Help! trouble codes
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Junior User
Joined: Apr 2008
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From: Brunswick, Ga
Help! trouble codes
91 f 150 5.8 It started last sunday, truck started stumbling and running bad. seemed to clear up so i went ahead and drove it to church. I thought it was just trash in the fuel or something. then coming home it quit and wouldnt start back. got to the house and started working on it and found numerous problems with the cooling system, radiator was bone dry, replaced thermostat, thermostat housing, hoses, and it seemed to run ok then. next day i cranked it up and it was back messing up. got a code reader and got codes 21-coolant temp sensor out of range, 26- vaf/maf out of range, and 24- coil primary sensor failure. where should i start?
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
Service Code 21 (ECT) or 24 (ACT) indicates that the corresponding sensor is out of Self-Test range. Correct range of measure is 0.3 to 3.7 volts.
Service Code 26 indicates the output of the Transmission Oil Temperature (TOT) sensor was out of Self-Test range.
Service Code 26 indicates the output of the Transmission Oil Temperature (TOT) sensor was out of Self-Test range.
Thread Starter
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Junior User
Joined: Apr 2008
Posts: 71
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From: Brunswick, Ga
If the codes are normal, what should i look for? sometimes it runs ok then sometimes it goes to stumbling and popping back thru the manifold. i havent been able to get it to run long enough to get up to normal operating temp today. no oil in coolant or anything so im doubtful its a head gasket. i would think that its timing related except that its intermittent. Im lost
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
You might check for a loose timing chain, I do not let one mine go for more than 4 degrees but someone said their book says 5 degrees is max.
You could also check the timing with a light with the SPOUT removed to see if it is set at 10 degrees BTDC.
Do you see any smoke out the tail pipe, if so is it white or black?
If it is black pull the vacuum line off the FPR and turn the key off and on with a cold engine. If any fuel comes out of the nipple the FPR is bad.
You may also check to make sure the EGR valve is not stuck open as it will do this also.
Just unscrew the big tube going in the bottom of the EGR valve and drop a penny in it and screw it back snug but not tight enough to mess up the tube seat.
You could also check the timing with a light with the SPOUT removed to see if it is set at 10 degrees BTDC.
Do you see any smoke out the tail pipe, if so is it white or black?
If it is black pull the vacuum line off the FPR and turn the key off and on with a cold engine. If any fuel comes out of the nipple the FPR is bad.
You may also check to make sure the EGR valve is not stuck open as it will do this also.
Just unscrew the big tube going in the bottom of the EGR valve and drop a penny in it and screw it back snug but not tight enough to mess up the tube seat.
