Requesting help with misfire evaluation

If you haven't yet , I would smoke the intake to be sure there is no air leaks. Maybe add propane to the intake and watch for O2 reactions. Just my 2 cents.

Brandon, thanks. Intake has been smoked. No leaks. In general and particularly in the #5 runner area. AFR and rear “oxygen” sensor reactions verified by fuel trim analysis. They're both awake and react to what's going down the tailpipe.

Any chance you can obtain 5 gas lambda reading at idle and at 2000 rpm? I like to get a lambda readings because it rules out or in a fuel control problem. Which helps to get direction. Lambda reading is not influenced by anything except fuel control, type of fuel ,air injection or exhaust leaks.

I don't think so Rod. This situation is motivating me to put more money into tooling, but I'd more likely put $$ toward a transducer (or transducer etc.) right now. I am not proud of this but financial constraints are a reality for us at this time. We are not an emissions testing state; I'm not sure there's even anyone in the vicinity with a 5 gas. If it matters to you, I think I've ruled out…

Hello Andrew, Here is a Non expensive in cylinder pressure tester that you might consider in the future. I purchased one a while back and it works well with every scope I have tried it with. Like you, I am not a big operation, so I am very careful when it comes to considering new equipment. If you check into this tester and think about buying one, I will also let you know it comes without a…

Those had really bad evap purge valves they used to fail constantly, specially when looking at the fuel trims. I would concentrate on the testing procedure of the code P2108. I just looked on identifix and its comprehensive I'm sure it will lead you the right way.

Thank you Jose, but I need to focus on what's taking cylinder 5 down specifically. I'd expect a purge valve failure to affect multiple cylinders together.

Andrew, do you have a cylinder pressure waveform? Your cranking amps look like a compression issue to me

Hi Norman. Thank you. I do not have a waveform (nor the requisite tooling to get one.) If that is required to get to the end here, I would like to know. This was my first time doing relative compression via amperage. I might know what you're after, but would you please explain it to me as you perceive it? The problem that you perceive and what you see in the waveform that's leading you to…

The 9 amps span would make me want to make sure that we don't have a significant compression difference. What I find odd is that the misfire is on the higher amperage draw cylinder. A pressure transducer is a must for the future of diagnostics. It is the best way to quickly see wiped out cam lobes, timing chain issues, broken valve springs, plugged converters, even vacuum leaks can be seen in a…

Is the problem worse when the vehicle is cold?

No sir. It will misfire at idle both cold and hot.

Since you said you can't scope the coils themselves try swapping them to see if the misfires change from cylinder to cylinder. Also you stated that the maintainance of the vehicle is questionable so maybe the oil changes were hap hazard as well so in that respect you might have VVT issues. Good luck.

Hello Stuart, thank you. No change with coil positions swapped. Oil level is acceptable at this time. I won't claim absolute confidence in VVT operation but it's a pretty happy car and engine once we get it on the road and off of idle. The problem (the worst problem that is) is specific to cylinder #5.

For engine ID, look in the trunk under the mat or cover for the code sticker. VW hides a lot of them there. I guess the logic is the label never get destroyed like they do under the hood.

That's a nice tip. Thank you, sir.

Hello Andrew, The fuel trims are commanding to enrichen the fuel mixture and #5 is the culprit. Use a propane torch with a pencil tip (unlit) and direct it at the #5 intake area. Check the whole intake while watching the fuel trim for obvious change moving toward 0. Don't forget to check all inlet piping as well.

Glenn, I think I got there in a different way. I smoked the intake, and there's nothing leaking. I paid extra attention to the #5 runner and gasket area. I have also run the vehicle with the intake manifold PCV supply blocked off, and this did not improve the symptom. As I perceive it, I have no clear evidence of an intake side or feed problem. Thank you. If you have anything else for me…

That vacuum seems low to me. At idle with misfire 15 to 18 sounds like a valve issue. I would consider taking the valve cover off to inspect next. Since you don't have a FLS to check vacuum while running or cranking, its probably the easiest next step. Plus with the relative compression showing something with cylinder 5, I would say its time to get a visual look at the whatever you can.

Richard, Yes. I agree. Even 18 in Hg would be lower than what I typically see at this elevation. I do not have an FLS, but if I recall correctly, perhaps a GM or Mitsubishi MAP sensor would work? Is there anything to look for there though? (no vac gauge needle flicker observed). Is there a possible benefit to getting an FLS (etc.) capture with cylinder sync? Regarding the relative…

I looked at the relative compression and took the filter off. 5 does indicate higher amps during cranking, but it's pretty slight. The FLS at cranking speed would give a good read on the opening and closing of the valves. Pico also sells leads that attach to bottom of your coils, which you could then put a colored or black secondary lead on to see secondary ignition.

BPR is SULEV and BPS is LEV2. They have radically different fuel control systems. BPR used a front wideband and 2 oxygen sensors, one in the middle of the converter and 1 behind. The BPS uses a front wideband and a single oxygen sensor behind the converter. BPR uses a frequency fuel control system whereas I am pretty sure the BPS uses a normal fuel control system. The evap system is different as…

Randy, thanks and extra thanks for this. I will pursue said data and get back to you.

Andrew- I dont have an answer, however misfire in one cylinder at idle only, usually indicates a valvetrain issue. This is not gospel, just my experience. A pressure transduce will greatly reduce guessing and doubt when dealing with a misfire. I strongly suggest getting one in order to rule out engine mechanical issues. Relative compression and static compression(via a gauge) tests are really…

Rudy, Glad to hear from you, and thanks. I will take these things into account. We are looking into acquiring a transducer. I noticed that you qualified with (via a gauge). Do you see more value in doing compression testing via other methods?

Yes, the transducer is a razor blade while the gauge is a butcher knife. The finer details the transducer provides cannot be acquired by any other method. The compression gauge only measures and captures peak pressure. A relative compression test is almost the same. A vacuum gauge can sometimes capture an issue, but Ive seen plenty of instances where it didn't. Minute pressure changes can…

Based on everything said I would focus on breathing issue at idle maybe valve timing advanced drives fine down the road im not sure but I would think that the running compression seems high if intake is slightly advance that would explain alot this wouldn’t cause high trims at idle though so I would focus on ruling out mechanical and breathing then move on to fuel it Sounds like time…

youtu​.​be/e59atXyNNPA. Try this to get the secondary waveform. Setting the scope to AC coupling and backprobing the MAP sensor will often give a usable intake manifold pressure waveform. A pressure sensor from the hi side of an air conditioner line can be used to get a decent in-cylinder capture. The RC capture shows #5 current higher BUT, it starts at a higher level. As though…

Have you tried artificially enrichening the mixture with propane to see if it has any effect?

Hi Andrew. I had another thought come to mind and want to offer it for consideration. If I am not mistaken, this is a 4 valve per cylinder engine. A leak down test with the valves closed on one cylinder at a time may give an indication of any internal issues. If one out of the two exhaust valves are leaking, the cylinder will still have some compression, but a portion of it will get pumped…

Do a visual check on the front of the cylinder head. I just had a 2.5 VW with very similar symptoms and one of the cam plugs was missing.

Having read your symptoms and test results, my feeling is valve sealing issue(s), not to say it's actual valve, but something tied to the upper end of the engine. A leak down test would be the next logical test as you don't have a transducer yet. However, valves rotate as engine runs and depending where they stop, may show leakage or not. Something to consider on your conviction of results to…

Andrew, being you don't have a pressure transducer can you do a cylinder leak down test for us? Also do you have means of measuring crankcase pressure at idle? (Manometer). Make sure you smoke test the crankcase too, I usually go through the oil fill cap. Lastly you can current ramp those ignition coils but I don't feel this is a ignition issue from the details you have given so far…

I check torque on the intake manifold on every misfiring 2.5L they are loose nearly every time.

Hi Andrew, it looks like you have another signal riding on the injector circuit. Looking at the wiring diagram, I don't see anything else on the circuit. Had a vehicle once that had very similar issues with a very similar waveform. The ECM connector was full of corrosion and the injector pin was shorted to the pin beside it, which in my case was for the ETC. Looking at the diagram for your…

Andrew, I agree with those who want a leak down test. Try adding air pressure very slowly if it is a valve sticking slightly, you may get to see it close and seal. There have been posts here in DN about old school leak down testing. Randy