Question for the C4 Tech crew
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Question for the C4 Tech crew
I would like you guys to list me out things on a Corvette or any vehicle than you have seen or know that will make a stock engine/stock chip run rich. The component and why. Open and closed loop.
I am going to start fresh and check over all things again. Thank you
I am going to start fresh and check over all things again. Thank you
Le Mans Master
Joined: Apr 2000
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From: DrunkDefender
CI 1-2-3-4-5-6-7-8 Veteran
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St. Jude Donor '07-'10
bad coolant temp sensor or unplugged/bad connecton on same
when its bad or unplugged/short the pcm will read by default way low (something like 15deg) and will really pour the fuel to it.
when its bad or unplugged/short the pcm will read by default way low (something like 15deg) and will really pour the fuel to it.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Well, those are good suggestions,,but we know your fuel components are new..injectors, fuel pressure regulator and 02 sensor...
CTS..yes
bad ECM, but you've tried two.
connections and circuitry to all fuel and air components, 02 sensor, MAF sensor, ECM etc.
vacumn leaks...and sometimes thoughs are hell to find, they can seem good at lower engine temps. but show there ugly heads when the engine warms up or just the opposite.
exhaust leaks.
valve train.
and sometimes you can ohm sensors til you're blue in the face and get good readings...but they need to be ohmed both hot and cold for a more accurate assesment which is difficult to do,or wiggle/twist the wires and you may find you have a bad circuit, one of the reasons we use scanners.
I'll also throw in weak spark.
CTS..yes
bad ECM, but you've tried two.
connections and circuitry to all fuel and air components, 02 sensor, MAF sensor, ECM etc.
vacumn leaks...and sometimes thoughs are hell to find, they can seem good at lower engine temps. but show there ugly heads when the engine warms up or just the opposite.
exhaust leaks.
valve train.
and sometimes you can ohm sensors til you're blue in the face and get good readings...but they need to be ohmed both hot and cold for a more accurate assesment which is difficult to do,or wiggle/twist the wires and you may find you have a bad circuit, one of the reasons we use scanners.
I'll also throw in weak spark.
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
MAF, but usually throws code
CTS
TPS problems, also typically throws something
bad regulator, injectors
O2
vac leaks
spark being too far gone
last thing is ECM
all i can think of at the moment
CTS
TPS problems, also typically throws something
bad regulator, injectors
O2
vac leaks
spark being too far gone
last thing is ECM
all i can think of at the moment
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
These are some of the things I can think of.
1. Leaky injectors (CSV where applicable)
2. Weak spark
3. Bad oxygen sensor....sensor/wiring/connection
4. Bad CTS....sensor/wiring/connection
5. Bad MAF sensor....sensor/wiring/connection/leaks in air duct
6. Faulty AIR....introducing air into the manifolds in closed loop
7. Bad MAT....sensor/wiring/connection
8. Bad EGR....valve/solenoid/wiring/connection
9. Vacuum leaks....introducing atmospheric air
10. Too much fuel pressure
11. EECS system....solenoid wiring/connection/vacuum leak or plug
12. Exhaust leak before the oxygen sensor giving false readings.
13. Alternator wiring
14. Bad TPS....sensor/wiring/connection/adjustment
15. Bad ECM
Just looking for other places.
1. Leaky injectors (CSV where applicable)
2. Weak spark
3. Bad oxygen sensor....sensor/wiring/connection
4. Bad CTS....sensor/wiring/connection
5. Bad MAF sensor....sensor/wiring/connection/leaks in air duct
6. Faulty AIR....introducing air into the manifolds in closed loop
7. Bad MAT....sensor/wiring/connection
8. Bad EGR....valve/solenoid/wiring/connection
9. Vacuum leaks....introducing atmospheric air
10. Too much fuel pressure
11. EECS system....solenoid wiring/connection/vacuum leak or plug
12. Exhaust leak before the oxygen sensor giving false readings.
13. Alternator wiring
14. Bad TPS....sensor/wiring/connection/adjustment
15. Bad ECM
Just looking for other places.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I had ohm tested the CTS a good while back and it tested fine when cold. I didn't test it when hot though. The connector clip is broken, but I get no code. I am trying to think of things that will make the engine run rich in open and closed loop. There are components on these cars that only work/send signal after the engine is a certain temp, when timers go off, and at certain speeds or throttle positions.
I ordered a new CTS and connector and will change it out. I hate to throw parts at it, but $15 for the sensor and $5 for the connector are not bad and stand the best chance of being the culprit since it's rich from start to shutdown. I'm having a hell of a time installing my cable on this laptop.
I ordered a new CTS and connector and will change it out. I hate to throw parts at it, but $15 for the sensor and $5 for the connector are not bad and stand the best chance of being the culprit since it's rich from start to shutdown. I'm having a hell of a time installing my cable on this laptop.
Safety Car
Joined: Sep 2003
Posts: 3,599
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From: Orange County NY
St. Jude Donor '10-'11-'12-'13
I had ohm tested the CTS a good while back and it tested fine when cold. I didn't test it when hot though. The connector clip is broken, but I get no code. I am trying to think of things that will make the engine run rich in open and closed loop. There are components on these cars that only work/send signal after the engine is a certain temp, when timers go off, and at certain speeds or throttle positions.
I ordered a new CTS and connector and will change it out. I hate to throw parts at it, but $15 for the sensor and $5 for the connector are not bad and stand the best chance of being the culprit since it's rich from start to shutdown. I'm having a hell of a time installing my cable on this laptop.
I ordered a new CTS and connector and will change it out. I hate to throw parts at it, but $15 for the sensor and $5 for the connector are not bad and stand the best chance of being the culprit since it's rich from start to shutdown. I'm having a hell of a time installing my cable on this laptop.
But yes - the CTS should be fixed, so I wouldn't call $20 for a new CTS and connector "throwing money at it"
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Pro
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From: Boynton Beach, FL
On early year C4's with only one O2 sensor you can have one of two problems. You can have leaking injector on non O2 sensor bank that O2 sensor won't pick up. Conversely you can have clogged injector on O2 bank causing ECM to richen both sides. You can also have a leaking cold start injector. 
Larry
Larry
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
All good advice, and this will get you TTT. The CSV can and will cause a problem....if the gasket allows leaking. So will others, the gasket or shaft at the TB. You've elimated things like injectors etc. But think about fuel pressure also....you maybe going the wrong direction here...just a thought, because fuel atomization can be a problem also!!!!!!
Also forget about the EGR, Vader has explained this, and if memory serves correct...you don't have a functional EGR?
Don't forget about the cannister too!
Here's something else, forget about open and closed loop, there's timers, heat, etc. that come into play, and IF you went to third gen, you'd get alot more understanding about that.Good Luck Dusty
Also forget about the EGR, Vader has explained this, and if memory serves correct...you don't have a functional EGR?
Don't forget about the cannister too!
Here's something else, forget about open and closed loop, there's timers, heat, etc. that come into play, and IF you went to third gen, you'd get alot more understanding about that.Good Luck Dusty
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
looks like most has been covered .................but, when you say rich, how rich? secondly, did you look at a scanner (stock tune)before, as in day one before anything was ever touched? the stock tune/chips I have seen can be+or-10 approx. in BLM numbers.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I got home this evening after work and check a few more things. I used the timing light to check for spark on all 8 wires...and all 8 showed good. I listened with my stethoscope at the injectors. I could hear all of them ticking the same. I set my minimal idle again as when I put the stock chip in, it changed it a little. I plugged off three vacuum lines that go to the EECS. TB line, rear vac line, and tank line. Fuel pressure at 39 psi idle and TPS at .56v.
I looked at the CTS with a light and yes the clip that firmly connects the connector is broken off and I could even wiggle it...it's loose. Put about 1/2 can of Seafoam and Heet in the tank and about 10 gal of 93 octane (highest here).
While I waited for it to warm up after starting it cold, I could tell there was a miss. But after it warmed up it idled smooth. This Corvette runs like crap. Even power braking it wouldn't turn the tires. Pitiful.
I looked at the CTS with a light and yes the clip that firmly connects the connector is broken off and I could even wiggle it...it's loose. Put about 1/2 can of Seafoam and Heet in the tank and about 10 gal of 93 octane (highest here).
While I waited for it to warm up after starting it cold, I could tell there was a miss. But after it warmed up it idled smooth. This Corvette runs like crap. Even power braking it wouldn't turn the tires. Pitiful.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
If you haven't been able to do a real time scan yet, stop trying to troubleshoot until you get the cable / laptop connection figured out - that will be your biggest asset, that's what you should focus on. The scan data should be able to give you a much better idea of what is happening.
But yes - the CTS should be fixed, so I wouldn't call $20 for a new CTS and connector "throwing money at it"
But yes - the CTS should be fixed, so I wouldn't call $20 for a new CTS and connector "throwing money at it"
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
On early year C4's with only one O2 sensor you can have one of two problems. You can have leaking injector on non O2 sensor bank that O2 sensor won't pick up. Conversely you can have clogged injector on O2 bank causing ECM to richen both sides. You can also have a leaking cold start injector.
Larry
Larry
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
All good advice, and this will get you TTT. The CSV can and will cause a problem....if the gasket allows leaking. So will others, the gasket or shaft at the TB. You've elimated things like injectors etc. But think about fuel pressure also....you maybe going the wrong direction here...just a thought, because fuel atomization can be a problem also!!!!!!
Also forget about the EGR, Vader has explained this, and if memory serves correct...you don't have a functional EGR?
Don't forget about the cannister too!
Here's something else, forget about open and closed loop, there's timers, heat, etc. that come into play, and IF you went to third gen, you'd get alot more understanding about that.Good Luck Dusty
Also forget about the EGR, Vader has explained this, and if memory serves correct...you don't have a functional EGR?
Don't forget about the cannister too!
Here's something else, forget about open and closed loop, there's timers, heat, etc. that come into play, and IF you went to third gen, you'd get alot more understanding about that.Good Luck Dusty
Last edited by RRT vette; Feb 5, 2007 at 09:15 PM.
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
RRT, I wish I could help you out but you are methodically troubleshooting as I would and as you helped me too.
I agree with the not throwing money at it. Right now I am between a short in a wire and a bad ECM with my left injectors not firing.
I would hate to buy a new ECM when it is just a wire.
Good luck!
I agree with the not throwing money at it. Right now I am between a short in a wire and a bad ECM with my left injectors not firing.
I would hate to buy a new ECM when it is just a wire.
Good luck!
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Oh, I have capped off the AIR pipe that feeds the exhaust manifolds. Haven't completely troubleshot the AIR system yet, but figured I could stop air from entering the exhaust in case it never switched to the cat.
Le Mans Master
Joined: May 2004
Posts: 5,866
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
When I answered your earlier post I should have elaborated a bit more on the MAF connection. Mine felt and looked tight but the engine would stop running rich when I held the plug off to one side a bit. I took the connection and cleaned both the male/female sides, then I used a tiny pick to tighten terminals on the female side, then I just very slightly bent the male terminals. The connection went back together much tighter and my rich condition disappeared. BTW, this condition threw no codes. I hope you find it soon, this sort of thing is maddening.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
RRT, I wish I could help you out but you are methodically troubleshooting as I would and as you helped me too.
I agree with the not throwing money at it. Right now I am between a short in a wire and a bad ECM with my left injectors not firing.
I would hate to buy a new ECM when it is just a wire.
Good luck!
I agree with the not throwing money at it. Right now I am between a short in a wire and a bad ECM with my left injectors not firing.
I would hate to buy a new ECM when it is just a wire.
Good luck!
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
When I answered your earlier post I should have elaborated a bit more on the MAF connection. Mine felt and looked tight but the engine would stop running rich when I held the plug off to one side a bit. I took the connection and cleaned both the male/female sides, then I used a tiny pick to tighten terminals on the female side, then I just very slightly bent the male terminals. The connection went back together much tighter and my rich condition disappeared. BTW, this condition threw no codes. I hope you find it soon, this sort of thing is maddening.