To not throw parts at it
#1
Drifting
Thread Starter
To not throw parts at it
So today I put a new battery into my 91 and since it was a warm enough for my summer tires took it on a short drive. Started fine, but would want stall when trying to pull away from a stop. If I feathered the accelerator just right I could sometimes keep it going. When it stalled the only way to get it restarted would be to hold the pedal to the floor as if it was flooded. Would also stall or start to if I slowed down to turn a corner unless I slipped it into neutral and feathered the gas to keep it at a higher RPM.
It had always started right up when cold and had planned to do a tune-up in spring since may not have many warm enough days to take it out. What direction do the knowledge trust among the members here think I should go it. Btw, the last time I had it out was earlier in December when the oil sensor was replaced to stop oil leak. It ran fine except for a little roughness at lower rpm.
It had always started right up when cold and had planned to do a tune-up in spring since may not have many warm enough days to take it out. What direction do the knowledge trust among the members here think I should go it. Btw, the last time I had it out was earlier in December when the oil sensor was replaced to stop oil leak. It ran fine except for a little roughness at lower rpm.
Last edited by CorvetteRules; 12-29-2018 at 12:09 PM.
#2
Race Director
Hook up a scanner and read the different sensor outputs. You want to see the outputs of the tps, coolant temperature, O2, and map sensors (if you have one). This will give you some direction. Also, if a car is misbehaving, I always start with a tuneup; spark plugs and wires, cap and root or if you have one.
#3
Drifting
Thread Starter
Problem with doing a tune-up now is that I currently don't have room in garage to do it and the weather is too iffy to do outside. On top of that having the summer tires would make it difficult to even test drive it.
#6
Safety Car
A higher rpm at idle and take off stumble and stalling can be a vacuum leak. Do you hear any hissing coming from anywhere? The main culprits are the brake booster, check valve or any old brittle vacuum lines. GM used plastic lines under the runners and plenum that dry out and crack.
As mentioned, getting a scanner on it and seeing whats going on is really a must.
You can check your TPS with a voltmeter for a dead spot. That can cause stalling at specific times.
You can check the throttle blade for carbon build up. You can check the throttle blade for play.
Any service engine soon light?
Theres a few ideas to start with...
As mentioned, getting a scanner on it and seeing whats going on is really a must.
You can check your TPS with a voltmeter for a dead spot. That can cause stalling at specific times.
You can check the throttle blade for carbon build up. You can check the throttle blade for play.
Any service engine soon light?
Theres a few ideas to start with...
Last edited by Dt86; 12-30-2018 at 10:00 AM.
#7
Race Director
You don't have to drive the car to check sensor outputs. Open the garage door, sit on the drivers seat, start the car and read the scanner.
#8
Team Owner
To check the CTS, you will need to buy a scanner. Most seem resistant to that, for whatever reason. Also get an infra red thermometer. Borrow a compression tester from Autozone. When it is cold, the CTS and the Oil temp should be the same based on what the ECM sees and not what the gauges say they see. As the temp rises, see what the CTS vs IR Thermometer on the CTS says. They should be about the same.
See what the fuel pressure is at Key On Engine Off. See if it bleeds down fast. Do a WOT run under load with the fuel pressure gauge taped on the glass. See if it holds pressure.
Check the plugs for crud on it and and especially the wires for leaking.
#9
Drifting
Thread Starter
Thanks to all for the advice. My mind was jumping all over the place while driving it yesterday, so it is great to have a place like this forum to hear from those that have a passion for corvettes. I'm very new to the club. but hope to learn from that passion.
#10
Drifting
Thread Starter
- AN UPDATE-
Had some free time today so spent some time looking at my 91. As always it started right up and idled fine. With it running looked and listened for any possible vacuum leaks. Didn't find anything so shut it down and started to feel around on all the lines and their connections and felt or saw no deteriorated lines. Based on appearances it looks like all the lines are not very old. After that I stated it again, fired right up and I started doing stuff in the interior and left it running.
It ran fine until it fully warmed up and then it started to run rough and stalled. At that point the only way to restart it was to hold the gas to the floor but would not stay running with out keeping at a much higher RPM. So, if no vacuum leaks and running perfect until it fully warmed up?
One thing I did notice is that the power seats (driver's and passenger) are not working. They were working, but since once my seat is set I normally never have reason to change it. Didn't have time to check the fuses, but if the fuse was blown does anyone know if it shares power with something that may cause the symptoms I'm seeing?
Had some free time today so spent some time looking at my 91. As always it started right up and idled fine. With it running looked and listened for any possible vacuum leaks. Didn't find anything so shut it down and started to feel around on all the lines and their connections and felt or saw no deteriorated lines. Based on appearances it looks like all the lines are not very old. After that I stated it again, fired right up and I started doing stuff in the interior and left it running.
It ran fine until it fully warmed up and then it started to run rough and stalled. At that point the only way to restart it was to hold the gas to the floor but would not stay running with out keeping at a much higher RPM. So, if no vacuum leaks and running perfect until it fully warmed up?
One thing I did notice is that the power seats (driver's and passenger) are not working. They were working, but since once my seat is set I normally never have reason to change it. Didn't have time to check the fuses, but if the fuse was blown does anyone know if it shares power with something that may cause the symptoms I'm seeing?
#11
Safety Car
Originally Posted by CorvetteRules
[b]- AN UPDATE-
It ran fine until it fully warmed up and then it started to run rough and stalled. At that point the only way to restart it was to hold the gas to the floor but would not stay running with out keeping at a much higher RPM. So, if no vacuum leaks and running perfect until it fully warmed up.
It ran fine until it fully warmed up and then it started to run rough and stalled. At that point the only way to restart it was to hold the gas to the floor but would not stay running with out keeping at a much higher RPM. So, if no vacuum leaks and running perfect until it fully warmed up.
#12
Team Owner
Maybe scan the ECM and see what it thinks for hot and cold and compare it to what the IR thermometer says?
#13
Drifting
Thread Starter
glass slippers thoughts regarding the CTS are very interesting because when cold car starts right up and runs nicely. It is not until it warms up that it starts running rough and will actually stall, which would make sense if the computer still thinks the engine is cold and keeps fuel to rich.
The cost of a new CTS is fairly inexpensive so my question is if it would b e reasonable to just replace it and see if all goes back to normal? I don't have my service manual yet, so don't any reference to go by. Also takes me back to my question on if the CTS is tied into a fuse that should be checked that would keep it from providing the correct reading to the computer?
The cost of a new CTS is fairly inexpensive so my question is if it would b e reasonable to just replace it and see if all goes back to normal? I don't have my service manual yet, so don't any reference to go by. Also takes me back to my question on if the CTS is tied into a fuse that should be checked that would keep it from providing the correct reading to the computer?
#14
Instructor
#15
Team Owner
#16
Drifting
Thread Starter
Yes, I agree, I'd rather not replace any parts since it was running fine but suddenly started not to run right once warm. Which brings me back to the suggestion glass slipper made in regards to the CTS could cause the exact issue of the computer keeping the fuel flow too rich. The problem I found with my power seats just stuck in my mind as to if the power to the seats may also be electrically connected to the CTS communication with computer and if not if there is a fuse to be checked that is tied to it's communication to computer.
#18
Drifting
Thread Starter
I Disconnect each injector connector and check the coil resistance with an Ohmeter. IIRC the resistance of a healthy Multec is about 17-18 Ohms. I've seen L98's with only one or two injectors with less than 10 ohms, and the engine did not idle properly.
Ohm the injectors.
Ohm the injectors.
#19
Team Owner
It's not the CTS. The cold engine correction ends at about 150deg F. CTS issues are generally associated with cold weather starting problems. Not stalling after it warms up.
I see you have a 91. The 91 has the notorious un-reliable Multec injectors. The Multecs have coil insulation that degrades with Ethanol fuel, and develop internal shorts which overload the circuitry in the ECM, and the ECM either shuts down, or can't control the injectors properly. After it warms up, and is running crummy, shut it down. Disconnect each injector connector and check the coil resistance with an Ohmeter. IIRC the resistance of a healthy Multec is about 17-18 Ohms. I've seen L98's with only one or two injectors with less than 10 ohms, and the engine did not idle properly.
Ohm the injectors.
I see you have a 91. The 91 has the notorious un-reliable Multec injectors. The Multecs have coil insulation that degrades with Ethanol fuel, and develop internal shorts which overload the circuitry in the ECM, and the ECM either shuts down, or can't control the injectors properly. After it warms up, and is running crummy, shut it down. Disconnect each injector connector and check the coil resistance with an Ohmeter. IIRC the resistance of a healthy Multec is about 17-18 Ohms. I've seen L98's with only one or two injectors with less than 10 ohms, and the engine did not idle properly.
Ohm the injectors.
#20
Team Owner
It could be relaying the wrong information. If you check what the pulse width is with a scanner, someone with a stock engine can tell you what their pulse width is so you can see if it is really enriching the engine.