89 vette not running once it heats up
03-09-2007, 12:21 PM
#1
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89 vette not running once it heats up
My 89 vette has a strange problem. i have taken it to a couple of different shops, and we cannot find the problem. it starts great, as long as the engine is cold. once it heats to 195 degrees, it enters a 'closed loop system", and it surges real bad. the vacuum surges from 17 to 5 inches, and usually ends up in the car stalling. i checked the fuel PSI, it is steady at 36 to 40 which is the spec for the car. after it stalls, it will not start again unless we inject LP gas into the PCV valves. The IAC, MAF, rotor, cap, plugs, and wires have all been changed. The ECM was also changed but showed no change in the symptoms. The only code that was flashed was for the MAF. once we replaced the MAF, the code went away and it has not tripped another code since.
Any info of where else to look would be great!! have been working on this for a couple weeks and am still at square 1!!!
Any info of where else to look would be great!! have been working on this for a couple weeks and am still at square 1!!!
03-09-2007, 03:09 PM
#2
Le Mans Master
Not having scan data makes it difficult to guess at, but assuming that all of the shops you've been to have verified that the sensors are performing as advertised (particularly the Coolant Temp Sensor), I'd guess that you have an ignition module that's headed south. Your vacuum data reflects an engine that's about to stall (and maybe it even does), so I'd expect an intermittent module once it heats up. Some Dealers/Shops/Discount Parts Supply stores have testers so you might take it out and try that route. Otherwise, some scan data would still be helpful.
03-09-2007, 06:59 PM
#3
Former Vendor
If you haven't checked injector pulse with a noid or test light,I would do that. If that's OK, check the resistance of the injectors. Shorting injectors can cause this problem.
Good Luck,Paul
Good Luck,Paul
03-10-2007, 12:18 AM
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Melting Slicks
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Corvettenewbie: I also have a 89 Vett! My engine will enter "closed loop" when the coolant temp gets to about 130 deg F. I am very surprised to see your car not enter the closed loop until the coolant is 195 deg F. This indicates a possible problem. Your engine is being controlled by preprogrammed conditions while it is in open loop mode and it appears to run correctly. When the O2 sensor heats up and supplies voltage to the ECM, you go into closed loop operation.......and your problem is experienced. Did one of the shops scan your engine sensors for you? Did they check to assure the O2 sensor is working properly? Tell us how this problem started? Been there for a while.....just started.....anyone recently worked on the car......anything else unusual? Have you been used fuel injector cleaner in the car?
03-12-2007, 11:01 PM
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I thought there were at least three sensor conditions that triggered closed loop:
- oxygen sensor
- engine coolant temperature (ECT)
- manifold air temperature (MAT)
I've read that the trigger for ECT is 160*
1 - What triggers the move to closed loop?
2 - how can you tell if the ECM is in open or closed loop?
Gary
03-12-2007, 11:25 PM
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Gary: I am somewhat new to understanding the fuel injection process and I do have a scan tool (http://www.turbo-link.com/). The scan tool will indicate the precise instant when the closed loop operation is reached. My scan tool will begin to display the O2 voltage as the closed loop is entered.
The ECT will control the idle RPM per the following programmed speeds (for my 89):
Idle RPM vs. Coolant Temperature
Deg F RPM
306 575.00
284 575.00
262 575.00
241 575.00
219 575.00
198 575.00
176 575.00
154 600.00
133 600.00
111 750.00
90 900.00
68 950.00
46 1050.00
24 1050.00
03 1050.00
-18 1050.00
-40 1050.00
The coolant temp sensor (CTS) data is being used by the ECM to control the ignition timing and pulse width for the injectors. I believe the O2 sensor achieving a certain temp (and starts to send volt data) will allow the car control system to enter closed loop operation.
Those who are more knowledgeable than ole Sam, please add your comments.
The ECT will control the idle RPM per the following programmed speeds (for my 89):
Idle RPM vs. Coolant Temperature
Deg F RPM
306 575.00
284 575.00
262 575.00
241 575.00
219 575.00
198 575.00
176 575.00
154 600.00
133 600.00
111 750.00
90 900.00
68 950.00
46 1050.00
24 1050.00
03 1050.00
-18 1050.00
-40 1050.00
The coolant temp sensor (CTS) data is being used by the ECM to control the ignition timing and pulse width for the injectors. I believe the O2 sensor achieving a certain temp (and starts to send volt data) will allow the car control system to enter closed loop operation.
Those who are more knowledgeable than ole Sam, please add your comments.
Last edited by Sam Lam; 04-18-2007 at 11:53 PM. Reason: error by ole Sam
03-13-2007, 12:55 PM
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Thanks, Sam. I just got my ALDL cable and have yet to scan. I'm glad to hear I'll be able to tell when it goes into closed loop by scanning.
Gary
Gary
04-14-2007, 09:47 AM
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My 89 vette has a strange problem. i have taken it to a couple of different shops, and we cannot find the problem. it starts great, as long as the engine is cold. once it heats to 195 degrees, it enters a 'closed loop system", and it surges real bad. the vacuum surges from 17 to 5 inches, and usually ends up in the car stalling. i checked the fuel PSI, it is steady at 36 to 40 which is the spec for the car. after it stalls, it will not start again unless we inject LP gas into the PCV valves. The IAC, MAF, rotor, cap, plugs, and wires have all been changed. The ECM was also changed but showed no change in the symptoms. The only code that was flashed was for the MAF. once we replaced the MAF, the code went away and it has not tripped another code since.
Any info of where else to look would be great!! have been working on this for a couple weeks and am still at square 1!!!
Any info of where else to look would be great!! have been working on this for a couple weeks and am still at square 1!!!
04-14-2007, 03:23 PM
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St. Jude Donor '11-'12-'13
Not having scan data makes it difficult to guess at, but assuming that all of the shops you've been to have verified that the sensors are performing as advertised (particularly the Coolant Temp Sensor), I'd guess that you have an ignition module that's headed south. Your vacuum data reflects an engine that's about to stall (and maybe it even does), so I'd expect an intermittent module once it heats up. Some Dealers/Shops/Discount Parts Supply stores have testers so you might take it out and try that route. Otherwise, some scan data would still be helpful.
I'd check that module again.
04-16-2007, 02:57 PM
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89 vette
i have the same problem it starts up and idle seems to go up and down just a little but take it for a drive come back park it and it wont start again till it cools off, anyone know what can cause this im not real good at trouble shooting but im tring . thanks for any help or info FXDC
04-16-2007, 03:22 PM
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i have the same problem it starts up and idle seems to go up and down just a little but take it for a drive come back park it and it wont start again till it cools off, anyone know what can cause this im not real good at trouble shooting but im tring . thanks for any help or info FXDC
http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
04-17-2007, 04:11 AM
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I believe that answering ghlkal's questions provide some insight into the original posted problem.
1 - What triggers the move to closed loop?
According to the 1988 Factory Shop Manual (FSM) page E3-C2-2, Three conditions must be met for closed loop operation.
a) The O2 sensor has varying voltage output showing that it is hot enough to operate properly.
b) The coolant sensor is above a specified temperature 40*C (104*F).
c) A specific amount of time has elapsed after starting the engine.
Note:
- The specific time value varies based upon the mem-cal being used. Generally it is about 2 minutes in the early C4s.
- The o2 sensor does not have to be working correctly, it just has to be working nominally.
2 - how can you tell if the ECM is in open or closed loop?
A scan tool is the best way (I sell them), but you can use a paper clip to tell when the system is going into closed loop mode and even see if the ECM “thinks” the mix is too rich or too lean.
From the 88 FSM : page 6E-5
- If the Diagnostic terminal (ALDL) is grounded with the engine running, the system will enter Field Service mode. In Open Loop the Service Engine Soon light flashes 2 and one-half times per second. In Closed Loop the Service Engine Soon light flashes once per second. Also in Closed Loop the light will stay OUT most of the time if the system is too lean. It will stay ON most of the time if the system is too rich.
You can check the open/closed loop status and ECM perceived rich/lean status with a simple paper at home. Try that and tell us what you find.
corvettenewbie, I agree with Sam Lam that if your car runs fine in open loop and starts acting odd immediately after entering closed loop, it is most likely your O2 sensor. I note that of all the parts listed as being swapped, an O2 sensor is not one of them. O2 sensors deteriorate and go bad out with age. They should last 50-75k miles, but anything after 50k is suspect in my book. Remember also that one of the required specs above (b) is that the coolant sensor is telling the ECM the correct temp above 104*F. SunCr mentioned the coolant sensor in his response and it is important here, because as Sam Lam pointed out, his 89 goes closed loop at 130*F. You report your engine requiring 195*F. That is probably too high a value. I would have the Coolant Temp Sensor and O2 sensors checked or replaced. Depending on their age, (like if they are original) I’d possibly skip checking them and just replace them. I don’t think you should throw parts at a problem, but some sensors go bad by slowly degrading over time. Just as I don’t wait for the cords to show before replacing my tires and I don't wait for the fuel filter to clog completely, I don’t let some critical parts get too old before replacing them.
The 89 FSM is very similar to the 88 and in the 88 FSM, section 6E3-B, pages 2-5 there are a list of symptoms and things to check for hard starts and rough running or stalling when warm. One very important group mentioned is the ignition components group and the ignition module. I’d definitely consider SunCr’s advice and put the ignition module high on my list as a possible culprit.
As has been mentioned, it could also be an injector problem as injectors can act different when hot than they do when cold. Usually however injectors don’t start having a problem at a specific temp. Also, it won’t restart when hot until you inject LP gas. Sounds like a possible fuel delivery issue, (way too lean) but at this point I’m not convinced that injectors are your problem. You can easily pull the injector connectors and test the resistance yourself with an ohmmeter. They should be around 16-17 ohms cold with no injector less than 12 ohms. They should be about the same when hot.
FXDC, you say you have the same problem, but you also state that your car runs fine until you shut it off. Corvettenewbie’s car starts having the problem while running as soon as it hits 195*. If you have no problem while running, but experience a hard start only after warm shutdown, I’d immediately guess leaky injectors. Very common and especially so on the 85-88 C4s with the Cold Start Valve (CSV) injector which was unique to those years. I had a similar issue. Post your specifics for more help.
1 - What triggers the move to closed loop?
According to the 1988 Factory Shop Manual (FSM) page E3-C2-2, Three conditions must be met for closed loop operation.
a) The O2 sensor has varying voltage output showing that it is hot enough to operate properly.
b) The coolant sensor is above a specified temperature 40*C (104*F).
c) A specific amount of time has elapsed after starting the engine.
Note:
- The specific time value varies based upon the mem-cal being used. Generally it is about 2 minutes in the early C4s.
- The o2 sensor does not have to be working correctly, it just has to be working nominally.
2 - how can you tell if the ECM is in open or closed loop?
A scan tool is the best way (I sell them), but you can use a paper clip to tell when the system is going into closed loop mode and even see if the ECM “thinks” the mix is too rich or too lean.
From the 88 FSM : page 6E-5
- If the Diagnostic terminal (ALDL) is grounded with the engine running, the system will enter Field Service mode. In Open Loop the Service Engine Soon light flashes 2 and one-half times per second. In Closed Loop the Service Engine Soon light flashes once per second. Also in Closed Loop the light will stay OUT most of the time if the system is too lean. It will stay ON most of the time if the system is too rich.
You can check the open/closed loop status and ECM perceived rich/lean status with a simple paper at home. Try that and tell us what you find.
corvettenewbie, I agree with Sam Lam that if your car runs fine in open loop and starts acting odd immediately after entering closed loop, it is most likely your O2 sensor. I note that of all the parts listed as being swapped, an O2 sensor is not one of them. O2 sensors deteriorate and go bad out with age. They should last 50-75k miles, but anything after 50k is suspect in my book. Remember also that one of the required specs above (b) is that the coolant sensor is telling the ECM the correct temp above 104*F. SunCr mentioned the coolant sensor in his response and it is important here, because as Sam Lam pointed out, his 89 goes closed loop at 130*F. You report your engine requiring 195*F. That is probably too high a value. I would have the Coolant Temp Sensor and O2 sensors checked or replaced. Depending on their age, (like if they are original) I’d possibly skip checking them and just replace them. I don’t think you should throw parts at a problem, but some sensors go bad by slowly degrading over time. Just as I don’t wait for the cords to show before replacing my tires and I don't wait for the fuel filter to clog completely, I don’t let some critical parts get too old before replacing them.
The 89 FSM is very similar to the 88 and in the 88 FSM, section 6E3-B, pages 2-5 there are a list of symptoms and things to check for hard starts and rough running or stalling when warm. One very important group mentioned is the ignition components group and the ignition module. I’d definitely consider SunCr’s advice and put the ignition module high on my list as a possible culprit.
As has been mentioned, it could also be an injector problem as injectors can act different when hot than they do when cold. Usually however injectors don’t start having a problem at a specific temp. Also, it won’t restart when hot until you inject LP gas. Sounds like a possible fuel delivery issue, (way too lean) but at this point I’m not convinced that injectors are your problem. You can easily pull the injector connectors and test the resistance yourself with an ohmmeter. They should be around 16-17 ohms cold with no injector less than 12 ohms. They should be about the same when hot.
FXDC, you say you have the same problem, but you also state that your car runs fine until you shut it off. Corvettenewbie’s car starts having the problem while running as soon as it hits 195*. If you have no problem while running, but experience a hard start only after warm shutdown, I’d immediately guess leaky injectors. Very common and especially so on the 85-88 C4s with the Cold Start Valve (CSV) injector which was unique to those years. I had a similar issue. Post your specifics for more help.
Last edited by Mike_88Z51; 05-13-2007 at 02:40 PM.
04-18-2007, 06:30 AM
#13
Burning Brakes
Another possibility for a temperature dependent/related roughness/surging/misfire: The ignition coil.
It's happened to me before - with no visible misfire apparent using a timing light. Yes, at idle. Car would start cold and run perfectly. As the underhood temps came up a roughness/surge would develop and by the time it was completely warmed up it was junk. At idle.
No codes. All sensor data normal (more or less) on the scan tool. New injectors didn't help. Fuel pressure, TPS setting, timing all good. No luck checking All of the wires with a timing light. Pulled hair out trying to find a vacuum leak, etc. Finally tried a coil, on the way down the parts list, and cured it...
It's happened to me before - with no visible misfire apparent using a timing light. Yes, at idle. Car would start cold and run perfectly. As the underhood temps came up a roughness/surge would develop and by the time it was completely warmed up it was junk. At idle.
No codes. All sensor data normal (more or less) on the scan tool. New injectors didn't help. Fuel pressure, TPS setting, timing all good. No luck checking All of the wires with a timing light. Pulled hair out trying to find a vacuum leak, etc. Finally tried a coil, on the way down the parts list, and cured it...
04-18-2007, 10:48 PM
#14
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great post
Mike, thoughtful and insightful post with great information 
Gary
Gary
04-18-2007, 11:55 PM
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04-19-2007, 07:34 AM
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89 vette
it starts right up idles good till normal op temp is reached then idle moves up and down just a bit then when fan starts the idle smooths out fan shuts down idle gos back to up and down just alittle so i let it run for awhile then shut it off then i try to start it , it trys to fire but wont start till it cools off. im goig to put a scan on it today i have a AUTO XRAY 6000 but what exactly am i lookig for ? IM a PLUMBER tring to be a MECHANIC, i want to learn how to do this stuff my self every time i need a part and mension corvette theres $$$$ signs. by the my corvette has 41,000 mile on it ive had it for 11 years this is the first time something big has happened also i would like to THANK ALL YOU GUYS for helping out people like me
it starts right up idles good till normal op temp is reached then idle moves up and down just a bit then when fan starts the idle smooths out fan shuts down idle gos back to up and down just alittle so i let it run for awhile then shut it off then i try to start it , it trys to fire but wont start till it cools off. im goig to put a scan on it today i have a AUTO XRAY 6000 but what exactly am i lookig for ? IM a PLUMBER tring to be a MECHANIC, i want to learn how to do this stuff my self every time i need a part and mension corvette theres $$$$ signs. by the my corvette has 41,000 mile on it ive had it for 11 years this is the first time something big has happened also i would like to THANK ALL YOU GUYS for helping out people like me
04-24-2007, 08:19 PM
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my spec.
prom id =4151
coolent temp=209.7
thottle sensor=0.50 volts
engine rpm=178
vehicle speed=0
oxygen sensor=408 volts
o2 cross count=0
block learn=128
block learn cell= 0
intergrador=128
idle air mtr pos=160 steps
desired idle=3187
engine load=255
manifold air tmp=113.0f
egr duty cyc.=0.0%
ccp duty cyc.=0.0%
battery volts=11.9
fuel pump sense=0.0volts
injector pulse=0.0
map sensor=2.21volts
mass air flow=23gr/sec
loop status =open
this is what i get with the key in the "on " position.
car not runnin.
desired idle?, mass airflow?
can any help or have any idea what i should do
i changed ecm coolent temp,electronic ingition modual,tune up,plugs plug wires,just orderd a new prom chip but i dont know still it gets to operating temp pulsates idle at 195 degrees from 6k to 7k back and fouth then if you shut car off it will not start till it cools off to about 125 degrees
prom id =4151
coolent temp=209.7
thottle sensor=0.50 volts
engine rpm=178
vehicle speed=0
oxygen sensor=408 volts
o2 cross count=0
block learn=128
block learn cell= 0
intergrador=128
idle air mtr pos=160 steps
desired idle=3187
engine load=255
manifold air tmp=113.0f
egr duty cyc.=0.0%
ccp duty cyc.=0.0%
battery volts=11.9
fuel pump sense=0.0volts
injector pulse=0.0
map sensor=2.21volts
mass air flow=23gr/sec
loop status =open
this is what i get with the key in the "on " position.
car not runnin.
desired idle?, mass airflow?
can any help or have any idea what i should do
i changed ecm coolent temp,electronic ingition modual,tune up,plugs plug wires,just orderd a new prom chip but i dont know still it gets to operating temp pulsates idle at 195 degrees from 6k to 7k back and fouth then if you shut car off it will not start till it cools off to about 125 degrees
04-26-2007, 06:28 AM
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89 vette heats up wont start
my spec.
prom id =4151
coolent temp=209.7
thottle sensor=0.50 volts
engine rpm=178
vehicle speed=0
oxygen sensor=408 volts
o2 cross count=0
block learn=128
block learn cell= 0
intergrador=128
idle air mtr pos=160 steps
desired idle=3187
engine load=255
manifold air tmp=113.0f
egr duty cyc.=0.0%
ccp duty cyc.=0.0%
battery volts=11.9
fuel pump sense=0.0volts
injector pulse=0.0
map sensor=2.21volts
mass air flow=23gr/sec
loop status =open
this is what i get with the key in the "on " position.
car not runnin.
desired idle?, mass airflow?
can any help or have any idea what i should do
i changed ecm coolent temp,electronic ingition modual,tune up,plugs plug wires,just orderd a new prom chip but i dont know still it gets to operating temp pulsates idle at 195 degrees from 6k to 7k back and fouth then if you shut car off it will not start till it cools off to about 125 degrees
prom id =4151
coolent temp=209.7
thottle sensor=0.50 volts
engine rpm=178
vehicle speed=0
oxygen sensor=408 volts
o2 cross count=0
block learn=128
block learn cell= 0
intergrador=128
idle air mtr pos=160 steps
desired idle=3187
engine load=255
manifold air tmp=113.0f
egr duty cyc.=0.0%
ccp duty cyc.=0.0%
battery volts=11.9
fuel pump sense=0.0volts
injector pulse=0.0
map sensor=2.21volts
mass air flow=23gr/sec
loop status =open
this is what i get with the key in the "on " position.
car not runnin.
desired idle?, mass airflow?
can any help or have any idea what i should do
i changed ecm coolent temp,electronic ingition modual,tune up,plugs plug wires,just orderd a new prom chip but i dont know still it gets to operating temp pulsates idle at 195 degrees from 6k to 7k back and fouth then if you shut car off it will not start till it cools off to about 125 degrees
04-26-2007, 12:05 PM
#19
Le Mans Master
Your readings are pretty normal for key on/engine off. Your IAC has parked at the restart position. You might reset your TPS to .54 - .56, but the car is ready to start, so try to capture data with it running; save at the point of the stall. With a new module, I would suspect that an injector is crapping out or maybe the coil. The Integrator reading might provide a clue. Check ohms across the injector coils while they're hot.
As to the data you asked about - desired idle is for restart - it will or should quickly change once started. MAF is meaningless but the hot or sensing wire is energized and reading the air that surrounds it. You don't have a MAP or Manifold Air Pressure Sensor so read you Scanner literature to find out what it's interpreting (my guess would be the Manifold Air Temp Sensor voltage).
As to the data you asked about - desired idle is for restart - it will or should quickly change once started. MAF is meaningless but the hot or sensing wire is energized and reading the air that surrounds it. You don't have a MAP or Manifold Air Pressure Sensor so read you Scanner literature to find out what it's interpreting (my guess would be the Manifold Air Temp Sensor voltage).
04-26-2007, 01:58 PM
#20
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89 vette heats up wont start
Your readings are pretty normal for key on/engine off. Your IAC has parked at the restart position. You might reset your TPS to .54 - .56, but the car is ready to start, so try to capture data with it running; save at the point of the stall. With a new module, I would suspect that an injector is crapping out or maybe the coil. The Integrator reading might provide a clue. Check ohms across the injector coils while they're hot.
As to the data you asked about - desired idle is for restart - it will or should quickly change once started. MAF is meaningless but the hot or sensing wire is energized and reading the air that surrounds it. You don't have a MAP or Manifold Air Pressure Sensor so read you Scanner literature to find out what it's interpreting (my guess would be the Manifold Air Temp Sensor voltage).
As to the data you asked about - desired idle is for restart - it will or should quickly change once started. MAF is meaningless but the hot or sensing wire is energized and reading the air that surrounds it. You don't have a MAP or Manifold Air Pressure Sensor so read you Scanner literature to find out what it's interpreting (my guess would be the Manifold Air Temp Sensor voltage).