Pinging

hytorksc

Registered User
Can a weak fuel pump cause part throttle pinging?

I'm getting 32psi fuel pressure at idle and 52psi at full throttle- is this bad?

I'm still having issues with this. It seems to come and go, and it only happens when accelerating hard but not WOT. I've done just about everything I could to stop it including changing gas brands. I only use 93 octane btw.

Does this sound like a intermittent problem with the knock sensor?

thanks-
 
boost is at 16 psi peak

dave,

it maybe more like 17 psi. i have a 5% OD pulley on a heavily ported early model supercharger. the thing is just too damn efficient. however i do use the stock exhaust with ported collectors and some porting on the resonator. if i put the stock pulley back on it still pins the needle at 15 psi at 5k+ rpm. It make a lot of boost very early like 11 psi at around 2.2k rpm. my cats are not stuffed at least i dont think they are because i am getting awesome torque from standstill. i get wheelspin up to 45 mph on a 50 degree day. is this normal output behavior for a mildly modded sc (no bottlenecks on the intake tubing except for the TB, and thats modded too)?

even with all that boost, i'm not getting hardly any pinging at WOT which leads me to believe that it's not leaning out on top.

i don't know, maybe it is- it all happening in the upper rpm range except for WOT (well maybe very slight but not all the time).
 
How are you measuring the fuel pressure. The reason I ask is because the fuel pressure regulator is designed to increase pressure pound for pound with boost.

Static pressure is 39-40 psi, so you should be seeing 54-55 psi with 15 lbs of boost.

Are you still running 30# injectors ? If you really are able to run low 14s or high 13s...you need bigger injectors.
 
Dave-

What i did was connect the FP guage onto the fuel rail and measured it at idle and then quickly moved the throttle to wide open by hand and noted the peak response, which was 52 psi. the only load was the engine itself.

did i need to measure it while driving to present an actual load on the engine, then measure it? if that's the case i don't think fuel pressure would have gone much above 52 psi. or am i wrong about this?

i don't have a timeslip to prove that i'm running low 14's or high 13's (i'm afraid to take it to the track for possibly blowing the HG's), i extrapolated this by the car's behavior in accelerating to 60 mph in under 6 seconds using a stop watch and it's behavior with other sports cars. I have accelerated toe to toe with older stock BMW M3's and keep up with WS6's (neither one of these can actually outrun me up to 100 mph), which both run about low 14's or high 13's. If you're running low 14's you are topping out around 98 mph in the quarter, and 13's around 100 to 105 mph likewise.

i think this is a reasonable assumption, i did not quote any tenths here- if i'm not in the low 14's, i know i'm definitely running 14's with the mods i have. i should be running at least low 14's with the mods on this car (it feels like it- i know what a strong stock mustang 5.0 with manual trans feels like and my car is faster with the aod).

sorry i got off the subject a little
 
I think you need to rig the gauge so that you can watch it while driving the car under a load. Boost and fuel pressure will get higher than quickly reving the motor.

What you want to see, is if the pressure stays constant under a load at wide open throttle. If the pump can't keep up, pressure will start dropping off as rpms increase. Since going lean makes more power initially, you can easily be fooled into thinking you have plenty of fuel when you are actually dangerously lean.

To do it right, you need to put the car on a dyno with a wide band o2 sensor to verify the A/F ratio while having someone watch the fuel pressure gauge. The fuel pressure isn't nearly as important as the air/fuel ratio. Wide open throttle A/F ratio should be around 12.4:1 to 12.7:1 for best power and safety. Anything leaner than 13.7:1 is likely to damage the engine.

Hope this helps.

David
 
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thanks-

thanks Dave-

I don't have access to a dyno in my area nor do i have the money to put this car on one. I could buy a long tube for the fuel pressure gauge to verify while driving under true load. should i just go ahead and put wide band o2's on it and find someone with a tuner and dial in the A/F ratio assuming the fuel pressure is ok?

Or-

Would it make more sense to just install a higher pressure fuel pump and an adjustible pressure regulator to increase fuel pressure by 5 psi or so?

i can't afford to go the full blown route, but i would absolutely hate having to either pull the octane plug and/or go back to the stock pulley- the car feels really great right now.
 
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You can get away with the larger pump and adjustable regulator for awhile (get the 255 lph forced induction). Eventually the EEC will re-learn and dial out the extra fuel provided by increasing the pressure, so you need to disconnect the battery about once every two months to reset the EEC.

I did the same thing for about a year and never had any problems.

David
 
found another way

experiment:

inserted a 25k resistor on the intake air temperature sensor lead to make the EEC read the intake air temperature a little warmer thus backing off timing very slightly and probably adding a little more fuel. The IAT sensor range is around 12k ohms when heated up and 30k ohms when cold. The leads going into the sensor measure 17.2k ohms. All i did was shift the average range a little which should not hurt anything. I dont know if the EEC will tune this out though- i wouldn't think so. When it gets really hot in the summer it would be interesting how my car performs with this mod. Anyway, i drove around and my performance did not degrade at all, but the pinging stopped at all throttle positions. Seems to be working fine for right now, only time will tell. the car seems to like it- not throwing any out of range codes yet.
 
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