The begining
Thread Starter
8th Gear
Joined: Jan 2020
Posts: 8
Likes: 1
From: York pa
The begining
The work begins. Car runs great on start up, but after running awhile and shutting off restart when warm, it spits and sputtered and misses. Seller said it needed a new distributor.
Where do I start?
Where do I start?
Safety Car
Joined: May 2001
Posts: 4,711
Likes: 1,624
From: Fairfax Virginia
First, Welcome to the Corvette Forum!
I would verify that all eight plugs are firing. I frequently do this using a timing light and rotate the Number One sensor around and see that the spark is hitting the plug at least. You could use a spark tester if you have one and just verify that all eight are getting a spark.
If the Corvette runs great on start up and then starts to miss after restarting the engine when warm the first thing I would do is measure the Fuel Pressure to be sure that it is staying in the proper pressure range. Judging from what you describe I would guess it has more to do with the fuel system than the distributor. With a fuel pressure gauge you will know very quickly.
I saw a Corvette that would start and run fine but on warm start-ups it the engine would misfire. It was an Injector that was old and leaky that kept dumping raw gasoline into the engine. It can be diagnosed easily with a Fuel Pressure gauge attached to the fuel rail of the car. The fitting to attach it is on the passengers side of the engine towards the rear of the intake manifold. If you monitor the fuel pressure after shutdown watch and see how fast it goes down, with a leaky injector it took only a couple minutes for the pressure to bleed down. Injectors are sold individually but replace all eight at one time from a reputable supplier (not Ebay) and you will get a set of matched injectors that will help your Corvette. If you need injectors there are a couple great options available.
When the Corvette's Coolant Temperature Switch goes bad it can send improper temperatures to the computer. If your engine is nice and warm but the computer says it is Hotter than it really is the ECU will try starting using less fuel thinking it is hotter than it really is. If it is sending a signal that says the engine is still cold then the engine will try starting with extra fuel as needed in cooler weather. To check the CTS is fairly easy as it is mounted on the front of the intake plenum and you can disconnect the harness and measure the resistance. With the resistance value you need to go to the Factory Service Manuals and there is a chart that shows the resistance values and their approximate temperature.
If the Distributor was bad the engine would run badly most of the time. I would not order a replacement yet...
I don't know much about your skills but you will need a couple things to be able to work on your Corvette. They are not hard to work on but do require some special tools for some of the jobs.
1. Factory Service Manuals for your particular year Corvette. Helm Publishers prints the manuals and they are accurate and very important for diagnostic help. Please don't try any aftermarket books in place of the FSM's from Helm. They can be expensive but are available on DVD on Fleabay if needed. For my 1988 C4 they are about $100 a set of $20 on DVD. I have two copies myself, one for the garage and one for the house when I read up on something.
2. Good Volt Ohm Meter
3. Fuel Pressure Gauge with long hose
4. OBD1 Scanner or code reader or you can use the paper clip method of reading the codes.
Corvettes are awesome vehicles. Some of the changes made in the mid to late 1980's involved the Electronic Fuel Injection systems. Many people do not understand how they operate so many folks just take a shot in the dark and guess. Be very careful getting some help with these Corvettes. Many mechanics are very fluent in L98 talk but there are many who know very little about the system.
Once you have worked on one of these Engines and their fuel systems it will all become clear to you how they operate. They are not hard to understand or work on once you understand "HOW" they work.
If the Corvette's Oxygen sensor is older than 24 months then it would be important to replace it with a new unit. The older sensors can really screw up the fuel system as they can read slower than the ECU wants the data and their signal changes over time. If you are not sure of the age then replace it. It is too important a sensor to your Corvette. It can affect the mileage and the performance. So essentially it will save you money on gas and give you a better performing Corvette!
I am a big believer in BG 44K Fuel system Cleaner. Try running a bottle of this through your fuel system and see what it does for you. It always helps my Corvette idle smoother and run better. I put a can through maybe once a year in the early season. Remember since it is a Corvette to not leave any of the modern gasoline with ethanol in it for more than 30 days without putting in an anti-ethanol additive in the fuel.
This should help get you started. The more information we have about your particular Corvette the better the answers will be for you. Here on the Corvette Forum we have experts for any year Corvette you have. I use it to help me maintain my two Corvettes that I have had for a long time.
Is this your First Corvette? At least you are close enough to get to Carlisle PA in August for the annual Corvettes@Carlisle the third weekend of August every year. There are some great deals to be had at Carlisle so start making your list now for this summer. I am frequently there myself but it is 103 miles from home and the weather has to be "right" fore me to drive my Corvettes up there. There will be 50,000 plus Corvette Nuts there every August, it is a great experience for fellow Corvette owners to find the parts they need.
Let us know when you have more questions! I hope that this helps you!
Best regards,
Chris
I would verify that all eight plugs are firing. I frequently do this using a timing light and rotate the Number One sensor around and see that the spark is hitting the plug at least. You could use a spark tester if you have one and just verify that all eight are getting a spark.
If the Corvette runs great on start up and then starts to miss after restarting the engine when warm the first thing I would do is measure the Fuel Pressure to be sure that it is staying in the proper pressure range. Judging from what you describe I would guess it has more to do with the fuel system than the distributor. With a fuel pressure gauge you will know very quickly.
I saw a Corvette that would start and run fine but on warm start-ups it the engine would misfire. It was an Injector that was old and leaky that kept dumping raw gasoline into the engine. It can be diagnosed easily with a Fuel Pressure gauge attached to the fuel rail of the car. The fitting to attach it is on the passengers side of the engine towards the rear of the intake manifold. If you monitor the fuel pressure after shutdown watch and see how fast it goes down, with a leaky injector it took only a couple minutes for the pressure to bleed down. Injectors are sold individually but replace all eight at one time from a reputable supplier (not Ebay) and you will get a set of matched injectors that will help your Corvette. If you need injectors there are a couple great options available.
When the Corvette's Coolant Temperature Switch goes bad it can send improper temperatures to the computer. If your engine is nice and warm but the computer says it is Hotter than it really is the ECU will try starting using less fuel thinking it is hotter than it really is. If it is sending a signal that says the engine is still cold then the engine will try starting with extra fuel as needed in cooler weather. To check the CTS is fairly easy as it is mounted on the front of the intake plenum and you can disconnect the harness and measure the resistance. With the resistance value you need to go to the Factory Service Manuals and there is a chart that shows the resistance values and their approximate temperature.
If the Distributor was bad the engine would run badly most of the time. I would not order a replacement yet...
I don't know much about your skills but you will need a couple things to be able to work on your Corvette. They are not hard to work on but do require some special tools for some of the jobs.
1. Factory Service Manuals for your particular year Corvette. Helm Publishers prints the manuals and they are accurate and very important for diagnostic help. Please don't try any aftermarket books in place of the FSM's from Helm. They can be expensive but are available on DVD on Fleabay if needed. For my 1988 C4 they are about $100 a set of $20 on DVD. I have two copies myself, one for the garage and one for the house when I read up on something.
2. Good Volt Ohm Meter
3. Fuel Pressure Gauge with long hose
4. OBD1 Scanner or code reader or you can use the paper clip method of reading the codes.
Corvettes are awesome vehicles. Some of the changes made in the mid to late 1980's involved the Electronic Fuel Injection systems. Many people do not understand how they operate so many folks just take a shot in the dark and guess. Be very careful getting some help with these Corvettes. Many mechanics are very fluent in L98 talk but there are many who know very little about the system.
Once you have worked on one of these Engines and their fuel systems it will all become clear to you how they operate. They are not hard to understand or work on once you understand "HOW" they work.
If the Corvette's Oxygen sensor is older than 24 months then it would be important to replace it with a new unit. The older sensors can really screw up the fuel system as they can read slower than the ECU wants the data and their signal changes over time. If you are not sure of the age then replace it. It is too important a sensor to your Corvette. It can affect the mileage and the performance. So essentially it will save you money on gas and give you a better performing Corvette!
I am a big believer in BG 44K Fuel system Cleaner. Try running a bottle of this through your fuel system and see what it does for you. It always helps my Corvette idle smoother and run better. I put a can through maybe once a year in the early season. Remember since it is a Corvette to not leave any of the modern gasoline with ethanol in it for more than 30 days without putting in an anti-ethanol additive in the fuel.
This should help get you started. The more information we have about your particular Corvette the better the answers will be for you. Here on the Corvette Forum we have experts for any year Corvette you have. I use it to help me maintain my two Corvettes that I have had for a long time.
Is this your First Corvette? At least you are close enough to get to Carlisle PA in August for the annual Corvettes@Carlisle the third weekend of August every year. There are some great deals to be had at Carlisle so start making your list now for this summer. I am frequently there myself but it is 103 miles from home and the weather has to be "right" fore me to drive my Corvettes up there. There will be 50,000 plus Corvette Nuts there every August, it is a great experience for fellow Corvette owners to find the parts they need.
Let us know when you have more questions! I hope that this helps you!
Best regards,
Chris
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
It would not hurt to check the Distributor. The coil should be free of rust and cracking.
Check pickup and distibutor pins for corrosion. As you work down inspect the rotor, remove.
Inspect the icm module and reapply thermal paste underneath very thin coat.
Check the shaft for wear. Check the wires to the icm are on all the way. Put it back reverse order and consider it
good to go.
Check pickup and distibutor pins for corrosion. As you work down inspect the rotor, remove.
Inspect the icm module and reapply thermal paste underneath very thin coat.
Check the shaft for wear. Check the wires to the icm are on all the way. Put it back reverse order and consider it
good to go.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Ok so it has an optispark distributor so you could look up the issues associated with that type of distributor.
The first thing to do is interrogate the ECM and get the trouble codes. The condition you have describe could be leaky injectors. You could try cranking with the throttle held to the floor when the engine is hot and see if it starts quicker. Holding your foot to the door clears a flood condition, if that works it could mean the injectors are poring too much fuel in a warm engine. But that’s just a guess the ECM trouble codes are your best bet.
The first thing to do is interrogate the ECM and get the trouble codes. The condition you have describe could be leaky injectors. You could try cranking with the throttle held to the floor when the engine is hot and see if it starts quicker. Holding your foot to the door clears a flood condition, if that works it could mean the injectors are poring too much fuel in a warm engine. But that’s just a guess the ECM trouble codes are your best bet.
