1986 Coupe..L98 Stock...AIR delete..EGR Delete

Brand new Bosch III injectors from FIC
Brand New Delphi fuel pump and pulsator
Brand new Napa Gold fuel filter

Strange thing happened when testing my fuel pressure??

Put gauge on the rail...key on 43lbs...slowly bled down to about 26lbs after about 40 mins. Then while it was still reading 26lbs pressure, i clamped off the supply line (yes the supply line) near the filler neck. As soon as i pinched the supply line the pressure went back up to 42lbs and held there for awhile...around 30 mins.

When i removed the vice grips from the supply line after 30 mins...the pressure dropped to 20 lbs immediately.

Whats going on here?? any ideas

My friend says FPR is shot??

 

The ball-check in the "new" pump is leaking back into the tank.

This may or may not be an issue with a semi-stock motor. Leaking back is more of a start-up problem that makes for longer crank times because the system has to refill the rails and allow the trapped air to be pushed out thru injector cycles. You can help the process by venting the air out thru the test valve so it can fill with fuel faster or wait Until the air escapes by injectors cycling thus allowing fuel to enter and repressurize the rails. Till then the engine won;t fire and run. A good tight system will hold the 40 psi for 1-2 hrs, drop a few lbs initially and then take all day to drop down to 20 or less. There should be near 20 in the morning when its stone cold after sitting all night.

IMO the pulsator is a waste of space because it is another possible source of leak backs. It does nothing that has any real effect on the performance. I can see why an engineer needed to justify his pay check that day.. Whenever there is a pulse type system certain rule books say there needs to be a dampner..or pulsator.. It Smooths out the miniscule pulses of a rotary pump holding tension on a pressure line that has 8 injectors cycling at a rapid rate....the faster the rpm the more frequent the pulses...the less time between...less shock in the system. All the pulsator is good for is to absorb what little surge there is (maybe 1 psi) when the pump has to make up for fuel used in the rails as the engine runs. The thing is, that the pump does not run ANY faster at higher rpm to make up that fuel being used, so those little dips in pretension are absolutely meaningless...You cannot even see it on a gauge when the engine is running..
You CAN see the injectors cycling during cranking if you watch the gauge...it will flicker as the engine rotates with each injector pulse.Thats the pre-charge pressure being used to start until the engine fires and sends the signal to run the pump again. As this pre-charge is used the gauge will flicker and drop with each cycle until it either fires and runs OR until the fuel pre-charge is used up and the key has to be returned to off then to run again for the 2 second prime. OR the oil pressure has reached 4 psi and the alternate power source to the pump is now available to make the pump run.
This cycling or pulsing suddenly gets so fast when the engine fires that it can no longer be seen on the gauge..

 

That was my first thought...but it is a new pump afterall? New pulsator too so i dont think its leaking there either. Apparently the old racetronix walbro was doing the same thing

I am confused as to how and why the pressure increased with a pinch of the supply line??

 

Pressure in the tank? Try that test with the gas cap off.

 

Thanks Cliff...the cap was removed when i did the test.....

 

........... Was the engine warm ? ............

 

Warm...Yes...about 140F

Sat for a few hours after it was run at operating temps

 

The fuel system is just a loop system.
The goal is to maintain pressure in the rails, where its able to apply that supply thru the injectors under fuel system pretension.There are a couple pts where the return/supply meet and could reverse their respective role in how the system works.

Depends on where you pinch off a supply line...where you did this time you gave the system opportunity to utilize the return line. The pressure can cross-over in the regulator too. Then there is the possibility that you didn;t pinch the line you thought you did...

Top of tank plate:
1:00 = high pressure out to fuel rail

4:00=low pressure return to tank from rails

8:00 vent from vapor recovery system low/no pressure

Some systems also have a "T" on the tank plate for 2 of these lines to merge with a check valve inline somewhere IIRC. Think its the vapor/return. Same difference..one is liquid other is vapor.

There is ALSO another devise mounted in the fuel lines just over the inline filter. I do not see much info on this in the FSM but it looks to be some form of pressure relief that might dump high pressure gas back into the return line without external involvement. I wouldn't swear to that, but IMHO the system could use a way to dump excess pressure and send it safely back to tank. Of all the things I've taken apart on a C4, thats one item that I know very little (nuthin actually) about...
Think I'll take it apart later to see what it does...

Then again, I could be AFU.....

 

....... When you pinched off the hose the residual heat was expanding the fuel in the rails and the pressure built up to the regulator's relief point .........

 

Makes perfect sense...thanks for the info

Does the system bleed back at a "quicker" pace when the engine is warm/hot ?

 

........ I can't see where it would matter ........ bleed-off is a symptom not a disease ......... How does your car run ? How did it run before you bought a fuel pressure gauge ? ............

 

The car was, and is experiencing poor starts after sitting overnight or for an extended period of time. Sputters and stutters until warm.

Mechanic suggested new pump and pulsator due to the pressure leak down...new parts did not solve the problem.

Mechanic now mentioned possible leaking injectors...these are 1 month old Bosch III injectors "Brand New" from FIC...not rebuilts. Seems unlikely new injectors would be leaking already??

To add another twist....while the car was in the shop they had a recent issue with the coil sparking under the cap due to a faulty ground issue to the coil...ground strap missing...new cap--rotor--ground piece and coil...now i have a long crank time due to this coil malfunction and still have the sputtering starts.

Car is in the shop and he will further diagnose the problem later this week

 

............ Does your mechanic have a kid in college ? ...........

 

Not college...University...afterall this is a C4 we're talking about.

He is not going to charge me the hour for the pump..just the parts.

Going forward....He's got the flow charts out for the proper diagnosis...

 

There are a couple obscure faults that most do not know about and they are not listed in the FSM. Those are the only flow charts worth looking at BTW.

Pull the fuel pressure regulator apart.
Look CLOSELY at the disc/plunger and where it seats. Look for matching spots where they meet. Now, IF you see such a thing, that indicates that the 2 pieces are meeting at that spot, evidenced by the wear. Inverted, this means that the rest of the disc is NOT seated against the body.The small holes (ports) that are seen under there are passages to return.
This can cause fuel to be sent around the regulator directly to return. System still shows pressure but instead of pressure against the injectors its being lost to the return line.
Cleaning the reg parts and a new diaphram will fix this. Check for fitment before final assy.
That problem can cause sputtering and loss of performance since fuel is being lost.

Check your variety of temp senders. Bad data makes the ECM offer a bad tune.

The problem that you describe is COMMON to the B-III upgrade. Nobody knows exactly WHY...but its common and everyone finds their own "fix" as they go thru the car.

First thing is to isolate the problem to fuel OR ignition.

Have someone help. Have someone stand there holding the fuel schrader valve OPEN when you turn the key. You most likely will get mostly air as the pump runs 2 seconds. Why, I don;t know.
Now, allow valve to close, key ON to charge the rails. This now fully charges the rails since the air has been purged.

Car WILL probably fire up and start easy.

My theory...
For whatever reason the fuel system leaks down overnight as it should, and there are now air voids in the rails and inj the next morning. Where the fuel goes and where the air comes from are 2 important questions. If the air is not purged out, it has to be forced out thru the brief injector cycling as you attempt to start up next morning. This takes quite a few cycles and can mean 5 seconds of cranking. Even after it fires, it may take a few more seconds for fuel to chase out all air and get all injectors operating again. Once that happens...its fine all day.
Sound familiar?
Use your fuel test gauge to watch the fuel and injector behavior. The needle moves and tells of fuel moving.

Understanding the problem is what will lead you to solving the problem. Since I have not been able to afford certain parts that are needed by my car, I simply key ON, off, key ON a 2nd time to crank. This seems to charge the rails enough to get a fire built the 2nd key on cycle. The 1st key ON just pushes air in the rails with no place to go until the engine cranks and injectors cycle.

Try purging the air out of the rails before cranking. That will prove one way or the other that the fuel system is behind this.
Good Luck

 

Fuel Pressure leakdown continues

Brand new (not rebuilts) Bosch III injectors from FIC
Brand New Delphi fuel pump
Brand new Napa Gold fuel filter
Brand New FPR Diaphram

Changed out the pulsator for a short piece of fuel hose...clamped tight.

I am still experiencing long crank times before it fires 6 secs
I am still experiencing fuel pressure loss

Key on--41 psi
1 min down to 30
10 mins to 20
35 mins to 6
1 hr to zero

1) These readings are roughly the same with supply line pinched off after key on
2) These readings are roughly the same with return line pinched off after key on

3) These readings are the same with both supply line and return line pinched off after key on

Lines are clamped tight....im confident nothing is leaking by the vice grips.

CSI was pulled out of intake and observed for leakage...none

with the above pressure reading i also tried releasing the vice grip on the (1) supply line after 1 min when the pressure dropped to about 30...as soon as i released the vice grips...the gauge dropped to 20psi and continued to drop to zero in about 30 mins??

not sure if i have more than one issue.

I cant believe the new BoschIII are leaking as the double line clamp off would indicate?

I dont really want to lift the rail to see if they are.

Runs like a champ after it starts up.

Starts up really decent all day when warmed

 

Might be worth pulling a few random plugs to see how its burning. I keep hearing stories that these B-III inj are over rated regarding the lbs/hr...so if that were true...they might be lean, causing a difficult start. Mine does something similar to what you describe. 1st start each day is longer...any other, even after sitting 4 hrs is right away. 1st start acts like its hitting on 5 cyl for several seconds. Odd...

 

Plugs looked good....mostly light brown/tan...a couple with a hint of white (lean) #6 had a bit of carbon on it...nothing serious

No smoke at start-up so it might not be leaking injectors.

Start-up seems fuel starved even after it fires for a few secs...like yours.

Im going to pull the cold start injector out of the side of the intake and check for leaking after rail is primed and then check to see if it actually sprays fuel during start-up

 

Cold start injector not spraying fuel at start-up...coolant temperature 65f so it should have been energized.

That would account for part of my longer crank times, but not all of it.

I still have massive fuel pressure leakdown to zero in a short time.

Leakdown is too fast to be injectors from what i have read.

New FPR diaphram...no fuel in the vacuum line to regulator

I will swap in another pump to see if it fixes or lengthens the leakdown time...have already done away with the pulsator and have a new pump on there right now.

where else can these systems leak internally....no external leaks

 

if it bleeds to zero in one hour or overnight, what does it matter? never knew that it was more than variance. the lines and rails are still filled with fuel.