LT4 drivability issues
Thread Starter
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
LT4 drivability issues
I have a newly rebuilt LT4 with the following mods:
bored 355 block
port heads flow 260
hotcam
52mm TB
30# injectors
LTCC coil conversion
EM long tubes
no cats
no secondary air system
Electric water pump
Ed wright re-program
I'm basically having two problems:
Engine surges back and forth a couple hundred RPM's at idle when cold.
Engine stumbles and pops under heavy load (75%-100% throttle)
no codes set. I have a Auto X-ray EZ-scan 4000.
Any ideas on the cause and what parameters I should check?
bored 355 block
port heads flow 260
hotcam
52mm TB
30# injectors
LTCC coil conversion
EM long tubes
no cats
no secondary air system
Electric water pump
Ed wright re-program
I'm basically having two problems:
Engine surges back and forth a couple hundred RPM's at idle when cold.
Engine stumbles and pops under heavy load (75%-100% throttle)
no codes set. I have a Auto X-ray EZ-scan 4000.
Any ideas on the cause and what parameters I should check?
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by 99svrcpe
I have a newly rebuilt LT4 with the following mods:
bored 355 block
port heads flow 260
hotcam
52mm TB
30# injectors
LTCC coil conversion
EM long tubes
no cats
no secondary air system
Electric water pump
Ed wright re-program
I'm basically having two problems:
Engine surges back and forth a couple hundred RPM's at idle when cold.
Engine stumbles and pops under heavy load (75%-100% throttle)
no codes set. I have a Auto X-ray EZ-scan 4000.
Any ideas on the cause and what parameters I should check?
bored 355 block
port heads flow 260
hotcam
52mm TB
30# injectors
LTCC coil conversion
EM long tubes
no cats
no secondary air system
Electric water pump
Ed wright re-program
I'm basically having two problems:
Engine surges back and forth a couple hundred RPM's at idle when cold.
Engine stumbles and pops under heavy load (75%-100% throttle)
no codes set. I have a Auto X-ray EZ-scan 4000.
Any ideas on the cause and what parameters I should check?
Thread Starter
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
Originally Posted by tjwong
Have you checked the throttle body minimum air rate adjustment? Is this stock but modified TB? Some aftermarket TB are not adusted properly. Set the TB so that when the IAC is closed, that it can idle at between 600 and 650 RPM. That way the IAC can be in control above and below that RPM.
How do I check or adjust the minimum air rate. It's the newer Edelbrock 52mm TB. Ed Wright set my computer to idle at 900
Race Director
Joined: Oct 2000
Posts: 14,060
Likes: 1,165
From: N. Alabama
I have similar mods and used LT1 edit to lower my ignition adv. to 18 at 400 rpm and 20 at 800 rpm, closed throttle from Ed's original 22 or 24 degrees at those rpm's. I then programmed the Idle for 850 and adjusted the TB (52mm) set screw to hold idle and idle count steady. Works like a charm. One can get a small hex inside the OEM TB opening from driver side rear to adjust while running. I don't know about aftermarket.
Thread Starter
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
Originally Posted by southern_son
I have similar mods and used LT1 edit to lower my ignition adv. to 18 at 400 rpm and 20 at 800 rpm, closed throttle from Ed's original 22 or 24 degrees at those rpm's. I then programmed the Idle for 850 and adjusted the TB (52mm) set screw to hold idle and idle count steady. Works like a charm. One can get a small hex inside the OEM TB opening from driver side rear to adjust while running. I don't know about aftermarket.
Hmmm..interesting according to my Auto xray scan Ed has my advance set at 35* @ 900RPM's.
