problem with LT4 rebuild
Thread Starter
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
problem with LT4 rebuild
I recently finished my LT4 355 rebuild. The problem is the engine will not idle and stumbles on acceleration when cold, however when the temp reaches about 180 it will idle (950 RPMs per ECM reprogram) and rev smoothly and quickly but the idle does have a tendency after warm-up jump +/- 75rpm's.
List of mods:
355 block 10.8:1
LT4 ported heads flow 268
Hotcam
Bosch 30# injectors
160 stat
52MM throttle body
Exotic Muscle long tubes
Meziere water pump
Ed Wright ECM reprogram
No trouble codes. Any ideas or suggestions?
List of mods:
355 block 10.8:1
LT4 ported heads flow 268
Hotcam
Bosch 30# injectors
160 stat
52MM throttle body
Exotic Muscle long tubes
Meziere water pump
Ed Wright ECM reprogram
No trouble codes. Any ideas or suggestions?
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
gee... a couple of thoughts...
1) Check the settings for the IAC and TPS
2) Those injectors are way large for what is essentially a mild rebuild. If you had a Supercharger or N2O, yea, but you don't.
3) The optispark is bad, but I doubt it... it would go nutso the other way around.
1) Check the settings for the IAC and TPS
2) Those injectors are way large for what is essentially a mild rebuild. If you had a Supercharger or N2O, yea, but you don't.
3) The optispark is bad, but I doubt it... it would go nutso the other way around.
Thread Starter
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
Originally Posted by bogus
gee... a couple of thoughts...
1) Check the settings for the IAC and TPS
2) Those injectors are way large for what is essentially a mild rebuild. If you had a Supercharger or N2O, yea, but you don't.
3) The optispark is bad, but I doubt it... it would go nutso the other way around.
1) Check the settings for the IAC and TPS
2) Those injectors are way large for what is essentially a mild rebuild. If you had a Supercharger or N2O, yea, but you don't.
3) The optispark is bad, but I doubt it... it would go nutso the other way around.
How do I check/ adjust the settings on the IAC and TPS?
I know the 30#'s were not neccessary however they were recommended by Mike @ Moore Performance. I figured why not since I was replacing the injectors anyway and reprogramming the PCM.
The opti is a brand new Dynaspark unit.
The IAC and TPS sounds like the best troubleshooting start point. I didn't realize they were adjustable
Le Mans Master
Joined: Jul 1999
Posts: 8,683
Likes: 6
From: Phoenix AZ
Considering that stock LT4's came with 28 lb injectors, I don't view 30 lb'ers as way too big. Are the4y completely necessary? No, but if the ECM is programmed correctly they should not cause a problem. Do you have access to a scan tool, like an AutoX-Ray? The first thing I would do is hook it up and see what that tells you.
Thread Starter
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
Originally Posted by Zix
Considering that stock LT4's came with 28 lb injectors, I don't view 30 lb'ers as way too big. Are the4y completely necessary? No, but if the ECM is programmed correctly they should not cause a problem. Do you have access to a scan tool, like an AutoX-Ray? The first thing I would do is hook it up and see what that tells you.
While my buildup is not extreme, I still should be pushing in the neighborhood of 450HP @ the flywheel
Yes, I do have a AutoX-Ray scanner. What should be looking for when I scan?
Last edited by 99svrcpe; Aug 2, 2004 at 02:11 PM.
