Hi, all -

I have recently installed a Vortech V-3, T-Trim supercharger along with a ported throttle-body, longtube headers & some other goodies. Now, in the first phase of tuning (trying to make the car driveable before going to the dyno), I am getting a lot of stumbling/misses/backfires at idle.

I have already inspected & changed sparkplugs & wires as well as tested each coil with a timing/strobe light. All are good.

Seems to be coming from the passenger side of the engine....when I scan it, it shows erractic LT & ST O2 readings for bank2 (bouncing all over the place) while bank1 is steady.

I am not running rear O2 sensors and the holes where the rear sensors would have gone have been sealed with a plug(s). When I put the front O2 sensors in the headers, I might have switched them around meaning the one that came out of the right or passenger side stock exhaust manifold might have been put into the driver's side longtube header. I can't remember.

Anyway, I've read a lot of posts while researching this problem talking about problems caused by switching the O2 sensors but I think they are referring to "switching the O2 sensor WIRES." I do not think switching the actual front sensors from driver's side to passengers side would make a difference as I think they are the identical part. I also do not see how you could wire them backwards as the wires for the front O2 sensors are so short and can only really be connected to their respective side.

By the way, all I did for the rear wire harness that would've gone to the rear O2 sensors was to cut it off a few inches after the plug (wanted to plug the connection point to keep moisture & debris out) and then tape up the cut wire with electrical tape. Then used HPTuners to tune out the error message for not running rear O2s.

Can someone confirm if switching the front O2 sensors side-to-side will either have an effect/have NO affect on tuning/performance.

I am also beginning to think that maybe the passenger-side O2 sensor is bad. Or maybe the backfires are caused by an exhaust leak? Also running rich as I can smell a lot of gas.....even though I am NOT running Cats that would burn up unspent fuel, it still smells like I'm dumping a ton of gas!

Thanks in advance for any input!

 

I'm betting cracked spark plug.

I went thru the last month. Round and Round with O2 sensors etc. Reading was erratic and the graph looked sawtoothed instead of smooth like to D side. Kept thinking it had to be O2 related.

Car backfired at idle.

Found #8 plug cracked insulator even though I had checked them twice.

I had the exact same things going on as you. Dumping fuel etc.

 

Thanks, Vega$Vette -

I remember reading your post & saw the pic of the hairline crack in one of your plugs. I'll doublecheck Bank2 (#2,4,6 & 8) but I've already replaced all 8 plugs once since this problem started. That's what is leading me to think it's O2 sensor-related.

Might just go out and buy one new front O2 sensor.

 

Had the same symptoms years ago...was a fouled plug; but do try new O2 sensors so we all will know for sure

 

I started thinking about the last time I scanned the car. Please note that every time I scan the car, the car is not actually being driven since it is still on jacks in my garage. I rarely run the engine (due to all the problems) past the point of warm-up, if it even gets that far. SO I GUESS I AM ALWAYS RUNNING IN "OPEN LOOP." Getting back to the scan, I noticed that Bank1 and Bank2 were WAY-DIFFERENT from each other even though this was in open-loop running off the MAF & tables. I still thought that Bank2 looked "weak" and was maybe giving a false low-voltage reading to the PCM, thereby dumping fuel and was the cause of the heavy fuel smell I was getting. But then again, maybe not since it was in open-loop, the O2 wouldn't be making any adjustments and the fuel smell could be from the misfirings & unburnt fuel coming out of the exhaust. Well, I know the O2 sensors hadn't heated up yet but the readings were so far off that I decided to replace Bank2's O2 sensor anyway.

After replacing Bank2's O2 sensor, I started the car again and this time she ran with more pronounced misses (misfiring) and then she started to stumble and threw out a P0336 (crankshaft position sensor fault - circuit performance) error code....I hope it's just due to all the misfiring. Anyway, still trying to diagnose the misfires -- MAYBE A BAD GROUND? MAYBE BURNT O2 SENSOR WIRES ON BANK2 (passenger side)?....I heard you can not splice O2 wires because it will give false readings?????

Can anyone suggest my next move?

 

As Posted exact same problem. I too over analyzed the problem and did the exact same thing you have been doing. Switched O2s etc.

Bad Plug. Changed it problem solved

 

Here's what I've done so far:
1) swapped sparkplugs, wires & coils from Bank 1 to Bank 2 (measured resistance in each sparkplug wire as well....all ok, each approx 44.5 ohms; also carefully inspected each plug for cracks....all ok. this is 2nd set of plugs & wires since problem started, by-the-way )
2) checked O2 & injector fuses...they're ok
3) retorqued manifold to 89 in/lbs
4) retorqued headers to 18 ft/lbs
5) checked that all injector connections were fully connected
6) checked vacuum at idle....very steady 17 in/Hg

Scanned her again while running and all problems that were there before ARE STILL PRESENT. Still misfiring on cylinder #1. I looked at the injector harness for Bank 1 when I was checking each injector connection and it looked fine but I will recheck it again due to posts I have read about it rubbing/chaffing and shorting some of the injector wires.

The only other things it can be at this point is:
a) bad injector - I will swap #1 injector this afternoon
b) busted valve....PITA because I have Katech valve covers and believe I have to remove alternator to remove Bank 1 valve cover to check springs/rocker.

In addition, when looking at my scan (those who have HPTuners can go to http://www.hptuners.com/forum/showth...318#post189318), I think my engine has 2 problems. The misfire issue stated above & also a bad Bank 1 O2 sensor or bad connectors to this sensor. I don't think this would have affected my misfire issue since during warmup I was still in Open Loop but it would lead to problems once warmed up....which I haven't done yet since I haven't let her run long enough due to the misfires/backfires.

One last thing......when I swapped the plugs, Bank 2 plugs all looked fine. Bank 1 cylinder #3 and #7 plugs had soot/carbon buildup BUT I WAS GETTING A P0301 (misfire on #1 cylinder). Plugs from cylinders #1 and #5 looked clean. Does this make sense to anyone?