LS1 long start when warm
Thread Starter
TECH Enthusiast
Joined: Aug 2002
Posts: 715
Likes: 7
From: Houston
LS1 long start when warm Hey all,
I've got a daily driver 02 T/A WS6 with about 140k miles on the original engine.
Car runs great, no misfires, codes, etc. However, after the car has warmed up and been driven around a bit then turned off, it exhibits a long start. It cranks just fine, but takes 2-3 seconds before it stumble/starts and then it immediately purrs no problem. No issues at all when it's cold first thing in the morning. Every morning it fires straight up with the slightest turn of the key.
Any ideas?
Thanks!
I've got a daily driver 02 T/A WS6 with about 140k miles on the original engine.
Car runs great, no misfires, codes, etc. However, after the car has warmed up and been driven around a bit then turned off, it exhibits a long start. It cranks just fine, but takes 2-3 seconds before it stumble/starts and then it immediately purrs no problem. No issues at all when it's cold first thing in the morning. Every morning it fires straight up with the slightest turn of the key.
Any ideas?
Thanks!
Launching!
Joined: Apr 2017
Posts: 276
Likes: 5
From: █▬█ █▄█ █▬█ █▄██▬█ █▄█ █▬█ █▄█
The fuel pump has a check valve. The check valves wear out and lets fuel pressure bleed back into the fuel tank when the pump isnt running. A combination of that and hot fuel rails can cause hard hot starts.
Last edited by Fuhnortoner; Aug 8, 2019 at 09:44 PM.
steps
1. try giving it 10-20% throttle when cranking, if that helps it needs less fuel in the cranking table at that temp (or more air)
2. visibly verify fuel pressure is there before cranking (drain back check valve, not all fuel pumps have them, e.g. 450 walbro no check valve)
Its usually too much fuel, most of the time on hptuners boards when people complain about hot starts the knee-jerk reaction is somebody saying "pull out 5-10% fuel each time until it fires up normally"
1. try giving it 10-20% throttle when cranking, if that helps it needs less fuel in the cranking table at that temp (or more air)
2. visibly verify fuel pressure is there before cranking (drain back check valve, not all fuel pumps have them, e.g. 450 walbro no check valve)
Its usually too much fuel, most of the time on hptuners boards when people complain about hot starts the knee-jerk reaction is somebody saying "pull out 5-10% fuel each time until it fires up normally"
Trending Topics
Launching!
Joined: Apr 2017
Posts: 276
Likes: 5
From: █▬█ █▄█ █▬█ █▄██▬█ █▄█ █▬█ █▄█
steps
1. try giving it 10-20% throttle when cranking, if that helps it needs less fuel in the cranking table at that temp (or more air)
2. visibly verify fuel pressure is there before cranking (drain back check valve, not all fuel pumps have them, e.g. 450 walbro no check valve)
Its usually too much fuel, most of the time on hptuners boards when people complain about hot starts the knee-jerk reaction is somebody saying "pull out 5-10% fuel each time until it fires up normally"
1. try giving it 10-20% throttle when cranking, if that helps it needs less fuel in the cranking table at that temp (or more air)
2. visibly verify fuel pressure is there before cranking (drain back check valve, not all fuel pumps have them, e.g. 450 walbro no check valve)
Its usually too much fuel, most of the time on hptuners boards when people complain about hot starts the knee-jerk reaction is somebody saying "pull out 5-10% fuel each time until it fires up normally"
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Another fix is to increase start up air at warmer temps and set your iac park position higher. That fixes slow warm starts most of the time.
My 99 TA did it when it was still bone stock
My 99 TA did it when it was still bone stock
I have the opposite problem... sitting a while it takes like 3-4 seconds then fires up but will fire up immediately after being off for a little bit (store runs and whatnot)
probably the way my fuel system is setup but who knows
probably the way my fuel system is setup but who knows
Thread Starter
TECH Enthusiast
Joined: Aug 2002
Posts: 715
Likes: 7
From: Houston
After heating up, the first time I crank, it will just keep turning over as long as I hold the key in start position without firing. As soon as I release the start position and crank a second time it fires up instantly.
Even if the first crank is only 1-2 seconds, the second crank always starts straight away.
I havent had had a chance to troubleshoot fuel pressure or IAC yet because I don’t drive it enough to have frequent hot stops (just to and from the office every day). Once I get some free time on the weekend I’ll give it a go and check.
Oh, if engine is original everything is original, simply start cleaning it and maintenance. stuff like IACV and intake ports gets full of carbon buildup (and oil) for example. The heads could stand to come off and clean up the valves and pistons probably. But don't do that obviously just pointing out everything has buildup which contributes in various ways. even in the exhaust ports it changes the tone of the engine over time.
Also clean up the fuel system, new filters (& in-tank sock) , injector cleaners,
sounds like typical inadequate iacv opening due to carbon buildup so try cleaning that first is a great idea
Also clean up the fuel system, new filters (& in-tank sock) , injector cleaners,
sounds like typical inadequate iacv opening due to carbon buildup so try cleaning that first is a great idea
Launching!
Joined: Apr 2017
Posts: 276
Likes: 5
From: █▬█ █▄█ █▬█ █▄██▬█ █▄█ █▬█ █▄█
I don’t understand why that wouldn’t be a problem in the morning though? The car would have been parked hot, the pressure would bleed back into the fuel tank overnight, and it should cause a hard start in the morning?
After heating up, the first time I crank, it will just keep turning over as long as I hold the key in start position without firing. As soon as I release the start position and crank a second time it fires up instantly.
Even if the first crank is only 1-2 seconds, the second crank always starts straight away.
I havent had had a chance to troubleshoot fuel pressure or IAC yet because I don’t drive it enough to have frequent hot stops (just to and from the office every day). Once I get some free time on the weekend I’ll give it a go and check.
After heating up, the first time I crank, it will just keep turning over as long as I hold the key in start position without firing. As soon as I release the start position and crank a second time it fires up instantly.
Even if the first crank is only 1-2 seconds, the second crank always starts straight away.
I havent had had a chance to troubleshoot fuel pressure or IAC yet because I don’t drive it enough to have frequent hot stops (just to and from the office every day). Once I get some free time on the weekend I’ll give it a go and check.
Thread Starter
TECH Enthusiast
Joined: Aug 2002
Posts: 715
Likes: 7
From: Houston
I can give that a try. I’ve currently been letting it sit for 10 seconds or so “priming” and then trying to start, unsuccessfully, but I’ve never tried to prime twice.
The hard part part is that it’s very intermittent. Sometimes the issue is there, other times not. It does seem to be dependent on how hot the vehicle is, and the outside temperature, with more heat being worse.
The hard part part is that it’s very intermittent. Sometimes the issue is there, other times not. It does seem to be dependent on how hot the vehicle is, and the outside temperature, with more heat being worse.
Launching!
Joined: Apr 2017
Posts: 276
Likes: 5
From: █▬█ █▄█ █▬█ █▄██▬█ █▄█ █▬█ █▄█
Thats just one theory anyways...