silenceikillyou

I've got what I think may be a vacuum leak, but I'm also thinking it may be a fuel problem.

The usual vacuum leak suspect is present:

Surging idle after decelerating (the engine actually kills sometimes if the A/C is on, which makes hot southern days that much more fun...)

And he brought some of his buddies too:

Hesitation

Random misfire under partial load (It feels like it's the same cylinder every time. It might sound crazy, but after all of the bad COPs in my F-150, I've pretty much been able to tell when it's one single cylinder misfire or more than one.)

Feels like it's staying in open loop operation instead of switching to closed loop

~1 mpg drop in fuel economy


The thing is that it's only affecting bank 2. Bank 1 is running a LTFT of ~1.07, which isn't too bad, but bank 2 LTFT is a constant 1.25 (hence the "lean condition bank 2" code).

When I had my clutch replaced, I got the guy to remove the 2 busted up catalytic converters and I put blanks in their place (regular exhaust tubing flared on one end). This "fixed" the exhaust leak caused by the bent up mouth of the catalytic converter on the bank 2 side (kept catching on things like speed bumps). So now, I don't hear any exhaust leak, and there are no signs on the block that show a bad exhaust gasket either.

So with that in mind, I'm wondering what could be the culprit. I've gone through "the list of things that could be wrong", but the majority of them, things like dirty MAF and such, should cause a lean condition on both banks, not just one, it would seem to me.

I was thinking fuel problems at one point, but while the hesitation, power loss, and stumbling are symptoms of that, I would expect them to get worse as fuel demand increased. But it doesn't seem like it's hitting a fuel flow/pressure ceiling because it doesn't keep getting worse as rpms increase. It's bad in like a rpm window if that makes sense.

I've also read about leaking intake manifold gaskets. Could this be my issue? I'm asking because it may be the final kick in the *** I need to get around to ordering a tune so I can put the FRPP intake manifold and throttle body on that's been sitting in a box since tax season.

So what do you guys think is the most likely culprit? I don't even know where to begin......

drewsky

Since your planning on installing the FRPP manifold you can check and see if the gaskets are dried out and cracked.. I always start with the stupid simple stuff. Throttle body, maf sensor, fuel filter, clogged jets, loose intake, brake booster lines cracked or just loose. Run some fuel injector cleaner through it also. But if it was me I would take off the manifold and install the new FRPP one. With all the parts off you can see hoses and stuff a lot easier and may be able to run into an obvious problem like a loose or dried up vac line. Also replace the plugs while you have it open too (if you haven't recently)

silenceikillyou

I put some Marvel Mystery Oil when I filled up this morning. My mpg was back to normal (if not better), it didn't sputter/misfire, and didn't surge at idle even with the a/c on. It's like all the symptoms went away. That has me thinking it's in the fuel system. I still need to see what my fuel trims are running, but other than that, it's running 10 times better....

jpplaw

Sounds like maybe you had an injector clogging or a load of crappy gas

302Travis

+1
Definitely seems like a fuel issue.

For future reference as a way to track down a vacuum leak, i have bought a cheap cigar, and blown smoke into a vacuum line, while covering the throttle body up with my hand. You can then see if the smoke leaves anywhere, just blow a few good puffs in there all at once so it fills it with smoke.

Not a healthy way to do it. But i enjoy a cigar every once in a while.

silenceikillyou

So the marvel mystery oil cleared it up a little, but I still have a vacuum leak. I'm just curious as to why it would affect only one bank.....

302Travis

What about an o2 sensor?

silenceikillyou

How would I test O2 sensors? Just swap them to opposite sides and see if it migrates to bank 1?

302Travis

There are a few ways using a multimeter, you can find what readings to look for and how to online. But swapping them is an easy way to find out.

In fact on a 93 f150 i had the way i checked was simply unplugging the o2 sensor. (Just the electical connector). In that case it would then run itself on the base fuel and spark maps in the ecu. Would run just fine. Idk if the mustangs would do the same being obd 2. But that would be another way to test it

jpplaw

When is the last time you erased the KAM (by disconnecting the battery or loading a tune)? I would do that first to erase all the adaptive fuel memory (thats what generates LTFT's in the first place). Then monitor LTFT's again and see if it goes back to 1.25.

How are your bank 1 & 2 STFT's? If the O2 is bad, you won't see the same STFT swings in both banks. If the O2 is telling the pcm the bank is lean, then the pcm will dump more fuel in that bank - you should see that in the STFT. With a LTFT of ~1.25, you should see a STFT of ~.75.

Swapping the O2's is another easy way to tell if it is a bad O2. Though the connections can be a PITA to get to.

An intake gasket leak on a particular runner will only affect the bank it is on.