Electrical guys, please help

ttt

Are you sure it's a spark miss? Why do you suspect fuel? You changed lifters, maby one is hung open? You need to find why it's missing first.

Check your grounds.

87stangdiddle said:

With my ohmeter i checked from coil power+ to the negative battery terminal i got 6 ohms of resistance, I dont think this sounds right to me so hopefully someone can clear this up for me. Im hoping its just a bad ground or loose connection or something.

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This is the wrong way to check the resistance of a powered on circuit. The proper method is to measure the voltage drop across the circuit. If you want to check the ignition circuit for resistance, turn the key to the run position and measure voltage drop between the coil power and the Positive terminal on the battery. You should see less that 1 volt.

Checking grounds:

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.

4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt for help troubleshooting voltage drops across grounds

I agree check grounf to motor and gorund to body, had simialr problem with bad motor ground

What did your plugs look like when removed?


Check your injector harness. Sometimes those clips break holding the injector connectors on. Especially 6,7,8 under the upper plenum. Also, check for vacuum leaks under there...rotted hoses are hidden well under the plenum.

Your DVM won't be able to check if your injectors are firing correctly. You need an oscilloscope for that. Plus, with no sync signal it is difficult to track the signal, especially if you have an erratic idle, vacuum leaks etc.

I don't think you can check anything about the injectors at the computer; the computer supplies the ground for the injectors - the power is supplied by VPWR if I remember correctly.

I would definately check all of your grounds like the others say.

Have your reset your TPS? I assume you don't have any check engine codes. Have you checked your timing w/ a timing light? Did you put your SPOUT connector back in?

Maybe check for vacuum leaks like one person mentioned.

What did you "do" to get it to idle fine in neutral, but still stall under load?

could be a plug wire too. my truck started missing under a load a few months ago after an oil change. i went through and presses all the plug wires down firmly and it quit

I am glad you got it. In one of your other threads, I thought you did a CBT to rule out a cylinder miss. My bad [memory] or I would have suggested doing so.

Glad you got it whipped.