Contour Enthusiasts Group Archives Forums Modifications Forced Induction Fuel Pressure Drop @ WOT...

Haven't posted in a while, thought this would be a terrific opportunity:

I just received the lastest iteration of the SCT chip from ADC for my forged turbo 3L (this one actually opens the secondaries... ). I took a run with the boost controller on "stock" (6 psi), and noticed that she still seems to fall on her face above 5k. Punched up the boost controller to my "high" setting (12.5 psi, max I could go w/o secondaries), and took a run. Again, fell on her face at around 5.5k. Out of the corner of my eye, I see the fuel pressure gauge doing something. So I stare right at the thing, mash the gas, and it drops to 20psi almost immediately over 4k. Needless to say, I got my lilly white a$$ off the accelerator. The turbo timer was reading 15.3:1...

I have the 255l/hr high-pressure Walbro pump. I have a new Purolator fuel filter, and the FPR is quite functional (immediate blip from 42psi @ idle to 65 at WOT), my vacuum/boost gauge is tapped right off the FPR fead.

Ideas? I ain't running this thing any higher than 50% throttle at stock boost. One suggestion was that the pump cannot get enough current under load, but I can't remember hearing any audible change in pitch of the pump during the run.

Silly question, but what MAF and injectors are you running? If the MAF doesn't have the correct function programmed in, it could very well lean out the car above 4K no matter the size of the injectors. Also, you could be maxing out your MAF airflow at that point and at 5 volts it will start to do funky things.

Rick

Hmm.
Fuel drops to 20 at 4K rpm.

Well it is going to richen the injectors on opening the secondaries.

What size injectors? You're saying you have a return-style system?

I'm guessing with that setup you have 39's or bigger. IF they all went static open then they might be able to drop the pressure significantly and the excess fuel would kill the power.

IF the car was starting to go lean then it should have had a bit more power before it got too lean but I'd guess at 12.5psi you'd have already hurt something.

If it is returnless like I thought most cougars were....then it is a programming issue I think.
Need to list injector size. I don't buy the whole voltage drop thing. The pcm code has parameters to change the fuel injector pulsewidth based on electrical system voltage. Meaning if the alternator died and the voltage dropped, the code will automatically adjust the injector parameters for it.

What does the maf voltage indicate when this happens? You probably should datalog with an obd scanner what the maf is doing and what the fuel trims look like when it happens.
You can easily watch the O2 sensor voltage and get an idea if it is falling or not to help narrow down a lean or rich condition, but don't trust a narrow band for exact fuel ratio.

99 cougars are return. He said he has a fuel pressure regulator which aren't found on returnless systems. He has 42's and a large enough maf.

I did have a similar issue once. One of the fittings on the pump wasn't seated right. This was before the focus SVT pump was available. I had to rig a Walbro. It sprayed gas back into the tank at WOT but the pressure only got too low when I exceeded 300 hp.

Yeah if he is returnless he NEEDS to ditch that Walbro, but he says he has a FPR, which would suggest he is return - so it should be ok with the Walbro. I would also check the fule lines. Might have a leak or tear in the hose in the tank.

Yeah, this is why I wanted him to clarify. Basically what stazi was saying is where I was going with that.

I know for sure that a walbro on stock lines has been more than enough fuel so far, even with 55psi WOT. The sudden loss of power sounds to me like a complete dump of fuel or a complete loss.
Too bad he can't datalog injector duty cycle. Thats one thing the eManage was excellent at. It would log maf voltage, injector pulse width and injector duty cycle by measuring those items directly. Along with TPS, RPM, pressure. With the EO1 you could display all that right to the screen in the car. And of course it worked well on top of a chipped car.

See that is another thing he said that threw me off...I've never heard of 65psi WOT so I'm again wondering if it is a returnless since I don't even know the fuel pressures that they hit.

Return you won't see more than 55psi at WOT IIRC. 65 is high.

True though Tom, if it is returnless and he doesn't have a 'smart' pump then it will go lean at the top end. I ran into that wall too.

Sorry I have responded sooner on this- Turkey Day and all...

Car setup:

-3L forged internal ADC T3/4 60 trim
-SVT Lightning MAF, as required by ADC
-42lb/hr injectors from SVT Lightning, as supplied by ADC
-ADC chip for turbo kit
-Return-style fuel system (otherwise I wouldn't be running the Walbro, folks !)

The Walbro pump has been getting progressively louder since I originally fired the engine. At first, it was barely louder than stock. Now (and since the problem manifested itself) it's clearly audible from the cabin, and quite loud from outside the car. Keyser may be onto something...

Looks like I'm dropping the tank again...

I didn't think you had to drop the tank to change the pump in our cars?

You don't I can pull my pump in like 30 mins.