L98ina25thZ28

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

theformula

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.

IROCKZ4me

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

L98ina25thZ28

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

theformula

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.