Fuel Pressure Drops with boost??

**MillCreekMafia** · 09-25-2005, 08:13 PM

(1990 5.0) I just installed my new S-trim kit, got the t-rex, 30# injectors, rpm 2 upper lower intake, 70mm TB, 190lph intank. I'm not sure what my problem is, but whenever i go to get on the car and boost starts to kick in, i lose fuel pressure and the car breaks up and loses all power. I tested the FMU because i assumed it was junk, but it's working correctly (or at least appears to be). I thought maybe the T-rex is messing up, but i can hear it and feel it and it's on and hooked up correctly, so i wouldn't think it's not working. The only other thing i can think of is that i probably need colder plugs, but that still doesn't fix the fuel issue. Also has anyone had their BTM just catch fire 10 minutes after install? I have no idea what happened there, you can't even hook that thing up wrong so i'm calling MSD about it tomorrow because i'm screwed without being able to retard the timing. Can someone please help me. Thank you.

i had fuel pressure set at 40, and it sat around 30 with vacum hooked up, and i moved it to 50, which sat it at 40 with vacuum and it still does the same thing. when i smash the throttle The car jumps from 40, to 50psi and then drops like a rock. I also thought maybe the air filter was turning inside out, and i took it out and tired it and it worked better, but then i tired it again like that and it still does it, i must have just got lucky. it breaks up around 3000 and above rpms.

***speedytang*** · 09-25-2005, 10:39 PM

Not enough fuel. 190lph and 190lph still only makes 190lph. The idea of the TRex was to make a 88lph work at 190lph so that lph could be increased without the dangers of the novice dropping the gas tank and using a metal punch to remove the compression ring and blowing themselves up. You need a 255lph pump or a larger size external pump to keep your fuel pressure up.

**MillCreekMafia** · 09-26-2005, 03:44 PM

Originally Posted by speedytang

Not enough fuel. 190lph and 190lph still only makes 190lph. The idea of the TRex was to make a 88lph work at 190lph so that lph could be increased without the dangers of the novice dropping the gas tank and using a metal punch to remove the compression ring and blowing themselves up. You need a 255lph pump or a larger size external pump to keep your fuel pressure up.

I was under the impression that 190lph should be more than enough for 30# injectors. how sure are you on this?

***speedytang*** · 09-26-2005, 06:46 PM

The FMU under boost needs you fuel pressure to climb to about 80psi at 6psi w/30lb injectors. Anything weak in the fuel system will not allow it which causes a lean condition. You have two items that can cause the problem other than a bad fuel filter a weak fuel pump or a bad pressure regulator. The FMU is not on the Regulator side of the fuel rail. Take your belt off and drive the car and see if you fuel pressure drops under 40psi at WOT. If it does not then your pumps can not keep up with the FMU demands.

**MillCreekMafia** · 09-26-2005, 08:02 PM

Originally Posted by speedytang

The FMU under boost needs you fuel pressure to climb to about 80psi at 6psi w/30lb injectors. Anything weak in the fuel system will not allow it which causes a lean condition. You have two items that can cause the problem other than a bad fuel filter a weak fuel pump or a bad pressure regulator. The FMU is not on the Regulator side of the fuel rail. Take your belt off and drive the car and see if you fuel pressure drops under 40psi at WOT. If it does not then your pumps can not keep up with the FMU demands.

alright thank you for the advice, i will keep you posted as i make progress towards fixing this. The pressure regulator is new, and i will change the fuel pump when i get a new one soon. Should i take out the t-rex if i get a 255 in tank or ?? and or should i get a 255 inline to go with the 255 walbro i'll be getting?

**MillCreekMafia** · 10-15-2005, 11:45 PM

Originally Posted by MillCreekMafia

alright thank you for the advice, i will keep you posted as i make progress towards fixing this. The pressure regulator is new, and i will change the fuel pump when i get a new one soon. Should i take out the t-rex if i get a 255 in tank or ?? and or should i get a 255 inline to go with the 255 walbro i'll be getting?

I went and bought a Walbro 255 In-Tank, and the Walbro 255 In-Line. My fuel pressure still drops. I'm still lost. I bought a PMS which i have not hooked up yet to use. So i still haven't been boosting it since my MSD BTM burnt up. I was fooling with it tonight, and from what i see the fuel pressure is set at 45 with vacuum unplugged. It sits around 35 with it plugged in. When i hit WOT, it jumps to about 65PSI of fuel pressure and thats when it cuts. Now i haven't put my new plugs in yet and this all may be cause because my spark is blowing out, i'm not sure and i will find this out soon i suppose. Just giving everyone an update. If anyone has any more suggestions i'd appreciate.

92stanglx · 10-21-2005, 12:25 PM

Originally Posted by MillCreekMafia

I went and bought a Walbro 255 In-Tank, and the Walbro 255 In-Line. My fuel pressure still drops. I'm still lost. I bought a PMS which i have not hooked up yet to use. So i still haven't been boosting it since my MSD BTM burnt up. I was fooling with it tonight, and from what i see the fuel pressure is set at 45 with vacuum unplugged. It sits around 35 with it plugged in. When i hit WOT, it jumps to about 65PSI of fuel pressure and thats when it cuts. Now i haven't put my new plugs in yet and this all may be cause because my spark is blowing out, i'm not sure and i will find this out soon i suppose. Just giving everyone an update. If anyone has any more suggestions i'd appreciate.

What calibration ring do you have in your FMU? If you pull your plugs make sure you re-gap them to the stock gap.

**MillCreekMafia** · 10-21-2005, 04:59 PM

FMU has the correct 30# disk, i just got my BTM back from msd i got a new one they sent, so i'm going to hook it up this weekend and put new colder plugs in and then see whats up. I have the PMS, not sure if i mentioned that yet, but i'm going to hold off and put it on over the winter when i have a little more time to mess with the settings, i'm trying to get this pig down the quarter before the season ends!.

Originally Posted by 92stanglx

What calibration ring do you have in your FMU? If you pull your plugs make sure you re-gap them to the stock gap.

**midnight** · 10-22-2005, 07:45 AM

1.Sounds to me like U may have the fuel lines from the FMU backwards.Make sure the line coming out of the bottom of the FMU is going to the smallest fuel line going back to the tank(Trace fuel line to frame rail). Even w/a MSD and/or BTM your gap should b no more than probably .032...of course at 6#'s stock gap shoud'nt b a prob.....If the belt is too loose(I don't suspect-but possible)it would react about the same way..pressure go up & fall as slipping occurs(boost goes down)...

**MillCreekMafia** · 10-23-2005, 06:32 PM

Okay, i have everything worked out right now. I put the new plugs in and i recieved my btm back in the mail from msd, and i have it all hooked up right now. I boosted it tonight, didn't get to see what my boost was because the gauge isn't hooked up, but I have the timing at 9* and on the btm it's a 2??? i think (it's gay to read.) and inside on the knob i have it at 2. I raced my buddy tonight in his 2000 TA, and it was a pretty even race. He actually pulls a little harder on me, than i do on him. It's a stock TA ws-6. i was wondering what everyone recommneds for timing. 12* with 1.5 on the box? i need to hook up the pms, but i've not the time to tune it yet.

***speedytang*** · 10-23-2005, 11:44 PM

If you set the timing at 14 degrees then set the MSD for 1degree-1psi and at 10psi you will have 20 total degrees of timing which is safe at 91+ octane. The PMS will do a better job of this and is accurate which the MSD is NOT. If you go lean then that is another problem. You really need a WideBand or go to a Dyno so they can watch the A/F under boost.

**MillCreekMafia** · 10-24-2005, 06:23 AM

Originally Posted by speedytang

If you set the timing at 14 degrees then set the MSD for 1degree-1psi and at 10psi you will have 20 total degrees of timing which is safe at 91+ octane. The PMS will do a better job of this and is accurate which the MSD is NOT. If you go lean then that is another problem. You really need a WideBand or go to a Dyno so they can watch the A/F under boost.

Alright, depending on the weather tonight, i'll try and give that a shot. All i know is that my timing seemed way down last night, and it didn't have the power i was looking for.

**93gt** · 10-24-2005, 03:23 PM

I would get those gauges hooked up so you know whats going on . I would hate to read about you blowing a gasket or worse.

**MillCreekMafia** · 10-25-2005, 11:39 AM

Originally Posted by 93gt

I would get those gauges hooked up so you know whats going on . I would hate to read about you blowing a gasket or worse.

heh, i'm taking this into consideration.. Maybe i'll even build up the courage to hook up the PMS and venture off into the land of the free. I got my battery relocation box delivered today, and I hope to get it installed and The MSD Installed. I need to put all of my cobalt gauges in, and and I'd like to throw my air filter into the fender well to get it out of the engine bay to get some cooler air, and free up some space. I still have not touched my timing as of yet, it's been raining for the past few days.