Cold Start Problems
Thread Starter
Pro
Joined: Apr 2013
Posts: 575
Likes: 56
From: Placitas, New Mexico
Cold Start Problems
I have a 2003 Z06 that has 42K miles on it. I recently had a set of Kooks headers, an X-pipe, and a Vararam intake installed, then I had the car tuned. Initially, the car ran great, then started having problems. The car would start fine and run great until it heated up.....then it would start missing. Finally, it died on me and I had to get towed in to my mechanic's shop. He diagnosed the problem as a damaged temperature sensor - he may have damaged it while doing the header installation. He replaced the sensor and the car seemed to run OK.
I later started the car after it sat all night in an unheated garage. The car fired up, then "bogged down" and almost stalled. I had to feather the gas pedal and keep the RPMs up until the car started running OK. It really was running "rocky" and was shaking the car back & forth until it heated up a bit. While driving, I noticed that the car would occasionally "hesitate" while going down the road. Once the car was thoroughly heated up, it ran OK, but still "hesitate" from time to time.
I brought the car in to the mechanic. He couldn't find any codes or any reason for the problem, except perhaps plugs & wires. I went ahead and had new plugs & wires installed.
Next morning, I started the car. Same problem, but perhaps a bit less pronounced. I brought the car back to the mechanic. He kept it overnight, then started it. He (and the tuner) said that the engine was running too lean and that the tuner worked on it and corrected the problem.
I started the car this morning....same problem. Not as pronounced, but still running really rocky - but not almost stalling out like it had before.
Some friends of mine....one of which is a mechanic....thought that I may have dirty fuel injectors and suggested using Lucas Injector Cleaner. I'm game....but has anyone had similar problems? Does anyone have a solution? Thanks! ......Steve Snider
I later started the car after it sat all night in an unheated garage. The car fired up, then "bogged down" and almost stalled. I had to feather the gas pedal and keep the RPMs up until the car started running OK. It really was running "rocky" and was shaking the car back & forth until it heated up a bit. While driving, I noticed that the car would occasionally "hesitate" while going down the road. Once the car was thoroughly heated up, it ran OK, but still "hesitate" from time to time.
I brought the car in to the mechanic. He couldn't find any codes or any reason for the problem, except perhaps plugs & wires. I went ahead and had new plugs & wires installed.
Next morning, I started the car. Same problem, but perhaps a bit less pronounced. I brought the car back to the mechanic. He kept it overnight, then started it. He (and the tuner) said that the engine was running too lean and that the tuner worked on it and corrected the problem.
I started the car this morning....same problem. Not as pronounced, but still running really rocky - but not almost stalling out like it had before.
Some friends of mine....one of which is a mechanic....thought that I may have dirty fuel injectors and suggested using Lucas Injector Cleaner. I'm game....but has anyone had similar problems? Does anyone have a solution? Thanks! ......Steve Snider
Thread Starter
Pro
Joined: Apr 2013
Posts: 575
Likes: 56
From: Placitas, New Mexico
No I didn't. It ran just fine with no issues. After the tune, the car ran great when it was cold, but because of the damaged temperature sensor, when the car heated up, it ran terribly! Now it runs OK when heated up, but really bad at cold start-up.
Team Owner
Joined: May 2001
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Also go through the ENTIRE exhaust system, front to back, looking for ANY signs of leaks. Bad ju-ju for tuning.........
Thread Starter
Pro
Joined: Apr 2013
Posts: 575
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From: Placitas, New Mexico
It was tuned with the damaged sensor. That's why it was re-tuned after the sensor was replaced and the car had sat for a couple of nights. I also understand that the exhaust system was inspected front to back after the second tune was completed. No defects or leaks discovered.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Your tuner should be able to data log the PCM and figure out what the heck is wrong.
Some things that I would take a GOOD SOLID LOOK AT are:
Air ducting between the MAF and the Throttle Body. NO air leaks that could let unmetered air in.
Vacuum leaks. Check the PCV fitting on the valve valley cover nipple and the fitting on the PCV nipple on the manifold. They crack and or rot and leak air.
Dirty MAF wires and or dirty throttle body blade. I would check the MAF wires for oil, dirt ect... Bad thing about dirty MAF wires is, the tuner will have to retune the MAF calibration to get it to run properly/efficiently
Bill
Some things that I would take a GOOD SOLID LOOK AT are:
Air ducting between the MAF and the Throttle Body. NO air leaks that could let unmetered air in.
Vacuum leaks. Check the PCV fitting on the valve valley cover nipple and the fitting on the PCV nipple on the manifold. They crack and or rot and leak air.
Dirty MAF wires and or dirty throttle body blade. I would check the MAF wires for oil, dirt ect... Bad thing about dirty MAF wires is, the tuner will have to retune the MAF calibration to get it to run properly/efficiently
Bill
Last edited by Bill Curlee; Dec 7, 2015 at 08:52 PM.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Definitely start with Bill's recommendations---
LT headers often can create tuning woes---As well as a Varraram intake---You have both !
Because on LT's the front 02 locations are often moved as much as 3' aft---The 02's tend not to heat up correctly and read incorrectly--However this should only affect the running after the car is warmed up or in closed loop--You need to have your tuner check your LTFT's to make sure they are at "0" or slightly negative ---LT's will make your engine run RICH at P/T
Same goes for the Varraram---The relocation of the MAF sensor will make your MAF read incorrectly and your tuner needs to check that--Often the Varraram will make your engine run LEAN at P/T but only after warmed or in closed loop
This may help you to better understand how it works
When the engine is 1st started the ECM is in OPEN LOOP---The fueling is running completely off the "open loop normal" table in your tune
When dead cold the coolant temp must reach apprx 140* before it will switch to CLOSED LOOP-----After the engine is warmed the trigger for the switch changes to a timer rather than coolant temp----That timer is normally like 20 seconds---In closed loop the fueling is constantly being adjusted at P/T to achieve the AFR to 14.68 using data from the front 02's --MAF sensor--via your LTFT's (long term fuel trims)
The 02's are NOT being used in open loop---Nor are there any LTFT corrections to fuel--This only happens in closed loop
Finally a tuner can adjust your open loop fueling by making changed to your open loop normal table in your tune---He can use the real time tuning part of the data logger and experiment with fueling while in open loop by changing the fuel ratio in order to find out whether to lean it down or richen-- Certain mods will require an adjustment to open loop for starting and running cold--Any mod that may add airflow--or relocate sensors
LT headers often can create tuning woes---As well as a Varraram intake---You have both !
Because on LT's the front 02 locations are often moved as much as 3' aft---The 02's tend not to heat up correctly and read incorrectly--However this should only affect the running after the car is warmed up or in closed loop--You need to have your tuner check your LTFT's to make sure they are at "0" or slightly negative ---LT's will make your engine run RICH at P/T
Same goes for the Varraram---The relocation of the MAF sensor will make your MAF read incorrectly and your tuner needs to check that--Often the Varraram will make your engine run LEAN at P/T but only after warmed or in closed loop
This may help you to better understand how it works
When the engine is 1st started the ECM is in OPEN LOOP---The fueling is running completely off the "open loop normal" table in your tune
When dead cold the coolant temp must reach apprx 140* before it will switch to CLOSED LOOP-----After the engine is warmed the trigger for the switch changes to a timer rather than coolant temp----That timer is normally like 20 seconds---In closed loop the fueling is constantly being adjusted at P/T to achieve the AFR to 14.68 using data from the front 02's --MAF sensor--via your LTFT's (long term fuel trims)
The 02's are NOT being used in open loop---Nor are there any LTFT corrections to fuel--This only happens in closed loop
Finally a tuner can adjust your open loop fueling by making changed to your open loop normal table in your tune---He can use the real time tuning part of the data logger and experiment with fueling while in open loop by changing the fuel ratio in order to find out whether to lean it down or richen-- Certain mods will require an adjustment to open loop for starting and running cold--Any mod that may add airflow--or relocate sensors
Thread Starter
Pro
Joined: Apr 2013
Posts: 575
Likes: 56
From: Placitas, New Mexico
Definitely start with Bill's recommendations---
LT headers often can create tuning woes---As well as a Varraram intake---You have both !
Because on LT's the front 02 locations are often moved as much as 3' aft---The 02's tend not to heat up correctly and read incorrectly--However this should only affect the running after the car is warmed up or in closed loop--You need to have your tuner check your LTFT's to make sure they are at "0" or slightly negative ---LT's will make your engine run RICH at P/T
Same goes for the Varraram---The relocation of the MAF sensor will make your MAF read incorrectly and your tuner needs to check that--Often the Varraram will make your engine run LEAN at P/T but only after warmed or in closed loop
This may help you to better understand how it works
When the engine is 1st started the ECM is in OPEN LOOP---The fueling is running completely off the "open loop normal" table in your tune
When dead cold the coolant temp must reach apprx 140* before it will switch to CLOSED LOOP-----After the engine is warmed the trigger for the switch changes to a timer rather than coolant temp----That timer is normally like 20 seconds---In closed loop the fueling is constantly being adjusted at P/T to achieve the AFR to 14.68 using data from the front 02's --MAF sensor--via your LTFT's (long term fuel trims)
The 02's are NOT being used in open loop---Nor are there any LTFT corrections to fuel--This only happens in closed loop
Finally a tuner can adjust your open loop fueling by making changed to your open loop normal table in your tune---He can use the real time tuning part of the data logger and experiment with fueling while in open loop by changing the fuel ratio in order to find out whether to lean it down or richen-- Certain mods will require an adjustment to open loop for starting and running cold--Any mod that may add airflow--or relocate sensors
LT headers often can create tuning woes---As well as a Varraram intake---You have both !
Because on LT's the front 02 locations are often moved as much as 3' aft---The 02's tend not to heat up correctly and read incorrectly--However this should only affect the running after the car is warmed up or in closed loop--You need to have your tuner check your LTFT's to make sure they are at "0" or slightly negative ---LT's will make your engine run RICH at P/T
Same goes for the Varraram---The relocation of the MAF sensor will make your MAF read incorrectly and your tuner needs to check that--Often the Varraram will make your engine run LEAN at P/T but only after warmed or in closed loop
This may help you to better understand how it works
When the engine is 1st started the ECM is in OPEN LOOP---The fueling is running completely off the "open loop normal" table in your tune
When dead cold the coolant temp must reach apprx 140* before it will switch to CLOSED LOOP-----After the engine is warmed the trigger for the switch changes to a timer rather than coolant temp----That timer is normally like 20 seconds---In closed loop the fueling is constantly being adjusted at P/T to achieve the AFR to 14.68 using data from the front 02's --MAF sensor--via your LTFT's (long term fuel trims)
The 02's are NOT being used in open loop---Nor are there any LTFT corrections to fuel--This only happens in closed loop
Finally a tuner can adjust your open loop fueling by making changed to your open loop normal table in your tune---He can use the real time tuning part of the data logger and experiment with fueling while in open loop by changing the fuel ratio in order to find out whether to lean it down or richen-- Certain mods will require an adjustment to open loop for starting and running cold--Any mod that may add airflow--or relocate sensors
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Thread Starter
Pro
Joined: Apr 2013
Posts: 575
Likes: 56
From: Placitas, New Mexico
Well, it's Sunday, 12/13/15. We got hammered by a snowstorm last night and the current temperature is about 30 degrees F. I went out to the unheated garage and started up the Z06. I'm pleased to report.....it started beautifully with no problems whatsoever! The new temp sensor seems to be working fine and it apparently was the root of the problem. I guess this is another example of how computerized our Corvettes are! Thanks everyone for your advice........Steve