing. I think that’s more common than an ejector getting plugged, but this could also happen. You can clean them out with a 9v battery and a contraption to push a cleaner through them. You can buy kits with seals and screens.
You didn’t mention if you tested or changed the TPS. You can check those with a multimeter.

tps tests fine with multimeter

 

[rusty ol ranger]

i used some BG 44K fuel system cleaner and it helped a little bit, i already bit the bullet and bought injectors though and ive cleaned those sensors, the sensor for the gauge is bad but the ecm one is fine, and the IAC i replaced with a cleaned working one

the egr is clean and working properly, i pulled upper and lower intakes to replace the factory gaskets, and the o2 wiring is not bad, no broken wires


tps tests fine with multimeter

Might be time to crack open the ecm