Engine Misfire 2001 Z3, 3.0 engine

[ghelton]

Previous OBD II code showed #6 injector had low voltage with Service Engine Light on. I cleared the code and continued to drive it and now engine is running rough.

Now codes are showing misfire P0301 and P0306 on #1 and #6. Misfire during start on #2,3,4,5. Also have P0171 and P0174 for fuel banks too rich. Just turned 100,000 miles.

I cleaned the MAF, cleared the codes, drove around the block and all codes are back. Before I start replacing parts, any advice on what causes all these codes at the same time. MAF, vacuum leak, fuel filter, coils (all 6???), spark plugs............

[rf900rkw]

First off, figure out what went wrong with your code clear. It is physically impossible to set misfire and lean codes (yes, those are lean codes) on the same drive cycle. And none of those codes will fully set in a single drive cycle. So if they fully set just bopping around the block once, they never cleared.

What is this "low voltage" code. Numbers, please. Descriptions from some generic scanner or googled from a Honda forum don't help.

Cleaning these MAFs is an utter waste of time. At best, you won't damage anything.


Now to the diagnosis. What are the fuel trims? Both short and long. At idle. While cruising. Have you looked for a vacuum leak? Three vacuum nipples at the back of the manifold. Intake boot. CCV I just fixed one that was a massive vacuum leak due to an improperly install valve cover gasket. Spray pointed shots of brake/carb clean at suspect points and watch the STFT. You likely won't hear a change, but the trims ought to slam rich if/when you hit the leak.

And finally, don't convince yourself it's a single problem. It could be, but often isn't. It is often a brew of several smaller problems.

[redlinealley]

Could it be bad ignition coils causing the problems. I had the same symptoms and #4 coil was bad.

[ghelton]

#6 injector code was a month ago, P0276 "circuit low" not low voltage, my bad. "Around the block" is 5 miles. separate drive cycles for each set of codes. Cleared all codes. Currently showing freeze data information:

P0171 Trouble code

ST FTRM 1 25.8
LT FTRM 1 1.6
ST FTRM 2 27.3
LT FTRM 2 0.0

MAF pressure 4.4

No easy to find vacuum leaks, I will do a smoke test if these numbers don't suggest a quick fix. This all happened overnight with no recent maintenance or repairs. Thanks for your help.

[ghelton]

Vacuum leaks due to oil filler cap not sealing and vacuum nipple on the back of the manifold was leaking. Problem solved.

[hydrocrust]

I had similar codes, also caused by vacuum leak, FWIW. Codes Fixed when leaks fixed (two of them).