#1 injector won't spray..

Mossy
Hickory
98 xj 4.0

OK this isn't making any sense... Finally got my jeep running.. But it sounds like a subaru lol..
Meaning its missing really bad..

Number 1 injector is not spraying..a far as we know..
Tested with volt meter.. 12.5 volts to the power side of injector... And getting continuity from the injector pin down to the ecu as far as ground goes.. So I should be getting fuel right.. Also was getting p0201...

What's weird is with the noid light hooked up to the clip number 1 is the only one that doesn't light up..

I thought to myself lets say that the ground wire was grounding out some where before the ecu.. Wouldn't I then have a completey open injector? Even more wouldn't the noid light stay lit up?


Changed ecu and no difference... I'm stomped.. Any suggestions

Have you tested the injector? Were you not getting a missfire code?

So far it sounds like a connector or wire problem to the injector, maybe the #1 ground at the ECU connector?

If all the others are firing and you tested with a noid light, then you either have a shorted injector, a bad wire back to the ECU, or a bad driver in the ECU. Start by swapping the wires going to the injectors and see if the noid light failure follows the injector. It it doesn't, the you should check the wiring. Disco the battery and use an ohmmeter to check from the ECU to the injector. If both the ground and power to the injector are both good and the power isn't shorted to ground, you most likely have a bad ECU. You might try reseating the connector on ECU.

old_man said:

Start by swapping the wires going to the injectors and see if the noid light failure follows the injector.

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Is there a typo in that, or am I miss reading it, or what?

If not, how in the world does one do that?

He has already tried another ECU. And tested the wire pair, disconnected from the injector with a noid light, and got no flashes.

I am surprised he has not tested the injector directly, with an ohm meter, and listening device to see if the injector opens, or told us he did. All it takes is a 9 volt battery to test the injector, to see if it opens.

Ecomike said:

Is there a typo in that, or am I miss reading it, or what?

If not, how in the world does one do that?

He has already tried another ECU. And tested the wire pair, disconnected from the injector with a noid light, and got no flashes.

I am surprised he has not tested the injector directly, with an ohm meter, and listening device to see if the injector opens, or told us he did. All it takes is a 9 volt battery to test the injector, to see if it opens.

Click to expand...

I havent tested the injector to see if it opens. I assumed since I wasn't even getting signal to it that there was no point in testing it.. That was my initial thought that the injector was stuck close... But before testing the injector I tested the wiring.. I'm getting p0201 as far as codes go... But what confuses me is I get 12v to all injectors including #1 and continuity in wire from clip to ecu .. 0 to 5 ohms.no more than 5.. That should assure me that there is no break or short in that path correct?.. But what puzzles me the most is I've changed the ecu but I'm still not getting the ground signal from the ecu.. If I have power and continuity then only thing I'm lacking is the signal correct? I believe it to be highly unlikely for both ecus to not get signal to the same injector.. Esp since the newest ecu came from a perfectlyrunning jeep..... I'm a decent mechanical mechanic.. But electrical is not my thing.. I'm mosley running off of common sense..I think I've done pretty decent so far.... So please understand I'm trying my best to gather as much data as possible

Ecomike said:

Is there a typo in that, or am I miss reading it, or what?

If not, how in the world does one do that?

He has already tried another ECU. And tested the wire pair, disconnected from the injector with a noid light, and got no flashes.

I am surprised he has not tested the injector directly, with an ohm meter, and listening device to see if the injector opens, or told us he did. All it takes is a 9 volt battery to test the injector, to see if it opens.

Click to expand...

What it means is swap the connectors between #1 and #2.

If the wire pair has actually been tested correctly, then the other ECU must be bad as well (not likely).

If the ECU is functioning correctly and the wiring is fine, then the noid light would have to light up.

I am not an EE, old_man is so maybe he will chime in again, but I have seen test meters read power, or grounds, or odd readings that were not really there once the load or ground was needed. In some cases it was the meter, LOL, dying battery, or me forgetting to move the damn connectors as I switched from volts to ohms or visa versa.

I would check both wires, do some creative stuff like ground one end of the noid light directly to battery negative post and then use the 12 V signal connection from the wires to see if the noid light lights up. Or do the opposite. Ans check the meter internal impedance (or resistance) and make sure it is measuring the ground accurately.

I suspect it may be the female pin the ECU bulk connector on the ground that is loose and not making good contact from all the details you have posted.

old_man said:

What it means is swap the connectors between #1 and #2.

If the wire pair has actually been tested correctly, then the other ECU must be bad as well (not likely).

If the ECU is functioning correctly and the wiring is fine, then the noid light would have to light up.

Click to expand...

Thanks. I agree.

Ok guys I'll be on it tom afternoon... Will be back to post results

Check the plug wire too,,,

Wayne Sihler said:

Check the plug wire too,,,

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I assume you mean check it for spark? I suspect he has already, but it may be a good idea just in case the computer is shutting down the injector signal due to a missfire detection, but is not bothering to tell the OP on a scanner yet.

I had a similar problem on an OBD-II rig recently, where the plug wire was disconnected, but the PCM never threw a code, because it had been reset and had not completed the relearn procedure. But in my case it had not shut off the spark, just had not thrown a code like I would have expected. So who knows what other code, no code idio-syncrasies exist in the error code processes.

So you are saying that there are conditions that can cause the pcm to shut down signal to a specific injector?

mossyoakblack said:

So you are saying that there are conditions that can cause the pcm to shut down signal to a specific injector?

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Yes indeed. When they throw a CEL light with a cylinder miss fire code, they shut off, stop firing, that cylinder, the one that was miss firong, to protect the catalytic converter from overheating (which is caused by too much unburned fuel), and and to protect the cylinder walls so un-ignited fuel can not wash down the oil and cause piston ring, and cylinder wall damage.

Ecomike said:

I assume you mean check it for spark? I suspect he has already, but it may be a good idea just in case the computer is shutting down the injector signal due to a missfire detection, but is not bothering to tell the OP on a scanner yet.

I had a similar problem on an OBD-II rig recently, where the plug wire was disconnected, but the PCM never threw a code, because it had been reset and had not completed the relearn procedure. But in my case it had not shut off the spark, just had not thrown a code like I would have expected. So who knows what other code, no code idio-syncrasies exist in the error code processes.

Click to expand...

Exactly...
Long ago the wifes 98 had a misfire...noid light check yielded Ok injector,cylinder still dead,plug wire ohme,d (sp) bad,replaced wire set ..All was good.

Don't forget to check the injector harness--follow it along back to the firewall testing it at intervals.

As my mind is the thing I miss most, my old memory seems to keep thinking of a weak connection in the harness around where the lead comes out for the distributor--worth a look-see if BOTH ECUs couldn't pass a signal.

I have seen several 4.0 in xj/zj and wj's with a misfire caused by the left rear head bolt stud rubbing through the main harness and shorting the signal wire for #x injector.