Welcome to the Corvette Forums at the Corvette Action Center!

Inexpensive Fix: C6 LS2 Fuel Pressure Loss at Shut-Off

compyelc4

Well-known member
Joined
May 1, 2002
Messages
609
Location
Dayton, Ohio
Corvette
'95 LT1 Coupe, Comp Yell; C6 Roadster, Vel Yell
Some of you may have read a thread about this condition on many C6 LS2's on this site and others. Mine, with 12K miles is one of them. Through fuel pressure checks at various ambient and engine temperatures I have determined that the most likely cause of my fuel pressure loss at cut-off (total loss of pressure within 1 minute) is a faulty fuel return check valve. Instead of paying a dealer prox $1200-1500 for a new fuel pump/check valve assy, or dropping the tank and doing it myself, I think I'd like to try installing an in-line fuel check valve first. I have read a few posts for different cars, including C6's, indicating that installing an external check valve somewhere on the fuel outlet line running from the driver's side tank to the fuel rail has worked very well. I read that even installing one between the firewall and injector rail is enough to cure the problem, although it seems like there would not be much room to make this a clean install.

Has anyone done this, and if so what were the results? What parts, P/N's did you use and what difficulties did you have with the install. I think I can do this for less than $80 US so I am very tempted to try it. I am no auto novice and I have a lift in my garage so access to underneath the car is not a problem (if in fact that is where I need to install the line, instead of in the engine compartment).

Thanks for the help.
 

Dad

Well-known member
Joined
Nov 18, 2001
Messages
611
Location
West Unity OH
Corvette
15Gray/8sp 72Blk/Blk4Spd 64Red/Red/Wht4spd
Section 6 of your repair manual looks a bit daunting but doable. I couldn't fine one of the many check valve problems you speak of so I'm no help there. My direction would be to replace the proper $300+ fuel pump rather than cobble something up that could be additional problems later. Pumps look like they came from a star fighter.


Let us know if you find the inexpensive fix. :thumb
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,457
Location
CenCoast CA
Corvette
71 04 12 19
The OP didn't mention the model year, but since the car has an LS2, I guessed 2006 and read the FSM for that year. The fuel system diagnosis is fairly time consuming and might be difficult for a DIY, but certainly not impossible–as long as he/she had the proper diagnostic equipment.

Couple of questions...

1) What model year is the car?
2) Have you run the fuel system diagnosis tests in the Service Manual which would rule-out an injector problem?
 

compyelc4

Well-known member
Joined
May 1, 2002
Messages
609
Location
Dayton, Ohio
Corvette
'95 LT1 Coupe, Comp Yell; C6 Roadster, Vel Yell
Thanks Dad and Hib,

Year: 2007
Injector Test: Did not run, but maybe will. The reason I'm looking rearward is that once she fires there is no stumbling, very smooth idle, no hesitation, no fuel smell, no black smoke.

I might add I ran a Tech III which showed no hard or soft codes.

Here are some other signs:
1. Static fuel pressure check shows zero if the engine has been sitting for more than a minute or two.
2. The only time I have this problem, cold or hot engine, is with ambient temps above 70 deg F. Below this, give or take 5 deg F and I get that extended crank.
3. If I allow fuel pump to "prime first" (holding in on the start button, foot off of brake) she will fire within 1 revolution whether the engine or ambient is is hot or cold.
4. I have not checked what the fuel pump does when the ambient is above 70 deg F, but at 60 deg F ambient the press goes from zero lbs to 62 lbs within 1 sec. for an immediate start, and she holds right there.
5. My next test was to wait for warmer weather and see what the fuel pressure registers and how long it may take to get the pressure from 0 to 62 lbs on a hot start, hot day.


I just hate to take it in to a garage for that $1200-$1500 rip because I've had so much trouble with this car already. I've studied the fuel pump removal writeups and I believe I can surely handle that task if and when the time comes. My '95 C4 is the reigning "queen" of the two right now. Gawd, I'm glad I decided to keep that fine little thing.
 

compyelc4

Well-known member
Joined
May 1, 2002
Messages
609
Location
Dayton, Ohio
Corvette
'95 LT1 Coupe, Comp Yell; C6 Roadster, Vel Yell
Oops. "2. The only time I have this problem, cold or hot engine, is with ambient temps above 70 deg F. Below this, give or take 5 deg F and I get that extended crank."

I mean to say..... "Below this, give or take 5 deg F and I don't get that extended crank."
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,457
Location
CenCoast CA
Corvette
71 04 12 19
My strong recommendation is to discontinue your current test program and rely on the diagnostic information in the Factory Service Manual. Before you start modifying the fuel system as a repair strategy, run the fuel system tests in the FSM. That may rule-out any problems with injectors.

Your symptoms (ie: rapid drop of fuel pressure after the pump shuts off) are typical of:
-leaking injectors
-faulty pressure regulator
-faulty check valve

I think you need to properly diagnose the fuel system to determine which of those components is problematic.

I'll guess that your problem is more likely a faulty injector than it is a failed check valve, but, again, I'm just guessing.
 
Joined
Mar 27, 2003
Messages
3,679
Location
Mustang, OK
Corvette
'13 427 60th vert - '21 Silver Flare Coupe - CTS V Wagon(4-door Vette)
Did you try a "good" fuel system cleaner like BG 44K first?
 

compyelc4

Well-known member
Joined
May 1, 2002
Messages
609
Location
Dayton, Ohio
Corvette
'95 LT1 Coupe, Comp Yell; C6 Roadster, Vel Yell
Thank you Hib. I will do more testing per manual. I do not currently have a shop manual but my brother is ASE Certified and is a professional subscriber to Mitchell On-line. It costs him a fortune but he says it is worth it. Have you ever used that service? I'll see what Mitchell's comes up with. If it falls short I'll purchase a GM manual. Funny story about manuals..... When I bought my C4 I had to replace the Opti Spark (only problem I have ever had). I completed the job without a Vette shop manual, but I thought I better purchase one. Well, I did and to this day I have not had to open the danged book!

Thank you Tuna. You know, the first couple of times I experienced this problem (only twice in 1 year) I used a bottle of Techron and the delayed crank stopped within 5 or 6 starts. When it happened again the following Summer, I shot some Techron again, and again the problem cleared up within a few starts. The third Summer it started was last year........so I shot Techron again, maybe a couple of times in a couple of weeks. Disappointed this time because the problem remained and lasted all through last Summer.
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Advertise with the Corvette Action Center!

Double Your Chances!

Our Partners

Top Bottom