My 89 IROC has a strange ticking noise until it warms up. This is not an internal engine noise or exhaust leak. It sounds a lot like a relay clicking on and off. From inside the car it actually sounds like it is in the dash, but I think it may be the AFPR. It does not make the noise if you are sitting still. When you go in gear and move everytime you push on the throttle you get a fast paced clicking sound. Cruise at an even pace...nothing. Push on the gas just a tad.....click, click, click...very fast paced. Back to steady state cruise and it stops. Once the car warms up it stops.
Another reason I think this may be related to the AFPR is that I have a consistency problem with my AFPR. When it is cold out the Fuel pressure can go up 10-20 PSI vs when it is warm out. It seems I have to constantly readjust it. I have compared my on car gauge to a hand held one and it isnt the gauge, it is definitely changing.
Looking for some feedback on how to tackle one or both of these problems.
Thanks,
Roy

 

That certainly sounds like a description of an exhaust leak, especially since it evidently stops once the engine is warmed. Are you sure there are no manifold cracks?

The FPR relief point is dependent upon pilot vacuum, the relief spring, and the hydraulics of the pump and return line. I suppose temperature could have an effect upon the relief pressure, but any change in pressure induced by temperature should be very gradual (and probably minor) change as opposed to something rapid enough to create noises.

 

Vader, I guess it could sound like an exhaust leak in my description now that I look at it, but it doesnt sound anything like an exhaust leak in person. Not RPM related, and way too loud and metallic. Sounds like a mini jackhammer turned on and off by touching the accelerator pedal.
And you dont even have to change the RPM much, you can be cruising at 30 MPH in OD, touch the pedal just a tad, and instant jackhammer.
I dont understand the change in FP either, but it is definitely happening.
Doing a search here and on Vetteforum did yield me other people who have had a clicking/ticking/hammering FPR but no cause or solution was ever reported.
I just didnt want to replace it if there was another problem.
Roy