Dave51

But if your point is "In the LL corner it says you're using 20V scale so that spike is off the charts!" maybe it is, cause my #1 injector ain't really what you're call in the best of shape:



But yeah it's on the "To Do" list. My gas mileage is horrible (I think)(figuring out that is on the "To Do" list too) but this could turn into an interesting case study.

Dave51

Or not.

Adding the measurement function (which is one of the things I'm not crazy about with the Hantek, there's no scale, you can only measure points or calculate it manually) shows #1 (as well as the other 5, not shown) peaking at about 60V (which IMO should be used as "normal" for 2000 XJ).

Dave51

Then with your current clamp, you can also measure the current simultaneously:

Dave51

So anyway, that beat up old injector is fine so on it lives!

awg

thanks its all part of the learning curve using a scope ( dont have one atm)

after reading up on using a scope to diagnose injectors, I see the pulse spikes up to 100V+ due to it being a coil opening and closing (I know coils work like that lol)

I was just thinking about 0-12V, (like most guys would be probably thinking also), so you need to know what you are looking at and for with a scope

BlueRidgeMark

Yes indeed!

CHGreen01

UPDATE: So I drove the Jeep all last week and it was running okay other than that roughness at low rpm. Checked everything, all new vacuum lines, any other tune up items I could think of that I hadn't done lately. Nothing would fix it. Then all of a sudden this weekend I got the fuel injector CEL again and the Jeep started running horribly again. Checked all the injectors with the noid light and #2 fails. Unplug it and plug it back in nothing changes with how the engine's running. So I check voltage on the positive wire and I get 13.9V, so that's good. Then I pull the PCM plug off and check resistance between pin 15 and the injector ground...0.3 ohms okay, then I check continuity between the same points and get a solid ring from my multimeter. It's gotta be the PCM right? If it was one of the two PCM grounds (Z12) wouldn't some other injectors have the same issue? Also, I had already checked that those grounds were good last week (cleaned it and checked resistance). Next I tried cleaning the actual PCM pins with some contact cleaner and a brush. No change. Should I take the PCM apart and check that pin connection? Replace the PCM? What do ya'll think?

Dave51

Those would be the next logical steps.

awg

as the PCM grounds the Injector, it probably must do so via an individual semi-conductor to handle that ~60V spike ( I think)..this may have failed

unless its the individual Injector itself ?

for a '95 a junkyard/ebay PCM should work without ant VIN coding, Google the part number on the PCM

Dave51

But if

and

it would seem the issue is between Pin 15 and Driver 2, or Driver 2 itself.

97grand4.0

Does sound like an injector driver issue, but good luck taking a PCM apart, I tried it, not worth it. You will ruin it, trust me. Better off replacing it, or locate one so you know you can go buy it. I got one for my 97 grand for about $100 at advance, a cardone rebuilt. Worked perfectly, and fixed a shifting issue with the transmission. So it didn't fix what I hoped, but fixed something completely unexpected.
Also you can chase your tail sometimes with the codes, too bad you don't have Dave51's scope to look at the injector waveform to verify bad. All I'm suggesting is maybe something else more global, like a cam sensor..which does time the injectors I think

BlueRidgeMark

Agreed. Been there, done that, didn't work. And electronics is my living. The problem is that the components are sealed with a goo that defies all solvents and can't even be removed mechanically.. I did some extensive research, and the only chemicals that will remove that stuff are horribly toxic and very expensive.

Don't bother.

97grand4.0

Yep. I watched some youtubes and the guy was claiming he was removing it with acetone, so I went for some acetone, and it didn't even touch it. By the time you scrub it with a brush or something you have wiped out hundreds of microscopic laser printed resistors and caps. Just ridiculous.

BlueRidgeMark

I actually talked for a while on the phone with the guy who owns one of the companies that refurbs them. He said the most common failure mode is that the electrolytic caps dry out and fail. They just cut the goo with a utility knife, and clip the caps out, and solder in new ones. Then they run them through a tester, trash the failures, reseal and resell the ones that pass.

Trying to replace any of the chips on the board would be more trouble than its worth.

Dave51

I've got a bagful of 220µF 35V capacitors (you probably have 25V but these are better). LMK if you need a few.