As stated I have high fuel trims LFTs are 19.5 getting a check engine light and restricted performance it clear codes and comes back. Fuel rail pressure is at 53 psi on idle. Smoke tested for vacuum leaks there are none. Properly reset the system removing battery leads and touching them together. Also replaced full load breather. Maybe O2 sensors but unlikely they were both go bad at the same time. Any ideas appreciated...

 

Manifold leak would be my first thought for trims that high, but smoke test should rule that out. What is the MAF reporting? Should be around 4.2 grams/sec at idle. Could also be a stuck open evap purge valve. I had to replace the AIR switching valve due to it sticking open, but system was able to compensate that small leak easily.

What are the total fuel trims (LT and ST) at idle and while holding rpm steady at 2000 rpm?

 

The long fuel trims come down nicely at around 2000 that's why I still suspect a vacuum leak...MAF has been changed... I'll have to take a look at the short fuel trims when I get home

 

It sounds like the smoke test just may not have revealed the leak.

Even a tiny leak will disturb idle trims a lot.

The MAF doesn't look like much of a suspect so far.

 

When my 04 XJ8 was having these codes, wound up being the eight little gaskets inside the intake manifold.
Bought them for less than a hundred dollars, off the computer.

 

Okay after retesting today short fuel trim is at 25.0 and long fuel trim is at 19.5 and at 2500 RPMs they stay very close to the same... and that's exactly where they are at idle. long fuels come down a little bit here and there are

 

That is for both bank 1 and bank 2? So your total trim(s) are almost 45%. That's crazy high.

If the MAF sensor is not under reporting airflow, I'd have to think you have a fueling issue. If you squirt some brake cleaner into a vacuum port, do the trims fall like a stone?

 

Okay I reset the computer and now the long fuel trims are coming down to around 3 or 4 at 2500 rpm but eventually we'll creep back up short fuel trim stay at 25 all the time no matter what I do... I will spray some carb spray in there and let you know thanks

 

I wouldn't keep resetting the PCM. It's not going to solve the issue, and will just take longer to diagnose because it has to adapt every time.

My suggestion would be to look at the rear O2 sensors as well as LT and ST fuel trims while giving it a little bit of brake cleaner. Rear O2s should spike rich, close to 0 volts. The upstream ARF sensors will momentarily peg on the rich side, which will be closer to 4-5v. The LT trim won't change, but the ST should hopefully swing to some negative value. That will at least show that your air/fuel sensor system is working properly. Then you can figure out why you don't have enough gas (or too much air) getting into the engine.

The fuel rail pressure sensor gave me issues on my car. It's not a common failure, but others have also had problems with it.

 

Great thanks I may have found something. I can hear a hiss in front of the motor I thought it was the full load breather but actually it's the hose that comes out of the front of it and if If I move it around I can hear the hiss change in pitch

slightly so I'm guessing this could be the problem. I did replace the full load breather as a PM recently....

 

A hiss is commonly a massive leak to OBD...

 

Yep, and that hose has been known to crack. Full manifold vac leak there.

Now, the PCV valve will have the sound of air rushing through it normally. But that hose shouldn't have any leaks. Another possibility is a leak in the brake booster, smoke might not show up there.

 

Hi viper1996,

I've had some success fixing that changing pitch leak by replacing the O-ring on the Norma connector of the breather pipe where it meets the crankcase vent (the disc-shaped part that looks like a PCV valve but there is no valve inside - it's more of an oil separator), so if you don't find a crack in the pipe, try changing the O-ring.

Cheers,

Don

 

thanks Don mine had a crack in it so I just replaced it I found to vacuum leak so far but apparently there's more

 

Did you notice when the issue started?
after MAF change possibly?

 

Second to bet on this. Once I had mine tube come of and immediately seen such big numbers as you now. Inspect it and give us a beer then))

 

Was your stuck open valve temperature sensitive wrt STFT readings or did it affect them at all?

 

Where would this hose fail?

 

Right on throttle body. That tiny tube. Mine came off when I decided to connect the tube directly on TB without small white plastic tube size adapter and piece of a little bigger tube attached to TB itself. Had to place all back. However it's strange construction to me, as more connections = more potential leaks

 

Hey Viper,
Did you ever get to the bottom of your issue?
I have been following your post as I have a similar problem.