1985 C4 idling issues and problem staying on.
03-13-2014, 09:19 PM
#1
Cruising
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1985 C4 idling issues and problem staying on.
I've reached a point on my project where i'm stuck in the mud.
Every now and then when I start my C4 she will start right up and run fine.. for a little while that is. It isn't long before she starts sounding bogged down or kind of like she isn't getting enough fuel to stay on, maybe?
Most of the time when she doesn't start right up she turns over and almost instantly dies.
What I've done so far on this vehicle is..
1.changed radiator (was overheating before, fixed)
2.changed starter. (problem starting, fixed)
3.changed plugs/wires. (was missing, fixed I think.)
4.changed distributor.
5.Set idle from around 1200 to 600. (a mechanic told me that these cars should actually be idling around 900-1000? Maybe someone can confirm this for me?) Also, now a couple weeks later the idle changes. sometimes when i put her in park she will idle at about 1300 and sometimes like today, she will idle at 600
6.changed fuel filter. (didn't fix the bogging down issue or not getting enough fuel??)
I have a fuel pump on stand by that i purchased but, some people keep telling me it's definitely NOT the fuel pump..
I've asked almost every mechanic and even the dealership what it might be. However, i keep getting the same answers, "We don't have a manual or documentation on a vehicle that old." or "we don't mess with cars like that." I even stopped at a restaurant and waiting on another man who owned a 55 Cadillac, however his response was he quit being a mechanic around the 70's.
Some help, PLEASE?
Every now and then when I start my C4 she will start right up and run fine.. for a little while that is. It isn't long before she starts sounding bogged down or kind of like she isn't getting enough fuel to stay on, maybe?
Most of the time when she doesn't start right up she turns over and almost instantly dies.
What I've done so far on this vehicle is..
1.changed radiator (was overheating before, fixed)
2.changed starter. (problem starting, fixed)
3.changed plugs/wires. (was missing, fixed I think.)
4.changed distributor.
5.Set idle from around 1200 to 600. (a mechanic told me that these cars should actually be idling around 900-1000? Maybe someone can confirm this for me?) Also, now a couple weeks later the idle changes. sometimes when i put her in park she will idle at about 1300 and sometimes like today, she will idle at 600
6.changed fuel filter. (didn't fix the bogging down issue or not getting enough fuel??)
I have a fuel pump on stand by that i purchased but, some people keep telling me it's definitely NOT the fuel pump..
I've asked almost every mechanic and even the dealership what it might be. However, i keep getting the same answers, "We don't have a manual or documentation on a vehicle that old." or "we don't mess with cars like that." I even stopped at a restaurant and waiting on another man who owned a 55 Cadillac, however his response was he quit being a mechanic around the 70's.
Some help, PLEASE?
Last edited by MarcusWrenn; 03-13-2014 at 09:21 PM. Reason: Left out some crucial information.
03-14-2014, 02:59 AM
#2
Race Director
Get a FSM (Factory Service Manual).
The correct mechanical idle is adjusted by the Minimum Idle Adjustment:
http://forums.corvetteforum.com/1570563689-post1.html
After you get that set up, the ECM controls the idle speed. If the minimum idle is not set correctly then the computer will go nuts trying to get the RPM to where it thinks it should be.
The idle speed is set in the "tune" in the ECM. It varies from year to year and depends on the coolant temperature. There is a tolerance on the idle RPM and the computer gets within 50 RPM (75 RPM in some cases) and calls it good enough. Your idle should be around 650 RPM in Park/Neutral and with the engine up to normal operating temperature.
The ECM adds 100 RPM to the idle speed when you put the trans in gear.
The correct mechanical idle is adjusted by the Minimum Idle Adjustment:
http://forums.corvetteforum.com/1570563689-post1.html
After you get that set up, the ECM controls the idle speed. If the minimum idle is not set correctly then the computer will go nuts trying to get the RPM to where it thinks it should be.
The idle speed is set in the "tune" in the ECM. It varies from year to year and depends on the coolant temperature. There is a tolerance on the idle RPM and the computer gets within 50 RPM (75 RPM in some cases) and calls it good enough. Your idle should be around 650 RPM in Park/Neutral and with the engine up to normal operating temperature.
The ECM adds 100 RPM to the idle speed when you put the trans in gear.
03-14-2014, 11:16 AM
#4
Burning Brakes
follow the link that Cliff sent. I would not recommend taking the throttle body apart, but would clean it. I would use small pins in the TPS wires.
also, you may have a number of things that are affecting the engine. fix the idle adjustment first.
also, you may have a number of things that are affecting the engine. fix the idle adjustment first.
03-14-2014, 01:40 PM
#5
Hi Marcus,i 've an 85' too,it's a one year car,since during 86 lot of things changed,ECM,heads,different MAF system...
At the basic this car need to be set at factory mechanical advance 6 degrees with est disconnected (a single connector orange wire near the battery).As told the most important starting point is the Minim Idle Adjustement, there is a service bullentin for 85 about minimum idle resetting cuz of stalling issue.
http://www.corvetteactioncenter.com/...Speed+Revision
You have to perform this procedure to have the minimum idle correctly setted,as told.Important parts to ceck are all the vacuum lines, for cracking.The IAC motor,is the device that regulates idle by opening and closing air passage through the TB.Clean the IAC housing and TB with carb cleaner spray.
Set the spark plugs gap as for factory specs,ceck all your spark plug wire for the correct firing order,ceck fuel pressure too at the rail valve it shuold be steady at 38-41 psi.
set correctly the car as told and move on...
You could have air entering the intake manifold behind the china wall (rear edge of lifters valley)
At the basic this car need to be set at factory mechanical advance 6 degrees with est disconnected (a single connector orange wire near the battery).As told the most important starting point is the Minim Idle Adjustement, there is a service bullentin for 85 about minimum idle resetting cuz of stalling issue.
http://www.corvetteactioncenter.com/...Speed+Revision
You have to perform this procedure to have the minimum idle correctly setted,as told.Important parts to ceck are all the vacuum lines, for cracking.The IAC motor,is the device that regulates idle by opening and closing air passage through the TB.Clean the IAC housing and TB with carb cleaner spray.
Set the spark plugs gap as for factory specs,ceck all your spark plug wire for the correct firing order,ceck fuel pressure too at the rail valve it shuold be steady at 38-41 psi.
set correctly the car as told and move on...
You could have air entering the intake manifold behind the china wall (rear edge of lifters valley)