What’s up y’all?

I just picked up my first corvette; its a 1986 and I love it but I have been having some issues with the fuel system that I'm hoping you guys can help me out with. Basically, it starts when it wants to and idles rough. When it actually drives, it runs and pulls great. It will; however, sometimes stall when driving and usually starts back up although recently i haven’t been so lucky.

Things i know:

1. Fuel pressure at the fuel rail is only intermittent; when there’s no fuel pressure, it won’t start (obviously). When there is, it’s normal (40 lbs) and holds after the car has been shut off (drops ~10 lbs/ hour). When there’s fuel pressure the car still idles rough.

2. I’ve replaced the fuel pump relay and the fuel pump. The wiring and hoses looked okay during the fuel pump install. I’m not a mechanic and i could have possibly installed the pump wrong although it was pretty straight forward.

3. Wiring is a mess on this car. The previous owner has everything cobbed up.

4. When the car stalls, I’ve noticed fuel pressure is dropping. Just today I took it to the end of the block; fuel pressure dropped to ~20 lbs and the car started to sputter but returned to normal after a few seconds.

5. CEL is on for code 33 which I believe is the mass airflow sensor (possibly causing the rough idle?). The intake is aftermarket but again looks very cobbed up.

6. There’s a draw on the battery (possibly unrelated). Battery and alternator appear okay. I’ve yet to use an ampmeter to try to find the source of the draw. It very well could be unrelated to the fuel issue.

7. The previous owner tells me there’s new plugs, wires, distributor, and fuel filter. The wires do seem fairly new so i sort of believe that.

Anybody have any ideas what to check next? I'm thinking maybe the regulator; theres a faint fuel smell in the vacuum line but no raw fuel. I'm thinking it could be an electrical issue too. All I know is that I drove it 50 miles the other day with absolutely no issues other than the rough idle. Now i can’t take it down the block without stalling.

Thanks in advance for any advice!!

 

That connector tucked behind the bumper can be an issue. Also, maybe a bad FP regulator, but I would think bad connection first. Was the old pump actually bad? Did you test it after you removed it? I almost changed one a few months ago until I tested it in a container with mineral spirits. It wasn't the pump, it was the connector.

 

The connector appears okay, no corrosion or anything, the wires look a little brittle but aren't cracked. I actually don't know how to test the fuel pump.

 

Don't forget to check the EGR (exhaust gas recirculation valve) is closing fully if it sticks partially open that can cause a rough idle.
You can connect a vacuum hose and shine a flashlight under the top inlet manifold runners, you can see the valve move with vacuum applied.
You can put a gasket in the egr tube on passenger side rear of rocker cover where the egr gets exhaust from on the 87.
Code 33 is mass airflow signal voltage high i believe, i pulled the below info from a google search hope it may help you.
Could be a simple bad connection on the maf wiring connector plug or maf relays? spray wd40 and brush the connectors clean.
Have you reset the ECM disconnected and reconnected the ecm plug near battery (or disconnect reconnect the battery)
Does the check engine light come on when the car is running or is it a one of error 33 code?


Service Bulletin Number: 87-270-6E
Bulletin Sequence Number: 031
Date of Bulletin: 8801
NHTSA Item Number: 98253
Make: CHEVROLET
Model: CORVETTE
Year: 1987
Component: ELECTRICAL SYSTEM:IGNITION:ELECTRONIC CONTROL UNIT
Summary: MASS AIR FLOW (MAF) SENSOR SYSTEM DIAGNOSIS CODES 33/34 AND 36-MAF POWER RELAY SHOULD BE P/N 10067925-IF NOT REPLACED WITH P/N 10067925-ALL 1986 TO 1987 CHEVROLET CAMARO AND CORVETTE MODELS WITH 5.0L OR 5.7L PFI ENGINES

Service Bulletin Number: 87-298-6E
Bulletin Sequence Number: 129
Date of Bulletin: 8809
NHTSA Item Number: SB002811
Make: CHEVROLET
Model: CORVETTE
Year: 1987
Component: ELECTRICAL SYSTEM:IGNITION:ELECTRONIC CONTROL UNIT
Summary: CODE 33 MASS AIR FLOW (MAF) SENSOR VOLTAGE HIGH DIAGNOSIS-CONDITION WHEREBY MAF SENSOR CIRCUIT CAN NOT ACCOMPLISH CAUSED IN-OPEN OR INTERMITTENT IN CIRCUIT 998-SHORT TO GROUND IN CIRCUIT 900 FAULTY OR INCORRECT BURNOFF RELAY-CONNECTIONS SHOULD BE INSPECTED FOR CORROSION AND/OR BENT PINS-ALL 1986/1987 CHEVROLET CAMARO AND CORVETTE MODELS WITH 5.0L OR 5.7L (VIN F, 8) ENGINE TLH

 

Once started the FP gets power from the oil pressure sw at the back of the left side of the engine. If that switch is dirty it may be causing the FP fall out.

Check manifold vacuum for potential leaks.

If you smell fuel through the FPR vac line it's time to replace the diaphragm.

 

I got the code 33 to clear but it still idles rough; I'm suspecting it will come back on with a little driving. I'm going to swap out the MAF sensor today and see if that makes a difference. The relays actually look like they've already been replaced which leads me to believe this is the issue that finally stumped the previous owner prompting the sale.

 

I'll have to check that and probably will end up replacing the FPR. Typically my pressure will drop to ~30-35 lbs immediately after I shut the car off but yesterday it actually held at 40 lbs after the car was off. Does this sound typical of a bad FPR?

 

No. Whats typical?

A bad diaphragm or spring will serve a host of issues. And the TPI FPR has a reputation for being problematic on 86's.
Get a new FPR repair kit and a FP test guage to ensure the work is complete.