Fuel Pressure question

My stock 96 Imp has been running poor lately. Missfiring, rough idle etc. The fuel pressure is showing at 38 psi. I think it should be 42+. If i pull the vacuum line it jumps to 60 and the pressure increases if you rev it when the vacuum drops. So I thought it might be the fuel presssure regulator and swapped on one than was on an L99 engine that I had. It still shows 38 psi at idle. It appears that if it had low low idle vacuum it would increase the pressure, so it isn't a vacuum leak.

Assuming that it is a fuel pressure issue, is it likely to be the fuel pump or pressure regulator?

BTW, last fall I installed a salvage yard Opti, new plugs and wires to overcome some similar issues.

Pete

Idle FP with vacuum line on and stock cam will drop down to 35 or so. Bigger cams will pull less vacuum and won't drop the FP as much.

I think my idle fuel pressure with a 227/235 cam was 37psi? I wouldn't worry about your idle pressure being in the high 30s as long as with the line off it jumps to ~43.

Thanks for your thoughts.
So if it isn't fuel pressure, my experience is that it could be Optispark issues.
When Opti's go bad is it usually electronic or physical issues & moisture? In other words will a new cap and rotor and dry out fix them?
I have a few Opti's. When I try and remove the cap's retainer screws they are corroded in and break off. Do new caps come with new screws? Do you typically have to drill out the old ones and find the right metric tap?
Just planning my next move.
Pete

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Originally Posted by rwd_pete

Thanks for your thoughts.
So if it isn't fuel pressure, my experience is that it could be Optispark issues.
When Opti's go bad is it usually electronic or physical issues & moisture? In other words will a new cap and rotor and dry out fix them?
I have a few Opti's. When I try and remove the cap's retainer screws they are corroded in and break off. Do new caps come with new screws? Do you typically have to drill out the old ones and find the right metric tap?
Just planning my next move.
Pete

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The idle FP doesn't necessarily rule out fuel issues, just means that your regulator is working. You need to hang a gauge off it and check the pressure under load - you may have perfect pressure idling and simulating WOT with vacuum off the regulator, but if your fuel pump can't keep up then at load it will fall off. My last build ran and drove fine, pressure checked out fine, but when I put it on a dyno I found out the fuel pump was going and it was starving the car above ~5k rpms.

Opti's usually go bad from either waterpump leaking from the weep hole right above which ruins the sensor, or improper vacuum routing causing ozone buildup and corrosion. I don't know if all new caps come with screws, but my MSD one did.