I need to buy a scope...

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someotherguy

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I don't know if it's the same alternator but many of the fullsize cars and Jeeps of the same era were under recall for alternator failure which sometimes resulted in the alternator catching fire. While the parts house alternators may be junk (and I'd agree most are) that doesn't mean Ma Mopar is immune to problems. Hopefully if you got one from the dealer today they would have learned their lesson and produced some that don't go nuclear on a whim.

Richard
 

Jeepwalker

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There are some pretty inexpensive scopes on ebay ..like cell phone style scopes. Rarely does a guy need one tho. Hope you zero in on the problem..
 

BPR Speed

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You can also look into used Fluke Biomedical scopo-meters if you want to invest in a quality piece. Even the 80's era scopes are pretty decent and the new ones will auto adjust for frequency and voltage. I use Fluke often when repairing medical equipment (my primary job). May not have the most desirable repair support as Fluke likes to change and update their support and new goodies every other year, but I've never have too much trouble with the scopes. I have about 30 pieces of test, measuring and diagnosing equipment from Fluke.

There's mulit-meters out there now over the counter and Amazon that can pick up wave forms but I've yet to get my hands on one.
 

Jeepwalker

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There's mulit-meters out there now over the counter and Amazon that can pick up wave forms but I've yet to get my hands on one.
I've seen them too, they look pretty enticing, don't they?!! I'd buy one but I already have two scopes that I've always been able to find the problems w/o them. But there's always a time and a place...
 

grey wolf

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I picked up a used Vantage Pro a while back, but I haven't really had a great opportunity to use it yet. Seems pretty easy to use, and there's guided component tests in there. Mine's updated to 2010, but I think they stopped making updates for it in 2014 or something, and you can no longer update them through Snap on. It doesn't matter unless you need the guided component tests for newer model vehicles though. If you know the parameters you are looking for and you set up the scope accordingly, it can be used on anything. Another warning, most likely a used one will need a new battery, which is still available from Snap on, but very expensive.

I've also heard good things about Pico scope, which hooks up to a laptop. The software on those is supposedly quite good and they are reasonably priced, relatively speaking.
 

stutaeng

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Well, I wound up buying a "KAL EQUIP" scope pretty cheap, which seems identical to the OTC. The guy I bought it from was a retired mechanic and just used it one time. It came in a case with instructions and a bunch of connectors.

As expected, the battery wasn't holding charge. I ordered and installed a new battery from Amazon for $10.

I was just playing around with it. It's pretty cool. It's like a graphing voltmeter with minivolts as a function of microseconds.

First up, since I really don't know what I'm looking at and how to interpret data: my 06 Suburban daily driver. No known issue and in this generation they had gone to that PWM ECU controlled alternator.

After playing around with the time settings, I was able to see different waveform as I went from everything inside off, to everything electrical turned on. First 2 photos.

Next, I went to the Chrysler. No real waveform, no matter what I turned on or off inside. Last photo.
 

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stutaeng

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Yep...that looks like my MATCO 'scope, a rebranded OTC.
Question for you Schurkey:

I know fuel pumps are sort of a "common" issue on these GM trucks...wether actually bad or misdiagnosed, who knows? I usually advocate getting properly diagnosed before changing them. I do own a few fuel pressure guages...

I must admit, I have never replaced a fuel pump in my life (don't laugh!) My 99 has 265k and it's the original pump. I bought it from the original owner and it only had around 88k in 2007, now living with a second engine & transmission...


My other trucks(GMT 400 K3500 w/ 204k, now 208k "weekend work truck"
; GMT 800 06 "daily" and GMT 800 04 w/ 186k "just sits", awaiting a future life), so I don't know the history on them. My 06 "daily" is close to 250k now, which I bought with 225k only 3 years ago...in short, all high-mileage old Chebby trucks.

Should I try to screw around with checking the fuel pump commutator with the scope? I've seen guys do that and it reveals a commutator that's worn out, usually when they are replacing the pump that has failed altogether.

Part of me says let sleeping dog lie...Then there's the aftermarket worries...I mean who changes fuel pumps as preventative maintenance? :D
 
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Schurkey

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After swapping out faulty #5 injector I'm finally runnin on 8 cylinders again. But now I'm getting map sensor low voltage code. I'm wondering before I tear intake off again if this could be caused by the upper intake rubber rolling out n getting a vac leak or I should look at anything else. Any advice appreciated

Question for you Schurkey:...

...Should I try to screw around with checking the fuel pump commutator with the scope?
ABSOLUTELY!!! You'll need a low-ampere probe (inductive would be most convenient.) I got mine from https://www.aeswave.com/low-current-probes-c496/ although the one I bought doesn't seem to be listed. It's very similar to the 0--60 Pico probe. It comes with a BNC connector, I had to buy an accessory harness to convert BNC to banana plugs--not too expensive.

Then you set up the 'scope to show the instantaneous current draw of the pump while it's running. Each armature bar produces a "hump" of current draw as it becomes aligned, is perfectly aligned, and then goes out-of-alignment with the motor brushes. The "average" current draw may be--for example--about six amps, but the peak and minimum current draw will be a little on either side of the average.

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It's best to connect your 'scope in conjunction with a fuel pressure gauge. Correlate the amperage draw with pressure produced.

1. Maybe you find out the fuel pump is wearing-out, and now you can plan to change it at your convenience instead of as an emergency repair.

2. You get familiar with the process, you get familiar with your scope, and you learn what the waveform is supposed to look like.

When you get the pattern set up and "Frozen" on your 'scope, you'll find that the waveform of each of the armature bars are like fingerprints. (Every fingerprint looks the same to the person who has to clean the window, but every fingerprint is different to the detective trying to find evidence.) You need to be more "Detective" than "Janitor". At some point, you'll find that the pattern of individual "humps" repeats. You'll count the number of humps before the repeat--8 humps on a fuel pump is common, but some brands have 12 or some other number. That represents the number of bars on the motor armature. Each bar has it's characteristic current draw, which shows up on the 'scope.

Then, using the magic of digital storage oscilloscopes, you'll find the amount of time it takes between repeating patterns. Divide 60,000 by the milliseconds for one pattern to calculate fuel pump motor RPM.

Keep a notebook of results from your tests--Vehicle, pump brand, average current draw, peak current draw, number of armature bars, fuel pressure developed, anything else that draws your attention--as you check more fuel pumps, you'll develop a history of known-good and known-defective pumps.

This technique works for other automotive electric motors besides the one powering the fuel pump--the HVAC blower, for example, or the motor that raises and lowers a power antenna. With appropriate set-up, you could get a pattern from AC motors, too--refrigerators, window Air Conditioners, fans--whatever.


I mean who changes fuel pumps as preventative maintenance? :D
Guilty as charged. My Trailblazer is due again.



Here's my thread--on another forum--with photos of my Snappy Counselor II scope and the fuel pump from my K1500. I just checked, the photos are visible. If you don't see 'em, it's likely due to an ad-blocker on your browser.
www.thirdgen.org/forums/tbi/612473-tbi-fuel-pump-upgrade.html

 
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