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Engine Management, Fuel, Spark, EGTs, and Air/Fuel Ratios This forum includes general electrical, modification, tuning, repair, replacement, identification and restoration of all components mentioned above including SMEC, SBEC, Logic Modules, aftermarket engine management, etc. Nitrous oxide posts go in here. This is the place

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Old 04-21-2005, 12:54 PM   #1
"Bouncing" fuel pressure after Accufab  
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prior to installing my new accufab AFPR i hooked up a fuel pressure gage to see what my current pressure is with the original Bosch unit, gage was rock solid steady at 48 psi.

installed the accufab, now the fuel pressure needle "bounces"....no matter where i set the pressure, needle shakes and no its not from the engine i am holding the gage in my hand. right now, needle is bouncing from 47-50 psi at about 3 cycles per second.

any ideas why this is occuring? thanks for the advise.
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Old 04-21-2005, 01:27 PM   #2
 
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How old is your fuel pump? Perhaps the check valve in the pump is on the way out?

FWIW, my fuel pressure was just as stable with the OEM regulator as it was with the Accufab, using the same gauge.
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Old 04-21-2005, 03:34 PM   #3
 
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thanx, got the new walbro 255 sittin here, ready to install prob next week, i believe my car has the original fuel pump in it, and original filters........whoah not good for the upcoming 20 psi engine.

but if it is fuel pump related, why then did i see no bounce w/ stock regulator? i mean i am still using same pump w/ the new accufab.......and ideas?
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Old 04-21-2005, 04:39 PM   #4
 
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Is your gauge liquid filled? Not sure why it would be any less stable with the Accufab than the OEM regulator unless there may be an internal problem.

I use a non-liquid filled gauge and the needle shakes a little bit, but it's good enough to estimate the base pressure. I may upgrade it with a glycerin filled gauge but it seems OK.
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Old 04-21-2005, 04:54 PM   #5
 
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no this is a hand-held gauge not installed permanently to the engine, so, its not liquid filled (liquid filled ones are designed to be mounted to a vibrating engine, liquid cushions the bounce due to engine vibration)....like i said before the accufab was installed the same gauge was rock solid steady, the only change was from the Bosch FPR to the Accufab AFPR, no other changes at all.....but now i got this bounce in the readings using same exact gauge........

guess what i am wondering is: do i have a defective AFPR?
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Old 04-22-2005, 04:55 PM   #6
 
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minimopar has really helped outminimopar has really helped outminimopar has really helped out
Try pinching the return hose to get the pressure up above the target regulated pressure. If the bouncing goes away, I would say it was the AFPR. Do are doing this with the vacuum lines disconnected, right?
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Old 04-22-2005, 04:58 PM   #7
 
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crazy thought: air in the line between the FP source and the guage?
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Old 04-22-2005, 08:45 PM   #8
 
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bled the air in the fuel pressure gauge, and pinching return line doesnt stop bouncing.

btw, (2) people using AFPR's have PM'd me saying the bouncing needle is normal and to not worry about it...
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Old 04-23-2005, 03:06 PM   #9
 
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What you're seeing is probably the "piston" in the FPR moving to control the pressure. It may be bigger in the Accufab regulator than in the stock one, and as such moves slower.
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Old 04-23-2005, 04:57 PM   #10
 
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^i was thinking same thing....the stock Bosch unit is not adjustable, perhaps only the adjustable regulators have this characteristic. i guess i need to ask people with AFPR's to comments on their experience with fuel pressure gauge behavior as the non-adjustable types might be an apples-to-oranges situation.
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Old 04-23-2005, 06:41 PM   #11
 
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Accufab unit and a fixed mounted autometer guage here and no bouncing. Guage is on the feed line just before the rail.
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Old 04-29-2005, 05:40 PM   #12
 
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+1 liquid filled isolator no bouncing...
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Old 04-30-2005, 06:50 AM   #13
 
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I am installing an Accufab AFPR today and I will report back what my guage does. Mike
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Old 04-30-2005, 01:53 PM   #14
 
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Put the AFPR on my T3 today and the guage read steady. I did have a couple of installation problems- I had to space out the regulater because it would not fit quite right and had a hard time finding a fitting that would work on the regulator outlet. I ended up using a GM fuel line the kind for fuel injection with an o-ring and putting a double flare on the the other side. The AFPR came with directions for a Grand National so I kind of thpought I would have to use this line.
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Old 04-30-2005, 05:25 PM   #15
 
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accufab universal adjustable here, no needle shaking.
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