Checking for spark?
 

Im trying to figure out why i cant get my 5.3 swap to fire. Can i check for spark
by removing plug, ground plug and then turn motor over and look for spark? And if that is correct and i see spark i would assume that means the coil is good and getting power? thanks for the help

Re: Checking for spark?
 

Yes you should be able to check for spark like that. Depending what it is you may need to check your tune it could have VATS or something like that still keeping it from running.
check for spark but it could be your injectors being "clogged" that is very common these days it seems the gas can gum up pretty quickly.

Re: Checking for spark?
 

thank, i will check for that first then more to fuel pressure and injectors

Re: Checking for spark?
 

Make sure VATS is off first and foremost.

Then check stuck injectors
Then check the little ground wires on the coilpack harnesses
These engines will start on like 4-5 cylinders, and since they run COP there really isn't a way to have multiple spark failures unless something else big is going on.

Even though it won't fire, sometimes you can cheat and use a codescanner. You will most likely have a bunch of false codes (Since the engine never actually ran), but in some cases you can pick the "odd one out" to help track down a problem.

We need some more info as well; stock motor or does it have cam etc? Who tuned it?

Re: Checking for spark?
 

Couldn't it also be a bad or disconnected cam or crank pickup sensor?

Re: Checking for spark?
 

stock motor base tune by lt1swap.com

Re: Checking for spark?
 

I am still betting on stuck injectors. Mine were and I keep reading of others with the same issues.

Re: Checking for spark?
 

spray some starter fuild in teh inatk and see if it starts if it does you have a fuel issuse

Re: Checking for spark?
 

Didnt think of that. Thanks will try

Re: Checking for spark?
 

So after trying to spray starter fluid in the throttle body it does try to start a little but doesnt completely start and run. Also, shouldnt the schrader valve on the fuel rail have pressure, cuz when i push it in i get no fuel spraying out. Another wierd thing is now when i turn the key i dont hear the fuel pump come on anymore

Re: Checking for spark?
 

So found out the ground on my fuel pump was loose, so it is kicking on again. What should the voltage read for that two second purge? just tested it before i have to leave for work and it only jumps to about 3-4 volts real quick

Re: Checking for spark?
 

That is great. so was this running before you posted this?
I would believe the voltage should be 12+ volts. Check it when it is started.

Re: Checking for spark?
 

the voltage coming from the pcm and going to the relay should be low like = or < 5v
but the juice coming from the relay and going to the pump should be >12v

Re: Checking for spark?
 

The PCM supplies 12v to the relay, so for the two second prime you should have 12v.

Re: Checking for spark?
 

no i have never heard this motor run

ok, i will have to figure out why it is not

Re: Checking for spark?
 

so like said here if you are checking the voltage coming from the computer it wont be 12 volts. The siginal from the PCP needs to go to a relay and it will trip the relay and supply the 12 volts to the pump.
good luck
Dave

Re: Checking for spark?
 

There are 5v references in the PCM that are for sensors, but it WILL BE 12v coming from the PCM to the fuel pump relay, it takes 12v to run a 12v relay. You can't just run the pump off of it because the pump will draw more amperage than the PCM can handle.

Re: Checking for spark?
 

You CAN jump the FP relay straight off a switched power source, just to make sure the pump turns on and everything works etc.

0-5v is usually considered reference voltage, for things like gauge outputs etc. 5v won't energize a 12v circuit

Re: Checking for spark?
 

after testing...so it only goes to about 11v for the first two seconds and down to around 9v when trying to start. Zero pressure at fuel rail (checked by just pressing schrader valve and no gas......could it be wire size and length for fuel pump? what i have is 12gauge wire from battery (rear of bed) to fuel pump relay (in cab) then 12gauge off relay to fuel pump (rear of bed).

Re: Checking for spark?
 

I have the same issue with my truck...I thought it was from not having enough gas in the tank but my buddy thinks it could be because of the vats. I hope its not that. also had my pcm tuned by Brendan from lt1swap...check out my starting vid...https://www.youtube.com/watch?v=XGUmroZK3Dw

Re: Checking for spark?
 

Watched your video..mine kinda does that if i spray starter fluid in throttle body but if not just cranks over only

Re: Checking for spark?
 

ill put more gas in it n hopefully it starts up...i'd hate to send my pcm back to Brendan...dnt need another set back

Re: Checking for spark?
 

Don't think its wire size and the voltage should come up when its running. Like BR3W said, jump the relay so it runs all the time to test it. Make sure the pump isn't wired backwards, sounds like that is your problem.

Re: Checking for spark?
 

I will try jumping it. when you say wired backwards just switch connections at terminal?

Re: Checking for spark?
 

So i pulled the fuel line after the fuel filter and turn the key on...the pump pushed a nice heavy flow of fuel out the line for the two seconds..that leads me to believe the pump is hooked up correctly. should i consider replacing the pressure regulator on fuel rail at this point because when i turn the key several time and try to crank it over i get no pressure out of the shrader valve after doing so, or will the pressure only be present durning crank?