Hello to all. This is a newbie post, so please bear with me. I have a '99 Ranger 4x4 3.0 flex fuel 72000 miles with a dead miss. I have been running moonshine in it for about 2 months and it has run perfect up til now. Once it started to miss, I got it to a garage and got it hooked up to a diagnostic computer. It shows a dead miss on cyl 4. checked spark, (good) and compression,(good)According to the mechanic it had to be the injector. Took three days to get one through the local NAPA, put it on and all back together, and it still shows a miss on cyl 4. Went through sequence again and have a request for the parts store to get another injector(may take quite some time). In the meantime, is there any way to test for an adequate signal to the injector while the plenum is in place, or to check if it is getting it's signal before putting the plenum back on? Thanks in advance to all who take time to read and/or respond. Ed


99 Ranger
96 Explorer
94 Explorer
90 Jeep Cherokee (kids these days)

 

Welcome to FTE!

First, what did the #4 spark plug look like? Any clues?

The fuel injectors are always "live" with 12V running to them. They are activated when the PCM provides ground to the circuit. The Red (R) wire is the 12V, the other wire is ground to the PCM.

One way to test the circuit is to jump the pins on the injector harness connector with a 12v test lamp (harness disconnected). It should blink while the engine is cranking.

Here's a couple more electrical tests you can try:

CHECKING FUEL INJECTOR HARNESS RESISTANCE
- Disconnect fuel injector harness connector at the suspect fuel injector.
- Measure resistance of VPWR circuit between PCM harness connector pin and the fuel injector harness connector.
- Measure resistance of fuel injector circuit between PCM harness connector pin and the fuel injector harness connector.

If resistance is NOT less than 5.0 ohms, then there is an open in the circuit.

CHECKING FUEL INJECTOR HARNESS CIRCUIT FOR SHORT TO POWER AND GROUND
- Disconnect PCM.
- Suspect fuel injector disconnected.
- Measure resistance between fuel injector signal and VPWR circuits; and between fuel injector signal and PWR GND circuits at the PCM harness connector.

If resistance is NOTgreater than 10,000 ohms, then there is a short in the circuit.

 

In reply to your question, the plugs on all cylinders were clean and white with just a little gray. They showed some age, but then I believe they were the originals. the one on the suspect cylinder showed a little more rounding of the electrode, but after 70 some thousand miles, nothing to cause me any alarm.

 

In case anyone is interested, here is the solution to the dead miss post of a few days ago. It started with a miss in cyl. #4, in a 3.0 1999 Ranger flex fuel that had been running on E-85. Spark was good, and compression was good. took plenum off to get at fuel injectors 4, 5, and 6 as the others checked good with an ohm meter. #4 checked bad with the meter, so we ordered one from the local NAPA store. After three days, they decided that they could not get it at all. (back ordered with no delivery date) Same with Auto Zone. Finally got one after another three day wait at Car Quest. Put that one in and still had the same problem, so I went through all the test procedures again. Thanks to Rockledge, I had some more tests I could do to assure myself, and the owner of the garage that helped me locate the problem, and the parts store that we needed a replacement. After another two days we got the second injector from Car Quest, and installed it, same problem, so now we were really stumped. Even took the valve cover off to check for an out of place push rod, and took off the intake manifold to look for a bad gasket. All checked out okay. Both replacements checked good with an ohm meter. after some head and rear scratching, I switched the #4 (new) injector with the #1 (original) injector. Bingo! Miss moved to cyl 1. Got another injector from the salvage yard from another flex fuel Ranger, and now it purrs like a kitten. I have gotten new parts that were bad before, but never two in a row. Thanks again to Rockledge for all the knowledge and effort that he puts into this site. It must be a labor of love. You all have a great day!
Ed

 

Thanks for the feedback.

There was a time when I would have been surprised that you got a bad injector out of the box, but no longer. IMO, the quality of aftermarket parts has been on the decline over the past several years...