Testing clogged injectors

Darren Technician Wisconsin Posted   Latest  

Without disassembly, fuel systems without a pressure regulator…..

what’s the best way to check for electrically good

but clogged injectors…..

I am keeping an open mind.

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Marvin Mechanic
Mississippi
Marvin
 

Find a diesel shop that tests gas injectors…its dangerous doing on vehicle with injector out in the air and spinning motor…I know a guy who did this a year ago ….injector spraying over engine al was well,spark from wire exploded it ,burned off all facial hair,eye brows and eye lashes…

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Cody Diagnostician
Illinois
Cody
 

Use a fuel pressure gauge and command each injector on one at a time for the same amount of time. Cycling the key each time to make sure the starting pressure is the same on each injector. One or two injectors should stand out with less pressure drop than the rest. I think one or two manufacturers have a test built into scan tool.

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Glenn Owner/Technician
Texas
Glenn
 

Hi Darren, A good scope works best. When an injector fires it has a smooth upward ramp, then collapses down. At the end of the collapse line there will be a slight hump/bump that will indicate the pintle is fully closed and the magnetic field has dissipated for the event. Scanner Danner and Real Fixes Real Fast on You Tube have some good examples. It takes some practice reading good patterns…

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Jürgen Owner
Mexico
Jürgen
 

A clogged injector may show pintle humps but not delivering the right volume. The pintle hump just proofs that it's functioning electrically, it still may have flow problems due to restrictions.

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Tim Curriculum Developer
California
Tim
 

I've been using a pressure drop test for each injector, where the fuel system is pressurized key-off and each injector is cycled to watch gauge or PID pressure drop. In the photo I'm back feeding the fuel pump circuit using a Lisle relay test block, then disconnecting to let the gauge stabilize. The only hard part is ensuring that each injector is energized for the same amount of time. I use the…

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Nelson Diagnostician
North Carolina
Nelson
 

For MP injectors on vehicles without a scan tool bi-directional control to pulse injectors, I use this OTC fuel injector tester and monitor fuel pressure drop using a fuel pressure guage. You might have to create your own lead attachments to adapter to your injector pins Perform this test on a cold engine or you could get false results on hot engine.

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Jürgen Owner
Mexico
Jürgen
 

On high(er) pressure systems like GDI and common rail that feature metal rail tubing you can put a piezo sensor onto it and scope the signal. Often it is possible to get a signal that allows to judge the relative pressure drop between injectors. You would sink to one injector to identify which is which. There are also dedicated pick-up sensors available for this purpose, I use the ones I bought…

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Stephen Owner/Technician
California
Stephen
 

Fuel pressure drop. Cycle the fuel pump get a baseline reading for your fuel pressure. Cycle each injector one at a time with a scan tool, and note the pressure drop. The ones with the least drop are the ones with the clog. Each injector test, you'll have to cycle the fuel pump

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Mike Instructor
Utah
Mike
 

What kind of vehicle? I usually install a fuel pressure gauge and use an injector pulse tester. Key on then off, note fuel pressure, pulse injector (usually 100 pulses @ 5ms each), note pressure drop. And repeat for each injector. Generic example, if I had 35 psi and it dropped to 25 psi after the pulse. I would want to see the same drop from each injector. If I had one only drop to 30 psi then…

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Benjamin Diagnostician
Connecticut
Benjamin
   

i haven't done this often enough, but i recall finding a faulty injector on an early 2000s Toyota Camry V6. I used a DSO to find that one of the injectors' waveforms was slightly different than the others (can't tell how, it was ten years ago). confirmed this with a stethoscope, that injector was kind of thudding into place where the others were more clicky. The problem was, if I recall, a…

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Randy Curriculum Developer
North Carolina
Randy
 

If it's returnless PFI I like to pressure drop test. GDI is automated in the scan tool but won't tell you about spray pattern. You can pass a balance test on GDI and still have a misfire due to spray pattern issues.

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Paul Owner/Technician
California
Paul
 

Some of the newer cars (2020 Prius for example) will set cylinder mixture imbalance codes based on the AF sensor output and the crankshaft position sensor. Check the code description for P219C00 for more information. You might be able to find a very fast micro-amp probe to monitor the AF sensor output with an oscilloscope, and then sync it to a cylinder with a little experimentation. It's…

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Glenn Owner/Technician
Texas
Glenn
 

Hi Darren, Is there a particular make and model you are dealing with? I expect answers will be all over the place because there is no ‘one size fits all’ methods when testing injectors. Going by the manufacturers service and testing recommendations is the best baseline to use.

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Darren Technician
Wisconsin
Darren
 

Nothing in particular,, just looking to be more efficient. wasn’t sure if o2 sensor readouts brought anything to the table, or possibly 5 gas analysis

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Rufino Technician
California
Rufino
 

I capture this waveform with a clogged injector 4 on a 96 Chevy Tahoe with a old style poppets, this car didn't have the option to perform injector balance and the pressure regulator is under the plenum. Blue trace is fuel pressure with 5x zoom, green is control to injector 1 and red trace is current to injector 4

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Ray Diagnostician
Ontario
Ray
 

Scope the primary coil winding volts or the secondary and do a steady 1500 rpm brake torque. This capture is from an 01 Infinity and I put a strip of aluminum tape on the tops of the 3 front COPs. I've connected the scope's secondary lead on one end of the aluminum tape. The left rising secondary spark plug's burn voltage shows the cylinder with the injector disconnected. The right secondary…

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Darren Technician
Wisconsin
Darren
 

So far , ignition analysis seems to be the most efficient!!! on flat rate, need to be quick and precise!!!

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Aaron Diagnostician
Iowa
Aaron
 

For one's that don't have the option built into the scan tool I use the OTC injector pulser. I like to find a common place to test all the injectors instead of at each injector. For instance on the E-450 the PCM is easy to access then I use the proper terminal probes and a connector end view to test the injector and the complete ckt from the PCM. I have also tried using a pressure transducer on…

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Darren Technician
Wisconsin
Darren
 

Good idea

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Dennis Owner/Technician
Utah
Dennis
 

When injectors are sent into us for cleaning and testing even looking down inside the fuel injector filter it is hard to tell how clogged they are. I have tested them on the car for fuel pressure drop before but unless you run each one into a measured test tube you do not know the volume. When we test them we make sure they are within 3% of each other. We have had cars in that had a lean code…

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Marvin Mechanic
Mississippi
Marvin
 

Dennis that was what I advised at first post,,,,a local shop here flow them at different pulse rates and flow a whole set at a time…

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Fatih Mobile Technician
Ontario
Fatih
 

I like scoping injector power wire with a low amp clamp. Here is an example from a 2012 dodge ram pickup with 5.7 liter hemi. Cylinder 2 had a missfire that did not go away with new coil and plugs. The shop called me in to diagnose problem. first picture is other cylinders. Notice how the current ramps up linearly. Second picture is faulty cylinder.

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