I noticed that my fuel pressure fluctuates rapidly while running. The variance is only around 4 psi. It didn't used to do this. I don't see anything in the service manual about a pulsator on this car. Does it have one? Where? I can actually feel the pulsation when holding the gauge. It still seems to run fine. It is a '92 Z with the L98.

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'92 Z28
5.7 TPI
T-56 six speed
Pro 5.0 shifter
3.73's
SLP 1-3/4" Headers
SLP Cat-Back
52mm TB
Extrude Honed Intake/Ported plenum
Hypertech Prom

 

Is it a water filled gauge? Analog gauge or interior mounted electric?

It could be a number of things.

How many miles on your fuel pump? Not sure abou the pulsator. Its located in-tank if you have one.

Fuel pumps inability to maintain consistancy could also be related to the pump. pray its not that. Maybe debris in your pressure regulator.

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom cold air intake w/K&N, SLP airfoil, ported plenum, Crane AFPR (47psi),Crane Ext Alum 1.6 full roller rockers, Timing set from 4*BTDC to 10*,MSD6AL, Holley 9mm Annihilator wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, Slp 1 5/8 headers and catback (all stainless steel!), 3:73s,JET 195* fan switch, Macewen white face gauges, Intellitronix Digital Gauges

Stock throttle body, runners,intake manifold,cam, and heads.

 

Asuming you are using the same gauge as before, you may have had some/a slightly leaky/dirty injector(s). If they/it were cleaned/replaced/cleared out on its own then it would pulse more now that it would be sealing good between pulses.
. Another posibility is that if the previous testing was done in warmer weather or on a warm engine and currently your testing is in colder weather & maybe a cold engine, that could be your difference. When I first fire my engine cold I get a little twitching in my dampened gauge. After running about 30-60 seconds or so it smooths out.

My '86 had a pusator on the outlet of the stock fuel pump. If the pulsator is cold it won't work as well. The rubber would be stiffer when cold.

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• 355 cid
• AFR heads
• Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
• modified SLP runners
• TRW forged pistons/ceramic coated
• fully balanced
• Edelbrock headers/ceramic coated
• SLP cat-back
• Paxton supercharger
• Nitrous Express nitrous oxide

My IROC-Z
EFI Performance Club on Yahoo

 

It was a plain ol' test fuel guage, "air-filled". I think it started after my car sat for a few months wiich makes me suspect something clogged or eroded.

Also, has anyone noticed excessive backfiring if the fuel pressure is too high (even by 2 psi) and the car coasts in low gear with the RPM above 2000. Mine started after I installed the six speed. I noticed I can make it go away by lowering the fuel pressure. I guess I need a new prom b/c I went from auto to manual?

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--------
'92 Z28
5.7 TPI
T-56 six speed
Pro 5.0 shifter
3.73's
SLP 1-3/4" Headers
SLP Cat-Back
52mm TB
Extrude Honed Intake/Ported plenum
Hypertech Prom

 

Your running rich if its backfiring. I had the same problem. Its simple, un-burnt gases. Have your friend rev up the engine and watch for black smoke. A custom prom would certainly help the problem. Do some fine tuning. Play with your timing. Try not to run THAT rich. I have found power is made when your lean right until it knocks.

As far as the car siting..that is a possiblity also.

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom cold air intake w/K&N, SLP airfoil, ported plenum, TB coolant bypass,Crane AFPR (47psi),94 octane,Crane Extruded Alum. 1.6 full roller rockers, Timing set from 4*BTDC to 10*BTDC,MSD6AL, Holley 9mm Annihilator Laser shot 50 wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, SLP 1 5/8 headers,SLP catback,3:73s,JET 195* fan switch, Macewen white face gauges, Intellitronix Digital Gauges

Stock throttle body, runners,intake manifold,cam, and heads.