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how to preassure test OEM fuel pump?

Joined
5 January 2011
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1,604
Location
Southern California
I am going CTSC this week and I have been advised to change my fuel pump to make sure I have good fuel delivery. But I dont want to spend money or time if not needed.

Any way to preassure test the fuel system to see if its working optimally? If so, how? and what psi should it read?

Thanks.
 
See page 11-87 in the '91 service manual. There's a pressure service port right above the fuel filter. At idle you should get 36-54psi. However, it's most critical to test it at wide open throttle near redline, since that's where you need the most flow. Either read a gauge in the engine bay while on a dyno, or use a remote gauge in the cabin and have someone read it while you run around on the street. Pressure should be 46-53 when you have it floored. If it drops below 46psi you likely need a new pump.
 
I am going CTSC this week and I have been advised to change my fuel pump to make sure I have good fuel delivery. But I dont want to spend money or time if not needed.
Mmmh, well, a new fuel pump is like an insurance with the CTSC. The CTSC adds fuel and runs rich in boost. Running lean -> BOOM.

How old is your fuel pump? My OEM was two years old, that was fine for me. But I'm going with a Walbro 255 in the future to throw the voltage booster electronic out.
 
For less than $200 (plus labor) you would have plenty of insurance against needing a new motor.

I'd hate to hear about your blown motor and how you should have bought the fuel pump...
 
What Deadalus said. Btw.. I miss that show :(

Unless you get an expensive set of gauges with an electronic sending unit it's hard to monitor fuel pressure from the cabin. The cheapest way to do this is via a mechanical gauge (usually on top of the fuel filter) but the car has to be on the dyno or you can get creative with a GoPro pointed at it while driving. I have an unopened B&M mechanical gauge I never used if you're interested.

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Just some additional thoughts for other people looking into this (been getting a few PM's on CTSCs lately)...

I'm certainly no expert but I've done quite a bit of tuning on my own lately and have learned quite a few things. This is running with a 7lb Autorotor on a Walbro 255.

1. The stock CTSC tune is designed adequately for a street driven car running the OEM fuel pump (read: OEM pump flow rate). It's not perfect especially during mid throttle and street driving (the AFRs are sort of all over the place) but at WOT the AFRS are pretty consistent. Some may think this isn't a problem. Some may be a lot more anal and consider this unacceptable for their beloved NSX. History has proven it's been fine *shrug*. YMMV

2. Our cars are much older now. Factory pumps are tired. You'd be remissed not to upgrade to a better pump (Walbro, Aeromotive, Denso, etc) if you're going thru a new pump install anyway. If you install a higher flow pump (i.e. Walbro 255 like did) it will run pig rich with the base CTSC tune (well, it did with mine). My AFRs were in the 10s. After some meticulous tweaking of the RRFPR i'm back at 12.3 WOT but my mid throttle AFRs are still bouncing around a bit.

3. I don't think removing the Boost-a-Pump is a good idea. 12.3 AFR for me can only be achieved at approx. 105-108psi fuel pressure. I have the logs to prove it. That's at the factory ECU controlled injector pulse widths. I'd be very curious if w/o the boost-a-pump you can still maintain that high of a fuel pressure. I'm eager to try myself if I had more time. goldNSX please keep us posted.

4. For an occasionally track driven car i'm simply uncomfortable using the RRFPR and running those high of fuel pressures. Therefore i've decided to try the RDX injectors, 1:1 AEM FPR, and F/IC. If Prospeed comes up with a base NA tune at 56-58psi i'll incorporate that as well.

5. Will you be ok on your old factory fuel pump. Probably, but if you value your motor at all it's a good idea to keep an eye on that fuel pressure at WOT and your AFR. The problem is.. if it decides to take a crap midpull it's sometimes too late. Just like if the injectors lockup at 100psi of pressure. It'll often be too late.

Ironically the limitations of the Comptech fueling is what everyone's been saying here all along. I just like to learn the hard way I guess. :smile:
 
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