Long term fuel trim

[dew22]

I put the car on the dyno and the power was way down.
My long term fuel trim is way out of whack

Longft1 -21
Longft2 -17

Called Kenne Bell and they said vacuum leak.

Could a vacuum leak cause my long term fuel readings to be so out of whack?

 

[jstreet0204]

I put the car on the dyno and the power was way down.
My long term fuel trim is way out of whack

Longft1 -21
Longft2 -17

Called Kenne Bell and they said vacuum leak.

Could a vacuum leak cause my long term fuel readings to be so out of whack?

Yes the vacuum leak is the most likely cause.

 

[dew22]

Yes the vacuum leak is the most likely cause.

Thanks


My short term fuel trim doesn't look bad + or - 3% am I missing something?

 

[squares98]

did you read this through the predator and a narrow band 02? If so disregard your results. They hardly ever show true 02 readings

 

[ToplessStang]

If your fuel trims are -21 and -17 as in NEGATIVE 21 and NEGATIVE 17, that is not caused by a vacuum leak. A vacuum leak would give you + fuel trim readings. Your car is running to rich if you got a negative reading.

As for your short fuel trims, yes they will always try to stay at around the 0 mark with the Long fuel trims compensating for any big changes.

 

[dew22]

If your fuel trims are -21 and -17 as in NEGATIVE 21 and NEGATIVE 17, that is not caused by a vacuum leak. A vacuum leak would give you + fuel trim readings. Your car is running to rich if you got a negative reading.

As for your short fuel trims, yes they will always try to stay at around the 0 mark with the Long fuel trims compensating for any big changes.

I'm confused the car keeps throwing code PO172 (rich bank 1) every time the long term fuel trim exceeds -25 on bank 1 it throws the code. I thought that the negative #'s were indicative of the computer compensating for a rich condition.

 

[dew22]

If it's a vacuume leak I'll know in about an hour. It's going on the smoke machine.

 

[jstreet0204]

If it's a vacuume leak I'll know in about an hour. It's going on the smoke machine.

Let us know how it turns out. It could be a vacuum leak or even an exhaust leak. They should check for both.

 

[ToplessStang]

I'm confused the car keeps throwing code PO172 (rich bank 1) every time the long term fuel trim exceeds -25 on bank 1 it throws the code. I thought that the negative #'s were indicative of the computer compensating for a rich condition.

The negative number means the PCM is cutting back fuel because the engine is running to rich. If it were a vacuum leak you'd be seeing a +25 for example. If you have negative fuel trims, the car is running rich which is not caused by a vacuum leak.

Some causes of a rich mixture are leaking injectors, badly blocked air filter ect.. but seeing as your F/I you must have a tune and other stuff that may not be working right causing it to run rich.

 

[dew22]

Smoke test done. No leak

Bad sensor? Which one?

Possibly something wrong with the chip I'll be talking to the KB tech's
Wed. They've been helpful and I'm sure we'll figure it out.

Also
I'm at sea level or very close the tech who smoke tested my car said he got a very unusual "Baro" reading (152) he said most cars around here show 156 157ish.

Any ideas?

Thanks
Dew

 

[dew22]

What are normal readings for long and short term fuel trim at idle?

 

[ToplessStang]

Smoke test done. No leak

Bad sensor? Which one?

Possibly something wrong with the chip I'll be talking to the KB tech's
Wed. They've been helpful and I'm sure we'll figure it out.

Also
I'm at sea level or very close the tech who smoke tested my car said he got a very unusual "Baro" reading (152) he said most cars around here show 156 157ish.

Any ideas?

Thanks
Dew

The baro at 152 is a bit low but not enough to cause a -21 fuel trim. Ideally the fuel trims will both stay at around 0 with the short trims always changing between + and - 6.

If for example the short fuel trims begin to go to high ie + 12, then after a predetermined amount of time the long fuel trims will move into the postive range to compensate so that the short trims can go back to switching at around the 0 mark.

 

[jstreet0204]

Did you have a wideband hooked up during the datalogs. If so, did the a/f ratio from the wideband verify the fuel trims. If it did, you need to look for a mechanical problem, like a leak, sticking injector, or something causing the fuel pressure to go to high. Otherwise, look for a bad sensor to be the cause.

 

[dew22]

Did you have a wideband hooked up during the datalogs. If so, did the a/f ratio from the wideband verify the fuel trims. If it did, you need to look for a mechanical problem, like a leak, sticking injector, or something causing the fuel pressure to go to high. Otherwise, look for a bad sensor to be the cause.

No

Hopefully getting it dataloged soon (per Kenne Bell request)

Does anyone know which sensor gives the computer the info for fuel trim?

 

[jstreet0204]

No

Hopefully getting it dataloged soon (per Kenne Bell request)

Does anyone know which sensor gives the computer the info for fuel trim?

It is a combination of the o2 sensors and the MAF that are used to determin fuel trims.

 

[dew22]

It is a combination of the o2 sensors and the MAF that are used to determin fuel trims.

Thanks

 

[Mike97gt]

sorry it took so long for me to get to this. I got your PM but I was out for a few days.

Well a long term fuel trim in the negitives means that the PCM is subtracting from the base fuel trim. -21 means 21 percent less fuel than base trim for that cell.

At -25 or higher the PCM is maxed at how much it can correct the mixture and you will get a code po172,po175 rich bank 1 and rich bank 2

one of the things you may want to check out is the fuel presure sensor on the fuel rail. this reports the fuel presure back to the pcm so the PCM can regulate the fuel presure, if this sensor was off a bit you might have the condiotion you have now.

 

[dew22]

Update

I haven’t had time to have the car wideband dataloged

changed mass air meter same model as before just new. (no change)

installed 2 new o2 sensors (no change)

had a small exhaust leak fixt (no change)

new fuel pressure sensor (no change)

I have noticed something while looking at the data I can get through my
predator the fuel trim at idle now looks much better ( long & short )

What I've noticed is when driving lets say 50 or 60mph and the light up ahead turns yellow and I let off the gas to coast up to the light the long term fuel trim spikes from anywhere between -3/-13 to -22/-26.

Also every other day or so I'll hit the gas from a stop (normal driving) and the car will stumble for just a split second.

 

[Dope 97GT]

sounds like the exact same problem my car is having and i cannot figure it out either. I am N/A but am throwing both the rich codes for bank 1 and 2. I am thinking about new injectors but thats gonna cost some loot especially if its not the problem.

 

[dew22]

I also took out 1 spark plug from each bank and they don't look like the car has been running rich. (whitish to light grey)