Deciphering Live Data.

[scott2093]

My MTG2500 scan tool had a few options within the "Engine" menu. There was an option for checking "Codes and Data", and an option for checking codes and data while road testing.

The road-test Codes & Data check allowed normal idle speed. The non-road-test code 'n' data check raised the idle to ~1000 rpm.


Depending on how your scan tool is set up, that's likely the reason for the higher rpm when the tool is connected.

Sounds similar to the discussions in another thread about ALDL cables/adapters and how activating the 10k resistor option which jumped terminals A&B to put scanner in ALDL mode could cause idle issues. Wonder what adapter the op is using with the app and if it has this 10k option. I know mine does and it's recommended to leave it off on all the TBI trucks.

 

[GoToGuy]

Yes as Mr schurkey said. There are instances where the connection places the vehicle in a test condition. It was discussed last year sometime. I don't remember if it was ALD connector or the testing program putting it in a " testing " .

 

[Nick88]

I believe you need the 10k ohm resistor on earlier tbi's like mine. I tried without it and I get data but its kinda choppy and I dont really get some data.

 

[Nick88]

So I have another question for everyone. It appears that the knocking is the issue and the truck is at max retard, which is sorta what I figured. Everything is new so I imagine its an issue with the exhaust noise. Is there a way to almost in a way tune the knock sensor by tightening or loosening it?

 

[scott2093]

I believe you need the 10k ohm resistor on earlier tbi's like mine. I tried without it and I get data but its kinda choppy and I dont really get some data.

Choppy could be because you'll have a slow 160 baud rate . Not getting all data while driving may just be a limitation of the older system. I'd want to verify what's going on for sure so you're not relieving yourself in the wind trying to figure things out.
Saw this on another Chevy forum...

 

[PlayingWithTBI]

I believe you need the 10k ohm resistor on earlier tbi's like mine. I tried without it and I get data but its kinda choppy and I dont really get some data.

No, you don't use the 10K resistor on any TBI GMT400 truck. I never use it on my 88. Disconnect the resistor, then look at your idle RPMs and IAC counts. At idle your IAC counts s/b somewhere ~40 or less. The best is ~10 with engine warmed up and nothing (like A/C) turned on. If it goes down to zero, someone probably dicked with the min idle screw.

 

[Nick88]

Alright good news! I did what you guys saod and took off the resistor and it idles fine now, I also did some switching around of stuff and replace my knock sensor wire with a normal 18 gauge wire. I switched distributor caps to my old accel since the dui seemed to hold moisture, and just in case im getting knocking from carbon I poured probably around a half gallon of water into the TBI to steam clean. Now the knock counter goes to 3 on start but doesnt seem to rise at all, the truck after the water ran like a race horse for a few blocks but feels kinda sluggish again now. Does anyone have any ideas?
Ill get a ss of idle right now also

 

[Nick88]

You must be registered for see images attach

 

[AuroraGirl]

nick, what is your condition of your knock sensors. If you hit your passenger manifold with a screwdriver and hammer, you should be able to create a knock count

You must be registered for see images attach

 

[scott2093]

Still curious what that TPS % is... If it's throttle position at 30% and the no throttle voltage looks good at .59, that wouldn't make sense....