Rough idle
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,462
Likes: 48
Rough idle
Hi guys,
My 85 4 plus 3 is still running rough. I changed the injectors. We found a wreck with injectors and installed them. Everything else is new O2, tPS, CTS, Ignition Module, plugs, cap rotor, FPR is at 43 psi. The car is running but still running very rich black plugs. I am able to start and run the car with the MAF disconnected. It runs pretty much the same as with the MAF connected. I disconnected the PVC hose to look for a change pretty much still the same. I did log and save a TunerPro RT file. I really do not know what I am looking at. IS there a way I can send you the file.
The BLM is 116 to about 128
The O2 sensor is near 450 to 850
The IAC is at 55 plus or minus 5
The injector BPW is 2.89 to 3.30
Coolant temp is 135 F
Running in closed loop
Plugs are black. Idle is rough. I really appreciate any help you can offer. I work for the Federal Gov and my time here is short. If I cannot get this car to run correctly they may not let me ship it home. 9K down the tubes.
Thank you
Joe
My 85 4 plus 3 is still running rough. I changed the injectors. We found a wreck with injectors and installed them. Everything else is new O2, tPS, CTS, Ignition Module, plugs, cap rotor, FPR is at 43 psi. The car is running but still running very rich black plugs. I am able to start and run the car with the MAF disconnected. It runs pretty much the same as with the MAF connected. I disconnected the PVC hose to look for a change pretty much still the same. I did log and save a TunerPro RT file. I really do not know what I am looking at. IS there a way I can send you the file.
The BLM is 116 to about 128
The O2 sensor is near 450 to 850
The IAC is at 55 plus or minus 5
The injector BPW is 2.89 to 3.30
Coolant temp is 135 F
Running in closed loop
Plugs are black. Idle is rough. I really appreciate any help you can offer. I work for the Federal Gov and my time here is short. If I cannot get this car to run correctly they may not let me ship it home. 9K down the tubes.
Thank you
Joe
Safety Car
Joined: May 2001
Posts: 4,752
Likes: 1,642
From: Fairfax Virginia
Hello there Joe,
It sounds like you replaced all the major "problem" makers on this Corvette. The Oxygen sensor was brand new when you installed it? I have purchased brand new Bosch Oxygen Sensors that were defective from the factory. If there is another available I might try it before going to far. This problem sounds like a O2 issue to me.
When the engine said the CTS was 135* was that as it was warming up or when? A faulty CTS can make a Corvette blow lots of black smoke. The CTS should indicate your actual coolant temperature so verify this by reading the signal and comparing the chart in the Factory Service manual. It needs to be accurate for the entire system to work properly.
You might want to pull the O2 sensor out and see if the Catalytic converter is partially plugged or something. If it was not before it will get plugged very quickly if you are making the plugs turn black. With the O2 removed there should be a little air coming out the hole but not a lot of air blowing out. "A lot of air" is (vague) an indicator that the Catalytic might be partially plugged. Frequently a plugged catalytic could make the engine run hotter than normal.
If you have a infra-red thermometer you should check the two mini-catalytics in the WYE pipe and the main catalytic for their temperatures. I would also check all eight cylinders at their exhaust manifolds to be sure they are all firing as normal. Consistency is important on the exhaust manifolds.
The MAF sensor is there to measure the volume of air being ingested into the engine. If the sensor doesn't work the car will have major drive-abity issues. It is imperative that there is NO air leakage between the MAF and the throttle body. Make sure the seal is good. Not knowing about your particular years usage of the MAF like my 1988 C4 came with or the MAP sensors they use today.
How old is the gasoline you are using currently? Did you replace the coil on top of the distributor? How do the sparks look?
Does your Corvette have an EGR valve in it like the L98's do? How much vacuum are you getting currently? Are all the Vacuum hoses connected up to the FPR and EGR and other parts?
I don't know if you have the famous "Cold Start Injector" a.k.a. the 9th injector on a 1985 but if you do is it connected? There would be a thermo switch on the front of the intake and the 9th injector is still a Fuel injector and they have been know to leak raw gas even while powered down. If the 9th injector was stuck in the "on" position you would definitely have Black sooty plugs.
Did you replace the Idle Air Control on this engine? Did you verify that the parts looked the same. I have seen the same part number with two different pintle shapes, one works and the other will not on my C4.
I hope there is a "tidbit" in this that might help you some way. We will be watching for your answers!
P.S. Don't forget that these Corvette are Electronically fuel injected so all your battery connections and in-car connections need to be clean. Another quick test, measure the battery voltage and then measure it again at the fuse panel, they should be the same or Very close to the same.
It sounds like you replaced all the major "problem" makers on this Corvette. The Oxygen sensor was brand new when you installed it? I have purchased brand new Bosch Oxygen Sensors that were defective from the factory. If there is another available I might try it before going to far. This problem sounds like a O2 issue to me.
When the engine said the CTS was 135* was that as it was warming up or when? A faulty CTS can make a Corvette blow lots of black smoke. The CTS should indicate your actual coolant temperature so verify this by reading the signal and comparing the chart in the Factory Service manual. It needs to be accurate for the entire system to work properly.
You might want to pull the O2 sensor out and see if the Catalytic converter is partially plugged or something. If it was not before it will get plugged very quickly if you are making the plugs turn black. With the O2 removed there should be a little air coming out the hole but not a lot of air blowing out. "A lot of air" is (vague) an indicator that the Catalytic might be partially plugged. Frequently a plugged catalytic could make the engine run hotter than normal.
If you have a infra-red thermometer you should check the two mini-catalytics in the WYE pipe and the main catalytic for their temperatures. I would also check all eight cylinders at their exhaust manifolds to be sure they are all firing as normal. Consistency is important on the exhaust manifolds.
The MAF sensor is there to measure the volume of air being ingested into the engine. If the sensor doesn't work the car will have major drive-abity issues. It is imperative that there is NO air leakage between the MAF and the throttle body. Make sure the seal is good. Not knowing about your particular years usage of the MAF like my 1988 C4 came with or the MAP sensors they use today.
How old is the gasoline you are using currently? Did you replace the coil on top of the distributor? How do the sparks look?
Does your Corvette have an EGR valve in it like the L98's do? How much vacuum are you getting currently? Are all the Vacuum hoses connected up to the FPR and EGR and other parts?
I don't know if you have the famous "Cold Start Injector" a.k.a. the 9th injector on a 1985 but if you do is it connected? There would be a thermo switch on the front of the intake and the 9th injector is still a Fuel injector and they have been know to leak raw gas even while powered down. If the 9th injector was stuck in the "on" position you would definitely have Black sooty plugs.
Did you replace the Idle Air Control on this engine? Did you verify that the parts looked the same. I have seen the same part number with two different pintle shapes, one works and the other will not on my C4.
I hope there is a "tidbit" in this that might help you some way. We will be watching for your answers!
P.S. Don't forget that these Corvette are Electronically fuel injected so all your battery connections and in-car connections need to be clean. Another quick test, measure the battery voltage and then measure it again at the fuse panel, they should be the same or Very close to the same.
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,462
Likes: 48
First thank you for the very thought full response.
Support Corvetteforum!
Member Since: May 2001
Location: Fairfax Virginia
Posts: 1,668
Likes: 335
Received 388 Likes on 325 Posts
DefaultHello there Joe,
It sounds like you replaced all the major "problem" makers on this Corvette. The Oxygen sensor was brand new when you installed it? I have purchased brand new Bosch Oxygen Sensors that were defective from the factory. If there is another available I might try it before going to far. This problem sounds like a O2 issue to me.
The O2 is one day old
When the engine said the CTS was 135* was that as it was warming up or when? A faulty CTS can make a Corvette blow lots of black smoke. The CTS should indicate your actual coolant temperature so verify this by reading the signal and comparing the chart in the Factory Service manual. It needs to be accurate for the entire system to work properly.
The temperature is accurate. I have bbe keeping it low. I turn the fan on manually as soon as I start the car.
You might want to pull the O2 sensor out and see if the Catalytic converter is partially plugged or something. If it was not before it will get plugged very quickly if you are making the plugs turn black. With the O2 removed there should be a little air coming out the hole but not a lot of air blowing out. "A lot of air" is (vague) an indicator that the Catalytic might be partially plugged. Frequently a plugged catalytic could make the engine run hotter than normal.
No Cat
If you have a infra-red thermometer you should check the two mini-catalytics in the WYE pipe and the main catalytic for their temperatures. I would also check all eight cylinders at their exhaust manifolds to be sure they are all firing as normal. Consistency is important on the exhaust manifolds.
The MAF sensor is there to measure the volume of air being ingested into the engine. If the sensor doesn't work the car will have major drive-abity issues. It is imperative that there is NO air leakage between the MAF and the throttle body. Make sure the seal is good. Not knowing about your particular years usage of the MAF like my 1988 C4 came with or the MAP sensors they use today.
I will make sure the seal is tight.
How old is the gasoline you are using currently? Did you replace the coil on top of the distributor? How do the sparks look?
New gas it's burning a lot of it.
Does your Corvette have an EGR valve in it like the L98's do? How much vacuum are you getting currently? Are all the Vacuum hoses connected up to the FPR and EGR and other parts?
EGR is gone
I don't know if you have the famous "Cold Start Injector" a.k.a. the 9th injector on a 1985 but if you do is it connected? There would be a thermo switch on the front of the intake and the 9th injector is still a Fuel injector and they have been know to leak raw gas even while powered down. If the 9th injector was stuck in the "on" position you would definitely have Black sooty plugs.
Good thought I will disconnect the wires. See if that helps.
Did you replace the Idle Air Control on this engine? Did you verify that the parts looked the same. I have seen the same part number with two different pintle shapes, one works and the other will not on my C4.
IAC is new one week or so.
I hope there is a "tidbit" in this that might help you some way. We will be watching for your answers!
P.S. Don't forget that these Corvette are Electronically fuel injected so all your battery connections and in-car connections need to be clean. Another quick test, measure the battery voltage and then measure it again at the fuse panel, they should be the same or Very close to the same.
Someone suggested a stuck FPR. How do you unstuck it.
And this is so nice of you thank you
Support Corvetteforum!
Member Since: May 2001
Location: Fairfax Virginia
Posts: 1,668
Likes: 335
Received 388 Likes on 325 Posts
DefaultHello there Joe,
It sounds like you replaced all the major "problem" makers on this Corvette. The Oxygen sensor was brand new when you installed it? I have purchased brand new Bosch Oxygen Sensors that were defective from the factory. If there is another available I might try it before going to far. This problem sounds like a O2 issue to me.
The O2 is one day old
When the engine said the CTS was 135* was that as it was warming up or when? A faulty CTS can make a Corvette blow lots of black smoke. The CTS should indicate your actual coolant temperature so verify this by reading the signal and comparing the chart in the Factory Service manual. It needs to be accurate for the entire system to work properly.
The temperature is accurate. I have bbe keeping it low. I turn the fan on manually as soon as I start the car.
You might want to pull the O2 sensor out and see if the Catalytic converter is partially plugged or something. If it was not before it will get plugged very quickly if you are making the plugs turn black. With the O2 removed there should be a little air coming out the hole but not a lot of air blowing out. "A lot of air" is (vague) an indicator that the Catalytic might be partially plugged. Frequently a plugged catalytic could make the engine run hotter than normal.
No Cat
If you have a infra-red thermometer you should check the two mini-catalytics in the WYE pipe and the main catalytic for their temperatures. I would also check all eight cylinders at their exhaust manifolds to be sure they are all firing as normal. Consistency is important on the exhaust manifolds.
The MAF sensor is there to measure the volume of air being ingested into the engine. If the sensor doesn't work the car will have major drive-abity issues. It is imperative that there is NO air leakage between the MAF and the throttle body. Make sure the seal is good. Not knowing about your particular years usage of the MAF like my 1988 C4 came with or the MAP sensors they use today.
I will make sure the seal is tight.
How old is the gasoline you are using currently? Did you replace the coil on top of the distributor? How do the sparks look?
New gas it's burning a lot of it.
Does your Corvette have an EGR valve in it like the L98's do? How much vacuum are you getting currently? Are all the Vacuum hoses connected up to the FPR and EGR and other parts?
EGR is gone
I don't know if you have the famous "Cold Start Injector" a.k.a. the 9th injector on a 1985 but if you do is it connected? There would be a thermo switch on the front of the intake and the 9th injector is still a Fuel injector and they have been know to leak raw gas even while powered down. If the 9th injector was stuck in the "on" position you would definitely have Black sooty plugs.
Good thought I will disconnect the wires. See if that helps.
Did you replace the Idle Air Control on this engine? Did you verify that the parts looked the same. I have seen the same part number with two different pintle shapes, one works and the other will not on my C4.
IAC is new one week or so.
I hope there is a "tidbit" in this that might help you some way. We will be watching for your answers!
P.S. Don't forget that these Corvette are Electronically fuel injected so all your battery connections and in-car connections need to be clean. Another quick test, measure the battery voltage and then measure it again at the fuse panel, they should be the same or Very close to the same.
Someone suggested a stuck FPR. How do you unstuck it.
And this is so nice of you thank you
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
@jseremba
On your other thread you posted:
Here you say:
Can you clarify what injectors you actually have? I emailed you an update of you .bin with the voltage offsets for Bosch3's that most buy from Southbay. They are notorius for causing rough idle issues on other TPI related forums. If these are factory injectors out of a wreck I would find them and the 9th injector suspect as I mentioned in your PM.
Knowing what injectors are in there will help us help you. The injectors are rated at 43.5PSI (Static - vac line off), and yes the 85 ran a lower pressure, but once you change the injectors we have to get the settings right on your car for what you are now running.
On your other thread you posted:
Knowing what injectors are in there will help us help you. The injectors are rated at 43.5PSI (Static - vac line off), and yes the 85 ran a lower pressure, but once you change the injectors we have to get the settings right on your car for what you are now running.
Last edited by KyleF; Jul 30, 2020 at 08:57 AM.
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,462
Likes: 48
Kyle,
I did have the South Bay Bosch 3 injectors. Presently, as of today I have the injectors from the wrecked Corvette i.e. GM injectors. In lieu of the fact that two of the cylinders are not firing and I used an inductive timing light to verify that they are getting spark. I have to assume that the two injectors are clogged or something. So we are pulling the fuel rail and make a decision with respect to the injectors later today, Guam time.
Thank you for the help
I did have the South Bay Bosch 3 injectors. Presently, as of today I have the injectors from the wrecked Corvette i.e. GM injectors. In lieu of the fact that two of the cylinders are not firing and I used an inductive timing light to verify that they are getting spark. I have to assume that the two injectors are clogged or something. So we are pulling the fuel rail and make a decision with respect to the injectors later today, Guam time.
Thank you for the help
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 164
From: Nashville TN
2017 C4 of Year Finalist
Kyle,
I did have the South Bay Bosch 3 injectors. Presently, as of today I have the injectors from the wrecked Corvette i.e. GM injectors. In lieu of the fact that two of the cylinders are not firing and I used an inductive timing light to verify that they are getting spark. I have to assume that the two injectors are clogged or something. So we are pulling the fuel rail and make a decision with respect to the injectors later today, Guam time.
Thank you for the help
I did have the South Bay Bosch 3 injectors. Presently, as of today I have the injectors from the wrecked Corvette i.e. GM injectors. In lieu of the fact that two of the cylinders are not firing and I used an inductive timing light to verify that they are getting spark. I have to assume that the two injectors are clogged or something. So we are pulling the fuel rail and make a decision with respect to the injectors later today, Guam time.
Thank you for the help
Another way to check if your injectors are the problem is to remove and rotate them to different cylinders, then see if the misfire moves to that cylinder. That will pretty much guarantee you've found your problem.
If it turns out you need injectors let me know, I've got a good set of stock injectors sitting around here someplace I'd let get for cheap.
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,462
Likes: 48
I will check the regulator. I think it is new. But, there are so many parts I've bought for this car. I forget. I need to look. We actually changed the injectors. My mechanic was given a wrecked C4. We pulled the injectors. The car runs better. but it still is a little rough.
Interesting thing occurred. I had been running the cooling fans from the key so when the car is on the fans are on. I decided to run them through the fans circuit and relay. The car ran good. but, when it got to 206/210 when the fans should come on it started to stall.
I am waiting for my House Hold Goods to arrive in the US. In them is my TunerPro RT stuff.
Thank you all
Interesting thing occurred. I had been running the cooling fans from the key so when the car is on the fans are on. I decided to run them through the fans circuit and relay. The car ran good. but, when it got to 206/210 when the fans should come on it started to stall.
I am waiting for my House Hold Goods to arrive in the US. In them is my TunerPro RT stuff.
Thank you all
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