FrankenFerrari - V12 Ferrari 308

When I was cranking the engine to prime the oil pump I noticed I had like 10psi oil pressure and thought it fine....but then noticed I also has around 10psi fuel pressure with the fuel tank empty and pump off.  Last night I discovered that the pressure transducers read just fine on the bench but when they are installed and the chassis grounded they have a 0 offset...270mV on the oil pres and 330-370mV on the fuel as it drifts around 30-40mV.  These are 2 brands from Amazon, as typical chinese stuff they look the same other than the marking on the casing...both are junk it seems.  I'll try 1 more where a couple reviews specifically mention no/low offset for fuel (don't care about the exact value for oil as long as its reading something so I know there is pressure and I can remove the offset in the ECU easily) before ordering a $200 Honeywell version cuz I do need to know fuel pres to calculate the correct mixture

mke said:

When I was cranking the engine to prime the oil pump I noticed I had like 10psi oil pressure and thought it fine....but then noticed I also has around 10psi fuel pressure with the fuel tank empty and pump off.  Last night I discovered that the pressure transducers read just fine on the bench but when they are installed and the chassis grounded they have a 0 offset...270mV on the oil pres and 330-370mV on the fuel as it drifts around 30-40mV.  These are 2 brands from Amazon, as typical chinese stuff they look the same other than the marking on the casing...both are junk it seems.  I'll try 1 more where a couple reviews specifically mention no/low offset for fuel (don't care about the exact value for oil as long as its reading something so I know there is pressure and I can remove the offset in the ECU easily) before ordering a $200 Honeywell version cuz I do need to know fuel pres to calculate the correct mixture

That sounds more like a ground path/ground loop issue than a sensor issue.  All of your ECU inputs should have the grounds tied together at a single point and, ideally be isolated from the chassis ground except for that single point.

For what it's worth, I'd be uncomfortable firing up a fresh engine with a new, untested oil pressure gauge system.  I pretty much always use a trusted mechanical gauge when I fire up an engine for the first time.

APEowner said:

That sounds more like a ground path/ground loop issue than a sensor issue.  All of your ECU inputs should have the grounds tied together at a single point and, ideally be isolated from the chassis ground except for that single point.

I said "bench" but what I meant was in the car connected to the ECU but not screwed into the engine or pressure regulator so the sensor housing is not grounded.  These are 3 wire sensors connected to 5V sensor supply from the ECU, Sensor GND from the ECU, ECU AN input pin,  so all leads go straight to the ECU through a shielded wire. 

The ECU itself is grounded though a star type setup, with I think 6 chassis points all tied together prior to the ECU...I think its right(?) and I don't see this issue with any other sensors. 

It really looks like there is leakage inside the sensor between the housing and what should be the isolated ground used by the electronics....not sure honestly but that is what it looks like and I did see a couple product reviews talk about having this issue exact of a 0 offset and the one I just ordered a review saying the  offset was just a few mV on the 4 he's bought and tested so fingers crossed.

I am confident these are both reading pressures, I"m just not confident in the calibration.  I can and did correct the 0 point but I'm not sure what happen with top....I left it at 4.5V but if this is ground offset then that would shift also I think so 150psi would be 4.5+0.270=4.77V  On oil pressure I'm not sure I car if its 60psi or 65 or 70 exactly as long as its consistent and I know for sure there is pressure so I'm not sure I need to solve the calibration there and for sure the factory gauge calibration was way off so I didn't make it worse....its annoying though.

The fuel pressure will alter the mixture....it will be mostly corrected in the tuning but I'd like it sorted.  The new sensor is 80psi which is more appropriate and will be more accurate then the 150psi I currently have and fingers crossede the casing is isolated as it should be.

APEowner said:

For what it's worth, I'd be uncomfortable firing up a fresh engine with a new, untested oil pressure gauge system.  I pretty much always use a trusted mechanical gauge when I fire up an engine for the first time.

A gauge like this that just mounts on the engine in a handy oiling system port is a good way to go if your engine config allows it, IMO.

The new fuel pres sensor is much better, 71mV offset and seems stable.  The oil pressure still reads 0 with the 270mV offset so it appears stable. 

The manifold o-rings came yesterday, I bought 3x8mm instead of the standard 3x14.5mm to make it a little easier to assemble and they seems fine.  Just waiting on UPS to bring the rail o-rings now.  The plan this time is make sure the injectors are seated in the rail then pop in the manifold end because the fuel needs to be sealed but  a small vacuum leak doesn't really matter so I want all the risk shifted to the manifold end as best I can.

In reply to Syscrush :

I have strong feelings about mechanical pressure gauges attached directly to an engine.

They usually rattle themselves to uselessness after a short time, and once I had a rail mounted fuel pressure gauge merrily spray C16 all over the engine bay.  Fortunately the test port was on the left side, and BGNs have the turbo on the right, so it didn't catch fire or anything.  That time.

For short term testing it's okay, but definitely something to take back off.

Well...its almost sealed this time.  It looks like  a mist coming from 1 injector on the end.  Hopefully 3's a charm.

Pete. (l33t FS) said:

For short term testing it's okay, but definitely something to take back off.

This is a great point - thanks very much for sharing. I definitely don't want my bike blasting oil out of that port at highway speeds, I may re-think this configuration.

mke said:

Well...its almost sealed this time.  It looks like  a mist coming from 1 injector on the end.  Hopefully 3's a charm.

We're all pulling for ya!

This is a challenging assembly.  I didn't have room for 2 fuel rails  or to assemble the rail to the TBs then drop the assembly into place so assembling relies on everything flexing enough to pop into place.

I decided the rail wasn't sitting just right and was torquing against the  injectors so I sawed the end off and repositioned it a bit....and then there was fuel pressure.

Not sure how you got the fuel rail de-fueled enough to want to hit it with fire, but glad that you found a smoking gun!

mke said:

This is a challenging assembly.  I didn't have room for 2 fuel rails  or to assemble the rail to the TBs then drop the assembly into place so assembling relies on everything flexing enough to pop into place.

I decided the rail wasn't sitting just right and was torquing against the  injectors so I sawed the end off and repositioned it a bit....and then there was fuel pressure.

Uhhh... Was that 11 pops, or 12?

Anyhow, you are an absolute madman and it's stuff like this that keeps us coming back. Very cool update, here's hoping it gets you to where you need to be.

I swore enough getting 6 injectors and three fuel rail pieces to stay dry above the manifold.  This is quite the challenge.  Better stock up on goats.

I don't want to be crass but I don't know how else to put this. You are a genius with the biggest balls I have ever seen.

Nader said:

Don't forget the spark plugs.  (you're welcome)

Right!  I put the plugs in then spent some time tring to get the boots to right right and the wires resembling neat

As long as I was making stuff a bit neating, I gorilla taped over the hack job I did on the stacks so they at least look right even if they aren't

oh yeah, then I started it....a little....on staring fluid.  I'll give everything a good look over and spend some time with the log now and be share everything there looks right before another go.

I cannot wait to hear the theottles crack open and this thing rev like a banshee 

as the younger kids say...... Yaaaasssss

sounds like all 12, at least.  your wife is a saint

congratulations, big step! I am sure more will come in the next hours and days.

In reply to New York Nick :

Yes, working on a floor now though, but will spare you all the pics 

Logs looked good other than an erratic fuel pressure, I will add more to the tank before proceeding just to get out of gas off the list.  I didn't save the first logs and had to re start it...started playing with adding more fuel and it stopped cranking....E36 M3!  NOT AGAIN!......no, wire just fell off the starter solenoid.  Back to need more fuel.

Dusterbd13-michael said:

I cannot wait to hear the theottles crack open and this thing rev like a banshee 

Here's 6-7k

In reply to mke :

I literally got an adrenaline rush listening to that thing fire right up and run so well. 

You must be stoked! 

what an amazing journey! Thank you for sharing it with us, I enjoy reading your adventures. The engine sounds amazing! I can't wait to see the car moving down the road!

speachless

In reply to mke :

That is so berkeleying awesome.

Congrats!