1997 Chevy Astro LQ4 Swap, Low Power

[chevyastroawd]

I swap a 03 LQ4 4L80E NP262 into my 97 Astro 5 years and since then i been trying to figured out why it has no power at WOT. Cant seem to find a right answer on fuel pressure. ive tried different FPR no change, New Pump no change, New fuel rail and fuel filter and 25lb injectors still nothing.



This video you can hear it bog down

[SMWS6TA]

Has it been tune? (Tuned for the transmission?)

LQ4's have 50 psi so it looks good.

I see 25lb injectors are the stock injector for LQ4's. Have they been tested or are they new?


Could be that you have a vacuum leak.

[chevyastroawd]

Stock tune, with trans pressure up'd and torque management disabled. New injectors all been flow matched, no vac leaks

[SMWS6TA]

Compression check?


Any codes popping up?

[chevyastroawd]

no codes, ill check comp, whats the range it should be around

[SMWS6TA]

should be around 180 psi.

More importantly is that they all should be within 10-15 psi.

[chevyastroawd]

Every Cly was 150

oi67.tinypic.com/2mmhhr7.jpg

[pajeff02]

Any spark knock or other signs of it leaning out? Have you check the color on the plugs? What does the fuel pressure read under load?

[chevyastroawd]

0 kr, pic in my last post, 65psi at wot

[SMWS6TA]

How many total miles on the LQ4?

Cyl pressure kinda low, but good news is they are all the same. Try a wet reading next. Squirt a little oil in through the spark plug hole, turn motor over a few times and then see if the pressure rises.



I've listen to the bottom video again and I'm not hearing anything, seems like it's healthy.



Could it be in the tune or transmission? Shift points not quite right....

[chevyastroawd]

Shift points were up'd too, I'll try wet, about 400k on the motor and trans.

[SMWS6TA]

400k.... :wow: Has it had a rebuild?

[chevyastroawd]

Nope not yet, all original besides being swapped from my truck to van

[SMWS6TA]

I'm amazed you have compression......I'm willing to bet it's time for some new rings and at least a line hone, if not flat out a mild bore like .005"

[chevyastroawd]

I've gone to 600k and still had comp, when I had the heads off to fix a valve you could still see the cross etching

[chevyastroawd]

I think I'm finally getting somewhere, after last night letting it idle and watching sensors I noticed the map sensor didn't really change even after raving it. So I unplugged it and let it use the default settings for it and now when I get on, it takes off. So gonna order a new map, crank, and cam sensors all are still original

[pajeff02]

Strange that it wasn't setting a code. If the MAP sensor is reading out of range the PCM will usually detect that and set a fault code.

[chevyastroawd]

Sometimes, I've seen alot that don't till the finally fail

[SMWS6TA]

Glad you think you found it. I was about to suggest checking the sensors.

[chevyastroawd]

I'm hoping, this has bugging me for years and never been able to narrow it down