92 Base model. The car has been hard to start in the mornings. Seems the fuel system is not holding a positive pressure over night. The walbro fuel pump has 2k miles on it and tests good. When primed, I am getting 45lbs at key-on. 41 lbs at idle. 40lbs at key off. The pressure drops to 0 within two hours. When I cycle the ignition switch to prime, I can hear what sounds like the fuel filter and or fuel rails filling up. I have replaced the fuel filter and seals. I see no fuel leaks at the filter, the regulator or anywhere else. Am I approaching this in the right direction?

 

I'd say you are UNLESS you have an aftermarket regulator. Mine is from the Holley Stealth Ram and I changed it to the Kirban unit. Both don't hold pressure for long.

 

oh boy....

1st, you must understand how this system actually works.

"cycling" the key on/off does absolutely NOTHING.....why?

'cause the 1st time the key is turned to ON.....the ECM allows 2 seconds of pump time to prime the rails. That's more than enough to fill the rails and build around 40 psi.
If you get 45 psi key ON, that's more than enough static pressure to start. Your hard to start issue is the fault of something else I suspect.

Once primed after the initial key On,
The ECM will NOT allow the pump to run again UNTIL it sees the engine running via a signal from the dist that tells the ECM the engine is running on its own and not the starter, This is to prevent flooding.

If you can crank on the starter and its NOT firing, you should be able to see the micro pulses of fuel injectors cycling on the fuel test gauge. This tells you that the pressure is there and being used. It takes quite a while cranking to absorb 20 psi of fuel pressure....about 10+ seconds of steady grinding on the starter. If the pressure is anywhere in the 30s...it should start.
NOTE: the injectors WILL cycle and operate when cranking but the PUMP will NOT run again until the engine is running on its own.
If the injectors have ALL passed the ohms test, I'd search elsewhere for the source of this problem.

Do you have a fuel pressure test gauge? assuming you do, since you are getting numbers from somewhere, Key ON fuel pressure should be 40psi more or less. It should hold that for a few hrs at least.
(2 hrs is acceptable, not great but ok) IF it is leaking down in minutes, then look at the regulator and/or the injectors. The pulsator has nothing to do with this. Its not a necessary item.

Pull the vac line off the reg. If its wet its a blown regulator. If its dry then move on the injectors.

You can still have a regulator leaking fuel internally past the disc/seat. IF Pinching the return will hold pressure for hours, rebuild the regulator. IF pinching does nothing, replace fuel injectors.
Simple.

IF you are 100% sure the fuel pressure is dropping off in minutes, because you have left the gauge attached and watched it over a period of several hours, or over nite, then proceed.

Sometimes a pump will have a faulty check valve that allows fuel to leak back thru the pressure line. This is difficult to prove since the ONLY real way is to replace that pump. If it is the pump, the pressure usually drops instantly.

Hard starts can also be the coolant temp sensor, weak spark, leaking emissions parts, vac leaks.
My best guess......old injectors, air leaks.

as with ANY unusual symptoms, clean ALL harness ground connections to the block, frame and power source connections at the distribution node by battery or on battery.

 

I had re-used the stock fuel pulsator when I did the fuel pump replacement. Mine is directly after the fuel pump. Realizing that a leak down at the fuel pump check valve and or the pulsator is hard to check, I remembered a tool I have that I used in my karting days to check the pressure holding capability of the 2 stroke crank case and the pop off pressure of the carburetor. I connected the tool to the pump outlet at the top of the tank, pumped up the pressure, and left it for a couple of hours. 15lbs leaked down in an hour. I pulled the pump assembly out of the tank, removed the pulsator, and connected directly to the pump outlet to find it held 15lbs for 2 hours. I reinstalled the fuel pump replacing the pulsator with in-tank fuel line, and tested again at the pump outlet at the top of the tank. Ah hah.. It held 15lbs for 2 hours. Seems my culprit was the leaking pulsator. It was leaking due to the poor fit with the aftermarket Weber pump. I should have used the included fuel line concept to begin with. Though, technically, the included fuel line was actually not in-tank rated. I used Gates 27093 as a substitute for the included fuel line.

 

Just to note: My OBD1 92 allows for cycling the ignition switch every 15 seconds for a 2 second fuel pump activation. Just saying.. But thanks for all the info.

 

It takes the ECM about 10 seconds to complete the shutdown procedure (MAF burnoff and IAC reset). It doesn't actually turn off until it finishes. That's why you have to wait about 15 seconds to get the fuel pump to run again and do the 2 second fuel rail prime.

 

FWIW, on my 96, very long cranking times were the result of a faulty FPR.

 

Since you seem to a have this system locked in, here's my issue:

Had all injectors and cold start valve refurbed and leak tested by FIC last August. Car never ran better, however have had starting problems. Went through injection test and found that after attaching pressure gauge to fuel rail:

1. Turn ignition to "ON." Pressure runs up to 40 PSI while pump is running for 2 seconds then quickly drops to 8 PSI with in about 10 to 20 seconds.

2. Engine running holds at about 40 PSI while at idle.

3. Can't find a place to pinch off return line. To complete other tests.

4. Original fuel pump and hardware still in tank.

5. When I remove the vacuum hose from the Fuel Pressure Regulator,it does not appear wet- but I can smell gasoline in the hose. Could my 1984 vintage fuel pressure regulator diaphragm be leaking after years of reformulated gasoline?

What do you think is the next best move?

 

PM sent to edobernig about your issue.

 

If your regulator is shot or your injectors are leaking, it might explain that.

Doesn't say much. Could be that the pump is keeping up.

Where does the return line go to? Fuel tank. So you have 3 lines. One would be vent and the other going so I would think the last one would be return. Been a long while since I ventured there so I am just thinking out loud.

I can't think why there should be gasoline in the hose. I would think that you need a new FPR based on what I am reading. That is, unless someone sees something else.

 

Some spare time reading:

http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf

 

When the diaphragm in the reg, splits it allows engine vac to pull fuel straight out of the reg vac port into the intake.
Presence of fuel in the vac line is the sure proof of a damaged diaphragm

 

http://forum.grumpysperformance.com/....php?f=32&t=33

Look at the pictures. The 2 hoses that are on the left side entering the tank are the "in" and the "out" so I think the 3rd on the right side is vent. I believe the upper one of the left is "out" so clamp off the "in".

Anyone see anything wrong with that?

 

100%

We know that the new age fuel can damage our stock fuel injectors. That comes up all the time. However, noone really talks about the regulator. I can do basically the same thing. My #1 vote is the FP regulator.

I'm going to go ahead and plug FIC. Those 24# injectors are awesome. They fit up great, even if they have the blue oval on them. Absolutally zero problems and she runs great now.

 

First I thought I had a cold start valve issue, so I sent the cold start valve along with all 8 injector to FIC for a refurbishment, flow and leak tests. FIC told me they were performing perfectly now and did not need replacement. Along with a fuel filter and a tune-up of plugs, cap, rotor and wires it ran like it was supercharged. Performance and throttle response is spectacular.

I still would have starting issues particularly when warm. Cleaned the MAF sensor and throttle body and I replaced some inexpensive sensors: coolant temperature and O2. The fuel pressure would build to 40 psi then quickly drop within a minute or two to 6 psi. When running it would maintain about 39 psi. To further test the fuel pump and isolate the leak I needed to find the fuel pump lines where they could be pinched off.

Got great help from the a forum member. To access the fuel pressure and return lines, you remove the gas tank lid and the panel under it which exposes the filler neck and fuel pump mounting panel. The top hose on the right with two hose clamps is the supply and the lower right hose is the return.

It was obvious that the fuel regulator was not leaking into the vacuum line, because when the vacuum line was removed and the system pressurized no fuel leaked out of the vacuum fitting on the regulator. (So I thought)

Pressurized system and clamped supply hose above the tank and pressure held so no leaking injectors or cold start valve.. Removed clamp pressure dropped immediately indicating bad fuel pump.

Replaced the fuel pump. Very simple to do by removing 8 bolts around filler neck and entire unit just lifts right out. Installed new pump in minutes. Also replaced the strainer and fuel filter. The system now holds pressure after cycling.

This solved my problems. I thought!

Then after the system was now holding pressure, it started great but after a long period it was again requiring a long crank, but restarting after a short period no problem. Now I smelled a slight gas odor under the hood. When I removed the fuel pressure regulator vacuum line I found it wet with gas and gas now weeping out of the regulator. It was not obvious and did not occur immediately after removing the vacuum line.

The now 40 psi static pressure, that was now holding after shut- down, was very slowly bleeding gas past the regulator diaphragm into the vacuum line and allowed it to be be sucked down the vacuum line. Since my primary pressure loss was from the bad fuel pump, it masked the slow leaking fuel pressure regulator diaphragm.

I am very confident that multiple issues were contributing to my starting problem. The replacement diaphragm is on order and now this should fix the starting issue!