My trusty '96 LongRanger started thowing P0171/174 codes recently and I was finding the truck a little down on power and harder to get good mileage. Now back in my younger days, my engines alway had a "lean code" because I drove Mopar slant sixes and 2.3 Vauxhalls -but that was before the days of OBD codes and all. The long and short term enrichments were both pegged - 40 and 25 on both banks. I also had a small exhaust noise which Ihad been putting up with for some time. Ends up the EGR tube was cracked off at the flare inside the nut on the back of the exhaust manifold. What a miseable SOB that was to get off with 378000Km and 26 years of extreme heat!!!The bolts holding the EGR valve on (starting out as 10mm) werer almost as bad as the tube nuts. One came off with a 3/8 inch 6 point socket after heating it and the valve red hot several times with the aceylene torch - the other was burned round and I was fortunate to have a set ot rounded nut remover sockets - I drove the little one on with the bolt almost dripping and managed to get it out too.I should have replaced all thet when the engine was out last fall!!!~ getting the new one on was, if anything, more challenging than getting the old one off - no room to swing a wrench ANYWHERE. ANyway - I got it back together - it was nice and quiet but no difference AT ALL on the fuel trims - and if anything it idled worse. Luckily I had the foresite to order a MAF sensor from Rock Auto along with the EGR parts (I had tried another "experienced" one previously - it made no difference but I wasn't convinced). I put in the new MAF and cleaned up the idle speed control valve and the trims dropped like a stone - and it hasn't run as well in several years.
ent for my test drive and NO VSS and NO SPEEDO!!!!!
I pulled the speed sensorout and checked it - no problem. Checked for signal at the ECU - nothing. I checked the bottom (transmission) harness - no problems -so I opened up the top (engine) harness looking for any damage and found where the grey and black wire exits the enbine compartment to the speedo and confirmed the splice in THAT wire wasn't the issue, then connected my continuity tester (beaper) to the engine harness pink/orange wire and the wire at the sensor - no beep - - -and to ground - also no beep - so SOMEWHERE there is a break in the ground circuit. I just spliced the pink and orange wire to the black ground wire wires in the harness up by the ECU there they bolt to the firewall, taped everything up and went for a ride. HALLEUJAH!!!!. All fixed.

 

UPDATE!!!

I have a 1996 Ford Ranger 4.0 5 speed long-box standard cab 2 wheel drive truck with no power windows. mirrors or locks. The speedometer has recently stopped working and I have found something that does NOT make any sense. with the ECU plug connected or disconnected and the engine-cab connector connected I get a DC voltage reading of about 8.5 volts with the key off, rising to 12 volts with the engine running, and at the same time an AC voltage - cannot remember the base when not running, but rising to 15+ volts with the engine running. When I disconnect the harness to the cab the voltage goes away. The speed censor gives me about 2.6 volts AC when spun by my Milwaukee battery drill and the signal can be read between pins 33 and 58 on the ecu - either connected or disconnected - as long as the cab harness is disconnected In the wiring diagrams the only thing these wires connect to in the cab are the speedo and the CTM / GEM. It would also connect to the speed controller amplifier/servo assembly if the truck had cruise control (which it does not) Pulling every fuse, one at a time, from the fuse panel in the end of the dash panel does NOT kill either the AC or DC voltage across the speed sensor. Is there any function or misfunction of the CTM/GEM on this vehicle that could/would feed either an AC or DC voltage back to the ECU/speed sensor circuit????
There are no codes and no CEL, but there is also no VSS signal most of the time. Sometimes I get a speed signal to my ScanGuage -(and a vss signal to the ECU) but no speedo. Sometimes I also get a speedo reading - sometimes erratic and occasionally steady (and accurate) - but most of the time NOTHING.
The problem all started immediately after having a lean engine code CEL and replacing the MAF sensor and EGR valve and tube. I will be replacing the speed sensor in the transmission because the housing was corroded and it came out in 2 pieces when I removed it to check it - but electrically it tests OK at just over 250 ohms and it puts out the expected signal when spun. Continuity in the engine main harness and the transmission sub-harness all checks out. I did add a ground to the pink and orange wire at pin 33 of the ECU - this was before finding out I had the AC and DC voltages across the speed sensor circuit.

Anyone with experience in this realm??? NOTE -it is a 1996 - not a 1995 or older or 1997 or newer. It does NOT use the ABS speed sensor on the rear axle for the speedometer, nor does it have a speedometer cable. It does NOT have a frequency converter to convert to 4000hz from 8000. I have not disconnected the plug from the back of the speedo or from the GEM/CTM yet to see if the voltage goes away. I have heard there is a CTM reset procedure involving disconnecting the battery and shorting the cables to drain charge from the CTM. I have not done that either (I got rained out). Hopefully I can find a knowlegeable Ford tech with an explanation/solution. (I am a retired auto tech - mostly Toyota experience pre 2K)