Okay, I'm a little stumped on this one.

Misfire with no codes... car is modded and tuned, but it's been driving fine for almost two years with no issue. Recently, last week, it started to have this odd misfire and hesitation at part throttle low RPM cruising.


Checked plugs. All good. Recently replaced the spark plug wires, so I thought they were a culprit. Replaced them again with a better set that gave an actual positive CLICK on both ends when installed. Ruled those out, problem still persists.

There's no MIL, no codes on the DIC, and nothing comes back when I plug in my handheld scanner, either.

The scanner I have is capable of doing some livedata, but not much. And I noticed the fuel trims were odd.

STFT B1 - 51.6%
LTFT B1 - 25.0%

STFT B2 - 1.6%
LTFT B2 - 6.3%

I talked to my tuner friend and he suggested it may be an issue with the injectors. I had problems with them before, so I decided to just buy a new set. Swapped those, and new intake gaskets last night and.... still doing it.

Where would you look from here? I'm thinking maybe look at the wiring for the oxygen sensors to see if it got burnt on the headers? Taking a little break for now but any insight or suggestions appreciated.

 

WOW !!…those fuel trims on bank 1 are maxed out !!…total fuel trim of almost 77% so bank 1 is adding 77% more fuel !!…when you have an injector misfire (lot of excess O2) your long terms will be really high !!…if your handheld scan tool is capable of reading generic OBD2 and shows mode 6 data you may find some misfires there…yes, look at your upstream O2 on bank 1 and see if it is “stuck” lean (below 450 Mv)…if stuck lean add some Brake Kleen or propane to a vacuum line…see if it goes rich…if not it’s a bad O2 sensor…if the car sits for a few hours see if the O2 sensor shows 450 Mv key ON but remove the O2 sensor heater fuse…if the sensor shows 100 Mv or below let’s say remove the connector off the O2 sensor and if it stays at 100 Mv you have a wiring issue !!…if it does respond with Brake Kleen you do have a lean condition on bank 1…you would need to do an injector balance test to confirm maybe clogged injector or injectors…are the injectors you bought OEM or aftermarket ??..you will need a fuel pressure gauge and a “pulser”…I would also check to see if with key ON you have power to each pink injector wire on bank 1…to confirm you have injector pulse connect a test light to battery positive and with engine running see if the test light blinks when you touch it to the other injector wire…it will blink dimly so check it in a darkened garage. With elevated fuel trims on only 1 bank it can only be something like leaking intake manifold gaskets on that side that were changed…recheck the torque !!

 

Thanks for that. Too bad I'm on the other side of the state from you. I'd buy you a beer or two.

So shoot some brake cleaner into the vacuum line. Alright I'll give it a shot here in a bit and report back.

 

First see if your bank 1 is stuck below 450 Mv..it should switch nicely between 200-800 Mv !!…if you want to drive here I’d look at it for you !!

 

Alright, going back out and will check.

On the subject of scanners, do you have one you recommend for a DIYer? Don't really want to spend a thousand dollars. I was considering ordering one of these to mess with:

 

You don’t have a MIL for that lean condition…P0171 ??…check for codes with the cars built in code reader…I would spend a little more an get an Autel MX808…touchscreen and very nice…I use my Autel MS906 as a backup !!…great scan tool !!

 

Nope - no MIL at all. Checked codes both ways with the on board and with the little handheld.

 

MMMM ??…with the key on do you see the check engine light ??…that’s strange if no MIL and no codes stored !!

 

Yes sir.

 

With those fuel trims you should have at least a P0171…ok, look at that bank 1 O2 and see if it is switching properly when warmed up and if stuck way below 450mv give it a toot of brake Kleen and see what happens…if responds raise RPM to 3000 and see if long terms decrease.. if they decrease you have a bank 1 specific vacuum leak like the injectors or manifold gaskets on that side…you can spray brake Kleen at the base of the injectors and see if the fuel trims go negative watching your fuel trims with your scan tool.

 

I put the car back together and drove it. It's definitely LESSENED after swapping the injectors and replacing the leaking DS valve cover gasket I found while I was in there.

Key off I got 0.145V from B1S1 and 0.420V from B2S1

Perhaps the B1 sensor is on its way out?

Letting it cool down before I go back out there.

 

To verify either wiring or sensor you will have to remove B1S1 connector and see if 450mv bias voltage returns to 450…if it goes to 450 you have a bad O2 and if it stays at 145mv you have a wiring issue !!…do you still see .145 with the engine running ??…my scan tool needs key ON to power it and the circuits up…why I said pull the O2 heater fuse is the 450mv bias voltage will decrease if the key is left on when the scan tool is powered up…I just want to make sure they stay at 450 !!

 

Okay so I'm in the car right now. Heater fused pulled.

Key on engine off

B1S1 0.445V
B1S2 0.440V
B2S1 0.440VB2S2 0.445V
Holding steady while the key is on.

When I start the car they all stay around that same except B1S1 drops to 0.335 to 0.385v

All the other sensors while running are going between 0.435 and 0.455v

With some throttle B1S1 is all over the place and is currently reading 0v.

 

Drove it around the block and it finally popped a P0171.

 

So reading 450 your wiring is good…with the fuse back in what do the O2 sensors look like with the engine running ??…switching between 200-800 or B1S1 stuck low ??

 

Fuse back in, engine idling...

B1S1 0.00V - think she's dead. B2S1 steadily dropping. Started out at 0.250 and now at 0.065v at idle. With throttle through the rev range it climbs as high as 1.055v then drops down to 0.065v

Should I replace both front o2s?

 

Watch this video !!..O2 should switch between 200-800 Mv…can you graph your O2’s ??…also the downstream O2 should be steady around 600-700 Mv !!…if bank 1 is 0.00 it’s dead !!…you can change bank 2…stay with AC Delco…you can get them at Rock Auto !!

 

Neither of them switch that much like in the video, or that fast, according to my scanner.

 

Don’t know what type of scan tool you have but the refresh rate probably isn’t the fastest !!

 

It's a cheapie handheld.

I'm going to bring it to work with me tomorrow and see if my used car guy will let me borrow his Solus. That'll give us an upgrade in computing power for sure. Thankfully I only live about half a mile from work.