Help asap!

[Flashback98]

89 4.0 Renix xj, had a stutter/misfire that would only show once a week after a long drive, would seem to disappear the next day.
Happened the other night, it died, took a few minutes to start back now the misfire is constant.

Thought it was a fuel issue, all injectors produced a change In idle when unplugged besides #1. Replaced injector #1, no change, pulled plug wires individually and showed the same thing cylinder #1 produced no change when unplugged.
Plugs are new and I have good spark from #1 plug wire. Cps was replaced about 2 months ago. What’s my next move please help??
Apart from what I listed above, what else besides compression issues can produce a misfire that seems to be exclusive to only one cylinder?

 

[Anak]

Put a noid light in that #1 injector plug. See what you get.

 

[Flashback98]

Put a noid light in that #1 injector plug. See what you get.

Thanks for the response, is this possible to check with a multimeter ?

 

[Saudade]

A "noid" light is merely a low wattage 12v bulb and a pair of jumpers (test light). Placed across the pins in the FI connector, the bulb should flash to indicate the injector is getting pulse.

You can use a mechanics stethoscope (or a long bladed screwdriver) to hear the injector clicking as the engine is running. Listen to the others to know what it should sound like.

A digital multimeter on volts may not work as the pulse is too fast (depends on the meter's response time). You can certainly try it. The reading will jump around, likely at a low voltage. An analog may work and you'll see the needle flicker.

You can also test the resistance across the pins on the injector. Check them all to compare readings.

You can check for ground on the negative side (black wire) of the connector. On Renix, all injectors share a common ground. Each one gets power from the ECU when it's their turn to fire.

You can also wiggle the main harness along the VC to see if there's an intermittent connection. Also check the connector for corrosion.

 

[Anak]

A set of noid lights is pretty cheap: $25 for a typical set on Amazon

If you are going to try to maintain an older, fuel injected, vehicle odds are good you are going to use these more than once.

Or you can probably "rent" them for free from your local auto parts store.

 

[Unclewolverine]

Yes oreillys rents them. Also switch the injector to a different cylinder and see if the misfire follows. If it does not you likely have a mechanical problem such as a bad valve, flat lobe, etc. Compression check may help.