"Crank Sensor Current Cylinder" & "Current Firing Cylinder"

[QBRacing74]

Hey all

My ls1 wont fire and its either going to be low fuel pressure across the injectors or a crank signal issue.

While I wait for a fuel pressure gauge to arrive I wanted to ask about two channels that the scanner can monitor, "Crank Sensor Current Cylinder" and "Current Firing Cylinder".

I have attached some short logs and they all seem to be doing the same thing.

1) "Crank Sensor Current Cylinder" seems to be a totally random number between 0 and 65000. There doesn't appear to be any normality to it that I can see at least in relation to "Current Firing Cylinder". Is this right or erroring?

2) "Current Firing Cylinder" seems to range between 0 and 8 = 9 cyinders ???. Looking at the attached logs sometimes it goes from 0-6 others 0-7 or even 0-8. What is it referring to? There is no cylinder 0 or why is it only going to 6 sometimes.
My firing sequence in editor appears to be right ... 1st=1, 2nd=8, 3rd=7, 4th=2, 5th=6, 6th=5, 7th=4, 8th=3
So why does it sometimes only fire to 6th then go back to 0 and what is 0?

The couple of times it farted and tried to start was from me using carb start down the throttle body

Any help appreciated.

Q

[5FDP]

Having the MAP sensor pegged at 105kpa is not helping either.

So that is a real problem with that sensor or you have the wrong data in the tune file for that sensor.

[QBRacing74]

Thanks 5FDP as always for the reply.

Why is having the MAP at 105kpa bad. My calculations make that about 15.1psi which is pretty close to atmospheric (14.7 at sea level).
When the engines not running it should be reading atmospheric shouldnt it.

The couple of times it tried to fire the MAP dropped down to 3-5psi which is kind of what i would expect for an NA car.

[5FDP]

Key on engine off should be ~99-101kpa at sea level and less if you live in higher elevations.

What MAP sensor are you running? Make sure that data is correct.

And make sure the coil pack harness and injector harness are on the correct banks, that could be a no start condition. As well as a VATS issues.

[QBRacing74]

The MAP sensor is factory LS1 from the original donor car the engine, loom, pcm come from. The vacuum pipe runs in to one of the rear ports on the Holley 4150 throttlebody (part number 112-587) that I am using.

I have confirmed the vats is disabled and the SES have been disable as well.

I checked the wiring the other day. As I am using the factory loom the colors match what is coming out from the PCM and what is arriving at the individual injectors and coils (colours do change at the main harness join beside the coil packs). I checked continuity on all the wires the other week when I rerouted and spliced the loom to run it in a better path. All were fine.

I also randomly checked 4 spark plugs for spark and all were fine and when I cranked while they were out I could see mist coming out the spark plug hole so the injectors were firing.

This go me to thinking. How much pressure do I have on the rail. I have a walbro 255lph in-tank pump going to the corvette filter regulator then up to the engine (no return line) so the rail should be at about 58psi.

I went and bought a fuel pressure gauge and when I hooked it up and I pressurized the system I couldn't get more than 30psi on the rails. At that pressure there wont be enough gas to crank so I gave the throttle body a squirt of carbstart and when I cranked it, it fired into life for a few seconds before dieing. I then also partially cranked the engine to trigger the fuel pump again and cold pulse the injectors. Then when I started it (after 4- pre cranks) it fires before dying.

This makes me think its a fuel pressure issue.

I have now ordered an external pressure regulator and a simple inline fuel filter which will replace the corvette filter regulator when they arrive.

If this doesn't fix it, it really can only be the pump simply not outputting what it should be so I may need another new pump.

[5FDP]

Yeah, 30psi is surely not enough. Once it's at 58psi it should be better.

[QBRacing74]

Ok, I've changed the corvette regulator/filter for a separate high pressure fuel filter and adjustable regulator and in a couple of minutes I was able to set the pressure right at 58psi.

Now when I crank it fires but doesn't keep running (no need to prime it like I did before).

I checked all 8 plugs on the leads to earth and they all spark when required.

Should I just dump 20% more gas in the VE table and see what happens? Im pretty sure its a fuel issue at this stage.

Here is a log from todays try it starting.

Q

[5FDP]

The MAP sensor data in the tune is for a LS3 style MAP sensor.

The LS1 MAP sensor needs the data as 94/10.33 if my memory is right, double check that with a factory LS1 tune file.

What injectors are installed? The flow rate is rather huge for a LS1 engine size, just want to make sure that is right.

[QBRacing74]

THANKYOU .... I see what you mean by the map sensor now.
He has it programmed as 128.13/-0.31 where my stock LS1 was 94/10.33 like you said. Ill change that back and upload this weekend.

As for injectors, I now have the later LS1/LS6 28lb injectors (originally I had the 24lbs).

I just did a compare on his file to my stock tune and see he has changed the firing sequence as well. By my calculations its now out by 45 degrees.
My stock LS1 was 7th=5, 8th=4, 1st=3, 2nd=1, 3rd=8, 4th=7, 5th=2, 6th=6
The tune he gave has 7th=4, 8th=3, 1st=1, 2nd=8, 3rd=7, 4th=2, 5th6, 6th=5

I will change the firing sequence back to the stock one on the weekend and suspect that will fix my issues.

Quintin

[5FDP]

Change your injector data back too, it says you are running some giant 100 something pounders.

[QBRacing74]

5fdp for president

long live 5fdp

Its alive and it sounds so good.

thanks or pointing m in the right direction on the map/injectors as the definitly helped once i sorted the firing order.