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      07-12-2018, 12:30 PM   #1
cyruscat
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Misfire Fault Analysis using shade tree methods

Persistent engine misfire growing worse until hard miss and cannot drive.
Car specs:
2007 Z4/E85/N52
101,000 miles

Already replaced parts:
O2 sensors
Vanos
Plugs with recommended NGK
Coils
MAF and MAP
Air filter
Oil and filter
Injector cleaner in gas, Technor couple tanks in row.

Basic engine operation requires air, ignition, fuel, compression, timing of all.

1. Test for air/vacuum leaks
A: Removed air intake pipe between MAF and throttle body. sealed one end and did smoke test under light pressure
RESULTS: No leak

B: Removed and cleaned throttle body, sealed opening of intake manifold and did smoke test under light pressure. Input thru CCV hose end.
RESULTS: No leak
Conclusion: Not source of problem

2. Ignition test for all cylinders/coils/plugs firing
A: Engine running I unplugged one coil wire at a time while monitoring engine idle.
RESULTS: Cylinders 1 - 5 gave little change in idle. Cyl. 6 gave major change with engine almost dying.
Conclusion: Cyl. 1 - 5 are very week. Cyl. 6 firing strong

B: Pulled one plug at time and reinserted in coil. grounded plug while assistant cranked engine and I monitored cylinder for compression stroke.
Results: All cylinders fired hot at same time it hit compression top dead center.
Conclusion: All Cyl. receiving hot ignition at top dead center of compression stroke.

3. Fuel test delivery
A: With engine running used infrared thermometer and measured temp. of each exhaust runner. Common exhaust temp. on warm engine will be 500-600F at head exit.
RESULTS: Cyl. 1 - 5 had low temps 350 - 447F. Cyl. 6 had 567F
Conclusion: Cyl. 1 - 5 not receiving enough fuel to run normal. Cyl. 6 in expected range.

B: Check fuel injectors for good wiring connections
RESULTS: all connectors missing spring locking clip. Someone has been here before and did poor job.

C: Cleaned and seated connectors firmly
RESULTS: No change in performance

D: Using mechanics stethoscope listened to each injector with engine running. Good injector will sound off with positive, firm click when it triggers.
RESULTS: Cyl. 1 - 5 have weal erratic rattle sound. Cyl 6 has loud positive Click.

Conclusion: Injectors 1 - 5 suspect. Next step is to use NOID tester on wiring harness to each injector to check firing pulse.

More to come............
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      07-13-2018, 09:58 AM   #2
Yapakanichi
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You know, I remember on my MR2 I had a similar issue. My injectors were not firing. Turned out to be an injector coil pack. Tested with a NOID tester.

Your injectors could be clogged and may need to be removed and cleaned. Sounds like you can do that from all your testing.
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      07-16-2018, 10:26 AM   #3
cyruscat
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Testing

Alright, got my Injector circuit test, also known as a NOID light.
All six give bright consistent flash every time intake stroke comes around.

Ordered a set of new injectors and expect them this week.

I wish fuel filter was not in tank so I could change it easier.

I'm thinking (Danger!) when I ran the fuel/injector cleaner thru car it broke loose some crud and plugged injectors.

Like the Z4 but wish I got to drive it more and work on it less
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      07-16-2018, 05:49 PM   #4
StickMon
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I used to pour a bottle of Techron through my cars/trucks every once in while, but I've resisted doing so on the Z.
I'll continue to resist, and instead mainly fill at Chevron, and get my Techron in small doses.
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      09-12-2018, 02:14 PM   #5
cyruscat
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Old thread but thought I would finish with final action that fixed my poor running car.

Wrong spark plugs in engine was culprit...........

So PO'd I would cuss but ya'll may not appreciate it.

Engine had new plugs in it from previous owner when I bought it. Misfire and rough running was not apparent to me until I drove it for couple hundred miles and got the feel for it.

I found wrong plugs were one digit off in part number. They were short reach when car required long reach length.

All my other work does leave me with a fine running engine that I know needs nothing now.
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      09-20-2018, 04:00 PM   #6
RossBMWZseries
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Good to hear it's running fine now. I have a '11 328i with the N52 engine. I've had a misfire since the beginning of the year. I got a few codes pointing to the MAF. Replaced it but misfire is still ongoing, specially when the engine is cold. SES light still on as well. I need to do everything you did (listed in post #1), but it feels like it's a lot of money just thrown out at these educated guesses.
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