1986 2.3 runs horrible

[TerryXn9]

I have a 2.3 5 speed that just runs horrible. Have checked the codes and i get a 21,31,33, and 41. I have replaced the o2 and the coolant temp sensor. I have replaced the egr and the positions sensor that goes on top. I also verified that the vacuum solenoids for the egr work and they do create vacuum when the truck is idled up. I'm leaning towards a bad computer or a bad harness. When ever the truck is first started it runs fine then it proceeds to stumble and almost sound like its misfiring. You can blip the throttle and it will settle back down and run more smoothly. The reason i think it may be computer related is because if you do a koer test it proceeds to run like complete crap after the test until you unplug the battery and reset the computer. Any thoughts as to what i could check? Also even with new egr components and o2 and coolant sensor they are still throwing codes. I'm stumped. Any help would be appreciated thanks.

 

[tomw]

I hate it when someone posts codes, and expects others to look them up or know them from memory. I won't and don't.
Not knowing the code meanings, I will throw out two things. 1) the MAP sensor can give bogus readings of intake manifold vacuum, and cause the computer to vary wildly the amount of fuel injected and 2) replacement EGR valve position sensors had a slightly off reading for their position at one end of their travel.
You can test MAP sensor if you can read Hz with a DVOM. You can disconnect and plug the vacuum line to the EGR diaphragm to see if the engine runs better.
There should be no vacuum to the EGR and no EGR flow at engine idle speed.
Lastly, check your fuel pressure and regulator. If inoperative or fuzzy, it can be diddling with fuel pressure, and the computer totally unaware, sending off the wall amounts of fuel.
tom

 

[TerryXn9]

21- engine coolant not at normal operating temp
31- egr not in its normal closed position
33- egr has not returned to normal position after test
41- system lean

ohmed the engine coolant sensor and its within range but still throws a code. New egr and egr position sensor. Verified the egr solenoid opens vacuum above idle. New o2 sensor. sorry for not explaining codes.

 

[tomw]

21 - run the engine more if it was tested 'cold', if warmed up, replace the thermostat, after checking that the temperature is actually off using a thermometer. There are two sensors, one a sending unit on the side of the block, above right of the oil filter. The other, I think, is mounted on the top of the intake manifold in some years, or near the thermostat. They vary. If your engine is slow to warm up, replace the thermostat, making sure it is seated into the housing tightly. Do not cheap out on the stat. Get a good one, Stant or Motorcraft or... pick your own. Do not buy Bob's private label unless it is a Stant or Motorcraft in drag.
31 - EGR not in normal closed position. This is 'known' by the computer by means of the variable resistor mounted on the egr valve. The resistance increases/decreases as the valve opens/closes. I don't know which way is decrease or increase, but you have a 50:50 of getting it right off the bat. Known 'closed' or 'at rest' resistance may be off because of wear, or, as I mentioned, manufacturing error(?) for replacement parts(this was some time ago, so ???). There is a 'known' resistance value for closed, and one for 'open', with values in between. It is not a binary (on/off) system. The vacuum solenoids on the passenger side under the plastic cover apply vacuum, and hold it as directed by the computer. One will 'dump' the vacuum on command(after holding the valve open as you drive) when you bring the engine to idle speed. FWIW.
33 - more of the same. I think you may have a dirty 'pintle' in the actual EGR valve that holds the sensor out of position, and possibly is allowing exhaust gas into the intake manifold at idle.
I'd remove the EGR from the intake, and take it apart enough to make sure it is clean, seats properly, and responds to vacuum applied at the diaphragm, and closes fully when vacuum is removed. If it won't, doesn't, and is dysfunctional, find a good replacement.
41 - sytem lean. You can get that from misfire, which leaves excess O2 molecules in the exhaust stream for the O2 sensor to find... it then says: "Whoaa!!! System LEAN!!!" real loud to the computer. It MAY be wrong if your engine has misfire. The fuel:air mix does not burn if you have misfire, leaving those O2's around for the sensor to find. Get it firing w/o misfire, and see if the 41 code goes away.
tom

 

[TerryXn9]

Thanks for the info and input! All test were done on a warm engine. New thermostat that open and closes as it should. Truck does get to operating temp and hold there. Egr solenoids will open and close ever valve as they should when accelerated. Egr is new and functions as it should. Egr position sensor is new. I'll have to check and make sure it operates as it should. I'm leaning towards a bad computer or bad engine harness at this point. New plugs and wires. And new distributor cap and button. There shouldn't be a missfire. Timing has been set properly but will not come down from 30degrees after engine is warm, which leads me to believe the system still thinks to run in warm up mode since the computer may be reading the coolant temp sensor wrong. I'm pretty much stumped at this point.

 

[tomw]

The computer will not diddle with the timing until the engine has warmed up, and thus it should be at a 10 degrees BTDC when checked on a cold engine, or with the SPOUT connector plug removed from the socket hanging onto the harness from the drivers side inner fender to the engine. It is a rectangular socket/plug, and the plug is removable to set base timing. If you are at 30 BTDC, I'd check base, non-computer diddled timing before doing more inquiry.
I suppose that the computer could be responding to a failed temperature sensor. I don't know the strategy it would use to handle an overheated engine. Perhaps the 30 BTDC is a response to that?
It is informing you that the temperature sensor (not sender) is reporting low coolant temperature. code 21. It will not work properly in 'closed loop' until it reaches full operating temperature. It is driving 'with the choke on, cold engine' until that happens.
Check the sensor wiring and the sensor. You can ohm the sensor and refer to a table to confirm/deny it matching ambient temperature ohm reading. Do the test engine cold, overnight so it matches ambient temperature.
tom

 

[mcw98000]

i was wondering if you ever came to a conclusion with this truck. i am having a lot of the same issues with my 89