So...I purchased a very nice 1988 ranger xlt 4x4 with a 2.9 a little over a year ago. It was owned by an elderly man and had sit for a number of years in his carport. It only has 90k original miles. When I purchased it, I changed out all the fluids, new tires and a new battery. The engine light, at first would come on sporadically and I never really worried about it. But over the last couple months, it has been getting worse, and losing alot of performance and mpgs. So, I thought I'd go ahead and replace very sensor and do a tune up.

new iac valve
new in line fuel pump
new fuel filter
new ECT sensor
new intake air temp sensor
new t stat
new dist cap and rotor and wires and plugs
took all the injectors out, cleaned and new orings
upper intake gaskets replaced
new map sensor
cleaned throttle body and upper intake
new tps
new o2 sensor
timed to 10 degrees
all vacum hoses have been inspected
new pcv and breather
new air filter
running 15w40 delo (diesel oil)

I figured that this stuff probably needed to be done anyways and that it'd probably take care of the cel coming on. But...it didn't. It starts right up and will go to the 1500 or so rpms and about a second or two later it drops down to normal idle and sometimes stumbles and dies unless I give it throttle. It is throwing code 54, which has to do with the ACT sensor. The ect and intake air temp sensor are both new. I measured the voltage with koeo and got 4.6 volts. Am i correct in thinking that this should be between 4.9 and 5.1 volts to be in spec? And would this be what is causing my problems? Could this be caused by a bad ground? The ecu looks brand new, and the harness and all pins look brand new too. I'm really stumped with this one.

 

Have you tried testing the old air temp sensor? Hook up your ohm meter and warm up the sensor with a hair dryer, the resistance should be high with a cold sensor and low when the sensor is warmed up
If you only see low resistance it would explain that code 54 "air temp sensor signal voltage too high"

 

Unfortunately, I threw out the old sensor. I'll do the test on the new sensor. I ran the truck for a couple months with the new sensor, when I pulled off the intake though, I noticed it had fuel in it, so I'm thinking I had a leaky injector. That should be fixed now. I also will be putting on a new FPR this weekend too. Could the fuel have of fouled the sensor?

 

I don't think gasoline fumes would screw up the sensor. but if the sensor is defective or if the wires to it are shorted together
it would explain the high signal voltage the PCM is seeing

This 88 sounds a lot like the 87 that I bought new and sold 3 years ago. it was still in very good shape but i didn't need a truck anymore and wanted something faster than the 2.9.
Got a 2.0 liter turbocharged 2014 VW Tiguan & it's a blast to drive.
Congrats on getting what sounds like a real nice 88

 

It wasn't fumes, but raw fuel, hoping the new orings and washers will fix the leaky injector.

It is a very nice truck, the interior is nearly perfect and the exterior is excellent as well. Best of all, it is unmolested and 100% stock, which is hard to find a 4x4 ranger of this year

 

1988 xlt 4x4 ford ranger

1988 xlt 4x4 ford ranger

 

That's one very nice looking truck, hopefully it's a 5 speed manual trans. The 5 speed TK trans in my 87 had 247,000 trouble free miles on it when I sold it, but the input shaft bearing was beginning to sound off a bit in neutral with the clutch out. If it is the manual trans the truck should give you a lot of pretty much trouble free miles
I used Amsoil 80/90 synthetic gear oil in the transmission
The 2.9 in mine was also pretty much trouble free, i used Amsoil synthetic 10/40 engine oil in it and since i mainly drove highway miles i changed it every 12,000 miles.
I guess with that sensor getting gas soaked it might have fouled it.
Any luck figuring out the code 54?

 

It's an auto. At the moment it shifts through all the gears nice and smooth.

I just got the new ATC sensor from rockauto in the mail, so I'll probably get to it this weekend and hopefully report back with good news. It's not my daily driver, so I'm not in a rush. Fingers crossed.

 

So I changed out the air intake temp sensor, and it runs perfect! The sensor that was in there I guess got fouled out from the raw fuel that was in the upper intake from a leaky injector.

 

Glad to hear it and congrats on the fix.