My68

I just purchased a 70k all stock 1988 from the 1st owner. Its very hard to start (4 or 5 attempts) So far Ive confirmed 40 pounds of fuel pressure at idle, however with just turning the to on ( without starting) I get a little more then 40 pounds for a few seconds then I hear what sounds like the brand new fuel pressure relay clicking then the FP goes to zero within a few seconds. I've tried clamping the return line with the car running (and not running) with no effect. I had my daughter turn the key to On without starting it and then clamped the main fuel line and again no effect. Pressure always drops to zero. I know the fuel pressure regulator is working fine without any leaks. Could injectors leak down that fast. It seems to idle fine ( but the plugs looked a bit black. Thanks in advance for any ideas.

Purple92

Leaking down to zero in a few seconds is not normal.

You could have a defective fuel pressure regulator, one or more leaky injectors - or even a defective fuel pump (I believe there is a check valve in the pump output side that doesn't let fuel flow backwards).

Clamping the fuel return line is one of the normal checks for the defective regulator - but clamping that line shut isn't the easiest thing to do - so unless you're sure that you have eliminated the possibility of fuel flowing through the line - don't be 100% sure the fuel pressure regulator is not the culprit. If you successfully clamped the line shut with the car idling - the fuel pressure should increase significantly...

I'd say your next step is probably to pull the injectors and see if they leak.

You said you pulled the plugs - did any of them look more fouled than their neighbors ??? (New plugs aren't expensive - maybe you want to throw a new set in and see how they look after 10 - 15 minutes of idling.

One other relatively easy test to do is to try starting it while a helper watches the fuel pressure - once you crank the engine - the fuel pump relay should keep the pump on. If you don't maintain fuel pressure while trying to start the car - that's guaranteed to cause the hard start. (I'm not 100% sure about the L98 motor - but on the LT1's (92 and on) - it's the oil pressure switch that supplies power to the fuel pump once the engine lights - so if there is a problem here - you're basically cranking long enough to build up oil pressure t the top of the block...

GREGGPENN

I would consider the possibility you have a shorted coil (or two) within injector(s). Because the O2 sensor only exists in one bank and only monitor half the cylinders, failure on THAT side can cause the other injectors to compensate (get richer). The result is black plugs and if the injector is stuck, fuel will leak right out of that injector.

Checking the resistance of your injector coils (across the plug contacts) is an easy way to diagnose this. If all don't measure approx the same (probably 16 ohm), THEN pull them for a new set....or, at least diagnosis.

FWIW, mechanics have an injector balance tool that can also let you know how the injectors are behaving. This does not require removal of the plenum, tubes, and rails to diagnose.

Kubs

These guys are on the right path. I will mention one issue I had back when my car was street driven. There are 2 coolant temp sensors. One in the head to send info to the gauge in the dash, and one in the front of the intake to send info to the ECM. The one in the intake went bad and caused long starts. Basically the temperature reading was off and the ECM was compensating by adding more fuel. I had really long starts as well, unless I held my foot to the floor while cranking (like a flooded carb) and fed the engine more air to go with the extra fuel. It fired up in seconds. This one was kind of random, but thought I would suggest it as well. Hold your foot to the floor and see if it starts quicker (obviously let off once it starts), that could tell you if your getting too much fuel from somewhere.

383vett

How do you test for leakage after pulling the injectors?

aklim

So you turn the key and with the return line at the tank crimped off with a hose crimper, NOT VISE GRIPS, you get 40 and it falls off quick? Lets try this also. It is a 2 man job unless you want to short the fuel pump circuit. Have someone turn the key and observe it get to 40 psi and you crimp the feed line. It should hold pressure. If it doesn't, you have a leak between that point and the return line. So if the FPR holds, injectors are leaking. In any case, I'd dump the old Multecs and get reman Bosch 3 from FIC and be done. They are probably crudded up to some extent anyways.

I don't place much stock in plug reading for EFI since the ECM changes the mixture often.

aklim

I don't think so unless they changed the circuit. Up to 91, and I'm looking at the circuit, the oil pressure is a backup

aklim

That would require he either buy the tool and use it as a X'mas ornament to get some value from it or pay someone with the tool to do it. I'd get a set of reman injectors that are tested and NOT Multecs. It's going to cost him probably a couple hundred bucks for labor.

aklim

Flow Bench?

Kubs

If the factory retainers on still in the fuel rail you could pull the rails out with the injectors still in them and turn the key on. Then see which ones spray or dribble fuel. Or you could use zip ties to hold them in the rail if the retainers are gone.

aklim

That is a lot of work to see if it leaks. Why not forget the whole thing and get a reman set and KNOW that it has been tested as opposed to seeing if this one leaks or not? It is probably varnished up to some point. Probably has Multec.

OP. does the fuel injector look like Multec?

GREGGPENN

Or, like me, borrow from a friend. It never hurts to know what options are out there for diagnosis.

383vett

I talking about a typical backyard mechanic

aklim

It takes a cup of SWAG and a sprinkle of wishful thinking.

aklim

Good point.

biggiefl

I just got a set of reman Bosch from FIC at $349 for 16 so cut that in half for price of 8. Mine are yellow. Not sure if LT5 are dif than L98 but I doubt it.

Purple92

Ok - Looking at the wiring diagram for a 1992 - you have power coming from B+ thru a fusible link to terminal "C" on the oil pressure switch. When you get oil pressure - the oil pressure switch closes - and power is applied to terminal "D" on that same switch. Power then flows to a junction. The other side of the junction is the output (Terminal "1") from the fuel pump relay. After the junction - power then flows through the fuel pump fuse to the fuel pump.

We can spend days discussing which is the primary and which is the secondary power supply to the fuel pump - but the fact is that if either the relay contacts or the oil pressure switch contacts are "closed" the fuel pump will run ...

ctmccloskey

I have a 1988 Coupe that was doing something similar to what you are describing and it might be worth checking at least.
In the back of the intake manifold is a switch which verifies the car has oil pressure when cranking. My car had a loose connection at one of the two connectors back there. Somebody had removed the factory connector and replaced it with a poorly installed one. If I pushed it in and seated it just "right" the car would start and run with no problems. When the fitting got loose it would make starting very difficult at times. Like you I had good pressure at the fuel rail but the Fuel Pump relay was shutting off the flow while cranking the car.

My 1988 maintained some pressure on the rail for several hours up to days after the last running. After a couple years I noticed the pressure dropped faster than my car normally did and found one of my injectors had started leaking gas. The oil smelled like gasoline when I changed it so I am glad I stopped it when I did. I bought a set of rebuilt BOSCH injectors from South Bay Injectors for less than $100 and that fixed my fuel pressure issues

Another weird thing I ran into was the electrical things were not always working as they should. It turned out that my fuse block and fuses themselves had corrosion on them. When I pulled the fuse it would look okay as you could see the fusible element inside was still intact. But when I measured their continuity with my meter there was none. The fuses had a fine layer of corrosion on them and that blocked any current transfer through them. I cleaned the fuse sockets with a old points file but a fingernail or Emory file would do in a pinch. Then I installed new fuses and many electrical gremlins went away. I also found corrosion on the grounds inside the car, after cleaning the connections from the battery back I was able to see full battery voltage at the radio power wires.

Good Luck with your 1988 Corvette, if you don't have them already be sure to get the Factory Service Manual AND the Electrical Supplement for your specific year. They are the best thing to have if you own a Corvette and can be a real life saver at times.

Good Luck with the "gremlins" in your fuel system!

Purple92

[QUOTE=ctmccloskey;1595808228]I
In the back of the intake manifold is a switch which verifies the car has oil pressure when cranking.

And that would be the oil pressure switch !!! Actually - it is closed (Current Flowing) whenever the car has oil pressure - not just on cranking.

aklim

As long as it sees 3 to 5 psi, IIRC, it will close. Regardless, you can disconnect it and the car will run. BTDT.