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Fuel Injector Question

robhauser

Member
Joined
Aug 4, 2005
Messages
22
Location
Richmond, VA
Corvette
1990 Coupe - White on Red
I have an occasional hard start condition that seems to only happen if I let the car sit for about 1 to 8 hours after driving. If it sits overnight, it starts right up. I am guessing that my fuel injectors are leaking down until the pressure is gone. And I think it starts normally after a long period of time because the excess fuel has time to evaporate. My question is whether you think I need a new set of injectors or if my seals might just be in need of replacing. Any insight would be greatly appreciated.

- Rob
90 Coupe
Richmond, VA
 
R

raidoman

Guest
injectors

My 87 did the same thing. Had them cleaned but it came back as they were worn. Best solution is to put a newe set in. Accel and Thomco are both good replacements as the original design wasn't that great.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
I have an occasional hard start condition that seems to only happen if I let the car sit for about 1 to 8 hours after driving. If it sits overnight, it starts right up. I am guessing that my fuel injectors are leaking down until the pressure is gone. And I think it starts normally after a long period of time because the excess fuel has time to evaporate. My question is whether you think I need a new set of injectors or if my seals might just be in need of replacing. Any insight would be greatly appreciated.

- Rob
90 Coupe
Richmond, VA

It is possible that, as you speculate above, you have leaking injectors, however, other faults can cause similar symptoms.

The way to begin a conclusive diagnosis?

Run the fuel pressure tests in the factory service manual.
 
S

speedmaster4

Guest
fuel pressure check is the first item of business...harbor fright sells a tester kit for abt $15 (often on sale for 1/2 price) chinese junk but serviceable...pressure should go to ''around'' 40 psi when ignition key is turned ''on'' (engine start up is not req'd) and should decay slowly when ign key is turned 'off', should still show 10 psi after 12 hour sit with ign ''off'' (you will not find that info in the factory service manual).

if initial pressure or 12 hr residual pressure is low, use the FSM procedure to isolate the problem, or just declare everything bad/ replace/ charge the customer for all new parts as the dealer does. :eyerole

same problem seen here in snow country, on occasion, when ''winter'' fuel blend is still in the vehicle or low-volume vendor storage tanks and ambient temps are high...try opening your hood immediately after stopping the car to avoid high underhood temp and fuel vaporization (similar to ancient 'vapor lock')
 

c4c5specialist

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
if initial pressure or 12 hr residual pressure is low, use the FSM procedure to isolate the problem, or just declare everything bad/ replace/ charge the customer for all new parts as the dealer does. :eyerole

quote]
Really???
Hm, actually, pressure drop off over 12 hours is NOT abnormal.
5 psi over 10 mins is.
Injector resistance, 16.5 ohms, plus or minus 1 ohm at ambient temperature.
35-45 psi key on/ engine off.
Flow rate of 1 quart in 30 seconds.
And c4 injector has been redesigned since the addition of ethanol, because it shortens injector electrical windings over time.
Allthebest, c4c5:W
 

robhauser

Member
Joined
Aug 4, 2005
Messages
22
Location
Richmond, VA
Corvette
1990 Coupe - White on Red
fuel pressure check is the first item of business...harbor fright sells a tester kit for abt $15 (often on sale for 1/2 price) chinese junk but serviceable...pressure should go to ''around'' 40 psi when ignition key is turned ''on'' (engine start up is not req'd) and should decay slowly when ign key is turned 'off', should still show 10 psi after 12 hour sit with ign ''off'' (you will not find that info in the factory service manual).

if initial pressure or 12 hr residual pressure is low, use the FSM procedure to isolate the problem, or just declare everything bad/ replace/ charge the customer for all new parts as the dealer does. :eyerole

same problem seen here in snow country, on occasion, when ''winter'' fuel blend is still in the vehicle or low-volume vendor storage tanks and ambient temps are high...try opening your hood immediately after stopping the car to avoid high underhood temp and fuel vaporization (similar to ancient 'vapor lock')

Speedmaster... I don't see a fuel pressure guage on the Harbor Frieght web site. Is this what you are referring to?... http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92699
 
S

speedmaster4

Guest
yessir, that's it...it comes with a whole bunch of adapters for ''inferior'' brand autos, i suggest that you permanently attach the GM fuel rail test port connector (aka schrader valve) adapter to the gauge (a dab of pipe thread sealant is nice) and recycle the others, unless you also are plagued by ''inferior'' units in your garage, as me is (depends on what the meaning of 'is' is)...when connecting the gauge adapter to the car, always put a drop of motor oil on the threads of the test port connector (pull the engine dipstick and touch the wet end of the dipstick to the top of the threads on the connector if a better oil supply is not convenient) to get a good seal and avoid wear on both male and female (connectors)...this tester CAN be used (with diminished accuracy due to high gauge scale) on 84 vettes and other TBI GM cars using the same adapter, but note that TBI's only run at abt 10 psi when healthy and TBI residual pressure will normally drop to '0' psi within seconds after the ign key is turned 'off'.
 
S

speedmaster4

Guest
[


quote]
Really???
Hm, actually, pressure drop off over 12 hours is NOT abnormal.
5 psi over 10 mins is.
Injector resistance, 16.5 ohms, plus or minus 1 ohm at ambient temperature.
35-45 psi key on/ engine off.
Flow rate of 1 quart in 30 seconds.
And c4 injector has been redesigned since the addition of ethanol, because it shortens injector electrical windings over time.
Allthebest, c4c5:W

REALLY :ugh... a number of friends have asked me why the dealership finds a bunch of bad parts which apparently all failed simultaneously, causing THE problem...as logical people they do not accept this ''coincidence'' as fact...nor do i, in every case where i have resorted to ''throwing parts at it till the problem is cured'', i have re-installed the parts which were not the 'cure' and the thing still worked.

as you are employed at a dealership, you might tactfully mention to the appropriate ''upper management'' that we ''the mushrooms'' are ''on to'' the game and are displeased with it...or not, might cost you your job ;squint:
 

c4c5specialist

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
Actually, I AM RESPONSIBLE for the actual diagnosis and repair of all Corvette in my dealership and that is a reponsibility I take more seriously then you can POSSIBLY comprehend.
And I dont have to mention it to anyone, because I follow a much higher standard, MY OWN. And everyone who knows me, here and in my dealership has seen that first hand.
I apologize for those who did not treat you well, but I am NOT one of those people. And if I was worried about my job security, I would NOT be posting on forums or boards.
Allthebest, c4c5
 

milehigreg

Well-known member
Joined
Dec 3, 2004
Messages
271
Location
Denver Colorado
Corvette
1989 Dark Red Coupe
Relax, Speed

Paul (C4C5 specialist) is a highly valued and well respected member of the CAC. He has been a speaker at Cruisefests and while there has been known to "participate in" (read perform) parking lot repairs for Cruisefesters. I have met Paul and can guarantee you that there was no ill will in his post. Take a look at his resume and you will see he has spent years training to become a true expert on these cars we love. :D
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
Paul (C4C5 specialist) is a highly valued and well respected member of the CAC. He has been a speaker at Cruisefests and while there has been known to "participate in" (read perform) parking lot repairs for Cruisefesters. I have met Paul and can guarantee you that there was no ill will in his post. Take a look at his resume and you will see he has spent years training to become a true expert on these cars we love. :D

I am going to jump on this wagon. I have been in Paul's seminars at cruisefest. I have never met a tech that comes anywhere close to his knowledge and ability. He has what I term " a Gift" for automotive. You can take everything he says as gospel when it comes to Vette tech. :BOW


Glenn
 

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