E38 Cranking Issues

[joecar]

Hmm.. No I didn't I adjusted for the fuel changes using the VE tables. Here is my B4001 table as it sits today:

Attachment 12740

Do you have the reference hose connected between the FPR and the manifold...?

If yes, then that IFR will give you wrong fueling and the VE won't be able to compensate IMO.

The 400 kPa value (or closest) should be used in all cells.

The reason is that the manifold reference adds MAP to the rail pressure, this keeps the pressure across each injector (top-to-bottom) constant regardless of MAP (you will need a 2 or 3 bar MAP sensor if you're boosting)... (MAP on top is cancelled out by MAP on bottom of injector).

[mirage]

Do you have the reference hose connected between the FPR and the manifold...?

If yes, then that IFR will give you wrong fueling and the VE won't be able to compensate IMO.

The 400 kPa value (or closest) should be used in all cells.

The reason is that the manifold reference adds MAP to the rail pressure, this keeps the pressure across each injector (top-to-bottom) constant regardless of MAP (you will need a 2 or 3 bar MAP sensor if you're boosting)... (MAP on top is cancelled out by MAP on bottom of injector).

The fuel system is setup with a -10an line coming from the tank to a Y-block with -8an lines going to each rail. Then from the rails they feed into the FPR which is referenced from a vacuum line. Based on your assessment it would indicate that I need to adjust the cells in B4001 to 400 kpa (or close to it). I think this is going to really mess with my current VE, but I'm willing to give it a shot if it is the correct way to do it.

[mirage]

Here is what I tried today:

First changed the hot cells as indicated by Swingtan. This appeared to help, but when the ECT's reached 90C I began to have the same issues. So I attempted to change the cranking AFR's back to stock levels and the car started great when cold, but at 90C it would no longer start. I had to depress the gas while cranking to get it to start.

Here are the hot cells changed:


Here is the STOCK Camaro cranking commanded fuel table that I used. After this I could not start the car when ECT's were 90C or above.


I changed back to these values and the car will start again, but has issues when ECT's are at 90C or above. Starts but turns over several times first. It will start faster if I depress the gas slightly, but obviously don't want to do this.



Based on these observations I would think this is fuel related, but what do I change from here?


Also, Joecar I changed my IFB table to reflect the contents at 400 kpa. (around 9). Still testing how far off my VE are, but it did not affect the cranking issues.

[joecar]

Hmmm.... you might want to check the rail pressure.

[mirage]

Hmmm.... you might want to check the rail pressure.

Since it is externally adjustable I may go ahead and increase it just to see if it makes a difference. I didn't like where the shop had placed it anyway because I thought it was fairly low pressure wise. I'll make some adjustments tomorrow and let you guys know what happens. If anyone has any other suggestions I'm certainly open.

Thanks for the help guys...

[joecar]

It should be 58 psi.

[mirage]

It should be 58 psi.

Fuel pressure is now a solid 58 PSI. It does crank better when ECT's are 90C, but still turns over multiple times before firing. Is it possible that the CPU is still thinking it is controlling the pressure and thus not running the pumps as much when the car is hot? The pump control is still handled by the computer based on where the shop wired the fuel pumps. I'm wondering if the rails are not pressurizing enough when the vehicle is hot. I'll need to get someone to help with monitoring in order to verify.

[Laychut]

Hi Mirage,
I had a similar issue, but mine was fixed by fitting a check valve after the pump. It must have been draining back a little.

Cheers,
Laychut

[mirage]

Finally got it fixed! So to help the rest of the community here is what ultimately fixed the problem. Joecar was real close basically my injector flow base was incorrect for the type of fuel system I was using. After making changes to the IFB and re-adjusting my VE and MAF I was able to bring the fueling quickly under control. Then I noticed that the hot start at ECT 90C was even worse than before. (ie the car was turning over numerous times before starting). Figuring this was a result of the fuel pressure changes and the IFB I decided to lean the cranking commanded fuel table at 90C. This resulted in a slightly quicker start. I continued adjusting until the car started with one turn just like a stock vehicle. For those of you using vacumm referenced external fuel pressure regulators, make sure you adjust your IFB to a flat line at whatever value you have at 400 kpa as Joecar indicated earlier in the thread. The car runs much smoother now and doesn't hunt during idle like it was doing prior to these changes. Thanks again for all the help guys especially Joecar and Swingtan you guys are great!