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ok so i got a 1993 f150 5.0 2wd runs rough - way too rich. this is intermittent. sometimes runs smooth as can be sometimes instantly first start runs rough sometimes it runs perfect for 30-45 minutes then chugg-a-lugg lugg starts running rough. little back story truck did set for year or little more and a previous mechanic tried to fix but couldn't so owner sold to me cheap - owner didn't tell me until later that someone already been trying to fix it. first off i tried 3 different old obd1 scanner none of them will read codes. one has a specific 1993 GM/FORD card and still wont read. I've narrowed it down to fuel injectors staying on way too long - when put a noid light on the fuel injector harness it doesn't flash but stays lit whole time. as the engine dies you can see it flash really fast for a second right before it dies so basically its flashing so fast it looks like its just lit solid. the duty cycle is way too fast. tested 2 different injectors and both staying on - 4 cylinders are on one feed 4 on another feed i tried #6 and #5 different feed circuits both staying lit up. started one time while noid light was one and it was running right was flashing perfect and i seen it mess up chug chug chug and instantly stay lit up. when i first got the truck it had obvious exhaust leak and the previous owner had a brand new egr tube sitting in the seat so i thought ok put that on. removed upper intake and egr tube was not broken. went ahead and replaced anyway and installed new intake gasket. no fix. (didnt think it would but part was there so replaced anyway). first i thought the driver in the PCM was stuck - replaced PCM (power train control module) or ECU some call it the "computer" no fix. i thought was fixed it ran great when first fired up but then bam started running rich again - very rich. ok so what input is makin the PCM turn on the injectors way too much? again even with a new PCM my good Cornwell scanner wont read codes. went to the the O2 sensor its brand new but has soot around the edge. found it loose - very loose like i pulled it straight out basically, someone pulled the threads out of the pipe and welded a nut onto the pipe like a makeshift bung weld to install new O2 but was wrong threads - close but no. i took a exhaust sensor tap and tapped over the threads in the nut they welded on and was able to get it good and tight and sealed but i thought maybe from giggling around the sensor was bad - replaced new O2 sensor -no fix. performed ohm test and voltage test on wires going from O2 sensor to PCM they ok put test light on O2 heater wires and it lights up power and ground going to O2 sensor is ok. one time I started it and ran rough so i unplugged vacuum line right on intake and it run smoother so I thought not enough air (before i had noid light on) installed new idle air control valve - no fix. so i tried unplugging the MAP (manifold pressure) sensor - no change. unplugged coolant temp sensor - no change. unplugged cylinder head temp sensor - no change went to wiring diagram found that the PIP signal that comes from the pick up inside the distributor feeds the main timing position to the PCM for ignition and injection timing. goes thru the ignition control module - swapped ignition control module out with a good one from a 5.8 - no fix. again i was tricked started it after and ran perfect it thought hell yes i got it then bam no started dumping in too much fuel again. put a inline spark tester on 2 different cylinders seems to be flashing ok. so i removed the distributor and cleaned it, lubed it and installed a new pick up coil in distributor - no fix. tricked again started it ran perfect for 45 minutes noid light flashing perfect then chug a lug bam it stated running rough i install noid light fast as can and its lit up solid again. so now we are at a new intake gasket, EGR tube, idle air control valve, O2 sensor, PCM, ignition module, cleaned spark plugs and tested spark, unplugged MAP sensor, coolant temp, and cylinder head temp no change. and new pick up coil inside distributor. when i key it on the noid light doesn't light up right away so a short to ground doesn't seem likely. and when i unplug the battery cables try to reset the PCM it will still run rough right away but then again sometime I start it after doing nothing and it'll run ok sometimes for 30 second sometimes for 5 minutes or longer. I have wiggle tested all over the harness and no change. any ideas? what input to the PCM is making it intermittently want to keep the fuel injectors on so much keeping the duty cycle so fast? next step is to take and osciliscope to it and back probe some wires see what kind of voltage signals are coming off the coil pick up and o2 sensor. also the check engine light goes on and off - off when its running ok and on when it starts running rich. but i cannot get it to read codes ive tried 3 different scanners.
 
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