LS Swap help please

[Caleb]

so im trying to get this dang thing working but i have no avail. its a 5.3/4l60e in a 86 k1500. it starts revs to about 3-3500k on its own and falls to 400-300 rpm for about 15 seconds before it dies. if i feather throttle i can keep it alive.cleaned TB cleaned intake and replaced gaskets to make sure no vacuum leak. im stumped i need this ready before college. im about to just take it somewhere and let them take my whole life savings. any advice would be great. im out of ideas. it does throw p0030,p0036,p0050,p0056. which are o2 sensor heaters i think. brand new sensors so idk? i bought this motor "ready to run". i also hear an occasional popping like noise from under the intake.

[ls1nova71]

Not enough info. What year is it? DBW or DBC? Could be many things, but if it's revving to 3500 by it's self, then you have issues, which I would suspect is a massive vacuum leak like from the power brake hose not being attached or something.

[BR3W CITY]

a) your frustrated, which means you'll never fix it unless you take a step back and CTFD
b) "ready to run" might as well mean "assembled". Unless someone was paid to do the swap, any motor package is still going to require other things to make it run. So lets start with

• ECM tuning; who tuned it, was all of the emissions stuff removed, was there any "performance" tweaking going on.. etc
• Which motor is this, and were any internal mods done to it either by you or the builder?
• What throttle type is this?
• Do you have fuel pressure, and adequate fuel system?

Considering its throwing o2 codes, its possible that something in the emissions deletes in the tune was done improperly. I would generally think it would throw cat efficiency codes as well if that were the case however.

If you have a drive-by-wire (DBW) truck, its possible that damaged wires near the throttle body actuator, or to and from the TAC or pedal assembly can cause haywire throttle issues. The IAC is located in the same spot and can also cause spiking and failure to idle.


We need to know more, and more about what you've tried. If you did the swap, then no one will know (and be able to describe) as much about the swap as you do. We have better odds of solving any problem when we know all the factors.

[Custom 68]

Brew knows what he is talking about so lets work thru this together.
One thing that has plagued others including me is stuck or dirty injectors. With "todays" gas they seem to get stuck easily. But first follow what they said above check fuel pressure and vacuum leaks that does sound very possible. Make sure your intake is tight. Check all your hoses.

[Hart_Rod]

Do you have the wiring for the O2 sensors crisscrossed?

[Caleb]

alright so just got off work but i found that i was missing a coolant temp sensor in the side of the head..... didnt do much but it stopped revving up. rented a fuel pressure gauge. no pressure at all. brand new fuel pump has nothing. it runs though. gonna pull in out and see if it has pressure when running off just a can of gas to see if pump or something in the tank. its an inline walbro 255, DBW, supposedly 2002 motor, idk about tranny. Jason from billet LSx swap out of topeka did it. not the first time her dropped the ball. i dont think the PCM was tuned right. and im calmed down now ended up smashing my phone when i lugged it around the block and found out he didnt tune the tranny right so i wont leave first. everything makes sense though, not enough fuel, its running lean and pinging. i think i found my culprit.

[Custom 68]

did you check the pressure on the rail? if so I assume you removed the little one way valve? You might just make sure your new pump had fuel to it since it was an inline. They push the fuel better than pulling out of the tank if that makes sense. Check your connections at the tranny.
The no temp sensor will do some weird things...
good luck and keep us posted.

[Caleb]

so bad fuel pressure gauge. turns out i have 51PSi on the rail. checked voltage and checked lines. 10.5 volts at pump. even hooked directly to battery nothing changed. is this pump maxed out? i though everyone used the walbro 255 on their swaps? im stumped guys. found out the problem but not why it is the problem. thanks again.

[Custom 68]

I had mentioned stuck injectors. I had my first swap do that but they are all stuck and it would not fire at all. Once I got them freed up they all worked like a champ.
You have go the temp sender working, do you have any codes now or still the same ones?

[Caleb]

still got bank 1,2 sensor 1,2. he didnt tune out the rear o2 obviously and he isnt texting me back about it. wonder what that says. came the conclusion bad fuel pump. found pump locally for 200, a car guru came out of the woodwork today ( hard not to after watching me for 2 weeks deal with this) got it for 100 bucks. 105-115 PSI. kinda nervous about this. says hes done swaps before and my guy probably screwed up the PCM. is 100+ psi gonna be too much for the stock regulator. its gonna show the weak link in my fuel system thats for sure. ill keep you posted as to if this works.

[BR3W CITY]

The reg will take a surprising amoutn of pressure. Most 255's can put out 85-125lbs at the outlet. The reg takes that down to 58-62 at the rail.

Also, when checking a pump, voltage will only tell you if the pump is GETTING power, not if its using it. You need to check Amp draw at the pump, that will tell you what its actually doing. Overamping smokes the pump, and you'll see quickly if you have a meter on it.

[Caleb]

snagged new fuel pump and same thing stuck at 50psi.... checked for kinks and restrictions. pulled plugs and they are fouled and wet. used scan tool to check a few things and found that at 450rpm i got between 20-22 degrees advanced. it idles around there before it poops out and dies. still throwing same codes. supplier still hasnt responded at all today about anything i called him on. i think hes done with me so i need to move on and find someone else. im stumped again. thought i had this thing nailed down. that about all the info i gathered today. what do you guys think? thanks again.

[BR3W CITY]

Does the FP change when u unplug the vac line from it? The reg itself might be dead.

It sounds like your tuner is an idiot tho, so its hard to go too far down any problem solving path if theres a high% of tuning error.

[Caleb]

unplugged the vac line no change. was gonna try and lug around the block for STFT but PS hose broke, forgot to bleed it out. i think im done for tonight.

[Caleb]

pulled all plugs and except number 2 they where all clean but wet? so does that tell me i have low fuel pressure because leaking injectors and i have lean condition because low pressure?

[BR3W CITY]

If every plug is wet, then you might actually be washing the piston (running so rich that your dumping liquid fuel into the chamber). Its possible that the injectors are stuck, but its also possible that the fuel tables are jacked.

[Caleb]

sounds good. ill either take a screwdriver or a piece of fuel line to the injectors tomorrow see if i cant come up with any ideas of whats going on.