Help! 1990 corvette runs terrible, slow as 1960 vw, mayhbe not quite.

[georgekthompson]

My 1990 Corvette standard started running sluggish 1 year or so ago. It only has 38,500 miles. Engine will rev to 6000, but not rapidly.

I have changed plugs, plug wires, tested module, coil, new cap and rotor. Fuel pump was changed in June, the new one was changed because the check valve was defective. Now the car is slow!!!! It idles good some times and other times I need another foot to keep it because it is rough and will stall, it then starts but not as easy as when it has been shut off after running good.

I checked fuel pressure today. No pressure after sitting from yesterday. key on 60lbs down to 25lbs immediately after the 2 second run and to 5lb within 60 seconds. fuel pressure 70lb at idle and drops slightly with bumping accelerator. Did resistance test on injectors but not the light test on wiring. Fuel pressure regulator vacuum tube did not have gas in it nor did it have gas odor.

What do I do next, thinking of changing the injectors since car sat for long periods prior to my purchasing 4 years ago, but it ran fine then.

I appreciate any info
George

 

[Kevo]

Check fuel pressure regulator for leaking fuel out vacuum port. With drop in pressure fuel has to be going somewhere. If this has been going on for a while cat converter could be restricted.

 

[Scottsredvette]

Check fuel pressure regulator for leaking fuel out vacuum port. With drop in pressure fuel has to be going somewhere. If this has been going on for a while cat converter could be restricted.

His description of how it runs/acts sounds just like when my pre-cats plugged up on my 89. New "off road" y pipe and all was good. Just a thought...

 

[georgekthompson]

follow-up

Check fuel pressure regulator for leaking fuel out vacuum port. With drop in pressure fuel has to be going somewhere. If this has been going on for a while cat converter could be restricted.

not leaking fuel from vacuum port

 

[Kevo]

for fuel pressure to bleed off the way it does fuel pump check valve is not holding or pulsator, a diaphragm between fuel pump and sender to reduce noise,is leaking if present. Leaking injectors, or FPR not sealing. If exhaust is disconnected from front of cat converter or disconnected from manifolds how does it run?

 

[forrest]

for fuel pressure to bleed off the way it does fuel pump check valve is not holding or pulsator, a diaphragm between fuel pump and sender to reduce noise,is leaking if present. Leaking injectors, or FPR not sealing. If exhaust is disconnected from front of cat converter or disconnected from manifolds how does it run?

First thing I think that fuel pressure is to high if memory is correct it should be closer to the 35 PSI running and all connected and running. I tend to agree with a possible clogged Catalytic converter, or even a stuck EGR

 

[georgekthompson]

follow-up

Thank you for the quick response
I will look at EGR and check for stuck injectors, but I am away for next week.
I replaced fuel pump last spring and had to replace it due to inoperative backflow valve
Will keep looking when I return

 

[Scottsredvette]

Thank you for the quick response
I will look at EGR and check for stuck injectors, but I am away for next week.
I replaced fuel pump last spring and had to replace it due to inoperative backflow valve
Will keep looking when I return

When you check the cats, don't forget that our C4's have pre cats in the front Y pipe. Those are what plugged on mine. I got rid of that Y pipe, went with a pipe without pre cats and to keep the fine people in the Colorado emissions program happy, I went with a high flow main cat.