Funny How Things Change
Thread Starter
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
Funny How Things Change
Well, my initial problem was presented in https://www.corvetteforum.com/forums...dden-miss.html . My problem was my 91 was hard to start and once started had a bad miss cold and warm. Some thoughts were the MAP sensor was the issue and reading up about it I thought that made sense, but after screwing around with it the sensor looked to be working as designed.
Today I had more time to snoop around and when I went to start the motor it cranked and cranked and would fire more and more over that time until it started. To me that indicated the mixture was not rich enough when cold. The thing is, once it started it ran fine. The miss was gone and idles fine. Did a short drive around the neighborhood was no problems. Had it turned off for a short time and then went for a longer drive. It started right up and gave me no issues on the trip.
So only time will tell for sure, but the only issue now is tough start when cold. A while back I had a bad CTS that caused it to stall when it reach temp. At least that was a easy since it threw a code that pointed directly at the CTS.
Now, when I decided to buy a 28 year old Corvette I went into it knowing over my ownership I'd be putting time and money into it. While I doubt the CTS is bad again I'll pull codes again to verify. What are the thoughts of the C-4 membership if I do rule out the CTS?
Today I had more time to snoop around and when I went to start the motor it cranked and cranked and would fire more and more over that time until it started. To me that indicated the mixture was not rich enough when cold. The thing is, once it started it ran fine. The miss was gone and idles fine. Did a short drive around the neighborhood was no problems. Had it turned off for a short time and then went for a longer drive. It started right up and gave me no issues on the trip.
So only time will tell for sure, but the only issue now is tough start when cold. A while back I had a bad CTS that caused it to stall when it reach temp. At least that was a easy since it threw a code that pointed directly at the CTS.
Now, when I decided to buy a 28 year old Corvette I went into it knowing over my ownership I'd be putting time and money into it. While I doubt the CTS is bad again I'll pull codes again to verify. What are the thoughts of the C-4 membership if I do rule out the CTS?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Why not simply TEST the CTS? When cold, we know it's what...about 70*F? Ohm the sensor and then reference this chart to see if the sensor is working correctly. If it is, we know that it's not the sensor and we can move on.
Thread Starter
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
Just got an interesting code when I checked to ensure the CTS wasn't coding again. Got a 33 which is MAP voltage too high. I didn't get any codes when looked last week. Matter of fact, when I pulled info last time it showed 0 voltage that lead to the possibility of a MAP issue. Maybe a wiring issue, sometimes not enough, sometimes too much ??
Race Director
Joined: Nov 2003
Posts: 12,221
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Hey! That's a nice chart to have. Is that universal to years?
Thread Starter
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
Since I've now gotten reading going in opposite directions as to the condition of the MAP and since it isn't expensive does it makes good sense to just throw a new one in there?
Thread Starter
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
So today I go out to play around with the MAP sensor that seemed to be related to the recent issues I've been having. In turning the key expecting a long crank before it started I was greeted with a immediate start and smooth idle in addition strong acceleration through the rpm range.
Earlier this week I did buy a new sensor just in case since they are low cost. Could the one I have in now have a fault that would allow it to read vacuum incorrectly at times and send the incorrect voltage?
Earlier this week I did buy a new sensor just in case since they are low cost. Could the one I have in now have a fault that would allow it to read vacuum incorrectly at times and send the incorrect voltage?
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Safety Car
Joined: May 2001
Posts: 4,757
Likes: 1,647
From: Fairfax Virginia
I would hold off on throwing a computer at it.
We here at the Forum see a fair amount of cars with CTS issues. To operate in "Closed Loop" your car needs to know the amount of air coming in (The Maf sensor), it needs to know what the mixture is instantly using your Oxygen sensor and then it needs to know how warm the engine is so it checks the "Coolant Temperature Sensor" for the temperature it is operating at then the ECM decides how much fuel to inject into the engine to get it to operate properly. The "MAF high" is probably just a glitch and may be a sign of things to come. Do replace all the relays associated with the MAF when you replaced the MAF itself?
The other trick I have seen work in the past is to clean all the electrical connectors and sometimes that even helps on your CTS. I use DeOxIt spray and clean things like that to assure they are making good contact. Also be sure to check your engine block's ground cables or straps as they can wreak havoc on an electrical system.
Best regards,
Chris
We here at the Forum see a fair amount of cars with CTS issues. To operate in "Closed Loop" your car needs to know the amount of air coming in (The Maf sensor), it needs to know what the mixture is instantly using your Oxygen sensor and then it needs to know how warm the engine is so it checks the "Coolant Temperature Sensor" for the temperature it is operating at then the ECM decides how much fuel to inject into the engine to get it to operate properly. The "MAF high" is probably just a glitch and may be a sign of things to come. Do replace all the relays associated with the MAF when you replaced the MAF itself?
The other trick I have seen work in the past is to clean all the electrical connectors and sometimes that even helps on your CTS. I use DeOxIt spray and clean things like that to assure they are making good contact. Also be sure to check your engine block's ground cables or straps as they can wreak havoc on an electrical system.
Best regards,
Chris
Thread Starter
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
You are probably 100% correct that it may have been a connection issue since I had removed the MAP sensor and checked the connection on both sides and ensured there was voltage being feed into sensor. At this point I'm not going to change sensor. I want to get some seat time over a period of time to see if the problem starts again.
Safety Car
Joined: May 2001
Posts: 4,757
Likes: 1,647
From: Fairfax Virginia
Try cleaning all the connections with some good de-oxidizer or whatever is available. I am a big DeOxIt user as this stuff melts away corrosion and leaves a clean surface for the best connection possible. It is available on Amazon.
The MAF sensor that my 1988 C4 came with is a very delicate piece of equipment. The wire is like 1/10th of a mm and gets dirty often. The relays that keep it clean are critical to it lasting a few years. Does your car have a MAF or does it have a MAP sensor?
The "reference voltage" used by the 1988 C4 is 5 Vdc, I don't like seeing less than 5 volts going in to any of the sensors. Clean connections are critical and you should see 5 Vdc on the reference voltage pin.
So many problems are made worse by the corrosion on the connectors. A lowered Reference Voltage should be a good indicator of this.
I start at the battery and clean every major connection, when done my radio had full battery voltage available to it and my fuel pump worked faster and better. Don't forget to do the same to the grounds all over the Corvette!
The MAF sensor that my 1988 C4 came with is a very delicate piece of equipment. The wire is like 1/10th of a mm and gets dirty often. The relays that keep it clean are critical to it lasting a few years. Does your car have a MAF or does it have a MAP sensor?
The "reference voltage" used by the 1988 C4 is 5 Vdc, I don't like seeing less than 5 volts going in to any of the sensors. Clean connections are critical and you should see 5 Vdc on the reference voltage pin.
So many problems are made worse by the corrosion on the connectors. A lowered Reference Voltage should be a good indicator of this.
I start at the battery and clean every major connection, when done my radio had full battery voltage available to it and my fuel pump worked faster and better. Don't forget to do the same to the grounds all over the Corvette!