Pressure Transducer Testing Fiat MultiAir
Customer complaint low power rough running and check engine light on.
Checked codes. History code P0016 crank/cam timing. Current codes P0340 cam position sensor and P0304 cylinder 4 misfire.
Cleared the codes and road tested. P0340 returns instantly as well as P0304. Cylinder 4 has new ignition coil from previous repair.
Uneven cranking suggests a lack of compression on one cylinder.
This Fiat has only 55 000 miles and is the 1.4 litre MultiAir engine technology. There is essentially no real intake camshaft. 4 extra lobes on the exhaust camshaft drive high pressure electro hydraulic intake valve actuators.
The intake valves are sort of driven like Ford diesel fuel injectors allowing them to vary lift, duration and valve timing.
I decided to diagnose the issues with in cylinder pressure testing. I did a running test first. First waveform is cylinder 3 (the good one).
The next is cylinder 4 the bad cylinder.
In both cases am I seeing advanced exhaust and intake valve timing or is this normal for this engine.
Fresh back from VisionKC where Brandon Steckler schooled me in Pressure Waveform & Analysis, I continued my diagnosis with a cranking compression test.
Then I did an exhaust pipe pressure waveform
and an intake manifold pressure waveform.
Correct me if I am wrong but I think #4 exhaust valve is leaking.
The P0016 history code and now the recurring P0340 has me also thinking the valve timing is out.
My next step is physically checking the valve timing and the exhaust valve (camera) and likely disassembly.
Seal a rubber glove over the tailpipe and do a cylinder leakage test on cyl 4
If #4's intake valve was not opening long enough, would that not cause the same thing? Like a worn cam lobe, only with no intake cam. Possibly a malfunction of the multi-air system isolated to cyl. 4. Just thinking out loud here.
The green CH C shows an intake valve not opening enough.
I suggest before you do repairs on the engine, check the hot engine oil pressure in gear. When you remove the valve cover, look for signs of the lack of oil changes. Remove the oil filter, cut it open and look for slivers of metal.
We have had valve cover off. It is very clean underneath still. Vehicle is new to our shop. No history. Not sure if we changed the oil yet on this vehicle. Going to look in cylinder with camera today.
Take a very close look of the camshaft lobe on number four they are common to crack and free wheel. While manually turning the crank take a very close look of the cam lobe with a flash light look for being crack and free wheeling
The valve timing does look early compared to a usual engine. But, 3 and 4 show the same timing. If timing was THE issue, both cylinders should be “bad”. It is normal for a cylinder, with a transducer in it, to show lower compression on an RC test. So I would retest the RC with the s… plug in cyl 4. Comparing the in-cylinder pressures of 4 to 3 would give a better result. The dip in the…
Cylinder 4 has low compression and very high leakage I know from mechanical gauge compression test and leak testing. We have yet to physically verify the leak to either exhaust, crankcase or intake other than the waveforms I have posted. To me my waveforms suggest the leakage on cylinder 4 is past the exhaust valves. That low compression I feel is not the result of a cam lobe problem. Cylinders…
The first GIF is the Fiat cyl 4 cranking compression of 102 psi. The expansion stroke towers are leaning and the expansion stroke's vacuum pocket measures -18.6 inches of vacuum The second GIF is from an 06 Escape 3.0. CH B is a pressure transducer on the dipstick tube and it shows compression blow-by pressures in the crankcase. CH C is the starter amps showing some cylinders with low cranking…
Did a crankcase waveform with WPS500 on dipstick tube. I do not have an FLS. diag.net/file/f4h2nhe5y… Did the rubber glove trick and verified leak through exhaust. Thanks
Got some pictures of the valves in cylinder. First one is the low compression cylinder 4 exhaust valves. Is that white one the issue? diag.net/file/f5vl9iv42… Next picture is an open exhaust valve in the good cylinder #3 diag.net/file/f670cgg84… Next picture is the bad cylinder #4 and a very white exhaust valve. diag.net/file/f3dmsu41o… The…
So did this turn out to be the bad exhaust valve in cylinder 4 you had predicted
Looks like it is. Time to take it apart. Need to check cam timing before disassembly.
What bore scope are you using to capture those images of the valves? very detailed and good coverage
ATS Inspection Camera
Hey Ron, I'm interested in a follow-up on this one since I have recently started to play with in-cylinder pressure transducers and pulse sensors. Looking through your data and the replies there does seem to be some "inconsistencies" or possibly a lack of knowledge on my side. Starting with the Exhaust waveform which you have an ignition sync on cyl 4. The first exhaust pulse after the sync which…
Hey Doug Here is a picture of the exhaust pressure waveform with a piston chart on it. diag.net/file/f6qll25ej… The way I am understanding the exhaust pulses at the highest points are a combination of the end of one cylinder exhaust stroke combined with the next cylinders exhaust valve opening at the end of the power stroke. The combination of these events produces the most…
Ron, thanks for follow-up. I like the explanation of the exhaust pulse contributions. Here is what I amassed from your explanation of Cylinder 1 exhaust pulse being the largest: A) Cylinder 1 exhaust stroke largest contribution followed by B) Cylinder 3 opening of Exhaust near the end of Cylinder 1 Exhaust stroke, and a third contribution C) Cylinder 4 air leakage through exhaust during its…
Doug I did verify an exhaust valve leak from cylinder 4 with a leak down test. We have not started do disassemble the vehicle. When we put it back together I will try and get the new waveforms. I have yet to put my mind to that intake waveform. More studying for me to do.
Thanks Ron! I am wondering if cranking only wave forms would make things less convoluted, with no combustion going on it may make for cleaner signals just a thought. Maybe others out there have tried this already?
I agree, the cranking only wave forms, with the transducer in the intake and in the exhaust, will find the small, idle only, misfires caused by the minor valve train problems.
My intake manifold and exhaust pressure waveforms are both cranking only.
Thanks Ron for clarification. Hey did you notice how cylinders 2, 1, and 3 on the relative compression humps appear to be no where near TDC as if those cylinders ignition timing is greatly advanced? I'm not sure if that has any significance to this situation I know you mentioned the valve timing conern early on. I noticed this when I was putting all your waveforms on one graph (see attachment).
Hi Doug, the overlay grid is evenly spaced while the crankshaft accelerates and decelerates somewhat due to varying compression in different cylinders. This causes the discrepancy.
Normally I would count on adding an ignition sync to my in-cylinder pressure wave form to compare to the compression stroke peak to identify if the timing was accurate are you saying this may not be a reliable way to check ignition timing? Would it be accurate if there are no compression issues?
If there are no compression issues such comparisons are good enough for diagnostic purposes -- 1. the speed of the crankshaft is changing very little; 2. the compression peak is very close to the actual TDC. Compression issues will skew the results -- sometimes a little bit, sometimes a lot. Here is a severe example: youtu.be/2EArs0mUpGg
Excellent - thanks for the feedback I am currently using the same Pressure Waveform Overlay tool so the video opened my eyes to the potential error with low compression cylinders when using in-cylinder pressure wave forms and looking at TDC
Finally got in to physically check the cam timing. The result concurs with the waveform. The cam is about 20 degrees advanced as shown by the special crank lock tool lining up 20 or so degrees counterclockwise of the bolt boss it should connect at when the cam lock tool is in place. diag.net/file/f4dw8af9g… The head comes off next to fix the leaking exhaust valve.