Goes lean when throttle is applied

[SleepinGVR4]

I've just had this problem develop. When I'm coasting with my foot off the throttle, and I then give my car gas it goes lean (16.0 - 17.0) before my WB02 reads stoich or goes rich if i give it alot of gas. It goes lean enough that i notice a hesitation. It only lasts for a second or two. I thought maybe my FPR was on its way out. The only reason i mention that is because when the problem started i added a little bit of fuel pressure and the problem went away. Now I haven't touched it and the problem is back. My FPR is one of the old school SX regulators.

I don't have anyway to watch the FP from inside the car. I started a thread the other day about having lean idle and now I noticed that my WB is sometimes all over the place at idle. Sometimes rich, sometimes lean, sometimes stoich.

 

[prove_it]

try compensating your wideband. You do have to carry that out every now and then for better accuracy. Depening on which WB you have, the calibration steps are different. Look it up. It's easy and a quick way to verify your conditions are accurate.
Otherwise:
Your TPS may be out of range or bad? /ubbthreads/images/graemlins/dunno.gif
Bad fuel filter? /ubbthreads/images/graemlins/dunno.gif

 

[SleepinGVR4]

I have a AEM WB. I'm not sure how to calibrate it. I looked at the manual the other day and didn't see anything in it about calibrating it. My fuel filter is brand new. And i'll have to double check my TPS.

 

What are your fueltrims doing? Raising the base fuel pressure would make the ECU react by leaning out the fueltrims more. You want to get the fueltrims to be closer to 100 for good driveability.

 

[SleepinGVR4]

Ok so I put the base fuel pressure as close to 37 - 38 psi as I could.

The low trim is at 81.2%
The medium trim is at 86.7%
And the high trim is at 114%

/ubbthreads/images/graemlins/dunno.gif

 

[prove_it]

How old are your spark plugs? Poor plugs can cause a hesitation.

 

Did you reset the ECU after adjusting the fuel pressure? Do you have an upgraded fuelpump? AFPR? It looks like you may be overrunning the stock FPR with your LOW TRIM that rich.

 

[prove_it]

He said he has an old school sx fuel regulator.

 

[Hertz]

What sort of A/F correction are you using? SAFC? MAFT?

 

[SleepinGVR4]

Spark plugs are brand new. I replace them quite often.

I have an old school SX regulator. I have a supra pump.

And i'm using an eprom chip Jeff burnt for my for my A/F correction. I have everything I could possibly need for my set up. I didn't half ass anything.

 

[Hertz]

I'm going to go with vacuum leak.

 

[prove_it]

It would be running poor at idle, could be he never mentioned if it was or not.

What about an exhaust leak before the WB sensor?

 

[Barnes]

Quoting prove_it:
What about an exhaust leak before the WB sensor?



Would that actually effect the AF reading? The WB only looks at a fraction of the exhaust flow anyways. I doubt losing some to a leak would change the reading.

 

[SleepinGVR4]

Nope idles fine. Since its getting colder out sometimes it idles a little low but then once it gets warmed up it idles fine. Well if there was an exhaust leak pre 02 sensor I should be able to hear it I thought. Its not like i'm not using gaskets or anything.

 

[SleepinGVR4]

Quoting BarnesMobile:
Quoting prove_it:
What about an exhaust leak before the WB sensor?



Would that actually effect the AF reading? The WB only looks at a fraction of the exhaust flow anyways. I doubt losing some to a leak would change the reading.



This is what I was told by another member also.

 

[SleepinGVR4]

Another thing i'm noticing is that under WOT my A/F ratio isn't correct. Its running way leaner than it should causing knock. Last night I saw as lean as 12.7, instead of the 11.0 - 11.5 that the eprom was burned at.

 

[prove_it]

Exhaust leaks will actually pull air in under high exhaust gas velocity. When it pulls air in the exhaust becomes mixed and you can't get a good reading on a sensor which will throw your tune off.

Something like that I think.
I bet Jeff could answer that better.
Someone tried to explain it to me once. I do know from experience, for example My turbo bolts came loose on my car and it throw my tune way off. I tightened them up and it's all good now. I was knocking becuase of that too, but I didn't even hear a leak. Only found it because I wanted to replace my heat sheild.
I'd look for an exhaust leak. It sounds kinda like what my car was doing.

 

Your mention of the SX regulator reminded me of a similar issue with mine about 5 years ago, when I took #1886 on that long trip out west. I stopped off at Gabor's house to look at the SX regulator, because my fuel pressure and fueltrims kept changing during the whole trip. It looked like the vacuum nipple was rubbing the spring, so I ground it down a little bit, but that didn't fix it. A couple days later I ended up stopping at a Walmart in Arkansas for a set of allen wrenches to open the regulator, and I found that the check ball on the diaphragm was actually offset slightly, and had a groove worn in it. So, sometimes the ball would seal good, and other times it wasn't sealing, so the fuel pressure kept changing on me. I simply reaigned the diaphragm slightly, so that is was centered, bolted it back together, and never had another issue with it.
What injectors are you running? What deadtime did I give you?

 

[SleepinGVR4]

I'll have to take it apart and see whats goin on inside of the FPR. My A/F ratio keeps changing also. Sometimes it pulls good has a good A/F ratio and has zero knock and sometimes it has a horrible A/F ratio and knocks bad until i let off the gas.

I bought the eprom and injectors from you as a package. I believe they are 850cc injectors. As for the deadtime, I'd have to look on the eprom slip that you sent with everything. But I can't right now because i'm in Virginia and not at my house in PA.

 

[SleepinGVR4]

Jeff,
I took the FPR apart and I didn't see any wear on anything. Is the ball bearing susposed to be attached the bottem of the diaphram or be free within the reguator? If its susposed to be free within the regulator then that could be a problem.