Hello,
1987 Corvette coupe auto. I am pretty sure I need injectors as they are original to the car. I also suspect the fuel pump for the same reason. The car starts fine when cold, and starts harder when warm. I suspect I have a drop in pressure at the injectors. I tested the fuel pump with a fuel pressure gauge. I get 40 lbs at the turn of the key. Pressure drops to 35 when at idle. Stayed steady at 35 lbs for 10 minutes at idle. When car is turned off the pressure goes back to 40 lbs. then a pretty quick drop in pressure...the pressure dropped to 15 lbs in 12 minutes. Stayed steady at 15 lbs to finally 0 in a total of 40 minutes or so. I also hear the pump whine at a quarter tank. I also almost ran out of gas last week at quarter tank. Forgot to mention that the vehicle has developed a noticeable miss while cruising. I've studied this forum and it's search ( great by the way on both) but want to be sure. Is my pump failing and should I replace. I'll do the injectors in spring when time and money are more plentiful. Thanks again for any advice

Kevin

 

Bump for the end of the weekend

 

I would think your numbers say the fuel pump is OK. I would suspect bad injectors or maybe a bad fuel pressure regulator. You can search these online for a lot of information.
The miss could be a lot of things. Do you know when the last tuneup was and when the plugs and wires were changed?.

 

Thanks for the quick reply. New plugs, cap, and rotor 2 months ago. New wires last year. Checked the FPR the only way I know how...pulled the vac hose. No fuel there. I'll replace the FPR in the spring when I do the injectors for good measure. The miss isn't real bad and the car can still be driven fine. I washed the engine down carefully 6 months ago and I read now that I could have messed up the opti-spark. Could I have caused a problem there. I usually hear horror stories when they fail. Mine not too bad. Thanks again

Kevin

 

Unless your motor has been replaced with a LT1 or later engine it does not have a opti-spark. Is the distributor at the back of the engine or front?

 

Lol. This is why I am not a mechanic. The distributor is in the back. Good to know that and thanks for clarifying for me. At least I am not looking at an expensive repair. I did burn a wire a bit back but it did not burn through. The ohms still seem right. I have tested other wires but still a slight miss. I will get another set and try that

Thanks again
Kevin

 

yeah, its time.

your pressure is ok. the leakdown rate is not acceptable though. The fuel is either going BACK to tank via a bad pump check valve, or thru the injectors, which I DOUBT. That much fuel that fast would result in a hard to start engine from being semi-flooded.

If the regulator vac test is ok, you can test the pump by pinching the return line THEN see how long it takes to loose the pressure. A decent system should hold in the 30s for a couple hrs....and not fall to 20 for 6-8 hrs. And hold at 20 over-nite.

Time or age, those stock injectors are due whether they work or not. Alcohol ruins these and they are partially clogged in the inj screen. Nozzels probably are not spraying as they should...spraying wet instead of atomized mist.

Call Jon @ FIC and he will fix you up. Time to rebuild the rails as well....all new O-rings will help you avoid a car-b-que. Don't skip that step...rails will leak bad with old hardened O-rings.

Until you buy the stuff you can pull some plugs and see what they look like. There will be a few that will be brown or darker than the others...that indicates inj spraying too much fuel or a rich condition. Bleached white can be clogged injectors.

BTW,
your 1/4 tank problem is common. There is a windage tray in the tank that breaks off the bottom and floats away. The pump now starves for fuel every time you make a turn under 1/2 tank. This WILL burn up the pump since its cooled and lubed by gasoline...
If this has been going on for a while...just get a new pump and be done with it. As pumps wear from running dry even for a second the wear particles off the rubber impeller go thru the system clogging the filter, the tank screen AND the injector baskets...Hello.

The 'fix' is to construct a "well" for the pump to sit down in so its never uncovered with fuel. I would buy a better pump BECAUSE at higher rpm this stock pump barely keeps up with demand by the engine, and add a clogged injector, the faster you go the more it starves for gas. If the car will stay stock, then a stock pump (good brand at least) will be ok for new injectors.

PS
buy the FSM set or you will never see the end of the guess work. The FSM would have this diagnosed for you long ago......and been right. Those books are a GOT-TO if you plan on doing ANY of your own work on the C4.

 

Thanks Leesvet for the information. I do gave a hard starting issue when warm thus my initial suspect injectors. I will test the fuel pump return line following your directions..I will replace the fuel pump either way but I like to learn a bit as I go. What is a good quality pump for me to get? Thanks also for the fuel rail suggestion. I will rebuild it also

Thanks again

Kevin

 

Most here would agree that the Racetronix pump is a good upgrade and has been reliable too.
There are lots out there...finding one that's affordable yet still an upgrade is all about shopping. Be sure to look at the catalog stores...madvet, eckelrs, corvette America///others..