Bank 1 misfire

[austin21]

Good morning, hoping someone can help me troubleshoot a bank 1 misfire im having.

Car: 99 Cobra, ProCharged, aftermarket fuel pump, stage 3 comp cams, BA2600 MAF

Issue: misfire on entire bank 1 (Cyl 1-4). Had a P0171 code a few months earlier but cleared it and it never came back. Can hear an audible misfire from the exhaust at idle.

What I have tried:

1. Replaced all 8 spark plugs
2. Coils were replaced in Jan 2024. Tested coils on bank 1 by grounding spark plug to engine and turning over. All 4 cylinders are sparking.
3. Fuel injectors were professionally cleaned, no issues
4. Verified injector voltage and ground on all 8 connectors with power probe. Getting 12v, ground is present.
5. Performed smoke test to check for vacuum / intake leaks. No visible leaks found.
6. Verified factory grounds are secure.
7. Replaced both upstream O2 sensors.

Now i have tried to unplug the fuel injectors while the car is running on bank 1, there is no change in tone or idle from the engine. I think this may be normal since apparently they are all 4 misfiring.

After letting the car run to get up to temp. The driver side (bank 2) high flow cat gets up to 400 Fahrenheit. Bank 1 cat is only 150 degrees. (Probably normal since bank 1 is not firing correctly).

Seems the car is running very lean, showing high fuel trims on both Bank 1 and Bank 2. When I rev the engine and hold it at 2k RPMs the fuel trims seem to even out pretty good.
At a loss here on what i can do next before sending it to a shop...

My next steps:
Test fuel pressure
Clean MAF (had to get a T20 security bit to remove)
Replace EGR

 

[alwayshi]

Another cheap idea could be fuel filter

 

[austin21]

Another cheap idea could be fuel filter

It could be, it was replaced probably 2021 but the car sat for about a year. Thanks for the input!

I am going to try to clean the MAF and check fuel pressure. If fuel pressure is low that will be on my list of things to check.

 

[alwayshi]

Sounds like a plan

If you have access to a dremel, carve a slot into that safety torx head so you can use a flat blade screwdriver

Also, assuming you have access to a datalog - datalog the MAF and see if the counts change. When my MAF went out, regardless of RPM the MAF counts stayed at 1.0….it was dead haha

 

[austin21]

Sounds like a plan

If you have access to a dremel, carve a slot into that safety torx head so you can use a flat blade screwdriver

Also, assuming you have access to a datalog - datalog the MAF and see if the counts change. When my MAF went out, regardless of RPM the MAF counts stayed at 1.0….it was dead haha

I think my OBD2 reader can see the MAF so i will check that as well. The MAF is the last thing i havent checked on the air side.

I have my SCT x4, but i need to get the software setup on my laptop to datalog.

 

[austin21]

MAF is good. Cleaned it and it wasn’t dirty at all. However I could see the increase when giving it throttle on my scanner.

EGR seems to be rusted on there pretty good. Need a 1 1/16 socket to get that off. Put some PB blaster on it and will try again in a day or so.

At this point I’ve basically narrowed it down it being a fuel issue besides EGR.

 

[alwayshi]

Get that sct software downloaded lol.
Log the fuel pump - how old is that thing?

 

[austin21]

The car had a lot of work done in 2021.

Comp cams, valve springs, camshaft drive kit, SCT 90mm MAF, deatschwerks dw300m fuel pump, 60lb ford performance injectors

I don’t see where the fuel filter was replaced so that could be something worth digging into.

 

[austin21]

Replaced the Idle air control valve and Fuel Pressure Injection sensor and the fuel trims are looking good now!

Now i cant tell if i still have a misfire or if its the cams...Will SCT x4 datalog misfire data? Or do i need to buy an expensive scanner to get misfire live data?

 

[Bullitt347]

If you still had a misfire then your STFT would be off a bunch, not sitting on zero

 

[austin21]

If you still had a misfire then your STFT would be off a bunch, not sitting on zero

Thanks for your input! Makes me feel better. Car also doesnt seem to be low on power.....

 

[alwayshi]

Glad it’s working out for you.

Cams can cause multiple misfire codes, gotta tune that out

 

[austin21]

Glad it’s working out for you.

Cams can cause multiple misfire codes, gotta tune that out

Never got a code for a misfire, only the lean fuel trims on both banks. I need to check temp of both catalytic converters because before I was only getting 150 degrees on the bank 1 side while bank 2 catalytic converter was 450 degrees

 

[alwayshi]

Never got a code for a misfire, only the lean fuel trims on both banks. I need to check temp of both catalytic converters because before I was only getting 150 degrees on the bank 1 side while bank 2 catalytic converter was 450 degrees

Copy that.

My cams were giving me a multiple misfire within first 1000 revolutions code. Marty from MO’s speed shop said that was normal and tuned it out - that’s the only reason I brought it up. Lol

 

[austin21]

So i am still getting very different temps on each catalytic convertor. I have Kooks high flow cats that are welded on to my x pipe.

Driver Side reads about 400 after warming up
Passenger side reaches about 150-160.....

Im also going to attach an idle video here...

View: https://www.youtube.com/shorts/bX5EKXIUC9c

 

[austin21]

Ok, i still have an issue.

I think the cat on the driver side (bank 2) could be an issue. Went out and let the car idle again and im showing a constant +22% on the Long term fuel trim for bank 2. What is odd is that the short term fuel trim does not go past +/- 3%. Even that said it still shows +22%.

I noticed Bank 2 Sensor 2 is getting 0 voltage. I dont know if the rears would have anything to do with the fuel trims. This is the only O2 sensor i did not replaced because it was seized up. It is plugged in though.

I drove the car around. The passenger side Catalytic convertor got up to temp (500-550 degrees). It could very well be the driver side cat has failed due to being lean without me knowing it....will post a live data graph below when its done uploading

 

[austin21]

Also the +22 lean on the long term fuel trim for bank 2 goes away after i start driving it a bit. It eventually goes back to an acceptable level. It seems its ONLY at idle.....


EDIT: maybe im wrong. The reason the Catalytic converter is getting so hot is because of the lean condition on bank 2. This is reported by the Bank 2 Sensor 1 O2 sensor BEFORE the catalytic convertor.....

Back to the drawing board, as I have no idea why the fuel trims are all of a sudden getting high, when before they were not...

 

[austin21]

View: https://www.youtube.com/shorts/IubmC9l5F2U

Heres a vid of the fuel trims

 

[Bullitt347]

When fuel trims are reset to zero, and I don't know if your scan tool can do that,
the STFT will start adding fuel, or subtracting fuel as necessary to try and achieve Stoic.
STFT is just that, short term, meaning now. LTFT is basically a History of what has been going on over time.
Once the STFT goes up or down by about 25%, it will revert back to zero, but the LTFT will now show the correction that the STFT had.
Once LTFT hits 25% or so, and the STFT hits 25% or so, then no more correction can be achieved to get to Stoic.
This is what will then set the CEL with a code of P0171 for a lean condition on bank 1 assuming the correction was always + (rich)
Bank 1 or Bank 2 sensor 1 is what reads oxygen content (not fuel) and switches pretty fast trying to achieve Stoic.
Bank 1 or Bank 2 sensor 2 (after catalyst) is simply a catalyst monitor. If the catalyst is doing it's job, then sensor 2 will switch very slowly as the exhaust after catalyst should be pretty clean, (all oxygen consumed) If sensor 2 is switching as fast as sensor 1 on that bank, then the catalyst is usually toast and a code of P0420 will set. The only fix for this is a new catalyst. Which, if you are putting new catalyst on, I personally recommend installing new O2 sensors with that catalyst.

 

[austin21]

When fuel trims are reset to zero, and I don't know if your scan tool can do that,
the STFT will start adding fuel, or subtracting fuel as necessary to try and achieve Stoic.
STFT is just that, short term, meaning now. LTFT is basically a History of what has been going on over time.
Once the STFT goes up or down by about 25%, it will revert back to zero, but the LTFT will now show the correction that the STFT had.
Once LTFT hits 25% or so, and the STFT hits 25% or so, then no more correction can be achieved to get to Stoic.
This is what will then set the CEL with a code of P0171 for a lean condition on bank 1 assuming the correction was always + (rich)
Bank 2 sensor 1 is what reads oxygen content (not fuel) and switches pretty fast trying to achieve Stoic.
Bank 2 sensor 2 (after catalyst) is simply a catalyst monitor. If the catalyst is doing it's job, then sensor 2 will switch very slowly as the exhaust after catalyst should be pretty clean. If sensor 2 is switching as fast as sensor 1 on that bank, then the catalyst is usually toast and a code of P0420 will set. The only fix for this is a new catalyst. Which, if you are putting new catalyst on, I personally recommend installing new O2 sensors with that catalyst.

Thanks for the detailed explanation. I am only getting p0174 now. I replaced both upstream o2 sensors last week.

I can reset the KAM with my SCT x4 tuner which may reset the fuel trims back to zero? I don’t think the innova can do that.

Would you say that my driver side catalytic converter needs to be replaced if I’m not getting p0420?