Engine surging
Safety Car
Joined: May 2001
Posts: 4,740
Likes: 1,639
From: Fairfax Virginia
Hello Jackson007!
I would check your M*** Air Flow sensor and make sure it is working properly. Sometimes a spray can of MAF cleaner can do the trick at getting the wire in the MAF cleaned. The MAF sensor is what measures the volume of air ingested by the engine. There is a very small diameter wire that is heated up and as the air flows past it the sensor can calculate the volume of air. The wire is used while the car is running and then upon shutoff the system can heat the wire up and burn off the crud that has built up on the surface of the wire. If the burn off function stops the MAF gets dirty pretty quickly. If you replace the MAF always replace the two relays that are part of the MAF system. One relay controls the power and the second controls the Burn Off function. They BOTH have to work for the MAF to operate properly and if either one fails the system will have issues.
It would be very helpful for us here on the Corvette Forum if you could fill out the profile page so we know what year Corvette and which engine you have. It keeps people from asking the same questions over and over.
The other thing I would check would be your Fuel Pressure at the plenum. Not knowing which year your Corvette is I don't know the precise numbers for your Corvette. On my 1988 it hovers around 42 psi and when the key is turned off the pressure should remain for a while. If the pressure drops off really fast then you likely have a leaky injector. The fuel pressure is critical on these EFI cars.
Since you were driving when this happened we will assume that your Corvette was in the "Closed Loop" and in this mode it uses 3 primary sensors to control the engine running down the highway. One is the Oxygen Sensor, another is the MAF sensor and the last is the Coolant Temperature Sensor.
Did you get any warning lights when this happened? Do you have a scanner or some way of reading the codes? Having the Factory Service Manual for your particular year is very important as they are a wealth of information and specs.
How old is the oxygen sensor? They were designed for 24 months of use and then be replaced. People get a lot more life out of them than they were made to produce. The Heated (Later) type O2 sensors last twice as long as the early non-heated type.
I had a 1990 and was driving to work one day when all the sudden the car started bucking and missing. It went away and would appear occasionally for a few seconds. I used a scanner and found that the O2 was dropping out and failing. The dealer would not install a new O2 unless they had proof of it being bad. I gave him five pages of printouts and you could see the O2 dropping out. They replaced the sensor and i never had any more trouble. The sensor on my car was less than a year old when it just up and died. The car could only idle and was in the "Limp Home" Mode keeping it below 25 mph so I got off the road and had it towed.
How long have you had this Corvette? Do you have any idea how old the O2 is on the Corvette? I always say "When in doubt, replace it" when it comes to parts for the emissions system.
The surging sounds more like the MAF but the symptoms sound like O2. Check your fuel pressure and let us know what you are dealing with.
Surging can also be a result of a bad Fuel Pressure regulator diaphragm. This is easy to test, find the vacuum line that goes to the round FPR under the rear of the plenum. Remove the vacuum line and smell it, if you smell raw gasoline then you have a bad fuel pressure regulator Diaphragm.
I would check your M*** Air Flow sensor and make sure it is working properly. Sometimes a spray can of MAF cleaner can do the trick at getting the wire in the MAF cleaned. The MAF sensor is what measures the volume of air ingested by the engine. There is a very small diameter wire that is heated up and as the air flows past it the sensor can calculate the volume of air. The wire is used while the car is running and then upon shutoff the system can heat the wire up and burn off the crud that has built up on the surface of the wire. If the burn off function stops the MAF gets dirty pretty quickly. If you replace the MAF always replace the two relays that are part of the MAF system. One relay controls the power and the second controls the Burn Off function. They BOTH have to work for the MAF to operate properly and if either one fails the system will have issues.
It would be very helpful for us here on the Corvette Forum if you could fill out the profile page so we know what year Corvette and which engine you have. It keeps people from asking the same questions over and over.
The other thing I would check would be your Fuel Pressure at the plenum. Not knowing which year your Corvette is I don't know the precise numbers for your Corvette. On my 1988 it hovers around 42 psi and when the key is turned off the pressure should remain for a while. If the pressure drops off really fast then you likely have a leaky injector. The fuel pressure is critical on these EFI cars.
Since you were driving when this happened we will assume that your Corvette was in the "Closed Loop" and in this mode it uses 3 primary sensors to control the engine running down the highway. One is the Oxygen Sensor, another is the MAF sensor and the last is the Coolant Temperature Sensor.
Did you get any warning lights when this happened? Do you have a scanner or some way of reading the codes? Having the Factory Service Manual for your particular year is very important as they are a wealth of information and specs.
How old is the oxygen sensor? They were designed for 24 months of use and then be replaced. People get a lot more life out of them than they were made to produce. The Heated (Later) type O2 sensors last twice as long as the early non-heated type.
I had a 1990 and was driving to work one day when all the sudden the car started bucking and missing. It went away and would appear occasionally for a few seconds. I used a scanner and found that the O2 was dropping out and failing. The dealer would not install a new O2 unless they had proof of it being bad. I gave him five pages of printouts and you could see the O2 dropping out. They replaced the sensor and i never had any more trouble. The sensor on my car was less than a year old when it just up and died. The car could only idle and was in the "Limp Home" Mode keeping it below 25 mph so I got off the road and had it towed.
How long have you had this Corvette? Do you have any idea how old the O2 is on the Corvette? I always say "When in doubt, replace it" when it comes to parts for the emissions system.
The surging sounds more like the MAF but the symptoms sound like O2. Check your fuel pressure and let us know what you are dealing with.
Surging can also be a result of a bad Fuel Pressure regulator diaphragm. This is easy to test, find the vacuum line that goes to the round FPR under the rear of the plenum. Remove the vacuum line and smell it, if you smell raw gasoline then you have a bad fuel pressure regulator Diaphragm.
Thread Starter
Intermediate
Joined: May 2021
Posts: 31
Likes: 1
1985 tpi 5.7L
I did replace the regulator before I put the 3rd fuel pump on it. The fuel pressure was at 43 when I left the house and drove 10 miles before it started surging. I have placed everything new on this car except for the MAF sensor and O2 sensor. My fuel psi won’t go up to 15psi now. Just put the new “3rd” pump on it in 4 weeks.
the first two pumps I found out later were only rated for 22 psi, but they held at 22. This new pump worked at first but 10 miles later it won’t go up to 15 psi now.
I feel like I am close to fixing the car but it’s frustrating. All new ignition coil components and fuel filter, pumps and regulator.
the first two pumps I found out later were only rated for 22 psi, but they held at 22. This new pump worked at first but 10 miles later it won’t go up to 15 psi now.
I feel like I am close to fixing the car but it’s frustrating. All new ignition coil components and fuel filter, pumps and regulator.
Safety Car
Joined: May 2001
Posts: 4,740
Likes: 1,639
From: Fairfax Virginia
Hello again Jackson007,
When you turn the car on the pressure in the loop is only going to 15 psi? Or does it go up to 42 and then drop to 15psi? When you replaced the pump(s) did you replace the fuel dampener that mounts above the fuel pump inside the tank? It is a part that most of us no longer have a need for. Like many folks I have replaced mine with a short section of fuel injection Hose designed to be submersed in gasoline. The reason we replace them is that few parts can tolerate ethanol and a section of hose is easy to get and will last a while. The dampeners will leak eventually and this will keep your Fuel pump from ever make full pressure at the schrader valve on the passengers side of the fuel rail.
What is the voltage being fed to the fuel pump? Is it close to battery voltage?
When you first start the engine take a clamp and clamp off the return line to no fuel can be returned to the tank. If you clamp the return line then your fuel pressure should stay stable or leak down very slowly. If it drops right away you might have a leaky injector.
I would also check to be sure that your vacuum system doesn't have a leak or that could have an effect on the fuel pump by making the pressure unstable. I think that last time I checked mine it was 17-18 inches of vacuum normally with the engine idling. There are so many places for vacuum leaks to occur on 30+ year old vacuum lines, I bought a roll of it and replaced every inch.
With Ethanol in the gasoline the fuel supply and return lines are prone to internal corrosion. When the lines rust shut internally you will get the right pressure but not a sufficient volume to let the engine run properly at speed.
If you are not sure of the age of the O2 sensor then I suggest you replace it. I would clean the MAF and verify that it is functioning properly. The O2 is not that expensive where the MAF for my 1988 C4 is very expensive. I would start with the O2 sensor as it has a lot to do with fuel mixtures when in closed loop.
If your Corvette is acting up and not showing a code I would think it is the O2. To be safe I would verify that your Check Engine light works, I found the bulb missing in my C4 when I bought it.
When you turn the car on the pressure in the loop is only going to 15 psi? Or does it go up to 42 and then drop to 15psi? When you replaced the pump(s) did you replace the fuel dampener that mounts above the fuel pump inside the tank? It is a part that most of us no longer have a need for. Like many folks I have replaced mine with a short section of fuel injection Hose designed to be submersed in gasoline. The reason we replace them is that few parts can tolerate ethanol and a section of hose is easy to get and will last a while. The dampeners will leak eventually and this will keep your Fuel pump from ever make full pressure at the schrader valve on the passengers side of the fuel rail.
What is the voltage being fed to the fuel pump? Is it close to battery voltage?
When you first start the engine take a clamp and clamp off the return line to no fuel can be returned to the tank. If you clamp the return line then your fuel pressure should stay stable or leak down very slowly. If it drops right away you might have a leaky injector.
I would also check to be sure that your vacuum system doesn't have a leak or that could have an effect on the fuel pump by making the pressure unstable. I think that last time I checked mine it was 17-18 inches of vacuum normally with the engine idling. There are so many places for vacuum leaks to occur on 30+ year old vacuum lines, I bought a roll of it and replaced every inch.
With Ethanol in the gasoline the fuel supply and return lines are prone to internal corrosion. When the lines rust shut internally you will get the right pressure but not a sufficient volume to let the engine run properly at speed.
If you are not sure of the age of the O2 sensor then I suggest you replace it. I would clean the MAF and verify that it is functioning properly. The O2 is not that expensive where the MAF for my 1988 C4 is very expensive. I would start with the O2 sensor as it has a lot to do with fuel mixtures when in closed loop.
If your Corvette is acting up and not showing a code I would think it is the O2. To be safe I would verify that your Check Engine light works, I found the bulb missing in my C4 when I bought it.
Thread Starter
Intermediate
Joined: May 2021
Posts: 31
Likes: 1
1985 tpi
Guys, maybe the bad ground was in the relay??? I replaced it, pretty cheap part and replaced the pump for a 4th time in 3 weeks. Drove it 15 miles with no issues. Fuel pressure is holding at 43 psi now. Might have a fouled plug but other than that it was smooth. Thanks for the help
Safety Car
Joined: May 2001
Posts: 4,740
Likes: 1,639
From: Fairfax Virginia
Congratulations Jackson007!
Great job getting your Corvette back on the highways! The Fuel Pump relay sees a lot of action and will wear out. If you have a lower voltage than normal it might speed it up. I like to keep a spare in the glove box just to be safe.
Great job getting your Corvette back on the highways! The Fuel Pump relay sees a lot of action and will wear out. If you have a lower voltage than normal it might speed it up. I like to keep a spare in the glove box just to be safe.
