1G Am I running out of fuel pump? (log included)

[Marchev]

Hey guys, I've got an intermittent lean issue here that got me confused a bit. Not always, but when doing a 3rd or 4th gear pull, at about 6k rpm the car starts running really lean. Mods are up to date with 1050cc injectors, wally 255, 16g@30 psi and e85. In the log, the injectors are not going over 70% IDC so I don't think they are the problem. Fuel filter was replaced about 6 months ago. This log is a 3rd throu 4th gear pull and right at the 6 second mark or 6000 rpm in 3rd, you can see the lean spot. In 4th there were no issues. Wideband is logged under LC2. Is the wally 255 running out of juice here?

 

[livedsm4g63]

Very interesting. Its as if something is clogging the system. Or you are losing pressure somewhere. You have an afpr? Your fuel system is plenty. Up top you only see around 70ish duty cycle. Reason why duty cycle is spiking over 100 is because it cannot get fuel in so it cranks up the duty cycle. I would assume a clogged injector or bad fuel pump/fuel pump seal. I would also rewire the pump. Now that I think of it, could be a bad afpr or fpr.

 

[Marchev]

The pump is rewired. Im running the stock fpr, since the fuel pump is not the high pressure unit. If the fpr was bad, wouldn't I have issues at all running rpm?

 

[mattp_65]

I think you need an aftermarket adjustable FPR. you are over running the stock FPR with that 255 HP or LP.

 

[Calan]

OP - For starters, you have MAF issues (look at the MAF and MAFRaw signals). The MAFRaw signal is pretty rough, but the final MAF signal that the ECU is using is terrible. Notice the spikes right in the area that you are seeing the issues, or more precisely... the dip right before the spikes.

Edit: I found an old log of mine, running a 16G on a GM MAF:

You must be logged in to view this image or video.

Notice the MAFRaw signal (magenta) is a little choppy, but it's within reason and is steadily increasing. The final MAF signal (white) is nice and smooth, and follows RPM and airflow as it should.


Now compare that with your log. Notice the point where the cursor is; even though airflow should be (and most likely is) steadily increasing, your MAFRaw signal suddenly drops. The ECU thinks less air is coming in, so it cuts the injector pulse width. Less fuel + same (or more air) = lean. A second later the MAF spikes high (twice), the ECU injects more fuel, and your wideband drops back down towards rich. Right after the shift to 4th, the same thing happens.

You must be logged in to view this image or video.

If you want to see what the ECU was telling your injectors to do, display the InjOn signal; that is the actual commanded pulse width that the ECU calculates at any given time. You'll see that it drops right after the MAFRaw drops. MAFRaw drops, ECU shortens pulse width, AFR goes lean... cause and effect.

*****

You need to resolve the MAF issue, reset your MAFComp curve (including that 17% global scalar), and start over. Better yet... trash that GM MAF and switch to SD.

Are you running a translator, or the MAF cable from ECMTuning?

Reason why duty cycle is spiking over 100 is because it cannot get fuel in so it cranks up the duty cycle.

That is not how it works. The ECU has no idea how much fuel is actually going into the cylinders, and doesn't "crank up the duty cycle"; it only knows what the resulting oxygen content is after combustion. Duty cycle is simply a calculated value that describes how hard the injector is working, based on the commanded pulse width.

You may want to check out this post.

 

[Calan]

BTW - If that wideband is reading correctly, you need to be very careful. You are hitting AFR's that are extremely lean, and with E85 you may not see any problem until things start melting. I suggest you get the MAF and any other issues fixed before you push it that hard.

You also need to log boost pressure.

 

[livedsm4g63]

Oh Im sorry, I didnt realize that a higher cycle makes you flow more fuel. How dumb of me.....

If the cycle is higher, yes it relates into the stress of the injector. However, it is a fact that at higher duty cycles the injector will flow more; equating to more fuel.

If stress is being placed onto the injectors and the afr's are not stabilizing, you can safely assume there is a leak or clog in the system. Or you have a bad 02/wideband; bad wiring.

 

[Calan]

Oh Im sorry, I didnt realize that a higher cycle makes you flow more fuel. How dumb of me.....

If the cycle is higher, yes it relates into the stress of the injector. However, it is a fact that at higher duty cycles the injector will flow more; equating to more fuel.

If stress is being placed onto the injectors and the afr's are not stabilizing, you can safely assume there is a leak or clog in the system. Or you have a bad 02/wideband; bad wiring.

Uhhh.... ok. I have no idea what you are trying to say, but it sounds impressive.

 

[Marchev]

That's some great information you guys are providing. I did not notice the erratic maf sensor readings. I am using the MAF cable from ECMtuning. Now I'm wondering if the gm maf could have gotten oil fouled since I'm running the stock pcv system and at such amount of boost + e85 I'm sure there is a lot more blow by than stock. Can't wait till that catch can comes in Calan

And the wideband was purchased new about 6 months ago, haven't had any issues with it so I trust it.

 

[Calan]

That's some great information you guys are providing. I did not notice the erratic maf sensor readings. I am using the MAF cable from ECMtuning. Now I'm wondering if the gm maf could have gotten oil fouled since I'm running the stock pcv system and at such amount of boost + e85 I'm sure there is a lot more blow by than stock. Can't wait till that catch can comes in Calan

And the wideband was purchased new about 6 months ago, haven't had any issues with it so I trust it.

Didn't recognize the name. That's twice that has happened this week.

I would definitely check that. The GM MAF's are pretty finicky about oil and moisture. You can also try turning it 90* in the piping, and see if the signal smooths out.

 

[Marchev]

Just got the Gm Maf out and it does not have any traces of oil on it. I bought the sensor used, and the previous owner took the honey combs out. Now I wonder if that has something to do with the erratic readings?

 

[thearkatek]

The honey comb is there to straighten and even out the air flow across the full area of the MAF. It would definitely throw your readings off, but at any rate why not just take a trip to the junkyard and find a new GM MAF.
They are really easy to get a hold of.

 

[Marchev]

The honey comb is there to straighten and even out the air flow across the full area of the MAF. It would definitely throw your readings off, but at any rate why not just take a trip to the junkyard and find a new GM MAF.
They are really easy to get a hold of.

Not a bad idea, but I think I'm just going to order the SD kit and be done with this maf business..

 

[Calan]

Tony... try rotating the MAF 90* like I mentioned. That can make a huge difference (or none at all) depending where the MAF is in the piping.

 

[Marchev]

Tony... try rotating the MAF 90* like I mentioned. That can make a huge difference (or none at all) depending where the MAF is in the piping.

I will try that first thing in the morning. The MAF is located right in front of the throttle body elbow.

 

[Marchev]

So I rotated the MAF 90* and it seems a lot better. Boost has been turned down to 22psi. Here are 2 logs, first one is 2nd and 3rd pull, the second is only 3rd. Readings are a lot smoother than they were, but I still feel like they should be even smoother.

 

[Calan]

That's a HUGE improvement, and it looks pretty normal now. As long as there isn't some weird intermittent issue, that should be good enough to let you get it dialed in and drive-able until the SD switch.

 

[Marchev]

Thanks for the help. SD is on the shopping list