Mystery misfire when warm only
03-09-2012, 10:02 AM
#21
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So definite improvement after replacing the cts. I don't know what brand was in before but it wasn't original, and I replaced it with a duralast unit. Before, after about half throttle the truck wouldn't pull any harder, so half throttle was equal to the pedal to the floor. Now the full pedal range will change acceleration, and for sure pulls less at half throttle than it did before. I'm thinking the other sensor was running richer at all pedal positions, hopefully I'll see my mileage go up too. I'm going to test that old one in water when I get a chance.
On the first drive once I got on the freeway, my dash temp sensor shot up almost to red super quick, so I pulled off, and a minute or so later the needle literally fell back down to the normal temp position and stayed there. So I think that was the computer re-calibrating to the new sensor because it hasn't done that since. I've driven about 30 miles so far without any problems, hopefully with more driving it'll still be ok. It does feel like it's running smoother though.
On the first drive once I got on the freeway, my dash temp sensor shot up almost to red super quick, so I pulled off, and a minute or so later the needle literally fell back down to the normal temp position and stayed there. So I think that was the computer re-calibrating to the new sensor because it hasn't done that since. I've driven about 30 miles so far without any problems, hopefully with more driving it'll still be ok. It does feel like it's running smoother though.
03-09-2012, 05:41 PM
#23
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i had the same problem.but mine was the tps sensor just being a mile off where it should be..get it in the right spot and since then!i am a happy camper!!!!
03-21-2012, 04:41 PM
#24
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Figured out my problem. I pulled my spark plug wires and number 2 was really green and where it meets the distributor was filled with corrosion. Swapped it out with new. And its seems better since. Weird that it would only cut out when warm.
03-21-2012, 07:45 PM
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My truck does the same thing starts perfect idles perfect after it runs for like 5 minutes it starts acting up misfiring I've adjusted valves checked gap on spark plugs cap and rotor clean i checked injectors resistance and also unplugged the injectors while the truck running they all make the idle change any ideas I would really appreciate it sorry for the tread jack
03-22-2012, 12:53 AM
#28
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ive been dealing with this exact issue. starts perfect, idles perfect but once its warm and i give it throttle its tries to choke out. ive now changed the CTS, thermostat, injectors, adjusted the TPS per FSM as well as adjusted by ear. I guess next ill try replacing the o2 sensor. I tested for codes and got 24 (IAT sensor) 31 (AFM) and 41 (TPS)
03-22-2012, 07:17 AM
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I will I know that it's going to be something small too
I too have gone through lots of things as well it kinda gets frustrating driving with that misfire I'll keep you posted if I find the problem
ive been dealing with this exact issue. starts perfect, idles perfect but once its warm and i give it throttle
its tries to choke out. ive now changed the CTS, thermostat, injectors, adjusted the TPS per FSM as well as adjusted by ear. I guess next ill try replacing the o2 sensor. I tested for codes and got 24 (IAT sensor) 31 (AFM) and 41 (TPS)
its tries to choke out. ive now changed the CTS, thermostat, injectors, adjusted the TPS per FSM as well as adjusted by ear. I guess next ill try replacing the o2 sensor. I tested for codes and got 24 (IAT sensor) 31 (AFM) and 41 (TPS)
03-22-2012, 05:45 PM
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03-25-2012, 10:43 PM
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Draga5
Your compression is pretty low. I don't know if you've replaced any internals recently, but did you do the compression test before or after readjusting the valves? Was the throttle wide open, efi fuse pulled, all other spark plugs out, battery hooked up to the charger? Did you try adding a squirt of oil to each cylinder and re-checking the compression? It could be unrelated, but I would figure that out first. A leak down test can tell you more.
Did you make any changes/replace any parts/do any damage to anything when this started happening? Since it's an intermittent issue try testing your injectors and and spark with a noid light while the engine is running. You'll have to rig some jumper wires so you can keep everything plugged in or get a light that runs inline. If it doesn't blink when you get the miss you found a problem. Have you tried grounding the spark plugs to the block and making sure you're getting a good blue spark? Does it still do it with the TPS unplugged?
Are you getting any codes? Can you narrow down when the misfire happens/make it happen consistently? What also helped me out was adjusting the idle air control screw. Screw it in more until you're idling near 750 (should be about 2.5 turns out from all the way in) and see if that changes anything. I went through lots of things before I replacing the cts.
Johnboy and Draga5, have you tested your AFM, TPS, and CTS with a volt meter at the ECU? My cts tested good with the ohm meter but the ecu was getting wacked voltage signals. The FSM explains how to do it. I picked up a multi-meter at harbor freight for 5 bucks and hasn't broken yet. I don't know about your year, but the iat sensor is in the afm on my 88, so could be a bad AFM. I'm curious to see what how the IAT and AFM check out.
Let us know how it goes.
Your compression is pretty low. I don't know if you've replaced any internals recently, but did you do the compression test before or after readjusting the valves? Was the throttle wide open, efi fuse pulled, all other spark plugs out, battery hooked up to the charger? Did you try adding a squirt of oil to each cylinder and re-checking the compression? It could be unrelated, but I would figure that out first. A leak down test can tell you more.
Did you make any changes/replace any parts/do any damage to anything when this started happening? Since it's an intermittent issue try testing your injectors and and spark with a noid light while the engine is running. You'll have to rig some jumper wires so you can keep everything plugged in or get a light that runs inline. If it doesn't blink when you get the miss you found a problem. Have you tried grounding the spark plugs to the block and making sure you're getting a good blue spark? Does it still do it with the TPS unplugged?
Are you getting any codes? Can you narrow down when the misfire happens/make it happen consistently? What also helped me out was adjusting the idle air control screw. Screw it in more until you're idling near 750 (should be about 2.5 turns out from all the way in) and see if that changes anything. I went through lots of things before I replacing the cts.
Johnboy and Draga5, have you tested your AFM, TPS, and CTS with a volt meter at the ECU? My cts tested good with the ohm meter but the ecu was getting wacked voltage signals. The FSM explains how to do it. I picked up a multi-meter at harbor freight for 5 bucks and hasn't broken yet. I don't know about your year, but the iat sensor is in the afm on my 88, so could be a bad AFM. I'm curious to see what how the IAT and AFM check out.
Let us know how it goes.
04-03-2012, 12:55 PM
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Ok I finaly figured y misfire I have fuel injector connectors that were cOming apart so while I was there I replaces the "o" rings and injectors I hope this helps others oh by the way on my noid light showed power to them but when I removed the injector boot that's when I was able to see the problem
Last edited by Draga5one0; 04-03-2012 at 12:58 PM.
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