Lope Lope Lope

[Kiqman]

My K5 won't hardly idle when I come to a stop sign and the engine is cold. It's like the fuel line is kinked. I'm running the 5.7 TBI with HP heads. Once the engine is warm I can come to a stop no problem. Runs like a top. Wouldn't a vaccum leak continue regardless of the engine temp? Also, when starting cold, my temp jumps through the roof even with my flex-a-lite fans for the first few minutes and then calmly comes back to 210. Problem is I worry about it getting that hot every time I run it. Should I switch to a 160 degree thermo? Is there a reason not to? Finally, I get a "lean" code nearly every time I drive but the vehicle seems to be operating fine? Is this due to the aftermarket heads or what? Shouldn't the motor be running really hot if it's lean? I took it in when the "check engine" lean light first came on and they replace the fuel pump? Didn't make the light stop coming off though. I'll quit with the questions now.

 

[bigbadchev84]

Sounds Like Your Thermostat Is Getting Stuck Then Will Open At A Hotter Temp

 

[Wingnutt]

First your temperature issue, you may want to try a new thermostat, it sounds like the one in there is sticking a bit before it opens. Also, don't go below 180 degrees without getting and installing ALDL for your computer (home type). This nifty little bit of software (when connected to your Blazer ) will let you see what every sensor is reading. The reason is to monitor you engine readings to ensure that it is going into closed loop mode when you install a cooler thermostat.

As far as the lean code, it is directly related to your cold idle problem, both of which are being caused by the heads. TBI heads are nortously restricive and you replaced them with more efficient ones letting the air flow quicker through the new heads. The vehicle computer sees the lowered MAF readings (think opposite of vaccum here, lower MAF values means the engine is working less) and interprets this as signal as needing less fuel, meanwhile the O2 sensor (a direct reading from the exhaust) is telling the computer that the fuel mixture is to lean, hence the lean code. Sounds like you need to do a little chip tuning to get it running right.

 

[Kiqman]

Good Stuff Wingnutt!

ALDL…never heard of it but love the idea of being able to plug my PC into the Blaze and have a chat. We’ve needed a heart-to-heart. What does ALDL stand for and where can I get my hands on this horse-whisperer technology?

When you say “closed loop” are you referring to the thermostat in closed position? What happens if you don’t achieve this “closed loop?” The coldest it gets here is about 40 degrees.

Will replace the thermostat with a new one to check the sticking theory. Glad you let me know not to automatically just get the 160-degree.

You mention, “chip tuning” to get rid of the lean code caused by my upgraded heads. Can I do anything like that on my old 1989? I know it has a CPU behind the glove box but I can’t modify it can I? I just figured it was too old for chips or computer controlled performance mods. What happens if I don't address the lean code...it seems to run fine and not overheat?

Can't believe I just found this site months ago!?!

 

[Wingnutt]

Ok stand by for the crash course in managed engines.

The phrase "open loop" refers to the mode the computer uses when you first start up a cold engine. During the warm up period (before the engine and O2 sensor heats up enough to start providing reliable data) the computer controls the engine by a set preprogramed paramiters in the chip. During this time, the computer is doing nothing except reading these preprogramed paramiters.

Once the engine reached a perdetermined temperature (again this is programed into the chip) it goes into what is called "closed loop" mode. The computer starts managing the air fuel (A/F) ratio and timing by compairing the various sensor readings to another differant set of paramiters (programed into the chip) and makes adjustments accordingly.

It *sounds* fairly simple and for the OBD I system, and it is, very, very tedious, but not to bad. Once you understand what the computer is looking at and how it controls everything you can start your own trouble shooting and eventually chip tuning.

Now to get started, you need a couple of things. First off you have to see what the engine computer is seeing. You do this with ALDL and a connector cable. This site has all the info you need: http://winaldl.joby.se

Then to learn what everything means and does, go over to www.thirdgen.org and start looking around. Those guys are primarly geared towards the third generation F-bodies, but they are more than willing to answer a truck guys questions. Believe me, those guys know thier stuff. Also a little advice, when you go to the DIY PROM board, do NOT ask where you can buy a chip. That is a seriously tabou subjuct on that board and they are very adiment when they let you know it too.

Last thing, use the search engines on both this board and any other you visit. It saves a LOT of time, and in 95% of the time, the same question or discussion has been asked many times before. I've answered a lot of TBI posts here, so hopefully that will get you started good. Anything else, feel free to ask.