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Discussion Starter · #1 · (Edited)
Hi Folks,

Please take a look at this graph. It is a high-bandwidth datalog of fuel rail pressure, air/fuel ratio (taken with an FJO wideband), and throttle angle. It was done on the road in 3rd gear at WOT.

You can see the correlation between the fluctuating pressure and air/fuel.....not a good scenario.

I have only a few far-fetched theories as to what is going on here. In order of probability they are:

1. failing fuel pump (highest prob.)
2. faulty fuel pulse dampener
3. faulty injector(s) [they are 50lb/hr]
4. cavitation/boiling of fuel in the rail

One more piece of data is this: after a WOT blast, if I coast for a while the fuel pressure starts to slowly ramp up to 70+psi. As soon as I touch the gas, it drops right back down to 39-40psi. It is my understanding that the PCM will do this to stop fuel from boiling in the rails but does this sound right?

One more thing, this problem seemed to rear its ugly head immediately after the installation of my longtubes, addition of 50lb/hr injectors, and increased boost from 12psi to 14psi.

Any help will be MUCH appreciated.

Thanks,

MJ
 

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Discussion Starter · #3 ·
Okay here's an update:

Today I removed the 50lb/hr injectors and reinstalled the stock injectors. I also removed the MAFterburner completely from the circuit (was recurving the MAF for the 50's). The result: NO CHANGE! Dang! That removes my #3 possibility from the list above (injector issue or mismatch between injectors and fuel pulse damper).

Time to install the new fuel pump assy. that I have on order. As of now all I can think of is the pump failing or the FPDM doing something weird.

MJ
 

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Discussion Starter · #7 ·
Here is tonight's run. This is going back to the stock 39lb/hr injectors, removing the MAFterburner, disabling the BAP, etc..

FYI, I have replaced the fuel filter and the FRP sensor (a few weeks back).

Thoughts?

MJ
 

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Discussion Starter · #9 ·
Hey Mike,

I removed all of my electronic gizmos (afterburner, mafterburner, BAP, etc.) yesterday and the problem still exists. At very little load, there is almost 1volt p-p variations of the FRP signal. One volt corresponds to almost 20psi of pressure fluctuation and would totally account for what I'm seeing when datalogging.

The only other symptom is: when I first turn the key on with the engine off and the PCM charges the fuel line by activating the fuel pump I get this VERY loud whistling sound. It sounds like fluid being pushed through a nozzle at high pressure....

Anyway, it's either the FPDM or the pump that's hosed....I'm sure of it. I'll be replacing the pump on Wed. and if the problem still exists the FPDM will be next. Beyond that.....I'm lost. :(

MJ
 

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pump is run by a PID controller. With your background I am sure you understand how that works. A good tuner with capabilites past 1 bank would know how to fix that.

In other words, I don't see any mechanical problems based on the info and charts you have given.

Brian
 

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That is on a almost stock car. The pid loop shouldn't need tuning. It almost looks like the gain to to high and/or the reset time is too short.
 

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up about 120RWHP from stock and you don't think it's going to change the fuel controls at all?

look at how much better it got when he took off the larger injectors and all of the electronic gadgets. Keep in mind it still was probably making well in the 400RWHP range. This is just more proof that there is more to a good tune than a/f correction.

Brian
 

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Discussion Starter · #13 ·
bjherron said:
up about 120RWHP from stock and you don't think it's going to change the fuel controls at all?

look at how much better it got when he took off the larger injectors and all of the electronic gadgets. Keep in mind it still was probably making well in the 400RWHP range. This is just more proof that there is more to a good tune than a/f correction.

Brian
Thanks for the input Brian. The second graph above was with the 39lb/hr injectors reinstalled, the MAFterburner tables zeroed out, and the BAP disabled. As evidenced by the higher than stock pressure, you can see that the eFPC was still enabled. What's weird about the second graph is that it did get better up until high RPM (high flow).

I also checked the system in closed-loop operation with the eFPC and MAFterburner completely removed from the circuit. There was no change.

The problem is that there is approximately 1volt p-p of voltage ripple on the FRP signal. It is my opinion that this is a true representation of delta_P (not electrical noise).

This condition has degraded over time (or possibly with the addition of longtubes and more boost). It could be possible that the system was underdamped from the get go and now the error disturbances are larger on the manifold pressure side due to the mods and therefore the result is poor steady-state pressure control. One thing that leads me to be skeptical of this hypothesis is that why aren't others complaining about this problem? I haven't heard one person even mention erratic fuel pressure. Any thoughts on this one? You'd think that if it were a system issue exacerbated by the addition of more boost (or other mods) than a lot more people would be seeing the same thing. No?

MJ
 

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Discussion Starter · #14 ·
PROBLEM SOLVED!!!!

Well, it was the fuel pump!

Here's the latest run (need to tune now because its running lean):

Thoughts?

MJ
 

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Snake Charmer
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Just one failing pump or both? Do you think it had to do with all the debris you pulled from injectors and pump socks that caused premature failure?
 

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Discussion Starter · #16 ·
Shadowgray03 said:
Just one failing pump or both? Do you think it had to do with all the debris you pulled from injectors and pump socks that caused premature failure?
Hi,

Don't actually know. I replaced the entire unit. I have no idea what made it fail.

MJ
 
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