Do you see the problem?

Bob Diagnostician East Longmeadow, Massachusetts Posted   Latest  
Discussion
Driveability
2007 Cadillac Escalade ESV 6.2L (8 L92) 6-spd (6L80)—1GYFK66887R234259
No Power
Runs Rough

There is a problem with this vehicle and this cranking waveform shows it. Do you see it?

process​.​filestackapi​.​com/resize=h:1000…

I had posted this on another site so if you saw it already please hold your comments for a bit so others can take a stab at it. I have more data but this capture is a hugh clue.

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Joe Diagnostician
Jersey City, New Jersey
Joe
 

Hey Bob thanks for the challenge. I see this is a cranking waveform and this appears normal. I am still learning the ropes with in-cylinder waveform interpretation. I see your ignition trigger is either exactly at Tdc or slightly after. So this would cause the fuel to burn later. I know during cranking the ignition timing is retarded. I am going to say the timing of the ignition is incorrect and

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

Joe, look at the details in the capture carefully and then remind yourself that this engine is cranking. I would recommend reading through Bernies series on transducer testing to find some clues. diag​.​net/msg/m27jar2apt…

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Joe Diagnostician
Jersey City, New Jersey
Joe
 

Ok will do.

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Joe Diagnostician
Jersey City, New Jersey
Joe
   

I see on your snap the exhaust is restricted. Now as I look at this picture for a 30th time, I see that the exhaust valve opening has no definite spot. The exhaust valve opening appears wicked advanced. The rounded pocket clues me in on the valve not opening period. Due to this flaw the in cylinder pressure ramps up very early and mimics the look of an advanced exhaust cam profile. The high

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

The cam is advanced but not due to a problem with the exhaust valve. The pattern looks very different when a valve doesn't open. Here's an example. process​.​filestackapi​.​com/resize=h:1000… As far as the advanced valve timing, see my latest response to Ray. I believe this is a normal condition on this engine.

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Danny Technician
Cleveland, Tennessee
Danny
 

looks like the timing is advance

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

The timing is just about tdc which is a normal condition during cranking.

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Stacey Technician
Brantford, Ontario
Stacey
 

Restricted exhaust on that bank should never see increase in pressure on the exhaust stroke during cranking. Hard to judge how much without scaling. Do you have a running waveform? Other clue is the pressure continues to rise at the end of the exhaust stroke pressure should be decreasing

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

Here's a good cylinder for comparison. process​.​filestackapi​.​com/resize=h:1000…

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Ray Diagnostician
North York, Ontario
Ray
 

I'm with Stacey, exhaust looks partially plugged. Ray

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
   

Ray and Stacey are on the right track. Here is an idle capture with overlay and a snap throttle. Also, let me know what you think of the cam timing and why it may be so. process​.​filestackapi​.​com/resize=h:1000… process​.​filestackapi​.​com/resize=h:1000…

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Ray Diagnostician
North York, Ontario
Ray
 

In the idle capture, the cam timing looks advanced, the EVO too early and the EVC, IVO too early. The WOT snap should not be used to determine if the exhaust is plugged because on some vehicle makes, the higher exhaust pressures at a WOT snap is normal. A better method to test for plugged exhaust with the engine running, is to do a brake torque at 1500 rpm and the exhaust pressure should not

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

Ray what kind of pressure under snap do think could be normal? In my capture it's rising to about 46psi. Plus, at idle it should be close to zero and I had approx 4psi. Now regarding the valve timing, I don't have a know good to check but I'm suspecting that is normal. After reading service information it states that the variable cam is normally parked in the advanced position when not

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Ray Diagnostician
North York, Ontario
Ray
 

I've seen many types of engines that show high exhaust back pressure on snap throttles, when the exhaust is not plugged. During cranking and at idle,the exhaust pressure should be at zero psi. To measure the valve timing accurately, the ckp sensor is more accurate than the overlay, to mark the 180, 360, 540, 720 crankshaft degrees, and to measure exactly where the EVO in crankshaft degrees

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

I believe the snap throttle works for back pressure testing if you know how to analyze it. I understand that you could see some back pressure on some engines under a hard snap but the place to look is at the exhaust valve opening point just as the throttle transitions from closed to open. When there is a back pressure problem you will see an immediate rise in pressure as the throttle is cracked

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Ray Diagnostician
North York, Ontario
Ray
   

This waveform is from a 2015 Ford Focus 2.0. The red CH B is the ckp sensor at 944 rpm. The green CH C is a WPS500 in cyl 1 The first step is to disable the cylinder's injector, before cranking or running the engine, so as not to wash the cylinder wall and not to add fuel into the oil pan, then use the scope to count the number of ckp teeth in 360 crankshaft degrees, or between the missing

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

Ray that's a great explanation of how to measure pressure waveforms but you didn't address anything in my previous post. Do you have any comment on the L92 engine and the cam being parked in the advanced position? Do you have any pressure waveforms from one of these engines?

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Ray Diagnostician
North York, Ontario
Ray
 

Hi Bob, I don't have any wave forms for the 6.2 engine. You can look at your scanner VCT cam desired and actual pids at idle and graph the scan data off idle on a test drive or you can use the scanner Function Mode to advance and or retard the cam timing off idle to keep the oil pressure high enough to turn the phasers. I would like to see a waveform of the running compression of when the

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

I guess I'm not being clear with my question, let me try again. I'm talking "theory" here. I'm not trying to analyze my specific waveform at the moment but rather, I'm interested in exploring what we are likely to see, or should see based on the particular engine/camshaft setups. Service information states that on this engine, when the cam IS NOT being phased, it will sit in the fully advanced

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Ray Diagnostician
North York, Ontario
Ray
   

Your right, on this 6.2L engine, the cam sits at 17 degrees advanced at idle. This car is a 2016 Kia Optima 2.4 and the first wave form, which is at 1,543 rpm, is at start up. The blue CH A intake cmp rises at 40 ckp degrees after the first ckp toggle The red CH B is the exhaust cmp and it's 2 ckp teeth after the first ckp toggle The green CH C is the ckp and I've marked a 360 crank

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Joe Diagnostician
Jersey City, New Jersey
Joe
 

So the initial problem has been discovered by Ray. If so thanks Ray.

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Ray Diagnostician
North York, Ontario
Ray
 

Stacey Fleming found that the exhaust was partially plugged before I did.

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Joe Diagnostician
Jersey City, New Jersey
Joe
 

I tip my hat to all. Very large pool of knowledge that weighed in on this question. Thanks to Bob and Ray for the hints and screenshots.

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Bob Diagnostician
East Longmeadow, Massachusetts
Bob
 

I repaired this truck this week and wanted to put up a little more data. Unfortunately I was up against the wall late on a friday so I didn't have time to put the pressure transducer in it but I'm sure it would have looked similar to the good bank waveform I already posted. When initially diagnosing this I suspected a restriction on one bank. I had mode 6 misfire counts on all bank 2

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Ray Diagnostician
North York, Ontario
Ray
 

Thank you for the update and the graphs! Ray

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