Random hard start long crank times
Thread Starter
Racer
Joined: Jun 2014
Posts: 493
Likes: 24
From: Peoria IL
Random hard start long crank times
Need some help here. Recently my z06 started having a hard time starting. It will crank for long periods of time, 4-5 seconds, and I can see in the logs the LTFT's are in the low teens on bank 2. Bank 1 is usually below 10, but not as high.
I swept the engine for vacuum leaks, but can't find anything. Is it possible I have a bad o2 throwing the trims off? Any help or advice would be appreciated.
I swept the engine for vacuum leaks, but can't find anything. Is it possible I have a bad o2 throwing the trims off? Any help or advice would be appreciated.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
I always ask the question when something works one day and doesn't work the next, what changed between when it worked and now that it doesn't?
Did you add any mods or do anything between when it started well and now that it doesn't?
Did you add any mods or do anything between when it started well and now that it doesn't?
Thread Starter
Racer
Joined: Jun 2014
Posts: 493
Likes: 24
From: Peoria IL
The only thing that changed was I have vararam that used the crappy plastic hose barb through the silicone boot. I changed to to mirror their setup now so the fresh air line is now in the same block aa the maf.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
If you've allowed unmetered air into the intake that's not getting measured by your MAF then it very well would likely cause the problem you're describing.
Thread Starter
Racer
Joined: Jun 2014
Posts: 493
Likes: 24
From: Peoria IL
Not quite sure what you mean, but does the car start properly if you put things back the way you had them when it started properly?
If you've allowed unmetered air into the intake that's not getting measured by your MAF then it very well would likely cause the problem you're describing.
If you've allowed unmetered air into the intake that's not getting measured by your MAF then it very well would likely cause the problem you're describing.
Of course the car hasn't actually had the long crank issue at all tonight so I'm all sorts of confused. LTFT's are still all over, i'm sort of surprised it's not throwing a code, one of the times I looked down the bank 2 ltft was at 19
I'm going to pull the o2's and swap them side to side and see if the high ltft follows the bank 2 sensor.
Racer
Joined: Mar 2015
Posts: 285
Likes: 6
Check fuel pressure before starting, should be 50-55 psi. Ignition on should jump to just under 60 psi immediately.
If the fuel pump's internal bypass fails, it causes a loss of fuel system pressure after shut off. This results in an extended crank until fuel pressure builds back up.
An easier way to test is to cycle ignition on, wait 15 seconds then crank. If it starts without the extended crank, you heed a new fuel pump.
If the fuel pump's internal bypass fails, it causes a loss of fuel system pressure after shut off. This results in an extended crank until fuel pressure builds back up.
An easier way to test is to cycle ignition on, wait 15 seconds then crank. If it starts without the extended crank, you heed a new fuel pump.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
I took the cannister line going to the dry sump off, plugged it, and plugged the port going into the air intake and not much change in the ltft.
Of course the car hasn't actually had the long crank issue at all tonight so I'm all sorts of confused. LTFT's are still all over, i'm sort of surprised it's not throwing a code, one of the times I looked down the bank 2 ltft was at 19
I'm going to pull the o2's and swap them side to side and see if the high ltft follows the bank 2 sensor.
Of course the car hasn't actually had the long crank issue at all tonight so I'm all sorts of confused. LTFT's are still all over, i'm sort of surprised it's not throwing a code, one of the times I looked down the bank 2 ltft was at 19
I'm going to pull the o2's and swap them side to side and see if the high ltft follows the bank 2 sensor.
You need to replace the MAF metered fresh air supply to your oil tank. By plugging your fresh air supply to your oil tank your engine is drawing vacuum on the crankcase via the port behind the throttle body to the lifter valley, but there is no fresh air supply to allow the engine to breathe. So it's going to draw fresh air from somewhere - your oil cap perhaps - but wherever it's drawing from is not metered by the maf so it's throwing off your fuel trims.
Replace that line and see if your fuel trims don't get better. And I suspect your starting will be better too.
It'll only set a CEL for LTFT's above 24% by the way.
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Thread Starter
Racer
Joined: Jun 2014
Posts: 493
Likes: 24
From: Peoria IL
I only pulled the cannister line off as a test to see if it was disrupting the maf. It's hooked back up the o2s metered fine. Well one only went up to .8v and seemed to decline as it got hotter so to be safe I am getting a new one.
Fuel pressure is dead steady at 57.9 psi.
Fuel pressure is dead steady at 57.9 psi.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
I only pulled the cannister line off as a test to see if it was disrupting the maf. It's hooked back up the o2s metered fine. Well one only went up to .8v and seemed to decline as it got hotter so to be safe I am getting a new one.
Fuel pressure is dead steady at 57.9 psi.
Fuel pressure is dead steady at 57.9 psi.
Any hard starts since you hooked the fresh air supply back up?
Thread Starter
Racer
Joined: Jun 2014
Posts: 493
Likes: 24
From: Peoria IL
the fresh air was hooked up the whole time, there was no change from when it was hooked up vs when it wasn't.
fyi, I was testing the o2 with it out of the car. you can put a torch to it and read the voltage. the one sensor went up to close to 1v and held there while the other one went to .8 and actually started to fall with the torch on it, which is bass ackwards...
fyi, I was testing the o2 with it out of the car. you can put a torch to it and read the voltage. the one sensor went up to close to 1v and held there while the other one went to .8 and actually started to fall with the torch on it, which is bass ackwards...
Pro
Joined: Jan 2008
Posts: 642
Likes: 48
From: New Jersey
I pulled that fresh air line off years ago. Plugged the hole and put a filter right at the oil tank. Its a little gas line filter about 3/4" diameter by 2" long. I guess you need a filter so you dont suck any bugs into the engine. There was no difference in any sensor readings.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
There are starting airflow tables and other tables to adjust for startup, but you normally don't need to mess with these unless you put in a cam.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
Another question I forgot to ask is, when it happens, if you give it some gas while cranking, does it start right up?
Often when you put a cam in a car you have to increase the starting airflow table, which is essentially like putting your foot on the gas when starting.
I can't imagine that's what your car needs with the stock cam, you have a different problem, but please try it and let us know if giving it some gas fixes it.
Often when you put a cam in a car you have to increase the starting airflow table, which is essentially like putting your foot on the gas when starting.
I can't imagine that's what your car needs with the stock cam, you have a different problem, but please try it and let us know if giving it some gas fixes it.
Thread Starter
Racer
Joined: Jun 2014
Posts: 493
Likes: 24
From: Peoria IL
the cam isn't stock, ls7R from texas speed.
When it starts it will sometimes stumble just a little then fire right up, once it's at idle it's fine, idles fine, and runs fine. It also diesels on shut down.
I threw the new o2's in and cleaned the MAF, I'm really thinking the tuning is just still pretty rough. I didn't get a chance to check the ltft's tonight. When I started it up it fired up pretty quick.
So enlighten me on the open loop/closed loop, I assume it's coolant temp and some triggers for time after start and/or possibly min engine speed?
When it starts it will sometimes stumble just a little then fire right up, once it's at idle it's fine, idles fine, and runs fine. It also diesels on shut down.
I threw the new o2's in and cleaned the MAF, I'm really thinking the tuning is just still pretty rough. I didn't get a chance to check the ltft's tonight. When I started it up it fired up pretty quick.
So enlighten me on the open loop/closed loop, I assume it's coolant temp and some triggers for time after start and/or possibly min engine speed?