No codes??
Thread Starter
5th Gear
Joined: Sep 2007
Posts: 5
Likes: 0
From: Twinsburg Ohio
No codes??
Hi all,
I'm new to the forum, have been reading for a while though! I have a problem that maybe someone else has had and can help with. I've done a lot of searching and haven't found a similar problem solved, so I guess now it's time to ask
I just picked up an '88 L98 convertible, My first C4; I had a C3 previously, which has an idle problem (go figure). It looks like someone had a cooling problem at one time and rewired the fan to come on at ignition. That's the only non-stock modification I can see. The problem is that the car idles at 800 rpm in drive and when the coolant is between 160 and 190 deg. the car wants to die. The check eng light comes and goes every couple of days and when I jumper the A and B terminals on the ALDL the light won't flash any codes not even 12, just stays lit. I could attribute the idle problem to a vacuum leak except it only happens between 160 and 190 deg.. Also the ECM won't go into diag mode?? Could it be a bad ECM? Will changing the ECM cause a problem with the VATS? Any help would be greatly appreciated. Great forum and thanks in advance for any help...
I'm new to the forum, have been reading for a while though! I have a problem that maybe someone else has had and can help with. I've done a lot of searching and haven't found a similar problem solved, so I guess now it's time to ask
I just picked up an '88 L98 convertible, My first C4; I had a C3 previously, which has an idle problem (go figure). It looks like someone had a cooling problem at one time and rewired the fan to come on at ignition. That's the only non-stock modification I can see. The problem is that the car idles at 800 rpm in drive and when the coolant is between 160 and 190 deg. the car wants to die. The check eng light comes and goes every couple of days and when I jumper the A and B terminals on the ALDL the light won't flash any codes not even 12, just stays lit. I could attribute the idle problem to a vacuum leak except it only happens between 160 and 190 deg.. Also the ECM won't go into diag mode?? Could it be a bad ECM? Will changing the ECM cause a problem with the VATS? Any help would be greatly appreciated. Great forum and thanks in advance for any help...
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
When you seek codes from the ECM, I assume you are doing the following:
1. Short/connect A to B on the ALDL connector
2. Turn ON key.....but do not start engine
3. Observe the SES light flashes
If this is correct and you do not get the initial 1 2 1 2 1 2 series of flashes , you have potential ECM problems. Before you start throwing $$$ at the car on parts, get a scan on you engine control system. Ask around as someone in your area will have this equipment to help you.
1. Short/connect A to B on the ALDL connector
2. Turn ON key.....but do not start engine
3. Observe the SES light flashes
If this is correct and you do not get the initial 1 2 1 2 1 2 series of flashes , you have potential ECM problems. Before you start throwing $$$ at the car on parts, get a scan on you engine control system. Ask around as someone in your area will have this equipment to help you.
Thread Starter
5th Gear
Joined: Sep 2007
Posts: 5
Likes: 0
From: Twinsburg Ohio
I did follow the above listed procedure (more than once.. I've done this on other GM products with no problems), the light just didn't flash, just stayed steady lit... I didn't want to have to order an ALDL cable but it looks like I'm gonna have to. Any suggestions as to the best quality vs. price vendor for the cables?
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
I know you are a new member and welcome to the forum 
After saying this, please complete your profile so that members such as myself will know the year of your car and the city - state in which you reside. Why is this important? Knowing where you are allows people in the area to help you. If you live in the St. Louis area, I have a scan tool (Turbo-Link) and will scan you car for you ...... cost = 1 cold beer!
Suggestions:
1. Remove the negative battery cable and let the car ECM reset itself and see if you can get the ECM into the diagnostic mode.
2. Before you buy a cable, contact some local Corvette people (look for Corvette Clubs in your area) and see if someone in the area will do a scan for you.
3. If you buy a new ECM, get a GM rebuilt unit and this will cost you about $100. There is dealer in Kansas City named Superior Chevy that will sell and ship the unit to you at a big discount.
Hope this is helpful and I look forward to seeing your posts on the forum
After saying this, please complete your profile so that members such as myself will know the year of your car and the city - state in which you reside. Why is this important? Knowing where you are allows people in the area to help you. If you live in the St. Louis area, I have a scan tool (Turbo-Link) and will scan you car for you ...... cost = 1 cold beer!
Suggestions:
1. Remove the negative battery cable and let the car ECM reset itself and see if you can get the ECM into the diagnostic mode.
2. Before you buy a cable, contact some local Corvette people (look for Corvette Clubs in your area) and see if someone in the area will do a scan for you.
3. If you buy a new ECM, get a GM rebuilt unit and this will cost you about $100. There is dealer in Kansas City named Superior Chevy that will sell and ship the unit to you at a big discount.
Hope this is helpful and I look forward to seeing your posts on the forum
Team Owner
Joined: Jan 2003
Posts: 20,293
Likes: 240
From: Summerland B.C. Canada
Thread Starter
5th Gear
Joined: Sep 2007
Posts: 5
Likes: 0
From: Twinsburg Ohio
You guys are the bomb! Thanks for the help, I'm sorry I didn't have the info filled out (rectifying that right now)...I'll look into the ECM and let you guys know what happens... Thanks again!!
