Problem w/scantool, forces open loop
Thread Starter
Racer
Joined: Oct 2004
Posts: 286
Likes: 1
From: Washington DC
Problem w/scantool, forces open loop
Hi, this is my first post here. I've long dreamed of owning a vette, but have never had the $$. After several years of saving up I've finally acquired an '85 with very little mileage. I look forward to contributing to the forum. Anyways, on to my problem.
I have an actron OBDII/OBDI scanner. I've used it on plenty of other vehicles with little to no problems. My vette has been idling rough, so I figured I'd look at tps voltage and IAC signal. Here's the issue, though. When I plug the scantool into the ALDL, it forces open loop. Idle jumps from 600RPM or so up to 1000-1050. I'm sure it's in open loop, of course, because the scanner tells me so. Am I doing something wrong? Is there a special procedure for hooking up a scanner to a vette that I don't know about?
Thanks,
Pablo
I have an actron OBDII/OBDI scanner. I've used it on plenty of other vehicles with little to no problems. My vette has been idling rough, so I figured I'd look at tps voltage and IAC signal. Here's the issue, though. When I plug the scantool into the ALDL, it forces open loop. Idle jumps from 600RPM or so up to 1000-1050. I'm sure it's in open loop, of course, because the scanner tells me so. Am I doing something wrong? Is there a special procedure for hooking up a scanner to a vette that I don't know about?
Thanks,
Pablo
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
Your scan tool does not seem to read the computer ?
When my car goes into open loop the computer has timed out.
But I use tts-datamaster,it does the high idle when the computer is not picking up information.
Also if I don't use the white thing that comes with the cable it will do what you said yours does.
The white conector in line allows information to be read by both computers.
Just my 02 but with my 86 I have to use a 10k ohm resistor for the computer in the car to pick the hand shake to talk to the other lap top computer.
When my car goes into open loop the computer has timed out.
But I use tts-datamaster,it does the high idle when the computer is not picking up information.
Also if I don't use the white thing that comes with the cable it will do what you said yours does.
The white conector in line allows information to be read by both computers.
Just my 02 but with my 86 I have to use a 10k ohm resistor for the computer in the car to pick the hand shake to talk to the other lap top computer.
Burning Brakes
Joined: Dec 2002
Posts: 1,088
Likes: 0
From: Lakeland fl
Its not necessarily in open loop, its in ALDL mode. This mode puts the above mentioned 10k resistance accross the a&b terminals to get the compter to send information. As far as I know, the 6870 ECM (used in 1985 only) will only send data in this mode. Now I have WinALDL that I used in my 85 when I had the 6870 ECM, and it would recieve a very,VERY, small amount of data without this resistor, but it wasnt much and it wasnt usefull. In the later 165 ECM's the 10K is only needed to initiate the data transmission, the it can be removed. In the eprom it is possible to alter the ALDL mode RPM, but you would need to burn a new chip for that.
Burning Brakes
Joined: Dec 2002
Posts: 1,088
Likes: 0
From: Lakeland fl
The car always starts in open loop. Theres a timer to heat the O2 sensor, it takes like 160 seconds or something, then it may go into closed loop. Irregardless, its not the open loop thats raising the idle, its the fact that the ALDL mode is doing it, and you probably wont get useable data about IAC counts when in that mode because of it.You can check your TPS with a regular digital volt meter, and you can still use your scan tool to check for O2 sensor voltage. Also, try cleaning your egr and IAC, checking your fuel pressure both running and when you shut the engine down to test for leaky injectors.
Racer
Joined: Apr 2003
Posts: 426
Likes: 0
From: Detroit MI
The 1984 manual states the timer is taken out. It should go to closed loop if all closed loop conditions are met.
The 1986 manual states that in10k mode the system operating conditions are modified as follows.
->Closed looptimers are bypassed.
->EST (spark) is advanced.
->IAC will control engine to 1000 rpm +/- 50 rpm.
->On some engines the canister purge soleniod will be enabled.
->Park/Neutral restrict functions will be disabled.
Sorry don't have a 1985 manual but it sounds like yours works like the 86 version.
You will have to wait for the system to go closed loop as the others have said. The system would also need the closed loop conditions met. I have not came across anything stating exactly what that is however for a early MAF car It would probably require the MAF,O2, and maybe the tps, egr systems to be in working order.
The 1986 manual states that in10k mode the system operating conditions are modified as follows.
->Closed looptimers are bypassed.
->EST (spark) is advanced.
->IAC will control engine to 1000 rpm +/- 50 rpm.
->On some engines the canister purge soleniod will be enabled.
->Park/Neutral restrict functions will be disabled.
Sorry don't have a 1985 manual but it sounds like yours works like the 86 version.
You will have to wait for the system to go closed loop as the others have said. The system would also need the closed loop conditions met. I have not came across anything stating exactly what that is however for a early MAF car It would probably require the MAF,O2, and maybe the tps, egr systems to be in working order.
