Just purchased my first Corvette, 1989 Coupe. I am 57 years old and not new to cars, just Corvettes & fuel injection systems. I'm an old carburetor guy. I know this subject has been beat to death but my fuel rail pressure drops from key on 42lbs to 0 in about 10 seconds. From what I have been reading, this is fast. I installed a new fuel pump Saturday, not necessarily trying to fix the problem, but to have a new pump for sound of mind on extended trips. I noticed a strange looking device connecting the fuel pump to the hard line, didn't know what it was at the time but installed it exactly the way it was. Has anyone removed the pulse dampener? I can see the need for it with maybe 2 or 3 cylinders but with 8 cylinders, how much hammering can occur from the injectors.
Could you simply replace it with a section of hose & clamps. I have also read about a loss of pressure through the fuel sender. I always thought a fuel sender was simply a rod with a float, a rheostat and a connector for the fuel gauge wire and ground. Granted, I didn't pay a lot of attention to the sender when I had it out because it is working fine and my focus was on the fuel pump. Ok.....back to my fast drop in pressure.....I know all the test procedures to narrow down the cause, will not get to doing that till next weekend. What I am reading is that a fast loss of pressure like that is most likely an injector. Would that mean the injector would cause performance problems as well? The car runs just fine after I crank on it for a while to get it started.

Thanks in advance!

 

Welcome to the Forum and the insanity of owning a Corvette..

You can eliminate the pulsator without a problem. If you are still losing pressure to 0 in ten seconds after replacing the pump, it COULD be the pulsator. Usually the quick loss of pressure is a bad check valve in the old pump. Take a pair of vice grips and with someone turning the key to the one position, clamp the FEED line close and watch the pressure if the pressure holds, then probably the pulsator. Replace with a piece of FUEL line and two screw clamps.

If pressure still drops, then next is have your helper turn on the key and now clamp off the return line. If pressure drops then likely a bad injector.

 

Thanks John.....I'll do as you said then check pressure again. I'll clamp the hoses as you mentioned as well. Also read that you can check the fuel pressure regulator by pulling off a vacuum hose to see if fuel is present. If the pressure drop exists with the return line pinched, that could mean a bad regulator as well,,,,correct? Also....are some people calling the fuel pump a fuel sender?

 

Everyone has their opinions but personally, I'd keep the pulse damper.
Why introduce more fuel pressure fluctuations than necessary?
I'm guessing if it was really unnecessary, GM bean counters could and would have saved the money.
Just my .02

 

1, you can remove it and many do, replacing w/just a piece of hose. I recently did this on my '96 Silverado and it seems to be fine.

2. On your car the "hammering" may be worse than you're thinking, b/c it's a batchfire system, meaning it's firing 4 injectors at a time.

3. See number 1.

 

Haven't decided yet....because of its slip on design...sure looks like a leak waiting to happened. I will do all the various tests to see which line has the leak, supply or return. Don't want to open the gas tank again if I don't have to. Won't be till the weekend that I will check this out. Will be sure to post my findings........thanks.

 

NOT true. All 8 injectors are connected together and all 8 fire at the same time.

I proved that in this thread:

https://www.corvetteforum.com/forums...-debunked.html

 

Well....I asked for opinions and I got them......this why I love forums. Being an old carburetor guy, I can't argue with any of the opinions. The dampener will stay unless I find it to be the source of the leak. Thanks for the help all.

Gary

 

I found that after installing a new pump and sending unit, a line was coming out of the pulsator and dumping fuel back into the tank...I replaced it with a piece of hose....haven't noticed any problems or differences without it.....

by the way....welcome to the forum....lots of good advice here....always list your year and be specifc with your issue......kind of like you did.......good job....good luck...

 

I am leaning towards replacing the pulse dampener with a section of hose. If I pinch off my supply line from my tank and have no drop in pressure, it is most likely the culprit since I just replaced the pump.......thanks for all the good advice.

Gary

 

Copy that. Great write up, pics and documentation, BTW!
What ever the case, my point was that there were multiple orcifces opening and closing at a time, which would increase "pulsations" when compared to a SFI system where only one opens at a time.

 

••••• TESTING FOR LOSS OF FUEL PRESSURE

... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator and plug the line.

 

The 87 has a fuel filter in the return line that does the same thing as the pulsator. I simply replaced the fuel filter which wasn't easy. The idea was to quiet the fuel lines.
Do what you want but I keep mine easy to service now.

 

I replaced my fuel level sending unit with one of the fancy stainless steel units (VERY nice). There was too much of a gap between the top of the fuel pump and the pressure line and the pulsator was not long enough. I replaced the pulsator with SUBMERSIBLE fuel line (normal fuel line is resistant to fuel on the INSIDE, but not on the OUTSIDE), so you need this stuff:

 

A fuel filter on the return line.....interesting. I understand the filter on the supply line is a booger to get to as well. Thanks for the information!

Gary

 

Good tip on the fuel line hose......that never occurred to me...have already placed my order from Amazon.

Gary

 

GM never installed fuel filters on return lines of any C4 (or any car for that matter). The filter in your picture was added after the fact.
Just looking at the logo on the canister you can tell that it's from the 60's.

 

I thought the fuel pulsing was from the pump, not the injectors

 

The fuel pump is a vane type pump that runs continuously, there are no pulses to speak of.
The pulses here are a result of the injectors opening and closing- Think of "water hammer" when you open and close a faucet in your house. The pipes vibrating is a result of the sudden change in pressure from closing the faucet suddenly. Same principle.

 

87 vette 81 big girl

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Quote:


Originally Posted by coupeguy2001 View Post

I'd like a pic of that

I can assure You that there is a return line fuel filter in place on all 1987 Corvettes in place unless a previous owner has removed it.

It is a small metal spin on canister style with a disposable internal fuel filter element.

No auto parts books anywhere shows that it does indeed exist.

I had a very hard time at my local GM dealership just trying to find a factory AC delco part number on the filter.

It has been discontinued by AC-Delco.

WIX brand still carries the filter. I managed to find a NOS AC Delco return line filter for my 1987 Vert.

It is very hard to reach on Vert. And heat shields in the way also on the Right front frame rail.

Sorry I cant take any photos for You. Photographing it would be best done on an Auto 2 or 4 post lift like I have a work.

I dont live far from Jason at Vette 2 Vette in Streator, IL.

He has plenty of those 1987 return fuel line filter assemblies.
I have seen at least a dozen on his shelves for myself within the last year.

That man Jason, has salvaged, dissasembled at least 200 C4 Corvettes from what I have seen. Incredible to see within his shop. LOL

He lets very few of the public inside of his shop.

Jason is a great guy too !
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Old 02-21-2010, 11:21 AM #5

GlennS87

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