2014 Malibu wont stay running. Any input is appreciated

Sam Mobile Technician Michigan Posted   Latest   Edited  
Resolved
Driveability
2014 Chevrolet Malibu LT 2.5L (L LKW) 6-spd
Stalls

I am a mobile tech in the Metro Detroit area. I do very few used car lots for a reason. If you know, you know. Not getting into that here. I get a lot of work from this used car lot and they are really good to me. I do a flat rate on diagnostics and I win some and lose some. Many times I tell them it is not worth fixing and just run back through the auction. Maybe I should have with this one. The purchased this 2014 Malibu with a check engine light on. No big deal here in Michigan. The front o2 sensor was unplugged. It appeared plugged in. Somebody has been trying to fix this. It has a new throttle body, and the front o2 has been replaced at least once. I could tap on the PCM and make the car act up. I called a ECM. thought it was an easy one. Nope no way. The replacement ECM no longer acts up when tapped. 

Here is what I know.

It runs fine until it goes to fuel control. Then it runs for 30 to 60 seconds at a time. Doesn't matter if you hold throttle or not. 

If the front o2 is unplugged it runs OK. It will drive down the road. 

The purge solenoid is not stuck open. 

The fuel trims stay around -25 total idling when it runs. 

CKP and CMP stays active through the stall. diag​.​net/file/f701uifuy…

I immediately suspected a shorted injector or coil. so I did amperage on the coils and injector voltages. All of the coils are on one amp clamp. The injector volts are seperate. 

diag​.​net/file/f5uv2azbj…

diag​.​net/file/f3j61gai5…

the fuel pressure stays around 60 PSI on the low side through the stall. I have not hooked the WPS to the fuel rail as I do not have an adapter. I am going to try to figure something out today. 

I have watched scan data looking for clues. The rear o2 initially was stuck rich. The rear o2 has been changed. 

I have watched intake oil pressure and it appears to go over 110 psi just before the event. 

diag​.​net/file/f7hia5bdl…

The rocker arm actuator has been replaced. I have not been back to vehicle since it was replaced. I have been told it still stalls. I am unsure if oil pressure has changed. 

I have scoped the CAN lines and powers and grounds. I cannot for the life of me determine why it even stalls. 

I have attached files of what I have tested. 

I know I have overlooked something. I just don't know what. 

Any suggestions would be greatly appreciated. The car is not perfect. They are willing to send it back to auction if I throw my hands up. To me it is a learning experience and I am determined to diagnose it. I have asked for them to keep it for now. 

UPDATE: I went back to the vehicle for some additional testing. Yes I had the AHA moment. A couple of people stated my exhaust cam timing was off. I did not have a known good and relying on others I could see it was off. I did not believe it was enough to justify the problem I am having. Anyway. In cylinder I went. 1st test it was apparent cylinder pressure was rising just before the stall. Indicating a cam timing problem. I decided to do a test. I allowed it to stall and immediately restarted numerous times to see if I could have several samples of it stalling and make sure I wasn't basing my test results on a single capture. 

diag​.​net/file/f62ye2o49…

Well the aha moment. diag​.​net/file/f6bqd1xi5… Yes it is apparent I have a cam timing problem. I typically do not do the repairs for the shops. This used car dealer would likely just put a used engine in. I may try to get the job and see if it is a phaser or crank keyway failure. I do not believe it to be a tensioner failure. I will let you know the results if I get the job. I may not as I am not cheap. 

+1
Interesting
Zeke Mechanic
Kentucky
Zeke
 

I can’t remember what year Malibu but there was a tsb for loose intake bolts..also the cam solenoid actuator valves go out on these a lot.

0
Ð Awarded
Sam Mobile Technician
Michigan
Sam
 

I have not check for loose intake bolts. I would suspect that would cause + fuel trims. due to vac leak

0
Ð Awarded
Jürgen Owner
Mexico
Jürgen
 

Does the front O2 (AF?) sensor show meaningful readings and react to induced enrichment or vacuum leak? Is there a possibility the wires got crossed/switched?

0
Ð Awarded
Sam Mobile Technician
Michigan
Sam
 

Yes the front o2 sensor has activity. It can be forced rich and lean with the brake pedal trick. I suspect it to be working properly.

0
Ð Awarded
Alan Mobile Technician
North Carolina
Alan
 

Are you sure you're not losing a cam signal there, that exhaust cam signal goes flat first, from what it looks like. Maybe try either heating up or cooling down that cam sensor while it's running and see if it drops out. Just a thought.

0
Ð Awarded
William Technician
West Virginia
William
 

GM front and rear 02 sensors? I have seen this with wrong aftermarket sensors even if they are bosch, denso, or NTK.

0
Ð Awarded
Marlon Owner/Technician
California
Marlon
 

I just had the same issue. Stalls due to engine vacuum would drop down to 8 inches of vacuum at idle. This would happen the same time the pcm was commanding the intake vvt to 20 percent. The issue was traced down to incorrect Ecotec engine installed. Run the engine part number on the front of the timing cover and make sure the engine is correct. Also bare in mind the option for flex fuel.

+1
Ð Awarded
Agree
Steven Mechanic
Washington
Steven
 

You said it runs okay with the front O2 sensor unplugged, and when it runs the fuel trims are -25 total. I would be checking for an air/fuel ratio problem. I'm not familiar with this engine. I know that cheap O2 sensors can cause that problem, but other than that I don't know if this engine is direct injected, if it is speed density or MAF, or if it is flex-fuel, but anything to do with…

+2
Ð Awarded
Agree
Caleb Diagnostician
Indiana
Caleb
 

The engine is NA, GDI, with MAP and MAF. It has 2 normal 02's. No AFR.

+1
Ð Awarded
Helpful
Stephen Technician
Tennessee
Stephen
 

It looks like, on the CKP capture, that the engine is slowing down from the start of the capture. As if it’s slowly stalling. I don’t understand the spiking in the cam solenoids pressure at idle. I wonder if an in-cylinder pressure capture with a secondary ignition capture, of a working cylinder would point to why the stall occurs, I also wonder what the engine vacuum looks like?

0
Ð Awarded
Dave Mobile Technician
Ohio
Dave
 

Hi Sam, I am curious about the oil pressure. The specs on this engine are under 40psi @700 rpms. Might it possibly be pumping up the lifters or pushing oil past the phaser solenoids at idle? I know that does not explain the o2 disconnected thing , but maybe that's just a fluke. Just thinking out loud here.

0
Ð Awarded
Caleb Diagnostician
Indiana
Caleb
 

The vehicle has 2 oil pressure sensors. One for the base oil pump pressure like any other engine. The second reads the oil pressure after the variable intake rocker arm lift solenoid. It checks for changes in oil pressure when the variable intake rocker arm solenoid is or is not commanded on. This solenoid is not the same as the VVT intake solenoid. The high pressure spikes are on the variable…

0
Ð Awarded
Dave Mobile Technician
Ohio
Dave
 

Thanks for the info.

0
Ð Awarded
Juan Technician
California
Juan
 

I recently fixed a Chevy truck around the same year as this car, came from another shop. Don't know the original problem, but I think it was check engine light for an oxygen sensor. I think he replaced 1, when the light didn't go away, he replaced all 4. After that, the truck would start & run when cold. After warm the computer would subtract fuel until the truck would die. I could see the…

+1
Ð Awarded
Agree
William Technician
West Virginia
William
 

Agreed. I have had this exact issue at least 10 separate times.

0
Ð Awarded
Randy Technician
North Carolina
Randy
   

Check your 02 sensors. Go off schematic and make sure the front is the front and back is the back. The harness is short both connectors right there. It is possible to plug them in backwards if someone takes the connector ends off. You have to swap them back and they plug up right. I had one that would run great until fuel control then it would surge and stumble until it died. Notice the black…

0
Ð Awarded
Steven Mechanic
Washington
Steven
 

Yes, I've seen that before as well. The car had different connectors for front and rear O2 sensors, so there was no way to mix up the connectors, but the tech can still accidentally put the front sensor in the rear, and vice versa, as long as they are close to each other. Having unique electrical connectors prevents plugging in the wrong one, but the O2 sensor bung holes are the same, so the…

+1
Ð Awarded
Randy Technician
North Carolina
Randy
   

The ends of the connector that are color coded are removable though. You can disconnect both sides and swap them for them to fit. I only know this because once I traced wiring and seen they were swapped I asked our parts guy to show me a new 02 sensor and he said oh well the last guy just swapped the ends on those because they didn't fit. I swapped them back like they should be and that was the…

+1
Ð Awarded
Helpful
Eric Technician
Maine
Eric
 

Seconded. I had an older Ford Ranger once with similar symptoms. Ran great in open loop, in closed loop is would get worse and worse, then die. The problem was oxygen sensors in the wrong locations. The definitive way to check this is to pull up all four O2 pids, then go unplug the sensors one by one and see which signals drop out. Good luck!

0
Ð Awarded
Scott Owner
California
Scott
 

Hi Sam, " I cannot for the life of me determine why it even stalls." Obviously this is what you're going to want to find out, as Captain Obvious points out. I guess it's me, but where are the scan data files when this occurs? Is this like someone turned off the key? Is running rough, surging as it stalls? No mention of DTC's - Powertrain, Body, Chassis? What has been done to determine why…

+4
Ð Awarded
Agree
Daniel Technician
Oregon
Daniel
 

Hello, looking at your CKP/CMP/CMP capture vs. a know good waveform, it appears that your exhaust camshaft is out of time. Check engine mechanical (chain) timing.

0
Ð Awarded
Arsalan Owner/Technician
District of Columbia
Arsalan
 

Hello Sam. I had a same vehicle here in my shop and what I found was 02 sensor wiring were melted some how right next to the 02 connector, You might will have to open the heat shrink to see it.

0
Ð Awarded
Ray Diagnostician
Ontario
Ray
 

Quick ck for the front 02 signal wire to PCM is to unplug the front 02 connector, connect a test light to B+ and tap the tip of the test light to the 02 terminal. The 02 scan data should show about .9v

+3
Ð Awarded
Helpful
Leon Owner/Technician
Ohio
Leon
 

“The fuel trims stay around -25 total idling when it runs. ” I'll suspect leaking high pressure fuel pump or leaking injector.

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

With crazy neg fuel trims, I would want to know engine vacuum. Both real, and what the MAP reports. Also try running with the MAF unplugged.

0
Ð Awarded
Tom Diagnostician
Illinois
Tom
 

Can you tell us something about the air going in. What about downstream o2 sensor is it stuck lean , reach or work correctly ?One GDS screen shot shows big vvt difference just before stall on exhaust side-have this and intake solenoid been replaced ?

0
Ð Awarded
Sam Mobile Technician
Michigan
Sam
 

I posted an update that should answer your question

0
Ð Awarded
Tom Diagnostician
Illinois
Tom
 

What about Downstream o2 sensor and vvt solenoid not rocker arm solenoid ?

0
Ð Awarded
Robert Diagnostician
Florida
Robert
   

Check fuel sample for alcohol maybe? Is this one that can have the fuel alcohol content reset in the scan tool? Negative fuel trims that high made me think of this as a definite check.

0
Ð Awarded
Sam Mobile Technician
Michigan
Sam Resolution
 

UPDATE: I went back to the vehicle for some additional testing. Yes I had the AHA moment. A couple of people stated my exhaust cam timing was off. I did not have a known good and relying on others I could see it was off. I did not believe it was enough to justify the problem I am having. Anyway. In cylinder I went. 1st test it was apparent cylinder pressure was rising just before the stall…

0
Resolution Ð Awarded