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Ron, ASE Certified Technician
Category: Acura
Satisfied Customers: 35858
Experience:  35 years As a ASE Tech
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01' Acura CL 3.2 Base model 95k miles. I just replaced the

Customer Question

01' Acura CL 3.2 Base model 95k miles. I just replaced the alternator and both valve cover gaskets. After starting, the car will miss on random cylinders. On test drive, CEL flashes. Misfire is felt more so after letting off throttle and at a stop, no miss when A/T is in park. Initially only o2s1 low voltage code appeared. Data showed o2s1 voltage dropping to zero occasionally so I replaced it. O2s1 voltage looked normal now and o2s1 switches normally but random cylinders are still missing with occasional p030X. Had 3 known good coils on hand and swapped 2 on bank #1, 1 on the bank #2. Misfire seems less severe but cylinders with known good coils still show a miss randomly. Removed fuel rails and inspected seals, all look good, some carbon deposits on injectors but nothing out of norm. EGR ports in upper intake slightly dirty but not clogged and plenums have been changed. Spark plugs looked ok and engine grounds look good even though they were never removed. Current fuel trim data shows ltft under +/-5% but stft at -14% about 2/3 of the time but will jump to +14%. 2,500 RPM shows same fuel trims and o2s1 reaction is slow now. Engine ran fine before alternator and vcg were replaced. Currently replacing one injector as I snapped the plastic tip off during removal. Will also replace the other three coils but I don't think that's it. Any ideas? What can cause fuel trim to bounce from too lean to too ***** *****ke that?
Submitted: 2 years ago.
Category: Acura
Expert:  Ron replied 2 years ago.
Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
The fuel trim readings of -14% indicate a lean engine and in most cases this is caused by an engine vacuum leak. When you replaced the plenum gaskets are you sure you got a good seal. A vacuum leak will also cause a lean engine misfire such as you are having. I would recheck to be sure your not dealing with a vacuum leak.
Customer: replied 2 years ago.
OK let me start all over, the problem is an intermittent misfire. The original problem was a bad alternator caused by a leaking valve cover gasket. I am an ASE mechanic that is just fixing this car for a friend. After noticing the misfire upon the vcg and alternator replacement, an intake leak was the first thing I suspected so I replaced the 2 upper manifold gaskets that were originally removed and re-torqued them, no difference. At that time the stft at idle was at -10% to -15% about 2/3 of the time, but would jump to +10% to +15% for a while before going negative again, skipping everything in between. At 2,500rpm it would range from -8% to +8% and switch regularly. Ltft has always remained consistent at around +/-5%. At this time the misfire is occurring intermittently when letting off the throttle or at a stop, and is not very evident under load or in park, CEL flashes and TCS light on. Scanner test showed random P030(x) codes along with an o2s1 low voltage code. Data showed random cylinders recorded misfires and o2s1 occasionally dropping to 0V, B+ at idle around 14.3-14.5V. O2s1 was replaced and no longer drops to 0.Since then, I have changed all spark plugs and ignition coils. One coil had a very slight crack above the boot. I also replaced injectors #1 and #3 because the plastic tips were damaged upon removal for inspection of the seals and quality of spray, which both looked good. Injectors had normal amounts of carbon deposits but I put sea foam in the fuel for good measure, tank was about 1/3 full. I also found a slight tear on the air duct. With no MAF, I thought it shouldn't make a difference but I sealed it up with silicone temporarily anyway. The duct is guaranteed 100% sealed. The stft at idle now stays around +3% to +5% and ltft holds steady at around +3 to +4%, both trims staying in the positives. At 2,500 rpm the stft ranges from -5% to +5%, ltft from -3% to +3%.The misfire now occurs intermittently under load and while starting, not when letting off the throttle or coming to a stop as it did originally. Data is showing cylinder #1 registering a miss almost every time under load, even when a miss is barely evident. Cylinders 6 and 4 also record misses intermittently, causing the miss to feel more severe when they occur with the cylinder 1 miss. The other 3 cylinders record misses very, very intermittently. I just came back from another test drive and the CEL finally came on, showing P0301. Data recorded cylinders 1 and 4 missed on that drive.Sorry for the novel but I wanted to be as thorough as possible so there's less back and forth. I'm in Hawaii so there's probably a big time difference. Where should I go from here?
Expert:  Ron replied 2 years ago.
I would concentrate on the P0301. With a new spark plug as well as coil I would assume you can rule them out but something is still not right here. I still think if you did not have this problem before changing the valve covers it is likely brought on by doing so. Are you secure the new spark plugs are okay.
Customer: replied 2 years ago.
The plugs are fine. Cylinder 1 always recorded the most misses even before I replaced the plugs and coils. I even swapped the brand new coils and plugs with cylinder 2 to rule out a part that might've been DOA.I was also convinced I must've screwed up somewhere so after replacing the O2 I retraced my steps and removed the valve covers again to double check if anything was out of norm but everything inside looked good and clean. That's when I discovered the slight crack on one coil and decided to replace them along with the plugs.
Expert:  Ron replied 2 years ago.
Well at this point Im out of ideas so if you would like I can reopen the question and see if someone else has a different Idea.
Customer: replied 2 years ago.
Yeah sure. I know it's a long shot finding an answer on here but I'm stumped. I was thinking of maybe replacing the alternator again at this point as I'm leaning towards an electrical problem because it's intermittent.
Expert:  Ron replied 2 years ago.
I'm going to relist it right now. Please do not respond back to me as it locks the question to me and others can not help if they can.