Problems w/scantool, forces open loop
Thread Starter
Racer
Joined: Oct 2004
Posts: 286
Likes: 1
From: Washington DC
Problems 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 $$. After several years of saving up I've finally acquired an '85 with very little mileage. I look forward to contributing to the forum. Anyways, on to my problem.
I have an actron OBDII/OBDI scanner. I've used it on plenty of other vehicles with little to no problems. My vette has been idling rough, so I figured I'd look at tps voltage and IAC signal. Here's the issue, though. When I plug the scantool into the ALDL, it forces open loop. Idle jumps from 600RPM or so up to 1000-1050. I'm sure it's in open loop, of course, because the scanner tells me so. Am I doing something wrong? Is there a special procedure for hooking up a scanner to a vette that I don't know about?
Thanks,
Pablo
I have an actron OBDII/OBDI scanner. I've used it on plenty of other vehicles with little to no problems. My vette has been idling rough, so I figured I'd look at tps voltage and IAC signal. Here's the issue, though. When I plug the scantool into the ALDL, it forces open loop. Idle jumps from 600RPM or so up to 1000-1050. I'm sure it's in open loop, of course, because the scanner tells me so. Am I doing something wrong? Is there a special procedure for hooking up a scanner to a vette that I don't know about?
Thanks,
Pablo
Safety Car
Joined: May 2003
Posts: 4,283
Likes: 0
From: Houston Texas
Post this in scan and tune. Can't see how it could make your car go into open loop. O2 sensor tells computer when it is time to go to closed loop. What is your O2 sensor readings. Also I didn't think Accutron made a scanner that measured both OBD1 and 2. I thought it was either or.
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
Originally Posted by C4Ownr24
Hi, this is my first post here. I've long dreamed of owning a vette, but have never had the $$. 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
For what I know about 85, I think that to go in ALDL mode and to be able to see the aldl stream, all corvettes from 85 to 89 NEEDS a cable with a 10k resistor between A & B pin.
90 and 91 models do not needs.
All cables (bought or DIY) for 85 to 89 corvette in order to perform datalog with a laptop and a free software are built with this resistor (10K).
-Beppe-
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
Originally Posted by C4Ownr24
Is there a source online for a cable with the resistor? The one I got says it does all GM 1985-19ninety-whenever they started using OBDII.
or i suggest you to write to Craig Moates (craig@moates.net) (at www.moates.net).
This guy is fantastic, He will reply to your mail the same day you ask!.
Explaine to him your problem and he will give you the right solution and the rigt equipment.
-No affiliation..bla bla... only an happy customer.
-Beppe-
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Another thing - the 1985 computer is very slow and crude. I had some issue with my FAST connection, it was causing some codes to appear, and, the idle would pick up. Some of that was caused by the computer going into Diagostic Mode.
I recommend you update the ECM to a 1987 or so... The added computer power and resolution will be worth it.
Think of it this way - in 1984, the ECM performed about 15 instructions per second (this is for the xfire engine), in 1987, the Chevy Truck ECU, same basic part, with an updated motherboard was performing 150(!) instructions per second! It is an easy swap, I have an article about this one some where.
I recommend you update the ECM to a 1987 or so... The added computer power and resolution will be worth it.
Think of it this way - in 1984, the ECM performed about 15 instructions per second (this is for the xfire engine), in 1987, the Chevy Truck ECU, same basic part, with an updated motherboard was performing 150(!) instructions per second! It is an easy swap, I have an article about this one some where.
Thread Starter
Racer
Joined: Oct 2004
Posts: 286
Likes: 1
From: Washington DC
I'd be interested in taking a look at that article, I've searched the forums for 20 minutes with no avail. Is it as simple as pulling the old ECM and plugging the new one in with no mods, or is there other stuff involved? I already know where I can get the computer, and would be happy to go buy a new one if it would resolve my aldl issues.
thanks,
pablo
thanks,
pablo
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
The problem may be with your '85 Vette ECM or the ALDL, though I think there's something with the early ECM.
I've tried without success to use my AutoXray on an '85 Vette, though it works fine on later models and even on my '86 IROC.
You may be able to tell something by using the ECM's Field Service mods, as described on my site. If that doesn't get at the problem, check the EGR valve for proper operation and for a leaking diaphram.
If it's missing at idle, hook a timing light onto each plug to see if the misses correspond to missed flashes.
I've tried without success to use my AutoXray on an '85 Vette, though it works fine on later models and even on my '86 IROC.
You may be able to tell something by using the ECM's Field Service mods, as described on my site. If that doesn't get at the problem, check the EGR valve for proper operation and for a leaking diaphram.
If it's missing at idle, hook a timing light onto each plug to see if the misses correspond to missed flashes.
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Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I don't have data on an '87 ECM but there are some differences in wiring between an '85 and an '88 ECM.
So, though it might not be a difficult adaption, it's not just plug-n-play to swap in an '87 ECM.
So, though it might not be a difficult adaption, it's not just plug-n-play to swap in an '87 ECM.
Instructor
Joined: Jun 2004
Posts: 155
Likes: 1
From: Melbourne Florida
I know the baud rates are different, the 85 run at 160 baud and the 86 and up run at 8192, that is one reason for the increase in performance going to the 86 and later ECM. I am not sure if the 85 and earlier sensors can react fast enough for the higher speed ECMs some delays may need to be programmed in for this to work properly, as I have not tried this it may plug in and run fine without any changes. I do not see why it would not work as most of the sensors are analog ( slow) in the first place. this is probably too much info. Bottom line is I don't see a problem as long as wiring matches. Maybe get wiring diagrams for both years and compare wires/ sensors etc.
good luck and PUMP IT UP !!!!!
good luck and PUMP IT UP !!!!!
