Sparky Posted November 18, 2021 Share Posted November 18, 2021 This is my first troubleshooting post for my 1986 XLT Lariat 2WD with 302 EFI/AOD. The problem I'm having is a high idle when I first start it (higher than normal cold idle) and then as it warms up the idle drops but is still higher than normal and it will momentarily drop and then go back to high idle. It does this repeatedly every 10 seconds or so. It also sounds rough, not very smooth. I verified the timing is at 10° BTDC with the spout connector disconnected but when it is connected it varies from 18-20° while idling. I pulled codes and I got CM codes of 22, 63, 31 and KOER codes of 41 and 13. It passed the KOEO self test. The book says to focus on the KOER codes first. I would think that code 13 (RPM at idle out of range/low) might be caused by code 41 (HO2S sensor low/system lean). I should also mention that I have a ticking sound when the engine is cold but it goes away as it warms up. I think it might be an exhaust manifold leak. What do you think? If that is the case, can that be causing an O2 sensor problem? I also plan to check my TPS based on the code 63 to make sure it's within specs. Should I focus on the O2 sensor first or could an exhaust manifold leak be causing the problem? Anything else I should be looking at? Hopefully I can clear up the KOER codes and then see if any of the CM codes come back. Link to comment Share on other sites More sharing options...
mat in tn Posted November 18, 2021 Share Posted November 18, 2021 The first thing that comes to mind is the tps. I have had times where ohming out the tps did not find the ghost in the machine. Voltage test also. Swapping in a new one and setting it to .85 volt at signal return is the best suggestion i can give. Over time they can corrode and give erroneous signals to the ecm. And keep in mind the ecm reads very minor changes and reacts. Link to comment Share on other sites More sharing options...
grumpin Posted November 18, 2021 Share Posted November 18, 2021 I have learned to do the first code first and it may clear later codes, so you are correct in doing 41 first. Link to comment Share on other sites More sharing options...
85lebaront2 Posted November 18, 2021 Share Posted November 18, 2021 I am going to reply directly to this one. We went through this with my son's 1986 F150 4WD, 302 EFI and AOD. He had idle issues and chattering EGR solenoids. The 1985/86 truck EFI system is different from the later ones in the idle setting procedure. The TPS has no adjustment other than the idle stop screw and is set to a voltage reading. First and very important, to check the "sweep" on a potentiometer correctly you need an analog meter as digital ones do not continuously update and you are looking for a smooth change. Second, idle on these is set to a voltage reading, 1.0 +/- 0.1 if I remember correctly. This can be done (and should be) engine off, key on. These systems do run the idle up on cold start, but should drop back shortly after starting. One of the reasons for setting the throttle (not idle speed) by voltage is the way the system works, the EGR comes in based on TPS voltage at a very low change so if the voltage is too high you get chattering EGR solenoids and a surging idle. The wiring on these first generation EFI systems can be a problem, I have seen harnesses with bare wires, crumbling insulation and really poor grounds. Good luck with it. Link to comment Share on other sites More sharing options...
Sparky Posted November 18, 2021 Author Share Posted November 18, 2021 I am going to reply directly to this one. We went through this with my son's 1986 F150 4WD, 302 EFI and AOD. He had idle issues and chattering EGR solenoids. The 1985/86 truck EFI system is different from the later ones in the idle setting procedure. The TPS has no adjustment other than the idle stop screw and is set to a voltage reading. First and very important, to check the "sweep" on a potentiometer correctly you need an analog meter as digital ones do not continuously update and you are looking for a smooth change. Second, idle on these is set to a voltage reading, 1.0 +/- 0.1 if I remember correctly. This can be done (and should be) engine off, key on. These systems do run the idle up on cold start, but should drop back shortly after starting. One of the reasons for setting the throttle (not idle speed) by voltage is the way the system works, the EGR comes in based on TPS voltage at a very low change so if the voltage is too high you get chattering EGR solenoids and a surging idle. The wiring on these first generation EFI systems can be a problem, I have seen harnesses with bare wires, crumbling insulation and really poor grounds. Good luck with it. Thanks Bill, I have ordered an analog meter. It should be here tomorrow. What do you think about my code 41 "running lean"? I will check the O2 sensor (as soon as I find it:nabble_smiley_blush:). Does it sound like I have an exhaust manifold leak? Could that be why I am running lean? I assume the TPS and the running lean are 2 separate issues. Link to comment Share on other sites More sharing options...
mat in tn Posted November 19, 2021 Share Posted November 19, 2021 Thanks Bill, I have ordered an analog meter. It should be here tomorrow. What do you think about my code 41 "running lean"? I will check the O2 sensor (as soon as I find it:nabble_smiley_blush:). Does it sound like I have an exhaust manifold leak? Could that be why I am running lean? I assume the TPS and the running lean are 2 separate issues. Assume nothing! Lean condition could be as simple as a clogged fuel filter. These are large canister , water separator type that are in constant circulation to help keep condensation in check. Yes water clogs them! Also it could be that the fuel injectors are not 100% . Even one or two could do it. Link to comment Share on other sites More sharing options...
Sparky Posted November 19, 2021 Author Share Posted November 19, 2021 Assume nothing! Lean condition could be as simple as a clogged fuel filter. These are large canister , water separator type that are in constant circulation to help keep condensation in check. Yes water clogs them! Also it could be that the fuel injectors are not 100% . Even one or two could do it. All true but I am trying to address the fault codes first before I move on to other things. I have a specific code for a lean condition so I might as well start there. Link to comment Share on other sites More sharing options...
mat in tn Posted November 19, 2021 Share Posted November 19, 2021 All true but I am trying to address the fault codes first before I move on to other things. I have a specific code for a lean condition so I might as well start there. Yes keep it simple. Start with routine maintenance items before moving on to mech failures. Fuel filter, vacuum lines etc. could cause a lean cond. especially if you dont know the full maint. history of the truck or if it sat for a long time. Old trucks dont do well sitting too long Link to comment Share on other sites More sharing options...
85lebaront2 Posted November 19, 2021 Share Posted November 19, 2021 Thanks Bill, I have ordered an analog meter. It should be here tomorrow. What do you think about my code 41 "running lean"? I will check the O2 sensor (as soon as I find it:nabble_smiley_blush:). Does it sound like I have an exhaust manifold leak? Could that be why I am running lean? I assume the TPS and the running lean are 2 separate issues. Your O2 sensor should be on the rear of the right exhaust manifold, one wire style. Be careful removing it, they love to strip the manifold. Link to comment Share on other sites More sharing options...
Sparky Posted December 13, 2021 Author Share Posted December 13, 2021 Your O2 sensor should be on the rear of the right exhaust manifold, one wire style. Be careful removing it, they love to strip the manifold. I just wanted to update on my progress. I checked for vacuum leaks using carb cleaner but did not find anything. I checked the TPS and it tested good. I also cleaned up some grounds and added a couple including a new negative battery cable to the engine block and frame. I attempted to tighten the exhaust manifold bolts to see if I could fix the exhaust leak but that did not go well. Rusted bolts and studs and I definitely don't want to break one so that is a project for another day. Next I focused on the O2 sensor. It tested bad so I replaced it. The idle sounded better but it still wasn't quite right. Too high and still surging a little bit. The previous owner must have adjusted the idle screw. I ended up backing it out 4 full turns and that seemed to allow the ECM to adjust the idle on it's own. I cleared the codes, took it for a drive and then checked the codes again. All codes are clear and the idle is much better! Now on to other issues. A question: is there an adjustment procedure for the idle screw for the 5.0L EFI? I have read that you are not supposed to touch it, but once it is out of adjustment how do you reset it? Or should I just leave it since it seems to be idling good (not sure what the RPMs are but it sounds pretty close to right). Link to comment Share on other sites More sharing options...
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