Hello,



I have an ls swap chevy G20 Van. LS engine build by a local tuner. 400 hp at the crank on the dyno.

Everything is new, expect it’s a stock truck intake.

The problem i have right now is it doesn’t fire up at the first key turn. ( 80% of the time it will not start, somethime it fire right up )

Did a fuel pressure check, everything is ok, there is a new wire harness from psi.

Somethimes I get the P0102 error.



So i turn key, crank for 10 sec, no start, i stop, turn key again and it fire right up.

If i turn key and keep on cranking it wil not fire up, but i hear backfire in the exhaust.

I measure Camshaft and crank shaft sensor with a fluke scope, they both give a signal wile cranking.



i did a check of the wires, i replace the camshaft and cranks shaft sensor, I replaced the ECU, no fix… when it runs, it runs file, no problems…



The wierd thing is that when I start with 50% trottle, it fire right up the first crank.

So, because I somethimes have a P0102 > does the MAF sensor measure the incoming air when starting? And maybe when I open the trottle a little bit it measure more air and give more fuel when starting? Prime tabels not good at the tune? Of bad MAF sensor ( it’s new… )



Any idea’s?



Thanks!!!

 

Is the starting issue related to cold or hot starts or does it behave the same way for both?

 

the same on both, cold or warm, it doesn't matter.

 

Is it DBW or DBC? Try starting it without the MAF plugged in?

 

it is DBC. I will try starting without the MAF plugged in, thanks for the tip.

 

If you turn the key to run and let the fuel pump run for two seconds before you turn the key to start, does it start every time? Maybe a leaky injector slowly letting fuel pressure drop while engine is off?

 

I suggest you stop throwing parts and $$ at the issue. Here is what I did to fix my issue. There is a table in the PCM that adds timing during the cranking time; it's not labeled as to what it actually does though. It fixed how fast it lights off and runs directly during cranking and for the next few seconds. If you add too much timing, it will hang for a while. adjusting the table solved the issue for several of the swaps i have done. I forget the table name but will look tomorrow and let you know what it is.

Note: My youtube channel has a vid showing it. It's a white yukon with a cam.

 

Tank you for you response.



They guy that did the engine build, has the same engine build in his caprice, with the same tune.

He even switch his ECU with mine but the same problem. ( so he told me ).

Fuel pressure is good. Checked the cam and crank sensor. He even switch them.

It’s verry strange, not always’s, but first key, no start, second key, starts immediately.

Don’t know where to search next…

He use HP tuners, I don’t know anything of this software, or how it’s work, if he “copy” his tune to my ECU, could it be the think you talk about? ( ignition? )



Thanks for your reply.

 

Oddly enough, a guy brought me his swap as it was running one day then stopped. I knew it wasn't getting spark so I replaced the crank sensor with a brand new one. It started BUT like your issue, after it fired up. It won't start on the first attempt here and there, it starts up on the 2nd. Im kind of wondering if the new crank sensor is only half new as in, the first go round it doesn't send spark but the second time it does? or maybe theres a small fuel issue somewhere? Or maybe plugs are just fouled? Just kind of brainstorming ideas as in a sense, this guys truck is having the same issues you are. Also, check your relays. I swapped relays with ones from another swap vehicle im working on and it seemed to have helped quite a bit but not sure how.

 

Cam sensor. A bad one starts on the second hit. All it does is determine which stroke #1 is on.

 

As said cam sensor. It's either a wiring or sensor issue. I know you said you checked them with a scope, but I'm willing to bet it's something with the cam sensor/wiring.