Silverado 4.8 Delayed start when warm
03-07-2019, 08:04 PM
#1
Registered User
Thread Starter
Join Date: Mar 2019
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Silverado 4.8 Delayed start when warm
Hello everyone,
I have a 2002 Sierra 1500 4.8L.
The truck has a hard time starting only when the engine has warmed up. First thing in the morning it starts up fine. Also once its warmed up if i turn it off and immediately re start it, its fine. Only when the engine is warm and I run into say the store for a few minutes and come back out it will crank for about 4 or 5 seconds.
Im assuming that the truck is starting fine in open loop and the problem is in closed loop? When its warm and I immediately re start it, the truck remembers the fuel trim and can start with the appropriate fuel but after sitting for a few minutes something resets and it tries to start in closed loop but with out remembering any of the fuel trims. ( I could be totally wrong on this)
Other than that it seems to run pretty good. Just cant seem to figure out the hard start when warm. Any thoughts? Thanks!!
Fuel pressure is 55 PSI regardless of engine temp (morning or after driving, sitting)
Fuel pressure regulator has been replaced
I have a 2002 Sierra 1500 4.8L.
The truck has a hard time starting only when the engine has warmed up. First thing in the morning it starts up fine. Also once its warmed up if i turn it off and immediately re start it, its fine. Only when the engine is warm and I run into say the store for a few minutes and come back out it will crank for about 4 or 5 seconds.
Im assuming that the truck is starting fine in open loop and the problem is in closed loop? When its warm and I immediately re start it, the truck remembers the fuel trim and can start with the appropriate fuel but after sitting for a few minutes something resets and it tries to start in closed loop but with out remembering any of the fuel trims. ( I could be totally wrong on this)
Other than that it seems to run pretty good. Just cant seem to figure out the hard start when warm. Any thoughts? Thanks!!
Fuel pressure is 55 PSI regardless of engine temp (morning or after driving, sitting)
Fuel pressure regulator has been replaced
Last edited by cherman99676; 03-30-2019 at 09:41 PM. Reason: wrong title
03-07-2019, 08:13 PM
#2
These engines always start in open loop, no matter the temp. The amount of time it takes to re-enter closed loop depends on engine temp, if it's already hot it takes less than 5 seconds most of the time if I remember viewing the tables right.
I'd try checking your fuel pressure cold and hot. Also checking the pressure after the fuel pump primes while hot. If it spikes up to 50-60 but then falls like a rock within no time, you could be dealing with a bad pressure regulator.
The misfire at heavy throttle could be fuel related or ignition system related. You'd have to do testing on both to see what's up.
I'd try checking your fuel pressure cold and hot. Also checking the pressure after the fuel pump primes while hot. If it spikes up to 50-60 but then falls like a rock within no time, you could be dealing with a bad pressure regulator.
The misfire at heavy throttle could be fuel related or ignition system related. You'd have to do testing on both to see what's up.
03-29-2019, 04:41 PM
#4
Registered User
Thread Starter
Join Date: Mar 2019
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Just an update. Ive changed a few things and my fuel trims are better but not perfect but the truck is still having trouble starting once warm. I live in Alaska and the truck has/had a snorkel on it. I realized that the snorkel was restricting air and causing the truck to pull fuel. Stock air box is back in and replaced the fuel pressure regulator and the truck has perfect fuel trims while driving now but still -10 long term trim at idle. As soon as I give it gas it returns to +2 or +3.
In the unrelated or maybe related problem that caused me to start this thread the truck still has a long crank when the engine has warmed up and you wait about 10 - 20 minutes to restart. It starts perfect every morning when cold
if i run it for an hour or till warm and shut it off and re start it immediately, it starts perfect
If I run it for any amount of time so that it can warm up and wait 10 minutes or longer it has a long crank
wait for it to cool down and it starts fine again
I have checked the fuel pressure at the rail and it is always at 55 PSI and holds there regardless of the temp of the engine and if it has trouble starting or not.
Could it be dirty MAF or a bad engine temp sensor? My gauge works fine but I read that the engine maybe getting a bad reading and add too much fuel thinking it was cold and causing it to not start?
Any help is appreciated!
In the unrelated or maybe related problem that caused me to start this thread the truck still has a long crank when the engine has warmed up and you wait about 10 - 20 minutes to restart. It starts perfect every morning when cold
if i run it for an hour or till warm and shut it off and re start it immediately, it starts perfect
If I run it for any amount of time so that it can warm up and wait 10 minutes or longer it has a long crank
wait for it to cool down and it starts fine again
I have checked the fuel pressure at the rail and it is always at 55 PSI and holds there regardless of the temp of the engine and if it has trouble starting or not.
Could it be dirty MAF or a bad engine temp sensor? My gauge works fine but I read that the engine maybe getting a bad reading and add too much fuel thinking it was cold and causing it to not start?
Any help is appreciated!
03-29-2019, 05:27 PM
#5
100% Redneck
My truck dose the exact same thing, cold fires right up, hot it takes 4 to 5 seconds with half throttle. I've traced it down to a bad check ball in the fuel pump. When it's hot I can cycle the key twice before engaging the starter and it has enough prime to fire it right off. So you're saying it holds at 55 psi at the rail when the engine is shutdown? Mine drops to zero in about 3 seconds but runs strong at 6500 with a A/F ratio at 12.2
03-29-2019, 05:49 PM
#6
Registered User
Thread Starter
Join Date: Mar 2019
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Sorry, to elaborate .. Its holds at 55 PSI with the key on and fuel pump primed. When the key is turned off it falls very slowly (like over a few minutes) like I believe is normal. A/F is a perfect 14.7/1
The fuel pressure gauge reads 55 PSI before it has the long crank and reads 55 PSI on a normal quick start making me think my fuel pump and any check valve inside might be good.
I appreciate the suggestions very much. I will try priming the pump a few times before my next warm start.
The fuel pressure gauge reads 55 PSI before it has the long crank and reads 55 PSI on a normal quick start making me think my fuel pump and any check valve inside might be good.
I appreciate the suggestions very much. I will try priming the pump a few times before my next warm start.
Last edited by cherman99676; 03-29-2019 at 05:59 PM.
Trending Topics
03-29-2019, 10:27 PM
#9
So, I'm gonna throw a really basic idea out there. Had a similar problem in an old power stroke. Starter could be getting weak. Cold you've got looser tolerances, hot everything is sealed up better. Idk, just a thought. If it's spinning fast hot I would rule it out, but if it's slowing down when warm, I wouldn't rule it out.