I posted this in a different section already but thought maybe someone here would have the answer

I have a 04 ls1 swap in my 00 silverado, truck intake, stock 241 heads, it runs like it's missing. Mods are lts, 42lb injectors, walbro 255lph pump, no cats, and mti r1 cam. Checked pushrods and valve springs, all 8 injectors firing, all 8 plugs firing, fuel rail pressure is 55 at idle 61 or 62 when cracking throttle open, new plugs and wires, new fuel filter, tried switching PCMs didnt change anything. When you give it very little throttle it's fine, but if you give it more than say 10% it sounds like it's missing and barely back firing. Ran fine after cam swap and that was maybe 6-7k miles ago. Here is the thing that makes me think it's the map sensor. I had one go bad before when I still had the 5.3 and it ran kinda crappy but when I sprayed nitrous it acted like it does now when you go wot. Also I unplugged the map and went around the block it ran the same as it does now, made absolutely no difference maybe even ran just a little bit better. I have been spending money guessing and I would just buy one and see if it changed anything but we just had our daughter and I want to be sure before I throw $50 at one.

Thanks
Jon

 

Has it been tuned? I had a 99 Tahoe vortec that my customer had, that wouldnt hardly run just after doing Long tubes on it and would back fire at a decent amount of throttle, tuned it, gave it the fuel it needed and cleaned everything up.. Too many variables it could be without more info..

 

Yes it's got a mail order tune from nelsons performance

 

Check your wiring. Did you use the truck harness?

 

Sup Jon, call ray see what hp tuners say???

 

Are you getting a check engine light? If so what are the codes. Some map codes will not throw check engine light but will store in the data section on a pcm. chances are you are going to also have a lean bank code. Although you have a walbro and new filter these could still be the issue. You can do a volt test at the map, pump to see if it is getting the required amount.

Im not sure where you are but if you have a Vantage diag tool or know someone who does its not a problem and can be sourced quickly. I just had a customer who had the same thing. Timing was retarded a bit and needed a new pump.

 

I checked the map test 1.4 v at 20 hg and 4.8 v at 0, guess I need to test the maf. This is extremely frustrating lol. Any other ideas?

 

And i might give ray a call this weekend. I see your cars goin to be goin soon? All I want is this truck to run right long enough to make a 7 second pass. I was trapping 86mph but running 8.9s lol just need some sticky tires and this thing to run right.

 

Just checked the maf I do believe I found my problem...

 

What was it? MAF are picky buggers.Mess the screen or touch the prong and it reaks havoc

 

Alright guess I did the test with multimeter wrong. The lbs per minute goes up when you open the throttle and it is a smooth graph upwards. The map though I got 29.2 hg with the key on motor off. I got 31.4 hg when I crack the throttle open really fast and 6.3 when it idled back down. Idle is 17.5 ish. 31.4 seems wrong how can I be 2.2 in's higher if I am N/A ? Is this enough to worry about.

 

My idle is 900 rpms if that maters

 

i have no knowledge on tuning however i do have two blown map sensors and a cam and the car runs better at WOT than at idle.

I would start with the plugs and make sure you dont have any exhaust leaks. i had a similar problem when the 02 sensors were getting cold readings from an exhaust leak

 

It's got plugs and wires with maybe 50 miles on them.

I unplugged the maf and it ran better no backfire but still not all there but I also have my air intake temp sensor in my maf and the scanner was reading -38. Also when I crack the throttle with my maf hooked up it jumps to 21lbs/min. Does that sound right to anyone. I wish it would just give me a trouble code to work with

 

try unplugging the map or tps. i had a tps go bad after sitting a year and cam swap. mine was running pretty rough though

 

Plulled plugs 1-4 looked good, 5 & 6 where black, 7 & 8 where shinny black. Very odd to me. I pulled the tb and looked into the intake I couldn't see anything in there. Crammed my hand in there and it felt really oily inside. I had kinda cleaned it about 5k miles ago when I put new lifters in. I also haunt ran a PVC into the intake in like 2 years, I have a catch can. Maybe my rings are taking a **** and slowly working themselves up. I always have atleast 40psi oil too?? I am so tired of dealing with this.