can fuel injection pulses be "seen" by an el cheapo Harbor Reight multimeter?

[Chris2012]

And does it matter if it's set tp ac or dc volts? 1992 3.1 Lumina sedan. Slowly trying to localize the reason it doesn't start.

 

We tried the mm thing. It didn't blink at all.

 

Is the computer (behind overflow bottle) difficult to dismantle? Maybe a cap blew. Will get a jump later and try to pull codes.

 

If an injector say is shorted, wouldn't that register a current draw w/all other fuses (radio,ecu, etc.) Pulled out?

[Schurkey]

If you care about accuracy, why would you choose bottom-of-the-barrel test equipment?

 

I would test fuel injection pulses with a 'noid light if possible. What is "the mm thing"?

 

While the ECM is a potential source of the fault, it would be far more likely that the problem is either lack of input from a faulty sensor, the wire harness, or the solenoid/actuator that the ECM controls.

 

PUT A REAL SCAN TOOL on that vehicle, and see what the data stream tells you.

[Chris2012]

The mm=multimeter was a friend's and was all that was available.

 

I'm sure many of us have had to get by with less than ideal equipment.

 

other than renting a scan tool is totally out of the question of the moment. I can see what is Vance has, but the morons at the local Autozone or not worth dealing with.

[RobertISaar]

pulses aren't seen easily, if at all, on a digital meter. on an analog, maybe, if the needle sweeps quick enough.

 

ideally, a silly scope would be used to watch the circuit.

 

a cheap high-speed light would be a single LED+resistor setup to operate at max current around 14 volts. you'll see the pulses on it pretty clearly.

[Turbocharged400sbc]

on the mpfi engines inj like to short out and pull down one/both banks and keeps the rest of the injectors from firing

 

so even if you dont see the noid light flash (cheap test lights work great btw) it may not be the ecm thats faulty it may be the inj is shorted

 

when i used to work on em all the damn time i had a list known good bank to bank resistance readings so i had an easy way of checking if things were ok or grossly wrong

 

if you have 1 bank (3 16ohm inj on one circuit in parallel) and one shorts out the others will barely have any power to open

 

also the crank position sensoris the other major issue i used to see

[Schurkey]

Have you ever tested the fuel pressure? Do you have spark? Having spark rules out the part of the circuit as the source of problem--proves the crank sensor is not at fault.

 

[Edited to remove reference to the incorrect noid light, and the distributor that I previously posted. Got my forums confused--mistakenly thought I was dealing with a TBI Camaro.]

Edited October 21, 2013 by Schurkey

[White93z34]

A simple 194 lamp can be used to verify pulse if that is all you are after, just spread out the leads and slide them in the injector plug. Its worked for me good in the past. No need to spend huge money on something so simple.

 

Pretty sure my Tech1 won't even tell me if I am getting pulse, and if it did it would just tell me what the ECM is commanding, not what may actually be happening. On my old Euro 3.4 I had a fuel injector die and it caused the entire injector circuit to be taken offline.

[Chris2012]

Am getting spark, at least on one plug.

 

So it ain't the crank sensor? That's a relief. Not happy to hear it could be an injector. But Ihave a hankering to pull out the ecm. Something tells me it might be that. Haven't even slapped it yet while cranking.

 

Friend who suggested the mm trick also said use a bulb. I wasn't sure if it would register or not. He was somehow.I'll try the bulb.. would like to use the oscilloscope, but there's no lectrick where I left the car LOL.also have. anold 1 mhz logic probe somewhere. Hope I didn't toss it. That works of circuit power, 5 or 12 vdc, can't remember.

 

Thanks immensely for the hot tips. One thing I know is I'll know loads more when I'm done. And.loads more then nothing is still a load!

[Turbocharged400sbc]

you can unplug the inj harness connector iirc and ohm each bank

 

i used to pull 2-8 upper plenums off those old bastards a week.

 

upper plenum gaskets are probably brittle as fuck anyways so its probably worth it to pop the plenum up a bit and ohm out each inj

 

i bet you have 3+ nearly shorted injectors

[Turbocharged400sbc]

i had a buddy with an old 2.8 wagon that had the inj behind the pump go bad so all we did was unplug it and he drove it on 5 for a week till he could work on it

[Chris2012]

you can unplug the inj harness connector iirc and ohm each bank

 

i used to pull 2-8 upper plenums off those old bastards a week.

 

upper plenum gaskets are probably brittle as fuck anyways so its probably worth it to pop the plenum up a bit and ohm out each inj

 

i bet you have 3+ nearly shorted injectors

 

Ok but the multimeter trick worked on his 2005 Ford minivan. I don't know how he got to metal, but he pushed the 2 probes from my 20$ Craftsman mm on his connected terminal while the van was running and there was a clear response on the meter (20 volt dc setting). I will point out we tried this while cranking my car with the connector unplugged.

 

This still may have something to do with shorted injectors, but I'm thinking the ECM. We tried like heck to open it, every screw was removed, and the sliding plastic thing, and after labeling the 4 connectors, they were removed. We tried prying it open but got scared. I know many of you have done this numerous times.

[Chris2012]

pulses aren't seen easily, if at all, on a digital meter. on an analog, maybe, if the needle sweeps quick enough.

 

ideally, a silly scope would be used to watch the circuit.

 

a cheap high-speed light would be a single LED+resistor setup to operate at max current around 14 volts. you'll see the

pulses on it pretty clearly.

 

For some reason I can't post the link, but ScannerDanner has a video on youtube "No Start Diagnostics (1992 Chevy Lumina)". It's not merely the presence of a pulse you need to be concerned about, but the amount of current being pulled. He uses a Mac graphing multimeter to capture an image of the pulse, alon

 

g with a current probe that registers the pulses current amplitude. Normally, according to him, .7 amps per injector times. 6 equals 4.2 amps (and they're all in series???). But he reads nearly 13 amps which leads to the conclusion that 1 or more injectors have shorted (internally? Not to ground?).

 

Can the intensity (current) be registered with a bulb, diode, fuse (-blowing) and be the means to determine there is indeed an injector problem?,

 

I dug out 2 harnesse/connectors. One (half gray, the other all black) has 2 light blue wires, one near the end, the other in the middle on the opposite row. It seems he was working with the end one, but I'll have to watch the video again. I could cut the *right* wire and install an inline bulb/diode/fuse. Or just wire something from the pin in the connector to ground?

 

It's threatening rain here so tomorrow maybe I can check the resistance at the 2 connectors/injectors, across the 2 pins in each connector I assume.. but that may not tell me anything.

[RobertISaar]

these injectors are not run in series, they're all parallel. internal shorts are very possible, that seems to be how most injectors fail.

[Chris2012]

these injectors are not run in series, they're all parallel. internal shorts are very possible, that seems to be how most injectors fail.

 

ADPTraining "injector circuit and wiring" is WRONG, current does NOT travel from ground to source-voltage. Not that is matters, I understand injectors a bit better. The original video stated all injectors fire simultaneously (?), I think, but regardless each injector pulls .7 amps from source to ground. My stating or questioning they were connected in series was incorrect and irrelevant. We all throw around the term "short", I even say I shorted A and B on the diagnostic connector together, when a short is something undesirable, and usually means a connection to ground. When it was stated injectors short internally, I was lead to believe there's a connection to ground/return, although again it's not a direct connection, as ADP states (it's flowing through 2 terminals of a transistor, the 3rd being the terminal that controls the flow between the other 2). And at least I was right on that point.

 

Regardless I'm going to try to determine if there's too much current flowing from that wire.

 

Exactly where do you get detailed info on the computer/harnesses?

[RobertISaar]

i pull the diagrams via alldata.

[Imp558]

Actually, current does flow opposite of voltage, not that it matters, but anyways you can test everything in the circuits with the tools you said you'r already using. I would try pulling resistance off the injectors, and then verify voltage on the pink wires with the ignition on. From there test continuity from the Injector plugs to the PCM one at a time and see if anything is out of the ordinary. From there if something hasn't turned up you could load the injector power wires with a large resistance like a light bulb or 2 and then see how much current is flowing, this would tell you if a splice could be corroded and limiting the available current. As far as reading the injector signal with something - again the oscilloscope is about the only game in town if you really want to see something, a 192 light bulb will tell you if it's firing the injector and that's all I've ever needed, fuel injectors are Pulse Width Modulated so they're kind of tough to read. Your car should be MPFI If I'm not mistaken, the video you saw must have been looking at something like a tuned port, batch firing a whole bank at a time, take a look at the Injector diagram for a 1993 LT1 Camaro or Firebird and you'll see an example. Hope this helps.

[RobertISaar]

with a 3.1, all injectors are fired at the same time, once per revolution. if you get down to a REALLY low pulse-width(around 1.3mS), the ECM will switch over to single-fire mode and fire the injectors once every other revolution, but for twice the duration.

 

that kind of pulsewidth is difficult to achieve though, i've never seen it happen at idle with stock injectors, you would need to bump up to near the 30 lb/hr range to cause it.

[Chris2012]

A simple 194 lamp can be used to verify pulse if that is all you are after, just spread out the leads and slide them in the injector plug. Its worked for me good in the past. No need to spend huge money on something so simple.

 

Pretty sure my Tech1 won't even tell me if I am getting pulse, and if it did it would just tell me what the ECM is commanding, not what may actually be happening. On my old Euro 3.4 I had a fuel injector die and it caused the entire injector circuit to be taken offline.

 

Ok ... 194 bulb borrowed from rear turn signsl, shoved in both plugs, either side of plenum. Nada.

 

Does this automatically mean bad ecm or could this still be a matter of injectors shorting - while cranking!? Ohmage checked out basically fine. Should I ... disconnect harness from ecm or just cut the line that pulses

the injectors and ground one end (or ground through a resistor) and check for a pulse, the bulb (would probably use a larger head light lamp at this point) that way?

 

I could lift the uim of course and ohm each injector, but I feel the bank resistance checks out with reasonable accuracy already.

 

In short, if the ecm was functioning properly and sending pulses, would the bulb trick not register on account of shorted inectors?