LQ4 Fires for half a second sputters and dies
06-23-2017, 09:09 PM
#1
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
LQ4 Fires for half a second sputters and dies New to the forum because i cant figure out whats going on with my engine for the life of me!
So im doing a swap into my mk3 supra. motor is a 2006 Lq4 from a silverado.
stock engine besides long tube headers.
so the problem im having (yes vats is bypassed) is that when i crank the engine it fires for less than a second and dies, and sometime will keep runing for a couple seconds on 1 cylinder.
what i have ruled out
fuel pressure/pump (56psi constant, running a walbro 255)
spark (all 8 are fine)
injectors are pulsing, cant test completely yet since no noid light
and it does run and idle on all 8 when spraying starting fluid in...
i pulled the fuel rails and injectors to see if they were plusing on crank and they all pulse fine on crank. i can crank the engine and it will fire sputter and die really quickly. but if i keep cranking it will not fire at all unless i leave it for a few seconds and crank again then it does the same thing and possibly runs on 1 cyl for a few seconds.
im stumped, any more info needed i can provide.
heres a video of what its doing
So im doing a swap into my mk3 supra. motor is a 2006 Lq4 from a silverado.
stock engine besides long tube headers.
so the problem im having (yes vats is bypassed) is that when i crank the engine it fires for less than a second and dies, and sometime will keep runing for a couple seconds on 1 cylinder.
what i have ruled out
fuel pressure/pump (56psi constant, running a walbro 255)
spark (all 8 are fine)
injectors are pulsing, cant test completely yet since no noid light
and it does run and idle on all 8 when spraying starting fluid in...
i pulled the fuel rails and injectors to see if they were plusing on crank and they all pulse fine on crank. i can crank the engine and it will fire sputter and die really quickly. but if i keep cranking it will not fire at all unless i leave it for a few seconds and crank again then it does the same thing and possibly runs on 1 cyl for a few seconds.
im stumped, any more info needed i can provide.
heres a video of what its doing
06-24-2017, 02:09 PM
#5
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
im gonna plug it into my girlfriends truck (also a 06 silverado lq4) and check the vats. Unfortunatly the scaner that i have doesnt have a vats in the livedata.
06-24-2017, 04:18 PM
#7
On The Tree
Join Date: Nov 2014
Location: NW Florida
Posts: 102
Likes: 0
Received 0 Likes
on
0 Posts
Is the MAF plugged in? Had a similar problem cutting out with the MAF plugged in, unplugged and it ran. Figured out it would run shitty and cut out with MAF unless I had the intake tube installed to funnel air around it.
Rock
Rock
Trending Topics
06-24-2017, 07:19 PM
#8
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
So found out 3 injectors were sticking. I ultrasonicly cleaned all 8. And cleaned them out. Now all are working. And it fires better now. But still doesnt stay running. Also iv tryed maf pluged in and disconected. No difference
06-25-2017, 11:57 AM
#9
Pull the injector rail and see it they are spraying or check rail PSI. Do you have the MAF inline of the TB? THIS was the last think keeping my brotherss swap from running.
06-25-2017, 10:45 PM
#10
it sounds like its not getting enough fuel. have you tried spraying starting fluid into the throttle body and then starting it? If it runs well for a few seconds then you can start looking at fuel issues.
If it does the same thing then check for good spark. put an extra spark plug in the end of the plug wire and lay it on the head. Crank the motor and check for a strong spark at the plug.
Also check all grounds, back of the head and PCM grounds are commonly missed.
If it does the same thing then check for good spark. put an extra spark plug in the end of the plug wire and lay it on the head. Crank the motor and check for a strong spark at the plug.
Also check all grounds, back of the head and PCM grounds are commonly missed.
06-25-2017, 11:15 PM
#11
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
already done and all firing fine when cranking. 56psi at the rail. And useing stock intake tract
06-25-2017, 11:40 PM
#12
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
it sounds like its not getting enough fuel. have you tried spraying starting fluid into the throttle body and then starting it? If it runs well for a few seconds then you can start looking at fuel issues.
If it does the same thing then check for good spark. put an extra spark plug in the end of the plug wire and lay it on the head. Crank the motor and check for a strong spark at the plug.
Also check all grounds, back of the head and PCM grounds are commonly missed.
If it does the same thing then check for good spark. put an extra spark plug in the end of the plug wire and lay it on the head. Crank the motor and check for a strong spark at the plug.
Also check all grounds, back of the head and PCM grounds are commonly missed.
tryed all of that already. Sprayed fuel in fires and runs fine. Its for sure a fuel issue. And grounds are fine.
i have a feeling its to do with the pcm. I put the computer in my girlfriends dads truck and got it to run and it was idling at 600 to 700 with the normal ecu and mine it idled at 300 ish. And would stall so i did the dbw tps re learn and got it back to normal so im gonna try this as soon as i get a new starter. While i was doing all of the pcm swaping and stuff. The starter went on her truck so i stole it out of mine just for temp. Lol. Im thinking its a pcm issue needing a remap
so thats where it sits. If that doesnt work il get video and see what you all think.
06-26-2017, 07:58 AM
#14
tryed all of that already. Sprayed fuel in fires and runs fine. Its for sure a fuel issue. And grounds are fine.
I have a feeling its to do with the pcm. I put the computer in my girlfriends dads truck and got it to run and it was idling at 600 to 700 with the normal ecu and mine it idled at 300 ish. And would stall so i did the dbw tps re learn and got it back to normal so im gonna try this as soon as i get a new starter. While i was doing all of the pcm swaping and stuff. The starter went on her truck so i stole it out of mine just for temp. Lol. Im thinking its a pcm issue needing a remap
so thats where it sits. If that doesnt work il get video and see what you all think.
I have a feeling its to do with the pcm. I put the computer in my girlfriends dads truck and got it to run and it was idling at 600 to 700 with the normal ecu and mine it idled at 300 ish. And would stall so i did the dbw tps re learn and got it back to normal so im gonna try this as soon as i get a new starter. While i was doing all of the pcm swaping and stuff. The starter went on her truck so i stole it out of mine just for temp. Lol. Im thinking its a pcm issue needing a remap
so thats where it sits. If that doesnt work il get video and see what you all think.
06-26-2017, 08:07 AM
#15
Ok, just reread the thread and it sounds like the fuel system is right so now I'm leaning towards you losing power in the crank position if the ignition switch. Did you check to make sure. The wire powering your harness has power at crank and run? A lot of circuits will lose power in crank. Maybe run a temporary constant hot to the harness then try and see if that is your problem
06-26-2017, 10:04 AM
#16
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
So which is it? You say its a fuel problem then say its probably a PCM problem. If you put the PCM in another truck and it ran fine, then its not a PCM problem but maybe a wiring issue. Have you put a fuel pressure gauge on it to see what your pressure is at? Also what pump are you using? Return rail or returnless? Are you sure its plumbed right? Seen a lot of people plumb the Vette filter/regulator backwards and have issues.
Its a return less system, and my girlfriends dads truck is also the same. its the identical engine. when i first fired it up before i did the TB relearn, it would idle at 300~ rpm, and stall out. after its idling at a solid 650 to 700. so i think it did the trick, havnt had a chance to fire my engine up with the ecu yet.
06-26-2017, 10:06 AM
#17
Registered User
Thread Starter
Join Date: Jun 2017
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Ok, just reread the thread and it sounds like the fuel system is right so now I'm leaning towards you losing power in the crank position if the ignition switch. Did you check to make sure. The wire powering your harness has power at crank and run? A lot of circuits will lose power in crank. Maybe run a temporary constant hot to the harness then try and see if that is your problem
thanks everyone for your input also!
10-14-2017, 02:28 AM
#19
I'm wondering too. I have the exact same issue and have done exactly what he has done. Checked power, ran noid lights, checked spark, fuel pressure. Runs for a second and dies. Squirt starting fluid and it runs. Checked injectors individually with a tester and they are working. 5.3 with an LS1 intake and PW harness. Had computer reprogrammed. Same problem. Actually got it to run two times when I was first assembling it and stopped running since. Hasn't run anymore. Bought a used LS1 harness from the classifieds here and am setting it up to see if that's the problem. Ah the joys of working on your own stuff. 
10-14-2017, 09:05 PM
#20
A friend of mine had a similar issue, his ended up being coil packs on the wrong side,
We just unbolted coil brackets from valve cover swapped sides and fired right up. Don't know if it was bad connections or what.
He bought the Beer that night.
We just unbolted coil brackets from valve cover swapped sides and fired right up. Don't know if it was bad connections or what.
He bought the Beer that night.
Last edited by slogo; 10-14-2017 at 09:16 PM.
