91 vette starts when it wants
Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
Likes: 0
91 vette starts when it wants
Quick review this vette was sitting for 20 years. done all tune up and cleaning of fuel system changed all fluids. I had a issue with smoking and found a couple faulty injectors. I burned up a couple ignition coils. When I changed the original cap rotor and coil out there was no ground bar on it so I did not realize it needed one. Dumb move lol. Anyways this problem has since been fixed and now it will start when it wants to and die as well. sometimes wont start at all. I do not have original remote to it for security. I also do not have original key. I had the key made and has worked fine til this point. If that has anything to do with the problem I don't know, I just know that the old chip in a key security system has been a pain for these years. Ive been leaning towards a security system issue but thinking about it now it did not have this issue until the ignition coil fried a wire. I checked the module at auto parts store and they said it was fine. I had a 97 camaro and when security would act up I could pull the radio fuse and it would start. I tried that and its not the case on this one. Without the ground at the coil could that cause an issue somewhere else in the car? This morning I started it up fired right away idled kind of rough and then died in about 5 minutes. Any ideas would be great
Safety Car
Joined: May 2001
Posts: 4,759
Likes: 1,647
From: Fairfax Virginia
Hello ryanpruitt,
Is the Corvette running only in the Open Loop mode? It sounds like the time your car wants to switch to Closed Loop the engine stalls. That would indicate that one of the primary components is not available and the engine shuts down. The three primary things required for Closed loop are the Oxygen sensor, Coolant temperature Sensor and the MAF or MAP system depending on which your car has. If any one of these is not functioning properly that would explain your shut downs.
Since your Oxygen sensor is past replacement time I would start with that. They are fairly inexpensive. The OBD1 oxygen sensors need to be every replaced at 24 months or 50k miles for them to work their best. The MAF or MAP systems measure the volume of air intake for the engine and constantly updates the engine on the amount of air going into the combustion chamber. These too can wreak havoc if not working properly. my C4 has a MAF but later models had
Have you tested the fuel pressure on this Corvette? What are the numbers? Having a Fuel pressure gauge is extremely valuable with a C4. If your pressure is off that also makes issues that won't go away until fixed. You should see about 42-43 psi with the engine idling. Also check your Fuel Pressure Regulator for a leaky diaphragm by simply pulling it's vacuum hose off and smelling the inside of the hose. If it smells like gasoline then you need to change the diaphragm to get the proper pressures required.
Try measuring your battery voltage at the battery and then at the fuse panel. If they are not the same there is corrosion in your electrical system. On my 1988 C4 the post behind the battery under the side cover supplies power to 7 fusible links and gets it power directly from the battery itself. There should be a smaller red cable going from the Battery to the post in question. I removed mine and cleaned it completely and suddenly I had full voltage at the fuse-panel and all the accessories were back to full battery voltage.
The key resistance chip is easy to disable. ZIP Products has a part that plugs into the system and never uses the resistance chip any more. You just need to know the resistance value of your factory chip.
After letting a Corvette sit for a long time water gets absorbed into the fuel and starts corroding the fuel supply and return lines from the inside. My 1988 C4 had the fuel supply line rusted almost sealed, a little gas would get through but not enough to run the engine. I ran a rubber line from the pump outlet to the fuel filter in and suddenly my car would start and stay running. I ended up replacing the fuel supply line to solve that issue. Then I moved to the brake lines as they too absorb water and rust away internally.
Are you getting any codes from the Corvette? Have you tried reading any codes if they are there? Do you have any kind of scanner that allows you to see OBD1 codes? Do you have access to any NOID Lights to test the injectors, That would be usefull as well as the resistance readings from your current injectors.
What do your spark plugs look like? Pull one out after the engine shuts itself down and check it. How about the spark plug wires? Are they all good? Have you tested them? I like to do the old move the timing light sensor from wire to wire to see ignition taking place at spark plug. It is important that you have a spark at all eight cylinders so please verify. One or two bad wires can make real trouble and lead to a rough running engine.
Have you purchased a set of the factory service manuals for your 1991? It is critical to have a set when working on one of these old C4's as the electrical supplement is extremely useful all by itself. The manuals have all the tests laid out nice and neatly for you. I have two sets for my 1988, one for the shop one for the house.
Best regards,
Chris
Is the Corvette running only in the Open Loop mode? It sounds like the time your car wants to switch to Closed Loop the engine stalls. That would indicate that one of the primary components is not available and the engine shuts down. The three primary things required for Closed loop are the Oxygen sensor, Coolant temperature Sensor and the MAF or MAP system depending on which your car has. If any one of these is not functioning properly that would explain your shut downs.
Since your Oxygen sensor is past replacement time I would start with that. They are fairly inexpensive. The OBD1 oxygen sensors need to be every replaced at 24 months or 50k miles for them to work their best. The MAF or MAP systems measure the volume of air intake for the engine and constantly updates the engine on the amount of air going into the combustion chamber. These too can wreak havoc if not working properly. my C4 has a MAF but later models had
Have you tested the fuel pressure on this Corvette? What are the numbers? Having a Fuel pressure gauge is extremely valuable with a C4. If your pressure is off that also makes issues that won't go away until fixed. You should see about 42-43 psi with the engine idling. Also check your Fuel Pressure Regulator for a leaky diaphragm by simply pulling it's vacuum hose off and smelling the inside of the hose. If it smells like gasoline then you need to change the diaphragm to get the proper pressures required.
Try measuring your battery voltage at the battery and then at the fuse panel. If they are not the same there is corrosion in your electrical system. On my 1988 C4 the post behind the battery under the side cover supplies power to 7 fusible links and gets it power directly from the battery itself. There should be a smaller red cable going from the Battery to the post in question. I removed mine and cleaned it completely and suddenly I had full voltage at the fuse-panel and all the accessories were back to full battery voltage.
The key resistance chip is easy to disable. ZIP Products has a part that plugs into the system and never uses the resistance chip any more. You just need to know the resistance value of your factory chip.
After letting a Corvette sit for a long time water gets absorbed into the fuel and starts corroding the fuel supply and return lines from the inside. My 1988 C4 had the fuel supply line rusted almost sealed, a little gas would get through but not enough to run the engine. I ran a rubber line from the pump outlet to the fuel filter in and suddenly my car would start and stay running. I ended up replacing the fuel supply line to solve that issue. Then I moved to the brake lines as they too absorb water and rust away internally.
Are you getting any codes from the Corvette? Have you tried reading any codes if they are there? Do you have any kind of scanner that allows you to see OBD1 codes? Do you have access to any NOID Lights to test the injectors, That would be usefull as well as the resistance readings from your current injectors.
What do your spark plugs look like? Pull one out after the engine shuts itself down and check it. How about the spark plug wires? Are they all good? Have you tested them? I like to do the old move the timing light sensor from wire to wire to see ignition taking place at spark plug. It is important that you have a spark at all eight cylinders so please verify. One or two bad wires can make real trouble and lead to a rough running engine.
Have you purchased a set of the factory service manuals for your 1991? It is critical to have a set when working on one of these old C4's as the electrical supplement is extremely useful all by itself. The manuals have all the tests laid out nice and neatly for you. I have two sets for my 1988, one for the shop one for the house.
Best regards,
Chris
Drifting
Joined: Aug 2019
Posts: 1,339
Likes: 225
When you say it won't start, does it crank over? If not then it's possible that the contacts for the key chip could be loose or bad. If it does crank, but does not start, do you have spark at the plugs? If you don't then you need to look why, If you consistently have spark, then the fuel system could be the issue. So....if you can answer those simple questions, we can go further, otherwise we'd be guessing.
Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
Likes: 0
New cap rotor coil plugs wires fuel pump and pressure regulator. Fuel lines cleaned and soaked in carb cleaner then manually pushed fuel through them. Fuel pressure is fine and yes getting spark. Yes it turns over. it can sit for a few days and fire right up then it may die after a few minutes it may not. It may not start again after. It wouldn't start one day I took the negative post off the battery and let it sit a few minutes plugged it back in cranked it for prolly 20 seconds and it fired up. drove it 20 miles parked it. then it wouldn't start days later. One day I came into a turn and accelerated and it started to die out on me. It kept running but lugged out big time.
