Strange Pressure Capture
I had an interesting capture today that I would like some help interpreting, more for my files and records of case studies and curiosity. Vehicle history is the customer towed it in to the shop after performing a lot of DIY work including head gaskets, timing chains twice ( bought the Amazon tensioners, they broke second set was FOMOCO), new crank sensor, new cam sensor, new plugs, wires, coils. The customer stated that the project started because the engine had dropped a valve. After performing the repair he said the vehicle drove good for about a week then started running poorly, stated he could smell fuel under the hood. After pulling codes, vehicle had a p0340 and a p0300. I did a visual and found some creative mounting of the cam sensor where a bolt had been broken off in the block during prior replacement but it was seated properly and no visual harness issues. I started the vehicle and could hear some compression issues and after firing verified the poor running condition and also experienced a backfire through the air box. I performed a relative compression test with a sync on # 1. After piecing together the terrible pattern with the firing order, it appeared as if I had no contribution from the entire second bank. I pulled a plug to do an in cylinder capture, and noticed an excessive amount of fuel in the cylinder. After pulling the other bank 2 plugs, all cylinders were fuel washed. I drained the oil replaced, added some oil to in each cylinder and slowly cranked with the injectors unhooked. Reinstalled the plugs and performed an in cylinder on each bank #1 and #7 respectively. The first psd file shows running comp on cylinder 1. This was a theoretical good and I saw no obvious issues so off to cylinder #7. The second psd file shows #7 same conditions. After seeing the initial waveform results, I saw that there appears to be no exhaust event at all. I rechecked my connections, re calibrated the WPS and re ran the test with the same results. I added a jpeg at idle for those that do not have psd files. I feel there is an obvious timing issue. I could not verify the cam/ crankdue to the p0340(no signal from the sensor or the bulk connector on the fire wall) code and the customer did not approve the time to get to the bottom of that issue. I do not believe this is going to move much further into a repair because the customer wants to do all of their own mechanical repairs. My questions are surrounding the exhaust pocket or lack there of. Or am I seeing a HUGE spike during the exhaust event? Steps to verify potential hypothesis? Thanks in advance for the help.
Yes you are correct Bank 2 is waaayyyy out of time. Why dont you add the #7 coil trigger to the #7 in cylinder so you can visually see the timing off for piece of mind?? Dont overthink this. Bank 2 is way off. This also indicated in fact that the RC test shows no compression humps on 5,6,7,8.
The exhaust valve is not opening during the exhaust stroke in cylinder 7
My guess is someone is going to find a set of cam followers sitting on the bench somewhere. In my experience a waveform like that is more indicative of a valves not opening not necessarily a timing issue. Let us know and good luck!
You are exactly right Joseph. I however saw in the post that he said the car ran fine for a week and then this happened. However there is a good chance the customer is not telling the truth.
These engines wear out the cam journals and the follower shoots out of place. It may have lost both intake and exhaust followers and they should be sitting on the head under the valve cover. This will cause the in cylinder pattern you have because the piston is just compressing the same air over and over as it cant get out. If the journals are worn out it will need an engine
Look for the alternator cable, if it is routed to close to the cam sensor wire, it can induce a wrong signal due to A/C wipple. I have seen it twice, the alternator wire tie to the cam sensor wiring with tie wrap on the front of the engine. Jus try to move away the alternator cable 3 or 4 inches away from the cam sensor wires and see if it solve the problem. If yes, you got a bad alternator.
I don't think either valve is opening, possible chain/cam not turning or followers aren't present.
I don’t see anything to indicate either valve opened on the in-cylinder. The smoothness of the bottom of the waveform, with no offset to indicate a change in pressure other than linear piston movement is the evidence for that. So, there is pressure(about 50) on every stroke. What I find “odd” is that that 50psi doesn’t seem to show on the relative compression at #7 position. But, it does show up…
Need ignition signal to see where computer thinks the cylinder should fire. It looks like you may have both valves staying shut and ignition signal will make that very obvious. You would see spark on every other pressure event. You noted WOT on that compression waveform and the speed of the engine increased but the pressure did not increase. I would have expected to see lower vacuum on intake…
Thanks for the input guys. Cam followers makes since I just couldn't believe that a whole bank would be missing but stranger things I guess. I did finally get approval to pull the valve cover, so I will have a better update with photos in the morning. TBC
And its broken timing chain for the win!! I cant believe there was no noise. But that explains the issue being present on the entire bank and also explains the lack of cam signal. I suspect there is something binding the cam.
I have never seem a modular ford engine's timing chain break. How may miles were on that? It looks unusually clean under that valve cover.
I had a F150 come in after another shop installed a remaned 5.4 for same issue. No cam signal and similar symptoms and pattern. Opened it up and lifted chain out- bank 2 also Cam did rotate. I suspected maybe something (bolt?) was dropped in when valve covers were transferred and got lodged between one of the gears and chain. I ended up installing warranted engine-couldn't open up the bad one…