CEL at higher speeds - can I get help interpret codes please? :)

[badshiba]

Howdy all!
I’d love some help interpreting the engine codes I’ve got; I’ll give a brief rundown,the Ranger’s specs, a code list, and my thoughts.

Recently bought a 93 Splash, drove fine from dealer, but gives intermittent CEL whenever I go about 60mph or higher. CEL sometimes disappears during these highway speeds, but always disappears once I’m back in town for a minute. (35-40mph)

Specs:
1993 Ranger, Splash trim, 4.0L V6, Automatic, 2WD, 25k miles (previous, original owner was a collector, and babied this thing!)

Codes:
KOEO- 111
CM- 185, 186 (MAF low, Injection Pulse Width Circuit high)
KOER- 536, 538 (BOO circuit not activated during KOER, throttle movement during test)

My Thoughts:
What concerns me more are the KOEO codes. The KOER codes I think are my fault not understanding the KOER sequence. I could have sworn that I should only do the wheel turn/brake pump etc if I get a 998 code in the first part of the test. Maybe something else is triggering the 546/538…
Anyways, MAFs I know can be finicky, so the 185 didn’t really surprise me. The 186, though…can’t say I’ve read exactly what that pulse width circuit is. What I *have* read through, other folks with a 186 seem to narrow down to a fuel delivery issue of some kind (injectors, fuel filter/pump, O2 sensors, etc).
Your Thoughts: I’d love to hear em! Have any of you experienced similar codes? Am I correct to start following the fuel delivery? Any quick, simple things I’m overlooking?

thank you in advance!!

 

[badshiba]

Quick aside:
-I meant to say, “what concerns me most are the CM codes”
-Symptoms: just the CEL. Truck runs great at all speeds, granted I’ve only been on about 6 or 7 drives with it. On a cold start, like overnight into morning, if I let it idle, it’ll lose revs and shutoff. If I wait a moment, try again, it starts up fine and stays idling between about 1K and ~500 RPMs. Not sure if that’s related, I figured that’s just the engine sitting cold for more than a few hours

 

[rubydist]

My experience is that these EEC IV engines will never run right with a mafs code, so you need to figure out if the mafs is just dirty, or sick, or if there is a connector or wiring issue to the mafs first of all. Once you get rid of the mafs codes, you will likely be fine.

 

[RonD]

Welcome to TRS

Clean MAF sensor, once a year

Replace ECT(engine coolant temp) sensor

All gasoline engines need to be CHOKED on cold start, fuel injection didn't change that, but without Jets the computer has to run the Choke, a choke plate wouldn't work

ECT sensor tells the computer engine temp, the colder it is the more Choke needs to be applied, already warm, then no choke
Choke means Rich Fuel Mix and High Idle, above 1,000rpm
Then as engine warms up computer gradually reduces the idle and leans out the fuel mix

If ECT sensor is not telling computer the correct temp then there will be idle issues and stalling warm or cold, and its not an expensive sensor or hard to change

So on any start up you should get a REV from engine, 1,200-1,500rpms, thats the IAC Valve working
Then a drop to 1,100rpm or so if cold engine or 750-800rpm when/if warm(with automatic, manual is 650)
Thats the IAC Valve, ECT sensor and computer all working correctly

Codes 536, 538 are tests, ignore them

Clean MAF sensor and swap out ECT sensor, that should clear the other codes

Heads up
The dash temp gauge uses a 12volt SENDER for engine temp, ECT sensor is 5volt so not interchangeable
These look similar
In a 1993 4.0l Ranger the SENDER will have just 1 wire, ECT sensor 2 wires
They are located near each other on lower intake manifold just behind thermostat housing, follow upper rad hose to engine, that's the t-stat housing

Look at air cleaner box, on the hose to engine you will see a 4 wire connector, that's the MAF sensor

 

[badshiba]

Rubydist, RonD, thank you both - excellent info, exactly what I was hoping for - that all makes sense, thank you both!!

will clean MAF, check out that ECT, and reply with results here for future users

 

[badshiba]

UPDATE 1: was able to remove and clean MAF sensor, used a dedicated “MAF Cleaner” spray. Checked the housing where the sensor sat, and noticed a few plastic pieces. Checked the sensor, and sure enough, saw one of four plastic tabs on either side of filaments…other three broke off :/ cleaned out sensor plate, tried very hard to not let anything drop into hole.
After letting sensor dry, reseated sensor, screwed in the torx screws, plugged in the sensor’s wires.
TEST DRIVE TIME!
let her warm up for a few minutes, drove around neighborhood (~30mph), no issue/CEL. Went through town, (~40mph) couple stoplights, then onto highway (~65mph). No issue/CEL in either, stopped at a small park off of highway.
RETURN TRIP:
Park had a couple rough spots on road, bounced pretty good and rearview mirror fell off (great 🥲). No CEL coming out of park (~20mph). Back on highway, while climbing up to speed, CEL came on at about 55. CEL stayed on the entire drive back home. Even spent a few minutes in neighborhood at lower speeds, where CEL would previously turn off, it still on.
after parking vehicle, turned engine off, waited a minute or two, turned it back on, no CEL present.
going to repair mirror tomorrow, then maybe do another test drive, time permitting.

I have a new ECT sensor in hand, don’t want to change too much at a time, so I can hopefully isolate the issue…but I haven’t forgotten about it

 

[badshiba]

UPDATE 2:

reaffixed mirror, gave time to set, stays on now

drove to a city an hour away, mostly highway speeds (60-75mph), no issue, no symptoms, no CEL on the way there.
however…
On RETURN TRIP:
spent about 20 minutes getting out of town, due to traffic. Mostly 40-50mph, some stop-and-go sections of the highway out. On second part of trip, after passing city limits (going ~70) CEL came on.
CEL stayed on for no more than a minute, turned off. About another minute later, came on intermittently for the remaining 30minutes of the trip
As in previous test rides, CEL would eventually turn off and stay off once I drove for several minutes at lower speeds (~35)
Parked vehicle, allowed to rest.
Ran codes again the next morning, same as before: KOEO 111; CM 185, 186; KOER 536, 538

next step for me is to investigate and/or replace the ECT Sensor, but open to other possibilities. Maybe replace entire MAF sensor.
As always, thanks for reading, any input is appreciated, and I’ll keep y’all posted!

 

[rubydist]

You still have a mafs problem. After what you described the mafs like, I suggest replacing that sensor.