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DISCUSSION => Engine + Driveline => Topic started by: Jaredmac11 on December 11, 2022, 10:31:28 AM

Title: Cylinder 1 isnt firing
Post by: Jaredmac11 on December 11, 2022, 10:31:28 AM

I have been living with a rough idle and pretty gnarly harmonics for awhile (certain RPMs would cause the car to vibrate from the cabin).  I just thought she was running rough but when I drove up to a car meet, my buddy said it sounded like a cylinder was off and I was running on 3 cylinders!

So later that day, I cranked her up, we pulled the ignition wire for cylinder 1/coil 1 (closest to the radiator, do I have the # right?), and it made no difference to how it ran.  Wild.
A few baseline items:  Its an e30 m42.  I have a coil on plug set up.  I have newly rebuilt orange top bosch injectors.

So I limped home in shame and started diagnostics.  Here is what I have found.

1)  I removed the coil and kept the spark in.  Cranked the engine and she's sparking.
2) I checked compression and I have 130 psi in cylinder 1.  Not great.  Not bad (I think).  Should be enough to fire (a little concerning however).
3) I checked the continuity from each coil wire to each ECU pin as prescribed below.  All match.
Coil #1 is DME connector pin 25.
Coil #2 is DME connector pin 52.
Coil #3 is DME connector pin 24.
Coil #4 is DME connector pin 51.
4) I pulled out my stethoscope and I can hear each injector ticking.  Some sound slightly different than others, but each have a distinct ticking sound, particularly injector 1.

So Im not sure where to go from here.  How can I test that Im getting fuel down the cylinder?  What else can I do?

Title: Re: Cylinder 1 isnt firing
Post by: Jaredmac11 on December 11, 2022, 12:22:29 PM

Here is plug 2 (left) and plug 1 (right). Plug one clearly hasn't been igniting for awhile.  :-X

[img][

Title: Re: Cylinder 1 isnt firing
Post by: Jaredmac11 on December 11, 2022, 12:45:07 PM

Reading 130 compression might be too low. What's acceptable?

Title: Re: Cylinder 1 isnt firing
Post by: keflaman on December 16, 2022, 06:38:30 AM

142 -156 PSI with no more than a 7 PSI differential between cylinders. Readings are done on a warm engine according to the manual, and crank each cylinder until the compression quits rising. You can always put a bit of motor oil down the spark plug hole and check again. If compression rises, the rings are worn. A leakdown test can differentiate leakage caused by worn rings or valves.

Title: Re: Cylinder 1 isnt firing
Post by: jsnppp on September 11, 2023, 08:13:07 PM

Curious if you found an answer? I have similar problem, only cylinder 4.

Thanks!