Injector pattern discussion starter

Justin Mobile Technician Utah Posted   Latest   Edited  
Discussion
Driveability
2010 Mazda CX-9 Grand Touring 3.7L (A) 6-spd (AW6AEL) — JM3TB3MA9A0202940
P0171 — System Too Lean Bank 1
P0316 — Engine Misfire Detected on Startup (First 1000 Revolutions),
P0201 — Cylinder 1 Injector "A" Circuit
Engine Misfire
MIL Flashing
Intermittent

This vehicle was not misfiring when I was at the shop to test. Freeze frame was only available on P0316. Open loop so no fuel trim data that would help. Currently no misfire felt and fuel trims currently were LT+18, ST -20 and trending to lower LT. So not happening while I was testing. This had a code for injector 1 circuit. So I decided to current ramp all injector coils. Cylinder 1 is in the rear under the intake. I chose to sync off #4 for speed. I have fixed this vehicle already. So not looking for help diagnostic help. This is only to help spark discussion. So I guess discuss. 

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Albin Diagnostician
Washington
Albin Default
 

You made the diag job way too easy :) Its way cool when you can get a scope capture of something wrong, when the engine is still running ok.

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Justin Mobile Technician
Utah
Justin Default
 

Thanks Albin

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Chad Technician
Florida
Chad Default
 

Injector#1 ramp is lower than the others. Since intermittent I would say that the injector breaks down more with heat causing the misfire

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Justin Mobile Technician
Utah
Justin Default
 

Except it misfires on startup. This was a warmed up engine.

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Chad Technician
Florida
Chad Default
 

Ok. I’m between jobs and don’t have access to service info. That being said. I know we have a current flow issue. You avoided syncing #1 because under the intake So obviously your not going to check the connector yet. I’m thinking there may have been an issue with a large harness connector. Some resistance that is effected by weather possibly. I believe we see the pintle moving off it’s seat…

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Justin Mobile Technician
Utah
Justin Default
 

What happens to amperage when resistance goes up?

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Chad Technician
Florida
Chad Default
 

Amperage goes down lol

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Justin Mobile Technician
Utah
Justin Default
 

Where is the most likely spot to find a temp related resistance change be? Would it be a connector?

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Chad Technician
Florida
Chad Default
 

Most likely would be injector itself. Second would be the control switch. Wiring and connectors are usually heat resistant unless damaged or aged.

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Lane Mobile Technician
Kentucky
Lane Default
 

Lean miss when cold, with a injector current ramp like that. Just for editing purposes, your post says you current ramped the coils, when i believe you meant to say injectors

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Justin Mobile Technician
Utah
Justin Default
 

Nice catch. Thanks.

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Brin Diagnostician
Florida
Brin Default
 

It looks like the firing order is 1-4-2-5-3-6. The current in the cylinder 1 injector circuit it low relatively speaking. The lower current in that circuit suggest that the injector has excessive resistance. That combined with the cylinder 1 injector circuit code, the cylinder misfire at start up code and the bank too lean code, I'd say that the cylinder 1 injector is the cause of your customers…

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Rassiel Technician
Florida
Rassiel Default
 

Lower amp draw on injector 1 which indicates high resistance, however there is pintle which indicates that the injector is mechanically ok and operating at this time, Longer dwell time caused by the fuel trim correction, DTC sets when cold on initial start up due to the open loop condition, ECM is not keeping that injector on long enough to get the pintle to move until it reaches closed loop. My…

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Justin Mobile Technician
Utah
Justin Default
 

I like it.

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Eric Owner/Technician
Michigan
Eric Default
 

While it’s true there is the pintle bump, the amplitude is much lower than normal. I suggest it moved, but very little and caused a lean cylinder.

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Bob Owner/Technician
Massachusetts
Bob Default
 

Hmmm, did the injector really open? I see a pintle hump but if you look at the pintle hump on the good injector, it is at the peak amperage of the bad injector. I think Eric is on the right track. The pintle may have moved but very little causing a lean miss.

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Justin Mobile Technician
Utah
Justin Default
 

I agree with your thinking Bob but, do you think this slight drop in amperage would be enough to set the P0201? The customer stated when it runs bad the engine light flashes and he can feel a noticeable running problem. This engine was smooth in all ranges when I was testing. fuel trims were correcting. I do think the injector was opening and flowing at the time of this capture.

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Richard Technician
Virginia
Richard Default
   

I think the pintle moved in your capture but due to the added resistance , the effective on time has been shortened because it took that much longer to build a magnetic field .Having a capture when it is cold, could show even more resistance and therefore a much shorter on time or the inability to reach enough current to move the pintle .

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Bob Owner/Technician
Massachusetts
Bob Default
 

It would have been nice to see the voltage pattern for the bad cylinder. I believe the computer looks at the fly back voltage to judge the health of the circuit and it was probably very weak on that cylinder.

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Rick Technical Support Specialist
Missouri
Rick Default
 

I do agree with bob, Just for giggles I would have liked to see the voltage on # 1. Great scope work and conversation.

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