Cylinder 4 Not Firing

[sheeshryan]

Hey y’all! Back again lol.

Found my car has a misfire, or well a cylinder not firing at all. Changed coil packs, changed spark plugs, still nothing. All cylinders work except #4. Tested each one by unplugging coils, all affect rpm except for #4. At a loss for what the issue could be. Plug gets warm, but not firing too.


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[gc325is]

you have to trace it back to the Computer. Does it send a fire signal out to the coil?

[sheeshryan]

I don’t have anything to read the computer sadly. It’s a 94’ 325i with the 20 pin connector under the hood. Do you recommend anything to be able to read that?


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[AJLM34A]

It is either the DME, a wiring harness issue, the o-ring on the intake for #4 is dried out, the head gasket is compromised at that cylinder (which is the usual suspect) or a valve/cam, piston, or ring issue.

Go to an auto parts store and get a compress gauge tester, remove all 6 spark plugs, remove the main relay for the DME, and while spinging the engine over, hold the throttle pedal to the floor.

I would test #4 first then either #3 or #5. If they are all equal and north of 150, then go ahead and check the other 3 cylinders so you know what they are. If #4 is around 100= head gasket.

[gc325is]

YOU might be able to use a DMM on the coil pact connector to see if voltage is present to activate the coil.

Diagnose Dan has a ignition coil driver video

Remember water in the DME also cause problems

If you swap coil 4 with another and the miss fire stays at 4 you have a problem at the #4 cylinder else it was the coil pack and moved to another location.
You should check the resistance on the coil pack to be sure it is withing specs too and not shorting out.


Details on how coils works here and what goes bad.

www.youtube.com/watch?v=RO12NiE5g1E

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Never seen the trouble shoot manual link from AJLM34A

[AstroM3]

I'm also having a cylinder #4 issue. Nothing wrong when the car is cold, runs fine.. When I start driving, after a few minutes, CEL comes on for code 1274, and engine begins shaking heavily.. I've swapped coil packs around, replaced spark plugs, and swapped/refreshed injectors, all with no change. I'm going to pick up a compression tester right now to see if it may be HG as said above.

EDIT: Compression numbers below

1- 198
2- 195
3- 197
4- 195
5- 195
6- 195

1995 m3 S50

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[AJLM34A]

If you give us a fault code, can you also give what the description of that code is so we don't have to search for it?

ignition Coil 4

1274

The next step is cheap and easy, get a volt-ohm meter/DMM and check the 3 wires from the coil connector to #4 back to the DME or splice.

http://wedophones.com/Manuals/BMW/

[AstroM3]

I will from now on sorry about that.. After I did the compression test, I took a break (engine cooled fully) and now I'm back in my garage, the code has changed to 1271 (Ignition coil #1) I did the compression test one at a time so the spark plugs are all on the same cylinder as they were prior to the test, however I did change coils around.. I cleared the codes and swapped the 1/2 coils, and the code stays on cylinder #1 (1271). I don't have a multimeter that can read down to level needed so I'll look into that tomorrow if you think it may still be electrical after it jumped to cylinder 1..
I appreciate your help!

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[sheeshryan]

Update on my situation lol.

Swapped injectors around, misfire still on cylinder #4. So not fuel, not spark. Still need to test compression. Tested voltage on two different wires, got 12v on cylinder #1, got 9.3v on cylinder #4 so obvious electrical issue. Would it be a DME issue or a bad wire/ground?


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[AJLM34A]

Update on my situation lol.

Swapped injectors around, misfire still on cylinder #4. So not fuel, not spark. Still need to test compression. Tested voltage on two different wires, got 12v on cylinder #1, got 9.3v on cylinder #4 so obvious electrical issue. Would it be a DME issue or a bad wire/ground?

Which wires did you test voltage on, coil or injector leads?

I would unplug the DME, use electric contact cleaner and then retest voltage.

[sheeshryan]

I tested the coil wires.


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[AJLM34A]

Here is the factory BMW wiring diagram for your car;
http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf

Here is the color code for abbreviations;
Screen Shot 2022-06-30 at 3.56.47 PM.png
Here is the wiring for the ignition coils;
Screen Shot 2022-06-30 at 3.54.17 PM.png

GN= green and on all coils it is pin #3 and all 6 are spliced in the engine harness(7-way). If you have 12v on pin 3 of coil #1 and 9.3v on pin 3 of coil # 4, you need to figure out why you are losing 2.7 volts from the splice to the coil.

[sheeshryan]

So tracing back from cylinder 4 coil pack to where it splices into the wiring harness to figure this out correct ? Could be a bad wire/splice/short? Not exactly too educated on electrical things like that, just trying to confirm what you mean.


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[sheeshryan]

bump

[Sailor Nick]

I had a very similar issue on my 328i. this is what I found on mine.

I traced no power from the coil plug back to the DME. I removed the DME, took off the DME cover, and found the transistor or whatever inside the DME that controls that specific cylinders ignition to be burnt up. It had just shorted out and fried. I then ordered a used and tuned DME from a tuner with EWS delete and other performance stuff, as well as a spare used coil, and it runs perfect now.

Try this and see what you find inside your DME.

Pic is of the inside of my DME and you can see the burnt up component

[sheeshryan]

I opened up my DME and am trying to find where to look for what controls the coil packs/ignition. What part of the DME should I be looking at ?


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[sheeshryan]

Here are some pictures of my dme.

[sheeshryan]

Did some more voltage checks on the pins of the coil pack wires.

Cylinder #1 ~13.97v
Cylinder #2: ~13.98v
Cylinder #3: ~13.58v
Cylinder #4: : ~9v
Cylinder #5: ~13.67v
Cylinder #6: ~13.77v


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[gc325is]

Did you watch the Dan video? The bad news is Dan the pro could not find a replacement part. Sailor Nick found a damaged FET in his DME but again without a part source you will be guessing what replacement part to buy. Then you have to remove it etc... looks like it to the right of the number 4 on the 1st photo. A high resistance inside the part has cause only 9 V.

[Eric93se]

A lot if those solder joints on those FET's look like crap. Find someone with solder skills to re flow them.

- - - Updated - - -

When transistors fail its going to be a 100% fail, the fact that you have a weak 9V makes it more probable that its just a bad solder joint.

[sheeshryan]

A lot if those solder joints on those FET's look like crap. Find someone with solder skills to re flow them.

- - - Updated - - -

When transistors fail its going to be a 100% fail, the fact that you have a weak 9V makes it more probable that its just a bad solder joint.

Waiting to test a different dme on my 325, will update with results.


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[sheeshryan]

Update: Borrowed my friends Bosch 413 silver label dme, obviously wouldn’t start because of ews 2 but good news the voltage was even across the all cylinders.


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[sheeshryan]

Major update for yall that care!

Got a new to me bosch 413 red label from another e36, slapped it in, car is good as new pretty much. Thank you all for the help!


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[gc325is]

I want to know if it is one of those FET gone, or a solder connection gone bad.