Which injector is going bad?
Instructor
Joined: Sep 2003
Posts: 109
Likes: 0
From: Ft. Lauderdale FL
Re: Which injector is going bad? (dburgjohn)
Basically, you need a fuel pressure gauge and an injector tester module.
With the injectors still on the car, cycle the key to pressurize the fuel system with the pressure gauge attached. Note pressure. Disconnect the wiring harness from one injector and connect the injector tester module. Run the module. The module will hold the injector open for a fixed, predetermined time. Note and record the pressure drop. Disconnect module and reconnect wiring harness. Go to next injector, disconnect wiring, hook-up module, presurize system, etc. You will probably see a notable difference in pressure drop at the bad injector(s).
Also, with an ohm-meter, check the resistance of each injector. Stock units are around 12.9 ohms each. If the internal coil of an injector is going bad, the ohm value will be noticibly different from the others.
Good luck.
With the injectors still on the car, cycle the key to pressurize the fuel system with the pressure gauge attached. Note pressure. Disconnect the wiring harness from one injector and connect the injector tester module. Run the module. The module will hold the injector open for a fixed, predetermined time. Note and record the pressure drop. Disconnect module and reconnect wiring harness. Go to next injector, disconnect wiring, hook-up module, presurize system, etc. You will probably see a notable difference in pressure drop at the bad injector(s).
Also, with an ohm-meter, check the resistance of each injector. Stock units are around 12.9 ohms each. If the internal coil of an injector is going bad, the ohm value will be noticibly different from the others.
Good luck.
Team Owner
Joined: Mar 2000
Posts: 83,383
Likes: 87
From: Boston, MA
Re: Which injector is going bad? (Br1dgeman)
If you have a REAL bad leakdown (like the gauge goes to 0 almost instantly when the fuel pump stops) then try this.
Remove the plenum/runners and unscrew the 6 bolts holding the fuel rail in place (4 on top, 2 in front). Pull the injectors out of their bungs and place a piece of light colored paper under each one. Turn the key on and then when the pump stops you should see a wet spot on the paper(s) with leaky injector(s).
Remove the plenum/runners and unscrew the 6 bolts holding the fuel rail in place (4 on top, 2 in front). Pull the injectors out of their bungs and place a piece of light colored paper under each one. Turn the key on and then when the pump stops you should see a wet spot on the paper(s) with leaky injector(s).
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,076
Likes: 281
From: Dyersburg TN
Re: Which injector is going bad? (scorp508)
Leakdown test as follows:
7:00 pm 40 psi
7:10 pm 26 psi
7:20 pm 18 psi
7:30 pm 14 psi
7:40 pm 12 psi
7:50 pm 9 psi
8:00 pm 6 psi
Injectors? Fuel pump? Ideas?
7:00 pm 40 psi
7:10 pm 26 psi
7:20 pm 18 psi
7:30 pm 14 psi
7:40 pm 12 psi
7:50 pm 9 psi
8:00 pm 6 psi
Injectors? Fuel pump? Ideas?
Team Owner
Joined: Mar 2000
Posts: 83,383
Likes: 87
From: Boston, MA
Re: Which injector is going bad? (dburgjohn)
Remove the lid from the gas fill area and pull the rubber neck in there too. With the fuel pump RUNNING clamp off both the feed and return rubber hoses and then pull the power to the pump. If the pressure still drops it is the injectors. Clamping both lines cuts off the fuel pump check valve and the regulator return line and isolates just the injectors.
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,076
Likes: 281
From: Dyersburg TN
Re: Which injector is going bad? (scorp508)
Did a leak down test again, but this time clamped the feed and return lines at the tank after pressure built up. 45 min and no loss in pressure. What is involved in changing the valve in the gas tank?
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Re: Which injector is going bad? (dburgjohn)
It is part of the fuel pump and it is not available separately. To replace the fuel pump, remove the hoses, bolts that you see around the perimeter, and disconnect the electrical connector at the sending unit. Then lift it out of the tank, being careful of the float that is part of the sender unit itself. Once out you will see the pump, it is pretty easy to replace.
You will need a new gasket, and pump strainer to install as well.
You will need a new gasket, and pump strainer to install as well.
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Instructor
Joined: Sep 2003
Posts: 109
Likes: 0
From: Ft. Lauderdale FL
Re: Which injector is going bad? (dburgjohn)
I tend to agree with Bluevette85. Check that first before you replace the pump. I did not and sensely replaced my pump only to have the same problem. Rubber hose is REAL cheap too!!
Instructor
Joined: Sep 2003
Posts: 109
Likes: 0
From: Ft. Lauderdale FL
Re: Which injector is going bad? (dburgjohn)
Pulse dampener is located above the fuel pump. The fuel pump discharges into it before the fuel goes into the actual fuel line and on up to the engine.
follow the instructions to remove your sending unit out of the tank like you would change a fuel pump, can't miss it.
follow the instructions to remove your sending unit out of the tank like you would change a fuel pump, can't miss it.
Instructor
Joined: Sep 2003
Posts: 109
Likes: 0
From: Ft. Lauderdale FL
Re: Which injector is going bad? (dburgjohn)
I honestly couldn't tell you if it is a "required" part. By replacing it with the hose, you might eliminate your pressure leakdown problem and save yourself the expense of changing the fuel pump. If it does not solve the problem, reinstall the bugger and change the fuel pump & strainer.
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,076
Likes: 281
From: Dyersburg TN
Re: Which injector is going bad? (Br1dgeman)
OK, its the fuel pump. I just had the windows re-tinted and got a good deal on a set of wheels, cash is a little low. How long does he have doc? Can he hold on while I save a few bucks up for the pump? I am one of those hard-headed cash only persons who hates credit (and owes no one BTW).
Instructor
Joined: Aug 2003
Posts: 107
Likes: 0
From: Aurora OH
Re: Which injector is going bad? (scorp508)
I've been able to diagnose several bad injectors over the years by checking the ohm resistance - but have never performed a pressure test.
I was wondering, would the addition of a digital fuel pressure gauge on the dash provide useful information (both during running operations and while performing the leak down test) for a street driven vehicle? I've been thinking of adding the both a fuel pressure and air fuel ratio gauge - or is that merely fluff?
I was wondering, would the addition of a digital fuel pressure gauge on the dash provide useful information (both during running operations and while performing the leak down test) for a street driven vehicle? I've been thinking of adding the both a fuel pressure and air fuel ratio gauge - or is that merely fluff?
Advanced
Joined: Sep 2000
Posts: 75
Likes: 0
Re: Which injector is going bad? (dburgjohn)
The only way to know for sure is be able to visually check the business end of the injector under pressure. When I test injectors, I check the at 20, 40, and 60lbs pressure. The various pressures will show if a leaker is there.
Plenty of shops that specialize in injectors have the equipment to test them.
Hope you get it figured out, if you do need your injectors serviced I have a 25% discount for fellow Forum members until the end of November.
Gordon
WitchHunter Performance
www.witchhunter.com
Plenty of shops that specialize in injectors have the equipment to test them.
Hope you get it figured out, if you do need your injectors serviced I have a 25% discount for fellow Forum members until the end of November.
Gordon
WitchHunter Performance
www.witchhunter.com
