Injector issue--no start

[TopsailBeach]

The injectors on my 1986 3.2 will not fire. Here's what I've done so far:

Replaced reference and speed sensors as they tested on the edge of specs
Checked reference and speed sensor plugs/harnesses to ensure no mix up
Tested cylinder head temp sensor and found within spec
Replaced DME, and it clicks when energized
Checked all grounds, all okay with minimal resistance
Sent the Motronic computer to ECU Specialists in FL for rebuild
Grounding the injectors results in each side firing and the engine sputters and runs until fuel is exhausted

I'm stuck.

A suggestion is that a flywheel pickup may have come off(?) and the next step is an oscilloscope to see if the reference/speed sensors are sending the proper signal.

Any other suggestions would be great. I keep thinking it's something really small and when I discover it...

[rick-l]

To see if the DME itself is powered you could turn the ignition on and see if the Idle stabilizer valve is vibrating.

[TopsailBeach]

Thanks--I checked the icv also and forgot to list that. It gently vibrates when engerized.

[88-diamondblue]

Check to make sure that the reference sensor leads are hooked up to the right connector. I had them reversed and the engine will not start. Just another thing that could cause it not to start.

[TopsailBeach]

And small it was. Really small.

Prior to the no start condition I did a major tune-up. Plugs, distributor cap, rotor, filters, valve adjust, oil change, the works. The only challenge as usual was getting the back cover clip on the air filter box, but I got it.

This morning when I went back at it, the injectors fired when manually grounded at the harness, but there was noticable sparking when the alligator clip was touched to the body to ground out the connection, meaning there was load on the circuit. No aha's yet. A trip back through the wiring diagrams, testing sensors, harness, grounds, you name it yielded nothing. No start.

Last time I tried, I could get the engine to fire using starting fluid, so I tried again. This time, nothing on several tries.

Now the aha (AKA the stupid) moment....in order to make sure the starting fluid was getting through the air filter, the side of the box was unclipped and removed.....AND THERE IT WAS. Although the harness for the injector wiring was ziptied to the fuel rail, it had ridden up and the wires to an injector were crimped, cut, touching and shorting the system. Thus the load and inability of the computer to ground the circuit for firing. Once the wires were separated the engine fired immediately and ran great.

Although I checked back through my work following the no start condition, I omitted the air filter replacement step. Who would imagine that the injector wires would be caught in the corner of the box when clipped on?

The lesson is to check every part of work completed, not just what seems logical. At least now, with my new sensors and tuned up computer, I'm good for another 200,000 miles.

[rick-l]

Originally Posted by TopsailBeach

This morning when I went back at it, the injectors fired when manually grounded at the harness, but there was noticable sparking when the alligator clip was touched to the body to ground out the connection, meaning there was load on the circuit.

This would be normal.

• Each wire controls 3 injectors
• They are wired in parallel, 1.5 ohms each
• Presents a load of 1/2 ohm
• At 12.5 volts within 100s of milliseconds you are conducting 25 amps.
• When you open the circuit that current isn't going to want to stop either due to the inductance in the injector.

Better do this real quick.