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tbi 350 running rich and dies

redbird00

redbird00

1/2 ton status
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Oct 18, 2007
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Location
San Antonio, TX
so i just got this blazer, its a 90 tbi 350. its a little tough to start when its cold and runs great, but once the motor gets warmed up, if it sits and idles for more than 5 mins or so, it gets real rich and ends up dying, and it seems the warmer it gets the quicker it dies. it has always refired and runs fine, its just sitting and idling thats a problem. as far as i know, only mods to it are open element filter, headers and exhaust.

any help diagnosing this problem would be great, also no check engine light or ses light, not sure what its supposed to be.
 
Go to the Buyers Guide link in my signature, then go to the end where it describes how to pull the ECM codes. What codes are present?

Before you do anything, figure out what the computer says is wrong, it can save you a LOT of hassle. All you need is a paperclip!
 
There's also a guide to trouble codes in the stickys!

With the headers the O2 is probably cooling off going to open loop then loading up. If you have a laptop then get a ALDL cable for it. Invauluble in fixing your own rig.
 
weather has been crazy down here, so haven't pulled codes yet.

i have it on my fbody, but would an O2 simulator work?
 
Never tried one? If it works on an F body then it'll probably work on the blazer. O2 circuit is the same on all cars, just one volt that the o2 sensor adjusts by reading left over oxygen.
 
Check the codes first!!! It takes 2 minutes and a paperclip!
 
We should take bets for when he pulls the codes.
1) O2 sensor (once warm goes into closed loop and runs too rich)
2) Coolant Temp Sensor (bad signal keeps rich A/F ratio even after engine warms up)
3) ??
 
ok, i've looked. where is the port to check the codes, i can't find it. i figured it would be under driver's side ip but i dont see it, anyone have a pic so i know what i'm looking for?

after reading a couple other posts the 02 sensor looks new, i bought another just in case. and the temp sensor isn't hooked up, could that be making it run rich? thanks!!
 
Temp sensor isn't hooked up?? Not sure what the computer does if it doesn't get a CTS signal, but it definitly could be part fo the problem. The coolant temp sensor creates the signal the computer uses to create a virtual "choke". If the coolant is cold, the computer enriches the A/F ratio to act like a choke. You should get these things all hooked up and see what is going on when they're plugged in.

Yes the port should be just below the dash on the drivers side, sorry I don't have a pic, but I bet if you google "read OBD 1 codes GM" you'll get tons of pics and instructions.
 
YES! Not having the CTS hooked up makes the ECM think it is -40F all the time. Fix that, then clear codes by disconecting the battery or pulling the fuse for a minute. Then fire it up and drive it around till warmed up and all should be fine unless there's another issue.

Heres a link to pictures of the OBD1 ALDL port your looking for.
http://winaldl.joby.se/aldlcable.htm
 
I am having the same problem with a 91 TBI. I bought the truck back in November and have changed the O2 sensor and the coolant temp sensor and the pigtails that hook it up. When I checked the codes before I replaced the coolant temp sensor it was throwing a 14. The check engine light was on before I replaced the coolant temp sensor as well and went off immediately after replacing it. I haven't checked the codes since I reset it, but does anyone have any other suggestions as to what I should start checking to find the problem?
 
OnTheLoose said:
I am having the same problem with a 91 TBI. I bought the truck back in November and have changed the O2 sensor and the coolant temp sensor and the pigtails that hook it up. When I checked the codes before I replaced the coolant temp sensor it was throwing a 14. The check engine light was on before I replaced the coolant temp sensor as well and went off immediately after replacing it. I haven't checked the codes since I reset it, but does anyone have any other suggestions as to what I should start checking to find the problem?
Click to expand...
Well if you cleared the codes awhile ago and have driven it around, then check the codes again. It's the first thing to do.

Then give us a little more information as to what your problem is?
 
Dies when it gets warmer....hmmm. What color is the spark coming from the coil when its cold? then, What color is the spark from it when its warm?
Temp related problem with the coil could be the problem.....weaker spark as it warms up,causing rich condition, engine loads up and quits?
Just a shot in the dark.
 
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Check the codes ... that should tell you a bad coolant or O2 sensor is to blame.
 
There you go. Remember that it will flash code 12 (which means "diagnostic mode") first, and then anything after that is the errors.
 
Same issue I had ended up being the o2 sensor. I had to replace it with a new 3 wire 02 and all was well.
 
If his temp sensor is unhooked I don't think the o2 will ever come into play. The o2 has temp settings in the ECM that must be met before it go look at the o2 values. Seems odd that if its running rich enough to die it should have a SES light on. If he just got it the bulb could have been removed to hide problems. This happens alot in Ohio where they dont check smog and most people don't know there is a self test for the bulb and circut everytime you turn the key on.
 
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