1998 Mark VIII CE

boylanp

boylanp

New member
I talked to the shop that tuned the car, and they said they didn't go over 5500 due to the lowering of fuel pressure. I only got to talk to the lady at the front desk, and she made it sound like they couldn't maintain a good air/fuel ratio. They suggested installing a booster. Several months ago, I installed an Airtex Master/Fuel Pump i bought from Auto Zone. Maybe I should've gone with the Walbro 255lph?
 
driller

driller

El Presidente
Gee, you would've thought they would've mentioned something about the A/F ratio. :(

You don't need a boost-a-pump, you need a good fuel pump to maintain pressure. I presume you have stock injectors?
 
KStromberg

KStromberg

Vortech kicked in yo
boylanp said:
Brand new from the factory, the Mark VIII LSC/CE came with 290bhp. Going by the old rule of thumb, 20% drivetrain loss for an automatic, the car should have had about 232 rwhp 'ish brand new. I've installed a Cobra intake manifold, k&n air filter, aluminum driveshaft, and removed the air intake silencer. All for a net gain of around 4 rwhp or 5 hp at the crank.
I would expect to have at least another 10 hp somewhere. Has the car lost this much power just in wear of the drivetrain/suspension and not being able to plant the power to the ground? Or is this an expected value?
Let me know what you guys think.
Thanks,
Patrick
Click to expand...
Patrick, the reality of it all is that regardless of the mathematics, the Mark8s put down 225ish rwhp when stock. So you made 11hp with apparent issues. Doesn't sound out of the ordinary at all to me concerning what was going on. Also keep in mind that as long as your exhaust is stock with log manifolds, you will never see nearly as much power from the Cobra intake because you have only covered half of the equation. You need better exhaust. If you take in more air, you need to find a way to exhaust it. Consider a full exhaust with headers and your numbers will rise dramatically with good A/F ratios and a fuel pump that can keep up. Your car should have been spun well past 6000 rpms, so if they cut it short for some reason, that is the first problem I would tackle.

My car made 268rwhp @ a sweltering 98 degrees Fahrenheit with the Cobra intake swap. Previously on the stock intake and full exhaust with headers and a chip tune I made 242rwhp.

Ignore the "booster" option. That's a bunch of hogwash and someone should be embarrassed for even suggesting such a thing otherwise they are just plain stupid. Twin Turbo Cobras run boosters, not a naturally aspirated Mark8. I am still running a stock fuel pump and injectors. Buy an SVT Focus green top per DLF's suggestion or get a new Motorcraft pump put in.

Oddly enough your A/F ratios look pretty steady at 13.0 all the way to the end of the pull which to me is pretty good unless they pulled it longer the first time and it was spiking lean??
 
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boylanp

boylanp

New member
Yeah I'll agree that the car has to be able to inhale and exhale. I'll have to start saving my dough up for a new exhaust. I thought that was kind of strange that he mentioned a booster also. I wonder if he was just trying to make some easy money for the shop.
 
boylanp

boylanp

New member
I finally got a chance to talk to the guy who tuned the car, and apparentley the lady I talked to before had me mistaken for another customer.
He mentioned that the fuel pump was at max duty cycle at 2500 RPM's when I brought it in, which maybe makes sense because of the extra air flow.
After tuning he said the fuel pump reached max duty cycle at 4000 RPM's, and that it started losing power at around 5400 RPM's.
DLF tipped me off to look into a Focus fuel pump which has a few more LPH.
I called airtex and talked to the tech support, and he assured me that my fuel pump was not the problem based on the old thumbrule that for each LPH of capacity of a fuel pump can support twice that in horsepower - which would be 550ish.
The fuel pump I have can support 550 hp, as far as he is concerned, and as far as the dyno tech is concerned, the pump is at max duty cycle at 4000 RPM's.
Hmm, I'll get it figured out.
 
Mad1stGen

Mad1stGen

Booster
I suggest you start a thread in the drivetrain section to figure this out.
Obviously there is some underlying issue as your typical stock fuel pump should keep up just fine with this stockish power level.
Either the Airtex pump wasn't installed correctly, or it isn't rated as stock one was.
Regardless, replacing it with an SVT focus pump is a good idea.
 
P

psychostang

Moderator
Hello and welcome. Fuel pumps don't have duty cycle's. Fuel injectors do. At WOT, the fuel pump should be getting full power. The FPDM's, are designed to reduce pump rpm via PWM during cruise and light loads. This reduces fuel heating and therefore emissions. My 96 has a seperate relay for WOT fuel pump power. I don't know if the Gen II's have this feature also. If it does and this circuit is inop, it could be your problem.
 
DLF

DLF

New member
Well....

In a Gen 2, using SCT software, the FPDM does report its output as a percentage via fp_duty_cycle. However, I don't know how accurate it is, as I've never seen a reading higher than 50%. In my logs the value ranges from 31% at idle to 50% at full throttle/redline. AFAIK there isn't a PID for fuel pump voltage.
 
P

psychostang

Moderator
I know that my start issue was due to the hose between pump and hat splitting and then popping a hole. The upper hose was overcrimped from the factory.
 
boylanp

boylanp

New member
I don't think it's a leak. I used the cut a hole under the back seat method to remove it and i haven't smelled any gas and the fuel mileage is fine. I'll start it and remove the backseat to verify. I've got an SCT tuner also so I can hook it up and see if the values are consistent with what DLF had. I appreciate all the input.
 
DLF

DLF

New member
If you're concerned about the pump, or about possible leaks between the pump and the hat (which is in the tank and wouldn't cause a smell), check the fuel pressure under load.
 
O

ONLYTONY

New member
Welcome

Welcome aboard. We need pics. And now that you did all that to your CE come and do it to mine:D:D Looks great but we want to see the whole car.
 
B

billcu

Head Moderator
DLF said:
Well....

In a Gen 2, using SCT software, the FPDM does report its output as a percentage via fp_duty_cycle. However, I don't know how accurate it is, as I've never seen a reading higher than 50%. In my logs the value ranges from 31% at idle to 50% at full throttle/redline. AFAIK there isn't a PID for fuel pump voltage.
Click to expand...
I think you're both right here.:)

The way I look at it, PWM and duty cycle are the same thing, just measured with different metrics. Frequency and percent.

When you Modulate the Pulse Width, you change the duty cycle of the waveform.:)
 
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