97 Ford Ranger injector driver

I have a 97 ford ranger that will wont fire the cylinder 4 injector at idle or low rpm and then intermitenly at high rpm. I know its a control problem because I tested the feed wiring and its ok . Could it be a short to ground on the control wire? Or computer driver?

ScannerDanner has many videos on how to test this type of circuit, named ground side switched circuit or pull-down circuit.

I suggest using a test light and perform a clear flood crank and see if the injector fires all the time. The reason I say this is perhaps the PCM is shutting down this cylinder since it is detecting a problem with this cylinder. Also, the reason I say at crank is that PCM will fire all cylinders; whereas after the car is started it might turn off a cylinder.

Are you able to perform a current graph of this injector? You might notice a short in it as it warms up if you can.

I also don't like noid lights since they don't necessarily tell you the driver circuit can deliver the necessary current for a real injector.

If you don't have equipment to perform these tests, swap the injector with another cylinder and see if the problem moves.

Thanks for awnsering me so quickly. It started off with a dead miss. It had a cylinder 4 misfire code. I checked for spark checked out ok. I put it on the 5 gas and O2 was 4.5 % and HC and Co were low. looked just like a no fuel problem. sprayed around with carb cleaner while on gas anallyzer got no change in readings. Performed relative compression test with verus all cylinders looked even and sounded good. checked injector voltage waveform on control side of injector at computer. couldnt get to injector its under intake on 4 cylinder. It would fire intermittenly. So me being inexperienced and working on flat rate I recommended an injector. Replaced it . still same problem. Can a transistor in the computer work intermittenly or do they just stop working all together? You mentioned test light. I tried the noid light. How do I connect the test light. aligator clip to bat pos and test light to control wire? thanks again

For the test light procedure, please look at the several ScannerDanner videos; he is the professional/master. But yes, you want to connect your test light's clip to battery positive and connect the tip to the control wire, since your test light is a load, you won't hurt the driver when it turns on. The light should flicker at idle. I suggest not revving the engine since you might not be able to perceive the blinking, for this type of test I use a scope.

DON'T DO THIS; the following paragraph was just discussed for clarity: For discussion sake, let's pretend you hooked your test light to ground. Since you are completing the control circuit, you might actually turn on the injector for a prolonged period of time (depending on the impedance of your test light), which could burn up the coil in the injector and/or could flood the cylinder with fuel. In all cases, clearly this is NOT good. I just thought I'd discuss this for clarity; I'm sure know this, but perhaps other readers would not.

Did you test the old injector? Was it shorted? If so, that 'could' have damaged the driver but not always a death sentence. Some PCMs are very cleverly built and designed.

What was the result of the NOID test?

Didn't you say you checked the injector driver at the PCM connector? Am I right in perceiving that you said it looked good there? Could you be experiencing a control side wiring issue, wiggle open condition, between PCM and injector?

In regards to a driver being flakey, since the driver is electronic, it could go south as it heats up or whatever. But, before condemning the PCM, you really want to determine what is really going on, since that could be a big expensive mistake.

How did you check for spark? Did you use a test light with a decent spark plug gap? ScannerDanner has many videos on this. I personally love this test. It's alive; it's alive. LOL

When I look at a five gas chart/graph, I can't find a condition where o2 is 4.5% and hc is low. From the graph I'm looking at, hc should be high(like 6.5%ish) when o2 is 4.5%ish. Does this imply it is being burnt but you have a condition allowing oxygen into the exhaust stream? Not sure on this. But definitely a question for me....

How are your fuel trims, long and short? What does mode $06 -> $53 indicate? Is it still complaining about cylinder 4? I know these aren't always reliable, but they are more useful if a cylinder is in really bad shape.

Ya I checked the injector at the pcm and it wouldnt fire at idle but when i reved it up it fired intermittenly . And when it did fire the waveform looked good. The noid light only lit when i reved to higher rpm. It wouldnt light at idle or slow speed. The HC is unburnt fuel and CO is carbon monoxide produced by an over rich condition. So when CO And HC are pretty much 0 and Oxygen is high its kinda like an air pump with no fuel . The fuel trim was pos i think.

I'm thinking about how to determine if the PCM is receiving all the input it needs, e.g. CPS and CKP which are used for spark and injection pulse timing.

When the injector is not firing, is the corresponding spark plug firing?

I ask this to see if the PCM is getting its necessary inputs to fire that cylinder. So, it would be odd if both all of a sudden don't work at the same time, which could mean the PCM is doing this on purpose.

So, I can tell you're leaning towards a bad driver in the PCM. I suggest you watch ScannerDanner videos where he validates drivers, verifies necessary PCM inputs, and then powers and grounds before giving the PCM its last rights. In addition, let's say the PCM did die, I would want to know why it died, e.g. did the old injector short out which cooked the driver? I wouldn't want to put in a new PCM and then have the same condition kill it.

Do you remember the Ohm value of the old injector? Did it match vehicle specifications?

I find it odd that it fires the injectors at high RPMs intermittently but not lower RPMs at all. This one has me scratching my head.

I thinking of a wiring issue vibration frequency can cause shorts and breaks to make and break contact. I think my next check would be to use a test light to determine when the injector is not firing if it is because of loss of +ve power or lack grounding via the control wire.
If it is the power side it should be an easy fix, control side might be more complex but the fact the injector is firing at raised RPM makes me think of wiring or soldered joint issue.

This is a great video showing intentional injector driver shut down on a Honda Odyssey.

Definitely some great suggestions in the posts above. I've been thinking about this one at work today, I'm curious to see where this ends up going.

Thanks guys for your interest in my post. And thanks for all the suggestions. Sorry about my spelling and grammar. I'm terrible at typing . I did check the control wire for with test light. I got the same thing at the computer and at the injector itself. the no flash at idle and intermitten at higher rpm. I think I'll take the advice and check the inputs. And check to see if the spark is shutting off too. Thanks again for the help.

I dont think a 20 year old vehicle would have intentional shut down of an injector. that's just the beginning of obd 2 almost.

I read multiple times in this thread about no pulse at idle and only intermittently at WOT.
The key with identifying "intentional shut-down" is viewing injector pulse during the initial start-up, for the first 5 seconds or so.
If it is there, you need to look away from the injector circuit and check ignition and compression on that cylinder.
If it is NOT there, then you need to follow Andy's advice about the wiring harness having an issue.