91 Blazer running rich after it warms up

[MR4WD]

91 Blazer with a bone stock TBI 350:

I've replaced the knock sensor and computer temp sender before I really thought about what's going on... It runs like [darn] when it's warm, and that's about 3 minutes of driving after start up... No power below 2500 RPM, lugging etc. Motor really hesitates when you get on the throttle, like in 4th gear up a hill I'll have to drop down to 3rd and wind the motor out...

I haven't even checked the O2 sensor, but that may be the problem. All I know is it's running really rich after it warms up (the tail pipe is full of really dark soot) It's not throwing any check engine light codes but it's getting to be a real pain in my butt.

If I had a carb, it'd be running perfect right now. Since it's TBI, I have no idea how to tune this engine. All I know is, I can climb hills and lean to angles my previous 496 would starve for fuel at and that's a step in the right direction~

Please lend me your advice and experiences with this matter,
Chad.

 

[k20]

Which temp sensor did you replace? The one in the head or the one in the manifold. The one in the manifold drives the computer, and the one in the head drives the gauge. If you replaced the manifold one, then I would say the o2 sensor, or maybe even the IAC. Maybe it is stuck so that no air goes past, causing it to richen up when it would need to lean out.

 

[K5Kell]

I would have to second what k20 said. I had the similar mistake of changing the "wrong" temp sensor. if it was the one on the intake manifold you changed /forums/images/graemlins/dunno.gif.
-Kell-

 

[Thunder]

Before you go throwing more parts and money at it.Check for trouble codes. Then post what the ECM tells you. It will help to solve the problem.
If you dont know how to get the codes here's how: GM trouble code info
Your ALDL connector is right below the steering collum

 

[MR4WD]

[ QUOTE ]
Before you go throwing more parts and money at it.Check for trouble codes. Then post what the ECM tells you. It will help to solve the problem.
If you dont know how to get the codes here's how: GM trouble code info
Your ALDL connector is right below the steering collum

[/ QUOTE ]

I thought I'd outlined that it's not throwing any codes at all right now in my first post. I also said I replaced the "computer temperature" sender, not the gauge sender.

In any event, perhaps I should throw in an 02 sensor for the heck of it, and have a look at the IAC.

I'm at at a loss for ideas, but I may check for vacuum leaks, as I've heard before this can cause many problems with these older TBI engines.

 

[k20]

just so you know your light might not be on if you have a code. For the heck of it one day i checked codes had one. No light. It mighta popped on one day just as i turned it off.

 

[Thunder]

Your first post was a little confusing. You said there were no CEL codes. There are two types of codes that the ECM stores. Hard codes whick light the CEL. And Soft codes which indicate a malfunction but dont light the CEL.
You said there were no codes stored
If you did do a scan you should of at least got a code 12. This indicates the ECM is working. If you did not get a code 12 the ECM may be bad.

 

[MR4WD]

I replaced the 02 sensor and still nothing. How would I "test" the IAC, and not just replace it on a wild ass guess?

I did the paper clip trick last year some time and I don't think I got a code 12, something like 36 or something but that's just a loose guess. What's that website that lists the codes and how to do it again?

It seems that with the new exhaust the truck is running "dangerously" rich. Dangerous in terms of me taking an axe to the tbi since it's annoying me so badly and if it was carbed, it would be running perfect by now.

Thanks,
Chad.

 

[Eric M.]

You should really pick up (or borrow) a scan tool and get the shop manual for your year electronic TBI. You're just shooting in the dark without it. The readings from the scan tool along with the manual will point you in the right direction.

Trouble shooting carbs and electronic fuel injection systems are 2 completly different things and there is a bit of a learning curve you'll need to get past, plus some new tools you'll need to pick up.

I went through the same thing 2 years ago. I finally broke down and got the right equipment and manuals which made solving problems much easier.

Eric M.