Intermittent Missfire

[nasco]

Well, I'm back. My E39 is having an issue that I'm kind of stumped on. On my 540,very recently I noticed that if I put the engine under high load the car would hesitate and or Shudder.
I noticed the issue becoming more persistent, I checked inpa and alas, no code. I then started Driving the P*ss out of the car, and forced the car to give me a code, no solid SES light, just a flash for a couple of seconds, while flooring it in 3rd @30mph-100mph, one time and one time only.
Code came up for Cylinder 6 with a Fuel Cut-off and a random misfire on any cylinder, I recently did the Spark Plugs ~10k miles ago, so I figured that's unlikely. I Pulled the coil packs on Cyl 5&6, and I see opa, the contact on the coil pack for Cyl 5 is a lot cleaner than the Coil pack for Cyl 6, I cleaned the contact using the appropriate cleaner. Slapped the Coil back in, put the car under high load again, car didn't shudder. I noticed I have a tiny bit of Oil in my chambers for the coil-packs, so I ordered the VCG kit I go home, crack open a cold one and celebrate.

Next day, I start the car, as the car is warming up, no shudder, once the car has completely warmed up, the shudder showed up again. I reinspect, Coil 5&6 and Cuka blyat, the coils are both equally as clean. I look back at INPA, the car still has only detected ONE misfire, after 60 miles of shuddering. Then I noticed something, the Engine Temp read as -48C, then I noticed that the issue would only show up when the car is fully warmed up.

I've ordered a new coil-pack which is set to arrive later this week, and I swapped the Coil pack between Cylinder 5&6, and I have not been able to have INPA re-transmit that there is a misfire. So I can't see if it's a bad coil pack. I unfortunately do not have an oscilloscope handy so I can't test the coil pack that way. However I have a feeling that the issue is not a bad coil, considering that the misfire only happens when the engine is not warmed up, the car doesn't trigger a solid SES light and INPA won't record another misfire, and the car shudders only slightly. I still do 0-60 in the Low 5's. I will be cleaning the maf shortly, but I sincerely doubt that is the root of my problem.


Where else should I look?, if you need me to clarify anything and or have any questions that would allow you to formulate a better hypothesis as to what the cause of this misfire is, ask away. Or if you have any (non)/constructive criticism, leave it below.

[TheAngryBear]

What is the engine temp reading throughout the cycle? And is that oil temp (I don’t think so) or coolant temp? What are the trims through the ranges? Any spikes in voltage?

Just trying to get a better feel for data before jumping to solutions.


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[nasco]

My KTEMP as shown through the OBC is 103-106. If it makes any difference, I recently did the water pump and fan clutch. I don't have a readout for my oil-temp (DAMMIT BMW). In regards to my engine temp (different from my Coolant Temp) I'm not 100% sure where I would need to look for that. My Battery Voltage has stayed pretty consistent, I however have not looked at fuel trims. I have't found that part of INPA for the M62TU either. If this makes a difference, it did rain a little bit last week, that's when the issue started but car was for the most part isolated from the weather and the temperature range goes from 48 in the morning to mid 80's throughout the day. This issue occurs at both temps tho.

[geargrinder]

... I see opa, ....Coil 5&6 and Cuka blyat

Well definitely its the opa and the Cuka blyat that are the problem.

Either that or your keyboard.

Srsly, if the DME has crazy wrong engine temp it will lookup way way wrong mixture and timing values. Given the seemingly very random intermittent nature of the issue, I wonder if your temp sender is going intermittent.

The engine has a dual temp sensor at the water pump. One half is used for the cluster and one for the engine. Supposedly the OBC check will show one of them in position 1 and the other in position 2 or something. Search for threads/posts on that here. You can also probably just check the resistance of each half from the engine bay w/ a DMM and see how closely they match up... but... if the sender is going intermittent it may not show the error all the time. Of course check the connector while you're at it for corrosion or for bad wires. If you decide to change it, replacing it is super easy, don't even have to drain the coolant, leave the cap on the tank and just swap it really quick and it'll barely lose a drop.

Fuel trims for M62TU BTW are under all the Analog Status values - there will be 4 of them - additive and multiplicative x bank 1 and bank 2.

[TheAngryBear]

Like geargrinder I was thinking about the temp sending unit but also the thermostat wiring. Sometimes the thermostat wiring can wick coolant to the DME and cause issues.

As these are not replacing but rather testing/examining I would say check the temp sender per geargrinder then check the DME for any signs of water intrusion.

Report back and we can go from there.


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[geargrinder]

^^^ another good tip, I'd thought about mentionin that too.

[nasco]

Fuel Trims seem well within reason compared to my friends' 540iA. I've noticed that when the Cluster and INPA read anything below 104c the shudder and hesitation is present. I ordered a new sensor, as I should have replaced it when I did the water pump a couple of weeks ago, as well as a new lower radiator temp sensor, also should have replaced that when I did new hoses and a new radiator as part of my cooling system refresh. I will also take a closer look at the wiring for the sensor, it seems a little harder towards edge, which may imply that there is an added resistance due to sheer age, no corrosion on any contacts.

[edjack]

I had a low-RPM/low speed dead miss. My mechanic found the bad coil by disconnecting each coil in turn. The bad coil showed no change in engine operation.

[nasco]

Unfortunately, mine is present all throughout the rev range, not specific to low RPM. On, a side note I'd love to sit down and have a cup of coffee with you, Apsensilber and Sterling Grey are two of my favorite E39 Colors and seeing our cars right next to each other would be awesome.

[nasco]

Issue has been fixed, I'm not sure specifically what it was but I did a multitude of things all at once and it fixed the issue at hand. After I made the post and @geargrinder and @TheAngryBear had mentioned coolant Temps I paid a little more close attention to the Temps when the Issue occurred, I found that ONLY when the temp was below 103c I would encounter the Shudder when the car was "Warmed Up". The farther below 103 the more aggressive the Shudder. I did however notice that for "103C" my Fan Clutch was engaging a little frequently so I had was absolutely certain it was the Temp Sensor before I even replaced it. This weekend I did the Dual Temp Sensor, I replaced my Radiator Fan Shroud, did a complete coolant Flush, replaced an old Tensioner, and the Accessory belt for the Alternator and AC, after bleeding the system I can confirm the car goes up to operating Temp of 105C issue free and has a rather smooth power delivery compared to as of recent. I did check the DME and Connectors, no corrosion or signs of water. Thank you So much to everyone who offered their thoughts and suggestions, My car is now operating as it use to, and even better in some Cases.

[TheAngryBear]

Awesome! Way to stick with it and validate your issues. Glad to hear it is back to spec.


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[geargrinder]

Nice. Bet it was that dual temp sensor. But all the other stuff was well invested too I'm sure.

[nasco]

Ironically enough the coil pack on Cylinder 6 just completely went today. It's a hard misfire now. LOL

[nasco]

Update, In addition to the Dual Temp Sensor Fixing things, the Spark Plug on cylinder 6 Disintegrated. All is well, for now.