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post #1 of (permalink) Old 11-26-2003, 09:25 AM Thread Starter
 
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what sensor to replace next

Well my truck has always has a little problem with the idle, nothing major just enough to be annoying. it seems to have a miss/ slight stumble problem at idle when warm and worse when in gear [img]images/graemlins/thud.gif[/img]. When its cold it seems to do better but does miss sometimes. Following are the things i have replaced:

TPS
MAP
ICM
Pick up Coil
Cap
Rotor
IAC
Plugs are fairly new
Fuel Pump
Fuel Filter

The plug wires look good and probalby don't have more than 20,000 miles on them. timing is set correct. Wires are connected correct. The engine has been replaced and has bout 35,000 on it or so. It was just a short block everything else was reused. Was done before i bought it. Heads just got rebuilt. Truck has 189,000 now. [img]images/graemlins/thud.gif[/img]
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post #2 of (permalink) Old 11-26-2003, 11:14 AM
 
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Re: what sensor to replace next

Ever get the injectors cleaned?

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post #3 of (permalink) Old 11-26-2003, 11:23 AM Thread Starter
 
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Re: what sensor to replace next

Professionally no... Taken them off, cleaned them myself, replaced little screen in bottom of themů yes. Spray pattern seems to be good. Would a dirty injector act differnt when cold vs hot engine?
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post #4 of (permalink) Old 11-26-2003, 01:30 PM
 
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Re: what sensor to replace next

Try the Oxygen sensor. My truck was doing the same thing. Then I dropped in another engine and it was much worse. I assumed that there was something done during the swap that caused the problem. I also replaced most of the sensors and had 2 diagnostic computers hooked up and ran every test and they came out normal. I hadn't replaced the O2 sensor and didn't bother since the diagnostic said it was fine. My truck worked OK cold and then would start crapping out when warm and if idling it would quit when I popped it in gear. Watching graphs on the diagnostic computer, I could see that the computer in my truck would gradually retard the timing and richen the mixture until it stalled. Then everything would go back to normal when it was restarted and then it would richen and retard.
I called a friend that owns a shop back east and he said he ran into a similar problem. It was a Dodge and the owner had installed headers and dual exhaust a few years ago. He taped up the O2 sensor and strapped it to the frame rail since there was no place to put it. The truck ran fine for 4 years and he plowed snow with it every winter. Then the computer crapped out so he installed a new one and put the original exhaust manifolds back on, and stuck in the old O2 sensor. The truck ran exactly like mine, good cold, worse warm and then quit. A few guys had a crack at it but couldn't figure it out. Then my friend Pete replaced the O2 sensor and it was instantly cured. Well, almost instantly. He said he had to drive the truck for 1/2 hour until the computer relearned to run with the new sensor. He thinks the old computer bypassed the O2 sensor when it was disconnected and the new computer was taking bad info from it.
I removed mine 2 days ago and it looked like a lump of coal, even though the tests said it was working properly. Since it was shot anyway I tried to revive it. I scraped the crap from it with a knife and file, cleaned more with a wire brush, and then dug out the little openings with a needle. I popped it back in, went for a spin, and it worked much better. I bought a new one and installed it last night and now she's mint. Try it.
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post #5 of (permalink) Old 11-26-2003, 01:35 PM
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Re: what sensor to replace next

You may have a vaccum leak. We got a 1990 2500 and work and it has a leak in the throttle body and it idles really bad.
post #6 of (permalink) Old 11-26-2003, 03:08 PM Thread Starter
 
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Re: what sensor to replace next

The o2 sensor has been replaced... unless i happen to get a bad one... the gasket on the throttle body is new... I just talked to my dad and he said at his work they have an some kind of ultrasonic cleaning system, said some ppl have cleaned there injectors with it. So i think i might take them off and let him try and clean them... worth a shot...
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post #7 of (permalink) Old 11-26-2003, 04:17 PM
 
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Re: what sensor to replace next

Try unplugging the timing advance wire and see if it idles in gear. Mine would idle fine with the wire unplugged since the computer couldn't retard the timing. Also check the vacuum to the EGR valve and check that the EGR valve isn't sticking. If it's dumping exhaust gasses into the intake it'll cause rough idle and stalling. Does it seem to be running rich?
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post #8 of (permalink) Old 11-26-2003, 04:35 PM Thread Starter
 
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Re: what sensor to replace next

ok i'll check that... i do have really poor gas mileage too. One thing i noticed when i took the air cleaner off it was a littly gummy looking.. The EGR has been cleaned not very long ago. If its running rich would it cause the throttle body to get all gunky like that?
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post #9 of (permalink) Old 11-27-2003, 08:05 AM
 
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Re: what sensor to replace next

Does yours look like this pic? I'm not sure, but I don't think that rich alone would gum it up. Mine was dirty looking also, like the engine was blowing back through the intake. I left the air cleaner off and drove it a bit and it definitely was shooting the occasional flame, like the timing was way off. Since the computer can play with the timing and fuel mixture while you drive it was hard to tell what was going on. Even though had just installed new plugs, I pulled 'em all out again and 1 was completely fouled and 2 others had a very weak spark, and all were covered with black suit. They should be light to medium brown if the mixture is right. I don't know a lot about how the computer changes things depending on the sensor info it gets, but if a plug or 2 isn't firing and raw fuel is hitting the O2 sensor it must think something's wrong.
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post #10 of (permalink) Old 11-30-2003, 09:34 PM Thread Starter
 
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Re: what sensor to replace next

sorry i've been out of town for thanksgiving. mine doesn't quite look near that bad. just a little gummy.. course that might be due to the fact i only drive it about a mile or 2 to work... i think i'm gonna try some new plugs and new wire set. then double check the timing.
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