Double crank to start. Not fuel pump or pressure related

[Scottyb6.0]

Having a issue with a swapped wrangler with a 2001 5.3. Intermittently and most cold starts it will not fire on the first crank. Ive checked all the usual suspects fuel,power and grounds. It does have a budget Amazon harness in it. Im getting cam signal to the pcm and ive checked for proper pin outs to the pcm. No codes related to the cam sensor. Ive tried to sync the cam and crank with hp but im not sure if its working properly. I wouldnt think that would cause a random double crank. If i unplug the cam sensor it does set the voltage code. The engine has a btr stage 1 cam. I havent yet scoped the signal but i have checked it at the pcm and i do get a voltage change up and down while running. wondering if anybody has seen this before?LJ Conversion 4.8 Base TUNE 5.hpt

[Alvin]

A fuel pressure gauge would be a easy thing to check.

[Scottyb6.0]

A fuel pressure gauge would be a easy thing to check.

Got you, but as i stated in my original post fuel pressure is not the problem. Fuel pressure primes first key cycle and holds.

[Alvin]

Got you, but as i stated in my original post fuel pressure is not the problem. Fuel pressure primes first key cycle and holds.

I'm sorry I read it wrong "as not sure if fuel pump or pressure related."

I've seen a few cam sensor issues with no accompanying codes. When they fail to start because of a cam sensor issue it will cough back though the intake and backfire/pop. Is that what is happening to you?

[Scottyb6.0]

I'm sorry I read it wrong "as not sure if fuel pump or pressure related."

I've seen a few cam sensor issues with no accompanying codes. When they fail to start because of a cam sensor issue it will cough back though the intake and backfire/pop. Is that what is happening to you?

No worries thanks for your time. Ive changed the sensor with two different brands and no improvement. Not through the intake but small bumps out the exhaust. Would the sync cause that? This issue has me super stumped, should i post a log?

[Alvin]

Are you still using the rear cam sensor or has this been converted to use the up front cam sensor?

[Scottyb6.0]

Are you still using the rear cam sensor or has this been converted to use the up front cam sensor?

Rear

[Alvin]

No chance the run circuit is loosing power while your cranking in start?

[Scottyb6.0]

I could run a constant B+ to the main relay and test that. Ill do it tomorrow first thing when i get back to the shop. But it does the pop out the exhaust so i dismissed that possibility at first.

[kevin87turbot]

I could run a constant B+ to the main relay and test that. Ill do it tomorrow first thing when i get back to the shop. But it does the pop out the exhaust so i dismissed that possibility at first.

If it's popping out the exhaust, it's firing at the incorrect time. Alvin is 100% correct. It's losing sync with the cam position sensor. Datalog it when you get a chance and you might be able to see the issue show up as a non-functional sensor.

[Scottyb6.0]

Best to log cam hi and low?

[kingtal0n]

If you are getting
Crank -> Backfire BANG!
crank -> Start

its the cam sensor, recently unplugged or disconnected or bad or bad wiring etc...

If you are getting
cranking cranking cranking -> No start (no backfire)
Crank second time -> Starts quickly

Its probably the FA Cranking multiplier table
Increase the valves in the temperature range of starting (70*F here In florida) so double or triple values
This tables on the left column starts with 0, and goes 1 2 3 4 5 6 7 8 9 10 etc...
This is each cylinder event, from what I understand,
usually notice the first cylinder event is 1.25 at the top, very little fuel going in on the first crank trigger
Change this to like 3 , 4 or 6
then interpolate down slightly 5.5 5.2 4.8 4.5 4.2 etc... to test

Look in my tune file for example of my 5.3L Starts very fast
https://forum.hptuners.com/showthrea...l=1#post686802

[Scottyb6.0]

If you are getting
Crank -> Backfire BANG!
crank -> Start

its the cam sensor, recently unplugged or disconnected or bad or bad wiring etc...

If you are getting
cranking cranking cranking -> No start (no backfire)
Crank second time -> Starts quickly

Its probably the FA Cranking multiplier table
Increase the valves in the temperature range of starting (70*F here In florida) so double or triple values
This tables on the left column starts with 0, and goes 1 2 3 4 5 6 7 8 9 10 etc...
This is each cylinder event, from what I understand,
usually notice the first cylinder event is 1.25 at the top, very little fuel going in on the first crank trigger
Change this to like 3 , 4 or 6
then interpolate down slightly 5.5 5.2 4.8 4.5 4.2 etc... to test

Look in my tune file for example of my 5.3L Starts very fast
https://forum.hptuners.com/showthrea...l=1#post686802

Thanks for the help, Its cranking with like a bump out the tail pipe like it wants to start. Not a real backfire like a bang its very mild. ill Check cranking fuel.

[Alvin]

I could run a constant B+ to the main relay and test that. Ill do it tomorrow first thing when i get back to the shop. But it does the pop out the exhaust so i dismissed that possibility at first.

This could still be a situation where things that should be hot in RUN are loosing power when you key to start. I'd investigate both. The bad cam sensor will sound like its out of time.. occasionally loud backfires. It won't sound like its trying to start normally.

When the ignition stuff isn't wired right it will typically pop a little as you lift off the key from crank.

[DougO]

Following, Mine does the same as the vehicle above

[DougO]

Following, Mine does the same as the vehicle above

I added 20% to my FA1 and FA2 tables and it starts every time first try.