john55blaze
06-02-2014, 09:58 AM
So I just finished putting an LS1 into my 55 chevy truck (not pro-touring, but an LS swap non the less) and wanted to do a quick write up on a few very small yet very big problems that I encountered during my LS swap.
A little background: I picked up a cheap LQ4, bought a truck maifold from one place and a throttle body from another place. All picked up on the cheap and purchased seperate. I modified the harness myself and had lt1swap.com program the computer for me (fast and cheap but don't expect much "after the fact" help).
I got everything wired up/bolted together and otherwise ready to run. Fired it up and right away the engine rev'd to the sky (4-5000 rpm before you could shut it off!). Long story short, It turned out that the throttle body was designed for a different manifold and had a port that bypassed the Idle Air Control thus allowing un metered air into the motor, to which the motor then added fuel in an attempt to keep the motor from running lean?! The moral of THIS part of the story is to make sure the parts work well together or are from the same motor!
The next issue that I had was a lot more fun to diagnose. With the previous problem solved I now had an engine that started right up and idled fine for about 5 seconds before the engine slowed way down and died. I tried everything to find the source of the problem, I used a handheld to "view" all the live data and everything looked fine. One at a time I unhooked injectors looking for a bad injector. I un hooked all of the sensors one at a time to see their affects on the motor with no luck until I got to the MAF sensor. I unhooked the MAF and the engine pured like a kitten but idled at about 1600 RMP. So i took the MAF off of my dads 2002 Silverado and swaped it out; same results; So I put the my MAF on my dads truck and it ran fine?! With the MAF sensor out of the loop so to speak I learned that the computer uses the MAP sensor in its place and goes into speed density mode.
Next I tried taking the manifold off and inspecting the gaskets thinking it could be a vacuum leak there, I used a stethoscope to listen for possible air leaks. I even thought there could be something wrong with my "tune".
Next I went as far as putting all of the sensors off of my dads truck (MAF,MAP, IAC, TPS etc.) everything that I could from his running truck onto my poorly running truck and same result. The problem ended up being the EGR blockoff plate! It was leaking a TINY bit of air, like 3 or 4 bubble soaking it with windex. Once I fixed that air leak my problem was solved! I couldn't believe such a small air leak could cause such a headache and such interesting symptoms.
Thinking about it after the problem was solved I came up with this conclusion. The small leak was adding un metered air to the motor (near the throttle body, not sure if that maters) to which the computer was trying to block off the air with the IAC which in turn closed all the way killing the motor. I must have read a hundred article and post's on vacuum leaks and now feel that they are akin to the electrical gremlins that arise from bad grounds!
Anyways, good luck to all you poor hot rodders out there and anybody else out there who is trying to swap in a fuel injected motor. MATCH parts, inspect for damaged gaskets, and look/listen/srpay for vacuum leaks.
A little background: I picked up a cheap LQ4, bought a truck maifold from one place and a throttle body from another place. All picked up on the cheap and purchased seperate. I modified the harness myself and had lt1swap.com program the computer for me (fast and cheap but don't expect much "after the fact" help).
I got everything wired up/bolted together and otherwise ready to run. Fired it up and right away the engine rev'd to the sky (4-5000 rpm before you could shut it off!). Long story short, It turned out that the throttle body was designed for a different manifold and had a port that bypassed the Idle Air Control thus allowing un metered air into the motor, to which the motor then added fuel in an attempt to keep the motor from running lean?! The moral of THIS part of the story is to make sure the parts work well together or are from the same motor!
The next issue that I had was a lot more fun to diagnose. With the previous problem solved I now had an engine that started right up and idled fine for about 5 seconds before the engine slowed way down and died. I tried everything to find the source of the problem, I used a handheld to "view" all the live data and everything looked fine. One at a time I unhooked injectors looking for a bad injector. I un hooked all of the sensors one at a time to see their affects on the motor with no luck until I got to the MAF sensor. I unhooked the MAF and the engine pured like a kitten but idled at about 1600 RMP. So i took the MAF off of my dads 2002 Silverado and swaped it out; same results; So I put the my MAF on my dads truck and it ran fine?! With the MAF sensor out of the loop so to speak I learned that the computer uses the MAP sensor in its place and goes into speed density mode.
Next I tried taking the manifold off and inspecting the gaskets thinking it could be a vacuum leak there, I used a stethoscope to listen for possible air leaks. I even thought there could be something wrong with my "tune".
Next I went as far as putting all of the sensors off of my dads truck (MAF,MAP, IAC, TPS etc.) everything that I could from his running truck onto my poorly running truck and same result. The problem ended up being the EGR blockoff plate! It was leaking a TINY bit of air, like 3 or 4 bubble soaking it with windex. Once I fixed that air leak my problem was solved! I couldn't believe such a small air leak could cause such a headache and such interesting symptoms.
Thinking about it after the problem was solved I came up with this conclusion. The small leak was adding un metered air to the motor (near the throttle body, not sure if that maters) to which the computer was trying to block off the air with the IAC which in turn closed all the way killing the motor. I must have read a hundred article and post's on vacuum leaks and now feel that they are akin to the electrical gremlins that arise from bad grounds!
Anyways, good luck to all you poor hot rodders out there and anybody else out there who is trying to swap in a fuel injected motor. MATCH parts, inspect for damaged gaskets, and look/listen/srpay for vacuum leaks.