5.3 idles but does not rev
Thread Starter
Teching In
Joined: Dec 2012
Posts: 13
Likes: 0
From: sonora ca
5.3 idles but does not rev hello LS1 fans, new here but i am having a problem with my new project. i put a 2004 5.3l motor in my jeep, also i have switched my harness, computer,and trottle body over to a 2001 drive by cable. installed the lock out computer tune. it starts up with ezz but will not rev up. any ideas out there where i should start.
Last edited by cleets; Dec 30, 2012 at 03:35 AM.
Thread Starter
Teching In
Joined: Dec 2012
Posts: 13
Likes: 0
From: sonora ca
I will check out the vacuum again for we were only running like NO vacuum off the motor. figured the no rev was a bigger deal.
Does not stall just bogs when throttling. checked vac sensor by sucking on it and it gave a reading to are computer.
THANKS
ok checking out motor more (motor has just been fired last up night). seems the rough idle is a misfire to 4 cylinders. knowing this by using a temp gun to each cylinder. checked compression on all 8 cylinders an average of 170psi. this motor has sat around for a couple of years. could it b plugged injectors?
just got done cleaning the injectors. still only firing on 4 SAME cylinders. I'm at a lost right now. any body out there have a tip i can try???? how can i trace the injectors to make sure they are firing?
-compression average 170psi
-spark at all 8
-injectors checked and cleaned
-TPS is NOT reading back to laptop display. confirmed it works by plugging sensor into the wife's car and got a reading back from it. checked and traced the wire all the way back to the computer.
-MAP is working by sucking on it and getting a reading, but not a strong vacuum is pulled from this motor. probably only hitting on 4 cylinders is why a low vac.
-MAF ? not too sure how to check that, i might call that out for don't think the MAF would misfire 4 cylinders.
PLEASE throw out me some ideas i will check them, for I'm really wanting to drive this hog...
Does not stall just bogs when throttling. checked vac sensor by sucking on it and it gave a reading to are computer.
THANKS
ok checking out motor more (motor has just been fired last up night). seems the rough idle is a misfire to 4 cylinders. knowing this by using a temp gun to each cylinder. checked compression on all 8 cylinders an average of 170psi. this motor has sat around for a couple of years. could it b plugged injectors?
just got done cleaning the injectors. still only firing on 4 SAME cylinders. I'm at a lost right now. any body out there have a tip i can try???? how can i trace the injectors to make sure they are firing?
-compression average 170psi
-spark at all 8
-injectors checked and cleaned
-TPS is NOT reading back to laptop display. confirmed it works by plugging sensor into the wife's car and got a reading back from it. checked and traced the wire all the way back to the computer.
-MAP is working by sucking on it and getting a reading, but not a strong vacuum is pulled from this motor. probably only hitting on 4 cylinders is why a low vac.
-MAF ? not too sure how to check that, i might call that out for don't think the MAF would misfire 4 cylinders.
PLEASE throw out me some ideas i will check them, for I'm really wanting to drive this hog...
Have you checked all your fuses? Do you have power on the 4 injectors that aren't firing? Are you sure you have a DBC tune? Some DBW PCM's are not capable of running a DBC application, are you sure yours will?
Thread Starter
Teching In
Joined: Dec 2012
Posts: 13
Likes: 0
From: sonora ca
Fuses looked good, this harness is re worked by a friend that has successfully done other LS1 harness but is the first time for a 5.3. He said there is much more on a truck harness but at the end the harness will run a LS1 motor.
Checked today that all 8 injectors are getting power at first start. The 5.3 starts with ezz at cold starts, and fires all 8 cylinders, than after 5 or so seconds the motor idles down and looses power to 5 injectors.
I watched EACH injector with a led that I rigged to the harness light up at first start, then flatlined after the motor ran for 4-7 seconds. Even when turning key on i saw that the motor squirted a little b4 start up.
SO they work but loses power after that 4-7 seconds after it starts.
Checked today that all 8 injectors are getting power at first start. The 5.3 starts with ezz at cold starts, and fires all 8 cylinders, than after 5 or so seconds the motor idles down and looses power to 5 injectors.
I watched EACH injector with a led that I rigged to the harness light up at first start, then flatlined after the motor ran for 4-7 seconds. Even when turning key on i saw that the motor squirted a little b4 start up.
SO they work but loses power after that 4-7 seconds after it starts.
If you havent already, put a noid light on the injectors for the cylinders that are missing. If the noid light illuminates, then the miss is most likely either clogged injector or spark related. If it doesnt illuminate, physically check the wires going back to the PCM for the 4 cylinders that are missing by continuity check and then looking at the crimps and pinout. If those check out, then check the PCM grounds at the back of the cylinder head and where ever the reworked put them (this is probably most likely where the issue is if the injectors arent pulsing). Hope that helps.
Jon
PSI
Jon
PSI
__________________
Your Source for LSX Conversion Parts!
www.psiconversion.com
Ebay Store
Facebook/psiconversion
Instagram/psiconversion
'Dont Let EFI Pass You By!'
Your Source for LSX Conversion Parts!
www.psiconversion.com
Ebay Store
Facebook/psiconversion
Instagram/psiconversion
'Dont Let EFI Pass You By!'
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
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 Thread Starter
Teching In
Joined: Dec 2012
Posts: 13
Likes: 0
From: sonora ca
Im afraid it will b the ECU. we installed the VAT delete, was around $100. plus going back to the dismantling yard and telling them that they sold me a bad ECU. B4 I go and spend again can i put my computer in the wifes car and see if it will do the same thing? also will the switch do anything to the wifes car with a modified computer?
This may explain why i was not getting a reading from the TPS!!! TPS works on wife's car, and made sure no wire disconnect from computer pin to the TPS plug.
This may explain why i was not getting a reading from the TPS!!! TPS works on wife's car, and made sure no wire disconnect from computer pin to the TPS plug.
Thread Starter
Teching In
Joined: Dec 2012
Posts: 13
Likes: 0
From: sonora ca
I plugged my TPS unit and laptop with the digital displays to here car and got a reading back from it. i do the same set up to my 5.3 jeep and can not get a reading from the TPS.
The TPS plug to the computer's pin is good. i got 5 amp reading to the TPS so its getting power to it but there s no signal out of the computer.
I am going to plug my 5.3 jeep computer to the wife's car and see if it will run different. hopefully, the VAT deletes wont mess with here car? ill check back tonight and let u know.
ok guys, getting closer to this problem. took my 5.3 jeep PCM, and plugged it in my wife's Tahoe and did same problem to here car. soo must b a bad computer. crap the VAT system is in that computer. know another problem is getting the HP tuner back out of the PCM and putting it in another computer. has it been done b4 or will i have to pay again for the VAT delete?
Getting back to" ls1nova71 "on DBC-DBW
The computer is DBC, also bought a DBC harness, and throttle body. we made sure we got the DBC tune. THANK YOU for asking that could have been a problem.
FIXED !!!!!!!!
7969 was right. put a new ECU in the jeep. RUNS great. Thank you all that has put a post for me for a tips on getting it running, hey i guess i can say this, i know much more about these motors and feel much more comfortable working on it. I'm hooked on these builds.
The TPS plug to the computer's pin is good. i got 5 amp reading to the TPS so its getting power to it but there s no signal out of the computer.
I am going to plug my 5.3 jeep computer to the wife's car and see if it will run different. hopefully, the VAT deletes wont mess with here car? ill check back tonight and let u know.
ok guys, getting closer to this problem. took my 5.3 jeep PCM, and plugged it in my wife's Tahoe and did same problem to here car. soo must b a bad computer. crap the VAT system is in that computer. know another problem is getting the HP tuner back out of the PCM and putting it in another computer. has it been done b4 or will i have to pay again for the VAT delete?
Getting back to" ls1nova71 "on DBC-DBW
The computer is DBC, also bought a DBC harness, and throttle body. we made sure we got the DBC tune. THANK YOU for asking that could have been a problem.
FIXED !!!!!!!!
7969 was right. put a new ECU in the jeep. RUNS great. Thank you all that has put a post for me for a tips on getting it running, hey i guess i can say this, i know much more about these motors and feel much more comfortable working on it. I'm hooked on these builds.
