Injector Question??

[scottmrit]

I have a 1994 Cobra that is having problems with the injectors. Car has a real bad idle. No Computer codes and On the Cylinder balance it brings up that the #6 has a problem. All plugs are nice and tan but the 6th plug and it is black. I swapped the injector, reset the computer and re-ran the test and same problem and the new plug is black again. What should the voltage to each injectors red power wire be at idle? Injectors 1-6 have from 1.7 volts to 3.2 volts, but the 7 and 8 have 12.5 volts at idle.
I unplugged the 7 and 8th injector and no change in idle at all. Is this a wiring problem? I then swapped injectors on 7 and 8 and they still have 12.5 volts. Is this the way that it is supposed to be? I also hooked up a noid light and ran the motor and on each the light is pulsing. ????

1994 cobra
rebuilt 302 ported gt40 heads and 2031 cam kit
24lb injectors stock maf and tb 1 5/8 lt and full exhaust
190 fuel pump and Has a lasota racing switch chip
I have now almost completely changed everything on this motor to find the cause of this bad idle.

On a full tank of gas and i got 198 miles. Car also has 373 gears. Friend mechanic told to me to get another injector harness, and there is no visible damage to harness right now.
Dunno what the problem is. ???

 

[divit250r]

Did this start after you put the chip in? Maybe the contacts aren't making a good connection. If not, then I would say that either the injector driver in the 'puter or the harness are the likely cause. Not experienced with this stuff though, so I'm sure you'll get a better answer. Good luck!

Scott

 

[scottmrit]

The idle problem has always been here. It will idle at 900 good but you can sit there and watch the motor shake while it is idling. I have swapped the computers already so I am leaning towards the harness since it has been in the car since i got it. This car was purchased totaled and I put it all back together. It also has a new dizzy in it, new plugs, wires, iac, tps , egr, and i have swapped coils.

 

[cbarr300]

see if you can get a buddy with a mustang (can be GT or cobra) and swap out the injector harness.

best of luck

 

[mo_dingo]

The computer pulses ground. That is what you need to check. But if the noid light is flashing on those cylinders, I would say that your wiring is fine. You need new injectors. Get some accel injectors, do not go the ford racing or cheap route, I did, and I regret it.
Scott

 

[HISSIN50]

I replied to your Corral thread but don't think you posted again with any follow-up questions.
Good luck.

 

[scottmrit]

how do I measure the ground pulse to the injector?

 

[jrichker]

Tools needed: Noid light, Mulitmeter (volts & ohms), 10 MM socket & extension, ratchet,

[/b]Note: Do all of the steps and do them in order. The results of the subsequent tests are based on the prior tests being successfully passed.[/b]

Some basics about the computer:
Remember that the computer does not supply power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

1.) Get a noid light form AutoZone or other auto parts store, or even better a set of them

This set is from http://www.toolking.com/ProductInfo.aspx?productid=12492 and costs $12.

2.) Use the noid light to determine that the injector pulses and isn’t stuck in the on position. It you have a set of them install all of the m and compare the pulse intensity. A light that doesn’t pulse and stays on has a short to ground in the computer side of the circuit. That can be either a wiring fault or a failed computer.
If this is the case, remove the passenger side lick panel and disconnect the computer connector. There is one 10 MM bolt holding it in place. Pull the connector all the way out of the computer so that you can see the computer side pins.

Use the list from the graphic below to find the fuel injector pins for the injectors that didn’t turn the noid light off.
3.)

Set the multimeter to low scale Ohms and measure between the computer ground located below the computer and the suspect fuel injector pins. You should see greater than 100 K Ohms resistance. If you see less than 100 Ohms, the wiring between the injector and the computer has a short to ground and needs service. Check the harness and look for damage, kinks or frayed spots.

4.) A light that never turns on is either a wiring fault, or a failed computer. Either the injector has no DC power or the computer has failed and cannot switch the injector circuit to ground. Determine if the injector has power by using the multimeter to check for 12 volts on the red wire on the suspect injector connector. No 12 volts and you have a wiring fault. Check the harness and look for damage, kinks or frayed spots. Check the 10 pin salt & pepper shaker connectors for bent pins, corrosion and damage.

See the graphic for the location of the 10 pin connectors:

See the graphic for the 10 pin connector circuit layout.

Once you have determined that the suspect injectors have good power, the computer is the likely suspect, since a ground is required to complete a circuit and make it function. The computer provides the ground: if doesn’t, then the noid light will not flash.

5.) If you have gotten this far, then the problem is likely ignition related. Remember the noid test using all of the noid lights? All of them were supposed to be equally bright. Since you have already tested all the electrical side of the fuel injector circuit, the one remaining common item is the pip sensor inside the distributor. A failing pip sensor, damaged shutter wheel or bent distributor shaft could all cause the pulse delivered to the injectors to be faulty.

6.) Spark plugs indicate one or more cylinders not firing: use the multimeter to measure the resistance of the spark plug wires. The wires should measure 2000 ohms perfoot of length. A 2 foot wire would be 4000 ohms and a 3 foot wire would be 6000 ohms. Some Taylor and Accel wires have metal cores and will measure much less: that’s OK.
Next examine the spark plug wires very carefully for burn spots, cracks and damaged insulation. One good thing to try is to start the engine while the car is a very dark area, open the hood and look for sparks or blue glow. They indicate the electricity is leaking out of the spark plug wires.