Not sure DI uses the same principle but on my mustang: NA motor you see 40 PSI of fuel pressure at idle, and try to hold 40 while pulling vacuum. At 0 vacuum you see ~ 60PSI (40 PSI + Vacuum). Add boost and you need even more PSI to push the fuel.

So in this case, assuming the same basic principle, lower boost on the 87 tune, means it has less resistance, up the boost, more resistance, pump cant maintain the pressure.

BUt again, I am not a DI guru, just seems logical to me.

I would suspect the LPFP over the HPFP...

I had a similar issue..stock tune I had no issues, logs looked great! The moment I dropped ANY tune on it my fuel pressure would go to crap.. I replaced the LPFP, HPFP, and the FPDM... all of which may no REAL noticeable impact.. at most the LPFP helped a TAD but I could have replaced the strainer for $10 and gotten to same results...

Here is a log of mine that almost look IDENTICAL... mine is commanding a higher load than yours... and your LTFT are already set where mine are not there yet...

You are recording with a SCT device correct? and IIRC you also experience the same issue with LMS tunes? So that would make two DIFFERENCE tuners that are having the same issue correct?

What ultimately ended up being the issue with mine was the tune I was being provided. That is why I ask.

I have to give LMS a chance to analyze the logs and mention that StealBlueSho had the same issue with a SCT programmer and a different tune which was ultimately fixed by a tune change. I hope this gets solved once and for all guys, I am absolutely willing to drive the 4 hours to LMS and let them have at it. Otherwise I'll setup a gofundme for a AJP tune in the end LMAO!

Quote from: polskifacet on January 14, 2017, 07:50:30 PM
I have to give LMS a chance to analyze the logs and mention that StealBlueSho had the same issue with a SCT programmer and a different tune which was ultimately fixed by a tune change. I hope this gets solved once and for all guys, I am absolutely willing to drive the 4 hours to LMS and let them have at it. Otherwise I'll setup a gofundme for a AJP tune in the end LMAO!

Can't go wrong with an AJPTurbo tune... are you datalogging with the LMS Mycal for LMS? I thought they wouldn't look at the logs from SCT?


Right, in the PM I said I had the same issues you are having when I was tuned with Unleashed which was ultimately resolved by AJPTurbo insisting that my fuel pressure woes were tune related. Both are SCT based tunes.

I would give LMS a good shot at it, haven't heard of anyone they couldn't help with their tune..plus you are invested in their tuner lol...


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Logging with SCT. mycal doesnt have the capability. They will look at them, I can't do any better without getting an invite to their shop.

Quote from: polskifacet on January 14, 2017, 09:39:23 PM
Logging with SCT. mycal doesnt have the capability. They will look at them, I can't do any better without getting an invite to their shop.

Glad they changed their stance on SCT logging... I would be curious if there are certain parameters they are having you record?

Historically they have said the SCT datalogging is not accurate and people don't look at the right parameters in order to make an informed decision...


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Quote from: StealBlueSho on January 14, 2017, 10:01:05 PM

Quote from: polskifacet on January 14, 2017, 09:39:23 PM
Logging with SCT. mycal doesnt have the capability. They will look at them, I can't do any better without getting an invite to their shop.

Glad they changed their stance on SCT logging... I would be curious if there are certain parameters they are having you record?

Historically they have said the SCT datalogging is not accurate and people don't look at the right parameters in order to make an informed decision...


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I can understand saying that about parameters that are logged, depending on the issue. However, the SCT logs are extremely accurate,and have an amazing resolution! I work with engine testing and dataloging for a living and the best resolution we can get is 20ms, and only ~20 parameters at that speed. Granted you can get to ~25 if that is all you log, and can log a whole bunch more parameters at 1500ms or so in a different data mode (less accurate and more prone to drop out).

But the PID read at 1 ms update rate that SCT has is pretty amazing.

Quote from: polskifacet on January 14, 2017, 09:39:23 PM
Logging with SCT. mycal doesnt have the capability. They will look at them, I can't do any better without getting an invite to their shop.

I can certainly try to request a personal invite for ya and hopefully get her dialed in and while your there you can put her on the Dyno. LMK.  Z

Quote from: derfdog15 on January 14, 2017, 10:14:56 PM
I can understand saying that about parameters that are logged, depending on the issue. However, the SCT logs are extremely accurate,and have an amazing resolution! I work with engine testing and dataloging for a living and the best resolution we can get is 20ms, and only ~20 parameters at that speed. Granted you can get to ~25 if that is all you log, and can log a whole bunch more parameters at 1500ms or so in a different data mode (less accurate and more prone to drop out).

But the PID read at 1 ms update rate that SCT has is pretty amazing.

30 ms readings MOST of the time with Forscan Lite and OBDLink MX BT, monitoring approx 65 PIDs.

PM sent. Z

Anyone have an idea on how to do a flow test? Hooking up the gauge to the Schrader valve and keeping the bypass open to a measuring container is fairly simple but how about energizing both pumps at 100% output? LMS is going to talk about my issue with their staff tomorrow, I am trying to gather required tools for testing what they may come up with for what to check.

I dont know how you would control or test 3000 psi of potential pressure without pro tools.  I suppose you could probe the wiring and inference that way, still a far cry from direct measurement.  Maybe some diesel guys have insight.

If you are going off the schrader valve that would be testing the LPFP....

Went I tested mine, I just tested the PSI output with a fuel pressure test kit. We hooked it up to the Schrader valve, snaked the line out of the top of hood, through the passenger windows, and my buddy held it in the passenger seat.

We did remove the cowl to fit the line through.


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HPFP keeps pressure on the stock tune so I will assume it is fine since its the same issue with 2 different HPFPs. I talked to a friend that has a mechanic shop, he's on vacation but next week I can go over there and we can hook up a line to the schrader valve and energize the in-tank pumps with his fancy diagnostic scan tool. He mentioned that they should both energize by jumping the relay but using the scan tool is easier.

Sounds good!  Hoping for a discovery.