LM7 383 Build Up

[PitchBlackC3]

Well I have an update after putting 1500 miles on it.

The new engine runs good. But it seems to lack some of the low end grunt that I want. It takes a bit of RPM and throttle to get it moving. And seems to always need a lot of throttle to keep it moving up hills. It seems that it sometimes has trouble getting into OD while cruising. Is this a product of my cam, torque converter, gears, maybe all three? It is fast from 3k RPM and up.

5500 lb ECSB truck
4wd
32 or 33in tall tires on 18 wheels
383 cubic inch
3.73 gears
220/220 .556/.556 114lsa
4L60E running a shift kit & Trailblazer I-6 Torque Converter
3.73 gears


what do you guys think?

The RPM and throttle to get it moving are because of the stall.

Are you sure your converter is locking at cruise?
Do some logging. A significant enough misfire count can keep the PCM from commanding TCC lock up.
If your RPMs surge with every hill to maintain the same speed, your converter isn't locked.

[blackout]

The RPM and throttle to get it moving are because of the stall.

Are you sure your converter is locking at cruise?
Do some logging. A significant enough misfire count can keep the PCM from commanding TCC lock up.
If your RPMs surge with every hill to maintain the same speed, your converter isn't locked.

hmmm interesting. what would cause this misfire count?

[blackout]

so the truck is getting horrid fuel economy now. like 8 to 9 mpg. when we first installed it the mpg was almost normal. what could be causing this? maybe the cats are causing too much backpressure cuz they are old (150k)? i am trying to save to get some long tubes and get rid of the shortys and cats. i dont know what to make of this? i run 92 octane all the time.

[flattopwill]

Any PCM codes? Does the truck run poor?

[RedHeartbeat]

very likely bad 02 sensors. Have the 02 levels scanned with a wideband

[blackout]

no SES light on. is an exhaust leak going to cause this type of symptom? I think i might have a small exhaust leak. But the o2 sensors are OE (150k)

[Dougalicious]

That sounds like O2 sensors. They have a tendency to not throw codes when they're spent, and they're definitely old enough that them going bad is very likely.

[blackout]

I will just replace the o2 sensors when I do the LTs. What brand of o2 sensors run the best in our trucks? (Bosch, Denso, NTK, Delco?) Now I have to decide on some headers. Stainless Works or LPPs?

[zebra]

if you ain't already got some LTs & are looking at 1 5/8, get the stainless eBay headers & ORY for $275.