trouble codes
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
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From: va
trouble codes
I'm starting a new tread the other one is to long. Thanks for the previoues replies.
My truck will run ok but every three minutes it misses ( idles real low of a second) and if it misses real bad it stalls. I ran it for half an hour today. When its hot and it stalled it wont restart. It will only start when its cold. Some raw fuel ( black spot on snow) is coming out of exhaust pipe. Moved truck and its still doing it. Today while running for 30 minutes the trouble codes I got were. I unhooked the groung on the battery and got the same codes.
31 EVP
12 ISC idle low
41 RUNNING Lean
33 EGR not opening
13 ISC idle high
When the ENGINE was Hot and not running the CODES I GOT TODAY were
11 ok
When the Engine was cold and not running the codes I got were 21 and 24. I think these are ok to get when engine is cold.
I don't have a ISC on my 4.9 wiring diagram. What is the ISC (idle speed control) for my engine? I have a pin point test for the egr that i will test tonite. 1987 f150 4.9
My truck will run ok but every three minutes it misses ( idles real low of a second) and if it misses real bad it stalls. I ran it for half an hour today. When its hot and it stalled it wont restart. It will only start when its cold. Some raw fuel ( black spot on snow) is coming out of exhaust pipe. Moved truck and its still doing it. Today while running for 30 minutes the trouble codes I got were. I unhooked the groung on the battery and got the same codes.
31 EVP
12 ISC idle low
41 RUNNING Lean
33 EGR not opening
13 ISC idle high
When the ENGINE was Hot and not running the CODES I GOT TODAY were
11 ok
When the Engine was cold and not running the codes I got were 21 and 24. I think these are ok to get when engine is cold.
I don't have a ISC on my 4.9 wiring diagram. What is the ISC (idle speed control) for my engine? I have a pin point test for the egr that i will test tonite. 1987 f150 4.9
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
I believe the ISC is another name for the IAC, or idle air control valve, aka idle air bypass valve. It sits right on the throttle body and allows the EEC to control the idle by letting air bypass the throttle butterfly. It gets gunked up and doesn't move as easily as it should after a lot of miles. New ones are about $75, as I recall, but you can try cleaning yours with carb cleaner.
Whenever there's a rough/erratic idle, that's the first part to suspect.
It also sounds like your EGR system isn't working. Either the EGR, the EVP, or both are shot.
Whenever there's a rough/erratic idle, that's the first part to suspect.
It also sounds like your EGR system isn't working. Either the EGR, the EVP, or both are shot.
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
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From: va
Iac or TAB sensor
Are there wires to IAC? How many for 4.9 Is it the TAB throttle air bypass valve? Mine is a two inch long tube with a sensor on the end, its on the throttle body. Two wires.
Last edited by mike L; Nov 17, 2004 at 08:03 PM.
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
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From: va
TAB sensor
I get 10.5 volts unpluged and .8 ohms on the 10 ohms scale. Is the Tab sensor ok? Sounds ok in the Haynes manual. I cleaned the TAB body out with carb cleaner it was dirty.
Lead Driver
Joined: Nov 2002
Posts: 9,555
Likes: 40
From: Concord, NC
The TAB (Thermactor air bypass) is a solonoid for air injection to the exhaust and is not related to your problem. The ISC is idle speed control, which is the solonoid mounted to the throttle body. Both are actuators, and not sensors for the engine. Have you checked the fuel pressure regulator yet? Somehow the computer thinks the mixture is lean and is trying to richen the mixture up, or it is getting too much fuel and it can't lean it out enough to make up for it. You might also want to test the wiring to your O2 sensor and see if it is correct (or even connected).
