Ford GT Fuel Pump: Fuel Pressure all over the place?

[Tripoli]

I just installed a Ford GT (supercar) fuel pump into my 2002 Mutang GT in preparation for my ProCharger which goes on in a week or two.

With my stock fuel pump, I saw the typical 39-43 PSI of fuel pressure, which would drop sharply to around 25 PSI when I left off and then punched the gas when shifting.

The Ford GT fuel pump is making the pressure go all over the place. While accelerating in gear or cruising, the pressure is more or less normal, but when shifting it drops dramatically (often to 0 PSI) and then spikes to over 50 PSI. The drop in pressure usually occurrs right when I'm stomping the gas again in the next gear, but since there's no pressure, the car falls on its face for half a second until the pressure comes back.

Is this normal, and should it be fixed when I get my new tune?

 

[wmburns]

What are you using for a fuel pump driver module (FPDM)?

How much current does the GT pump need? Is it possible that the GT pump needs more power than the FPDM can provide?

Might be handy to monitor the FPRM to PCM return signal. See if the FPRM is reporting errors back to the PCM.

Also possible the FPRM module responds to an over pressurization event by shutting down (FP goes to zero).

 

[Tripoli]

The FPDM is stock. No idea what voltages the stock pump and the Ford GT pump require. Your last scenario seems the most probable, and fits my symptoms perfectly. The pressure spikes above normal, then promptly drops, then promptly recovers, but again goes too high, then repeats. This cycle takes about 3 seconds and just keeps repeating. It seems to be least problematic when I'm just ideling. To me, this suggests that my new tune should be able to resolve this by adjusting the voltage table for the FPDM. Or so I hope.

 

[Trav4011]

I have this same exact problem.. I was told that there's a table that needs to be adjusted in the ECM, when you change a fuel pump out. I'm in the middle of rebuilding my car, from the ground on up, and plan to use dual stock FPDM's, with twin GT pumps, in a Cobra tank. I will also upgrade the wiring..

Travis

 

[Tripoli]

The plot thickens. Thew a code because of this today. When I left work, the fuel pressure was just cyclical. In about 1 second, the pressure would spike to 50 then drop to 20, then repeat. After a few minutes of driving, the pressure suddenly dropped to about 5 PSI and just stayed there. The engine ideled at about 400 RPM and wouldn't do anything else. I shut her down and restated and she would run again, with the same cyclical fuel pressure. This happened 3 times on my 10 mile drive home. When I got home I pulled the code, P0190, which if I understand correctly is just a low fuel pressure code.

Am I going to mess something up driving gently like this for another 5-12 days? And I ask again, will the tune correct this?

 

[wmburns]

From the DTC codes, it is possible that the Fuel pressure sensor (circuit wiring or sensor) is bad.

Of course the PCM could be Interrupting the wildly bouncing FP as a failure in the FP sensor.

Note, If it were my car I would be concerned about a lean condition occuring each time the FP spikes. Seams like a repeated made to order situation to hurt a motor to me.

While I am not a tuning expert, it seams logical to me that the PCM has to know about the flow characteristics of the fuel pump. A larger FP means different flow for a given duty cycle. I vote to wait for a tune.

>>From Ford service CD
P0190 - Fuel Rail Pressure Sensor Circuit Malfunction (FRP)

The comprehensive component monitor (CCM) monitors the FRP sensor to the PCM for VREF voltage. The test fails when the VREF voltage from the PCM drops to a voltage less than a minimum calibrated value.

VREF open in harness.
VREF open in sensor.
VREF open in PCM.

Verify VREF voltage between 4.0 and 6.0V.

 

[Tripoli]

I guess I should have waited and done this upgrade at the same time as the blower. I wonder if there's any way to trick the computer temporarily. Like maybe unplugging the fuel pressure sensor or something.

 

[Trav4011]

While it may be the PCM/tune, that code sounds like you have a bad fuel pressure sensor.

 

[Tripoli]

I think it's just because the pressure dropped to 5 PSI and stayed there for some reason.

I'm just trying to drive the car really gently for now. It's my daily, so I have to drive it.

 

[wmburns]

I guess I should have waited and done this upgrade at the same time as the blower. I wonder if there's any way to trick the computer temporarily. Like maybe unplugging the fuel pressure sensor or something.

Bad idea. Will make problem worse as it will destroy the PCM's referenced fuel pressure. The FP will be too high at idle and too low under power. This will make AF ratio go from rich to lean on every application of the throttle.

Under boost, the results would be an even greater progressively leaner AF as power increased.

Are you absolutely sure the FP sensor is good? Wires tested?

 

[Tripoli]

Not absolutely sure, but the issue started immediately after installing the new pump. I see nothing that makes me think there's a problem with the sensor, and I can't believe it would have gone out at the time exact time I put the pump in. When the pressure gets low, it raises the pressure, when it gets too high, it drops the pressure. It's just doing both too well.

I really should have just waited to do the pump until the day of the install. I just had no idea this would happen. It's been a real pain. She died 8 times on my way home from work today. I'm half-tempted to try to put the old pump back in for the next 11 days.

 

[Cobra123089]

how did you put the stock fuel line on the pump outlet? Maybe its leaking or something. I know it does not explain the increase in pressure but maybe something is happening. I put my GT pump in today and have had no problems, but i also have not driven the car yet, just idling

 

[Tripoli]

I used submersible fuel line and some stainless hose clamps. I'll be curious to see what yours does if you drive it a bit (do it gently ). Mine was fine ideling at first, but seems to be getting worse the more I drive it. My tune is tentatively scheduled for March 1st, so I'm hoping I can get away with this setup until then.

 

[Cobra123089]

i used heat shrink on the GT outlet and just used the stock fuel outlets. Guess we will see when i go for a drive, just waiting for my seat brackets to come in. Does the pressure bounce at all while idling? I might go hook up a gauge to mine to see if its all weird...

 

[Tripoli]

Mine does bounce around when ideling, yes. Although, it didn't do it at first. At first the pressure would spike sometimes, then drop dramatically. Now, it's just cyclical. In a 1-second period the pressure spikes to 50 PSI, then drops to around 20 PSI, then repeats. I spoke to a couple tuners and they agreed that it's just a tune issue. Apparently my idea to save time on blower install day was a very bad idea. I'm now borrowing a friend's VW until the blower kit comes in.

 

[Trav4011]

Mine randomly did the same thing.. every once in a while, it would bounce between 30 and 50psi.. It was something in the tune.

Travis

 

[Don 95Vert]

First off, it COULD be the sensor - putting that pump in without a tune could have spiked FP at one point and blown it. Usually won't throw a code like that unless something like that is wrong. Could be a bad FPDM also.

Not all that useful to watch fuel pressure on a returnless fuel car - the PCM uses fuel pressure drop across the injectors, which should stay around 30-40ish - it'd vary pressure to maintain that. If you can log that (with SCT you can) then that's what you should look at.

In the tune, the fuel pump voltage needs to be logged and the logged results need to be applied to the FP voltage table. The values in this table are learned by the PCM, but it's always better to get closer to the correct values and let the PCM fine tune the values. FYI - On battery disconnect, it'd have to re-learn again, so it'd start learning at whatever was established in the tune to begin with. Additionally, you do need to adjust some other things in the tune like the FP controller PIDs.

When you add a blower/turbo and make a lot more power, you also need to scale a few things or you'll hit a hard fuel flow limit in the returnless fuel pump values as well.

Hope this helps.

Don

 

[Tripoli]

Thanks, Don. That's some good info.

I'm confident that the sensor is fine. The way the car would react when the pressure was low and when it stalled in relation to what my fuel pressure gauge was saying seemed to be in sync. Plus, it wasn't over pressurizing too badly. With the stock pump I'd see up to about 43 PSI, and this was jumping up to about 50. I can't believe that'd be enough to hurt anything.

From what I've heard here and from some of my local tuners is that we just need to adjust the tune for the pump, along with all the other stuff they do for a blower tune, and everything will be fine.

I've parked the car and am borrowing a friend's for the next week. Since we're not driving it, we're going to start prepping it for the blower (reinstall stock pulleys and start removing old parts like injectors and my intake) this weekend. I was just notified that the blower should ship Monday or Tuesday and be here before Friday of next week. That puts me on schedule for a March 1st tune with the boys at HPP.

 

[Tripoli]

Well, got the car on the dyno yesterday and this problem persisted. And this is no run-of-the-mill tuner, it's Manny at HPP Racing. He adjusted the tune for the Ford GT fuel pump, something he's done many times without issue, and the fluctuation in fuel pressure was still a problem. (The computer's fuel pressure reading matched what my gauge was outputting.) At cruising speed, it would spike to 68 PSI and drop to 20. He blipped the throttle and the car would promptly die. We're still not sure what the problem is, but we're ditching the single Ford GT pump setup and upgrading to stock Cobra tank setup with the stock Cobra pumps. That'll be borderline on delivering enough fuel for 450 RWHP, so we'll drop a Boost-a-Pump on if we have to.

 

[hotmustang331]

Fuel pump voltage table is what typically causes the bouncing around at idle...mine did it as well.
The no pressure between shifts is due to the PPRV which I'm guessing you did not remove. It dumps fuel pressure anytime there is a large spike.
But your problem sounds like an internal leak. U didn't reuse that stock hat did you?