I have an 86 F150 w/ 4.9L I6. It was running fine (warm dry day in 80's) when I stopped, but when I started it again I noticed a "bucking" when I would decelerate or coast. The truck began to run rougher and very rich. After coaxing it home I ran diagnostics (key on eng. off). I got a code 63, indicating a look at the Throttle Position Sensor (procedure DH10). When I disconnected the sensor and shorted TP to Vref, per the procedure I got a code 23. This implies a bad TPS. I thought I had this one solved. I put in a new TPS, but I have the same problem, in fact I can't even get the truck started. I probed the voltage on the TP line with the TPS connected and I get the expected 1v. It also ramps up in voltage when I open the throttle (note I thought it ramped up well beyond 5 v ??, but I'll have to check that again this evening).

I redid the diagnostics tests and all indications are the EEC thinks the TPS is bad, but it doesn't seem to be.

I'm a little baffled on this one. Looking for ideas to try. Thanks. dz

 

Also check to make sure the Tps wiring is ok . A short to ground will cause the problems youve described . Does the throttle operate smoothly , any binding ? Follow all the diagnostic routines from DH 10 and you should find out whats going on .
Paul

 

Red Herring? - I took a look again last night. I still had the KOEO "63" code, but this time I measured the TP voltage at <0.2 V (my earlier measurement must have been in error). I ended up fixing this by removing the TPS, and reversing the metal washer with the slot in the edge (and double flats in the center). Doing this put the slot or key in a different position relative to the TPS, and thus sets the TPS to a resistance for ~1 V. It also varies up to about 4.8v over the throttle range. With this sure enough the static 63 code went away. Now, the washer didn't suddenly become flipped, so this must have been this way all along, and can't be the cause of my rough running problem.

I was able to start the engine although it ran VERY rough and did two KOER tests. The second time the truck ran even worse. The first test gave me codes of 21 and 41. The second test gave me codes of 12, 13, 42, & 58. ECT seemed OK and I swapped in an old (but likely good) FBC which didn't have any effect. Some of the codes might be the result of the idle speed control components trying to stabilize a very erratic idle, caused by the "main" problem.

I checked the plugs, wires and cap. All look good and are reasonabley new. My next plan is to check compression (possible timing chain problem?. Truck still runs VERY rich, producing a fair amount of smoke and petro odor(should probably check coolant for signs of headgasket problem). Runs worse as it gets warmer. Also need to check EGO sensor, but I can't believe that would make it run this bad. I'd like to check base timing except that the timing mark was never in the expected location (it was down underneath when timed to #1 instead of near the marks. That's another issue I wonder if anyone out there has seen with this type engine ).

 

I am having similar problems. My manual suggests cleaning the throttle bypass valve to correct rough idle. I am also going to replace the O2 sensor since I am now over 10ok miles. Conduct a wiggle test on the sensor wires your codes indicate are bad. dakota

 

When ever I see Ford Injected engines running rich I check the fuel pressure regulator. I don't know where yours is but the V8's is on the fuel rail. When you pull the vacuum line off if it is wet with gas replace it. This happened to me and I chased codes for a couple of weeks before I took it to a shop.

 

If its running rich enough to put out black smoke and gas odor, you'd better get your fuel pressure regulator checked pronto. Doesn't cost but about $15. If its bad, the replacement will cost you under $100 (parts & labor).

 

Well I have an update on this situation. I had taken the carb off and checked it over, checked the float and settings, and cleaned it up with Gumount carb cleaner as best I could. But that didn't change anything (I've rebuild it twice in 144K miles). Turns out gas was just flooding into the intake. After the carb was pulled again and rebuilt it ran much better, except for "hunting and surge" problem when idling or accelerating. Now I had a KOEO code of 68. Since I didn't have this before and the Idle speed control motor was fairly new, I went hunting for a bad connection. I noticed a green residue on a wire crimped into the harness for the ISC motor. Looked like it was connected but it had oxidized. Popped that pin out with a round punch (good technique suggested by my wife by the way) and resoldered it. So finally it was running near perfect, but had a 41 for the KOER test, which might be a build up of carbon on the O2. I'll let that one go for awhile to see if it burns off. But I'd say this one is case closed. Thanks for the suggestions.

 

Oh, and regarding the base timing mark, I had found the correct mark and the right numbers on the housing to use. I had forgotten that I finally solved that one (in case anyone experiences the same confusion I had on this, use the depression, and not the groove, and the marks on the right side looking at the engine from the front, and remember to open the "SPOUT" connector at the base of the distributor (single wire connector)