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Websites for diagnostics?

C

chuggins143

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I bought my 90 K5 a few weeks ago and it's starting to throw code 44 which is Lean Exhaust which according to cfm-tech is an indication of "Low O2 Sensor Voltage". Now, it has what looks to be a brand new O2 sensor in it, and I don't just want to start throwing parts at this thing so where is a good place to start? Is there a OBD1 reader that will give me more info than just the codes?? ...maybe some sort of jumper or cable to plug into my laptop? This is my first jump back on the Chevy band wagon in a long time. (Probably been over 15 years since I owned my last bow tie)

Basically, what it's doing is when I first start it, it'll rev up to idle and then down to almost dieing and repeat about 5-6 times... then it'll just idle fine for a while, and after a few min it'll rev down and almost die again and rev back up. I can't see the RPM's since this truck doesn't have a tach... first manual rig I've ever owned that didn't have a tach, which I thought was wierd, but I digress... any thoughts or directions to other sites? Any direction or help would be much appreciated!!
:bow::bow:
Chad
 
If it looks brand new then start checking the wiring . Wiggle the wiring while it's idling and see if it changes anything . Listen to see if it goes up or down or smooths out. Is the check engine light on ? Maybe someone has Monitor 4000 near you to plug in and check the sensor readings .A bad O2 sensor will do that .
 
is this when u start up when its cold? cus if so your oxy sensor isnt in play yet cus your truck is in open loop, when it warms up enough it goes into closed loop and your oxy sensor is in play.
 
o and http://www.aldlcable.com/ thers a cable and software for your laptop.
check for vacuum leaks, thats where i would start cheap and easy, make sure your fuel filter isnt clogged. but there is alot of stuff besides the sensor itself that can cause the computer to throw that code, it could be as stupid as a bad computer ground
 
things thay will throw a Code 44 and give a bad idle.
Vaccum leaks. Check all hoses and throttle body base for leaks. Bad TB base gasket is a common problem.
EGR valve stuck open slightly or EGR soelenoid stuck open and allowing vaccum to EGR at idle..
Idle air controll valve stuck or dirty.

Check for Vaccum leaks first. They are the most common problen for a bad idle.

Other things that can cause a 44 are a clogged fuel filter or bad fuel pump.
Bad ground as said above

Software for your laptop:
Go here:http://winaldl.joby.se/ and Download WINaldl its free. Then All you need is the cable which you can build or buy.

As far as Scaners go Auto X Ray has a OBD1 scanner that gives real time operating data. I have one it works good. You can usually find them on Ebay cheap. OBD1 is brand specific you will need one with cable for GM.
 
Wow! Thanks for all the input there guys! :bow: I now have some places to start... Much appreciated!

To answer the question... yes, it's cold when it does the idle up and down thing... Once it's warmed up, I can be driving down the street and I'll pull up to a light and it'll idle fine, but once I start letting out on the clutch and giving it a little gas, it'll fall on its face... looses all power, it won't die, but will just go powerless. Now, I can push the clutch back in and rev it up a bit and slip the clutch and it'll get moving and once I'm going as long as I'm gentle with the peddle, it runs pretty good, but if I try to really mash the gas, it'll fall on its face again. Dunno, really weird.

Anywho, thanks for all the ideas!
Much appreciated!
Chad
 
Ok, so the saga continues... I went out today and started messing around with the Blazer and removed a bunch of wiring for extra lights and crap that were very poorly installed and found that the O2 sensor that was installed was a 3 wire unit. It had a wire (hopefully the ground) that was just screwed to the firewall, one that was spliced into a switched hot, and one that was plugged into a wire that goes through the firewall over by the AC hoses! :eek1: Through the same penitration that the vacuum line goes through for the climate controls. Not sure what that wire is acutally for, but I can probably assume that it is not for the O2 sensor since both diagrams that I've been looking at show the single wire coming from the wiring harness. Ok, so now my question is does anyone have a clue as to what color wire I'm looking for?? Obviously this was hacked together and done incorrectly. My harness is looking pretty shabby right now, but I'm slowly making progress on cleaning it up... also, is the main wire bundle supposed to go over or under the brake booster assembly?
Thanks! :bow::bow:
Chad

Edit... Ok, I found that it's a small Purple wire coming from the ECM connector (the D7 wire to be exact) More to follow as it becomes available...

Edit2... Someone had mentioned that a clogged fuel filter might be something to look at, but it appears to have a new filter on it.
 
Last edited:
Three wire o2 is a good thing it'll go into closed loop and stay there a lot quicker, just make sure it's installed correctly. Three wires, Switched 12V, Ground and Data = Purple (D7)
 
Slapperbar said:
Three wire o2 is a good thing it'll go into closed loop and stay there a lot quicker, just make sure it's installed correctly. Three wires, Switched 12V, Ground and Data = Purple (D7)
Click to expand...

Hmm, ok... I guess I could hook it back up the way it was... and I thought I was on to something, rats! ...and I did find that the random black wire that was running to the sensor wire was actually spliced to the D7 wire, so it was hooked up right, just not through the harness. Do you have any idea of how much current it pulls to heat up?

Ok, I'll keep searching...
Thanks!
Chad
 
All I know is you need to find what brand o2 is in there and hook it up right. If memory serves, the black is the ground, not the data line. People who know will PLEASE correct me if'n i'm wrong.
 
had a buddies 91 burb doing like you mention, we changed o2 same thing put new injectors in it same thing...turned out to be a screwy temp sending unit sending crazy info to ecm, telling ecm it was -30f then change to 200f it was just varying it ohms to the ecm wildly and everything else was changing to match what the temp sending unit was telling the ecm and it was idling erratic, we found it after we had replaced dang near everything possible, we didn't think the temp sending unit would effect so much, a gm tech mentioned it, we changed it out, ran like a champ.
 
blazin_blazer said:
had a buddies 91 burb doing like you mention, we changed o2 same thing put new injectors in it same thing...turned out to be a screwy temp sending unit sending crazy info to ecm, telling ecm it was -30f then change to 200f it was just varying it ohms to the ecm wildly and everything else was changing to match what the temp sending unit was telling the ecm and it was idling erratic, we found it after we had replaced dang near everything possible, we didn't think the temp sending unit would effect so much, a gm tech mentioned it, we changed it out, ran like a champ.
Click to expand...

Do you know what kind of signal the temp sensor sends? (mV, ohms, giga-hertz) I'm figuring ohms, but thought I'd ask.
THX
Chad
 
i do believe the temp sending unit sends a signal to the ecm by means of ohms, I'm not sure what its supposed to be when it is correct, but know it was vareying wildly and ecm thought it was correct and adjusting for the differences causing it to idle erraticaly .
 
blazin_blazer said:
i do believe the temp sending unit sends a signal to the ecm by means of ohms, I'm not sure what its supposed to be when it is correct, but know it was vareying wildly and ecm thought it was correct and adjusting for the differences causing it to idle erraticaly .
Click to expand...

That's kinda what I figured... I'll pull one of the Fluke meters from work and check it. I went and picked up a new temp sensor tonight and will try that too.
Thanks,
Chad
 
One wire is the reference voltage (5V IIRC) the other is obviously the voltage through the sensor.

A scantool will tell you coolant temp. Can't recommend sticking the multimeter probes through the wiring insulation.

Really need to run down the troubleshooting flow chart. Your varying idle when cold has nothing to do with O2. Also won't affect WOT runs.
 
Dorian, I just read your link and I have a website I can host your TBI/TPI troubleshooting manual. E-mail it to me and I will add it to my sticky in the injection section.

Looks like someone replaced the O2 with heated and fuel filter on this rig so if you can't find a vacuum leak or other things mentioned above it really points to low fuel presure.
 
Fuel pressure... that's easy enough to check, I'll pull my fuel pressure test kit tomorrow after work and see what it's running at. What is the fuel pressure supposed to be?
THX
C
 
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