I will get a log if needed. I?m having an issue where I go to start my car for the first time of day and I have to pedal it to keep it running . If I turn the engine back off then start again it will idle properly. Is this IAC related ?
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I will get a log if needed. I?m having an issue where I go to start my car for the first time of day and I have to pedal it to keep it running . If I turn the engine back off then start again it will idle properly. Is this IAC related ?
4.8 dbc speed density . I will get a log this evening .
Fuel pump rest pressure
Fuel pump not priming would be my initial suspicion. Many cars, will prime the pump soon as the car is unlocked, door opened or some other way in which the cars wakes from it's hibernation so to speak. But this problem is exasperated when or if you have a pressure decay issue.
This may be some kind of bug... you didn't say what you are working with, but it's seen most prominently in 01-02 OS's for whatever reason, and more often in SD. There used to be a years-long running thread about it in the Beta section of the forum here, but that whole section got removed and that post died with it.
Do this: add the Cold Start status bit to your scanner. Here's what you notice.... you start up cold and that bit is set. It idles kinda weakly, and if you scan idle trims, they will be ADDING airflow. You shut the car off when it's mostly warm. You re-crank. Cold start bit is now NOT set. It starts up noticeably stronger. The idle airflow trims are now subtracting everywhere (with not tune change) and it idles much more "strongly", even returns to idle slower instead of dropping like a rock.
Trying to solve this problem myself.
I have one doing this same thing. I can run the pump continuously it makes no difference. I can just cycle the switch not even try to start it. On the second cycle it will start and run perfect. If I do not cycle the switch it will not run unless you baby it with the throttle pedal.
Steve, I have a customer experiencing this on his 02 Silverado now. Have you noticed it to be more common on the 12216125 OS? Do you think something is corrupted during the flash? Have you tried doing a Write Entire on any of those? What about changing the OS to an earlier OS?Quote:
Originally Posted by Frost
Thanks!
Kevin
I have a similar issue on a 2001 firebird OS. On mine I don't get a fire on first turn of the key, and if it does fire it runs very poorly. But if I turn the key on then back off then start it it fires right up with a good strong idle.
this scenario is true no matter what, I live in Wyoming so it gets a bit cold here and it does this in the dead of winter or in the middle of the summer.
At first I thought it might be a fueling issue related to the pump pressuring up. SO I would turn on the key wait for the fuel pressure to come on the gauge for the regulator then crank it over and get the same result. Turn it off and go right to crank and it fires. I have not been able to figure it out and gave up on it since it really doesn't bother to much. It would be nice to have it fire on the first turn of the key though. Especially if I go to a push button start.
Fuel pump only primes for 3 seconds when the key is turned on or the car is awakened. If there is no fuel pressure left in the lines, due to a pressure decay issue, just turning the key on once wont generate much fuel pressure from say 0 psi. Your fuel system shouldn't ever drop below around 20 psi after sitting for a period of time (in a general sense, each system has its own specifications). You should check your fuel pressure while its running and pumped up, shut the car off and see how far it drops overnight. It really shouldn't drop a whole lot. It should be able to achieve desired fuel pressure after it primes the system just once.
I can run the pump for as long as I want. It makes no difference. It takes two cycles of the power to make it run good.Quote:
Originally Posted by danmw2003
Have seen it quite a few times; if it matches what I describe. On swaps, I go drastically different to get away from it. On some OE vehicles you are just seemingly stuck with it. There is criteria that enables/disables that cold-start status bit. We are not given it, in the editor. On the affected vehicles, idle airflow tuning is a complete waste of time if you "follow the steps" given here. You will get a log of very high demanded and when you put those numbers in and re-flash, you will have a buttload too much everywhere (once that status bit has cleared). It's a huge PITA and it never went away. It's very common with the '156 OS.Quote:
Originally Posted by kevin87turbot