So let me start off by stating I am new to the LS scene and this is my first motor. I recent swapped a 5.3/4L60E into my 55'. It has a CAI and long tubes. It drove great and had great power. My only complaint was I thought the idle was a little high until I was at a dead stop. Figure that would be taken care of when I eventually got her tuned. Well I blew the pump after about 2 days on the new tranny and had it rebuilt. Ever since (not sure if it is even related to the issue), I get a bog and wot. It will fall flat on its face sometimes. I tried cleaning the MAF really good with CRC MAF cleaner wig no impact. It's really frustrating to invest the money and time only to have this issue. So could the MAF be faulty, TPS? Will be throwing a Maggie 112 on it soon so I haven't invested in the tune yet until I get the boost maker installed as I don want to spend twice. It feels down on power as well across the board. Any help or ides here would be greatly appreciated. Wish I was familiar with someone in the SoCal area that could plug in and let me know what's going with out charging an arm and a leg. I'm going to borrow a scanner today and see what I can find. My knowledge is limited so I won't know everything I'm looking at.

 

Do you have a wideband 02 sensor?

If not what are your factory 02 sensors doing at WOT? If they are going lean that can be a good indication that you are running out of fuel; clogged fuel filter and/or weak fuel pump.

It could also be the MAF was went bad. At WOT when it's bogging look to see if the MAF hz is continuing to increase.

Is the bog right after you got 100% throttle or is it later in the run?

You said it started doing this after the trans fix(which may or nay not be related) Is it shifting properly?

 

Well no wide band yet. I haven't figured out how I want to incorporate all the gauges that I want and not clutter the interior of the 55'. I wasn't able to pick up the scanner today but probably wouldn't have done much good as I didn't have a lot of motivation in 106 degree heat with no ac lol. When I hook it up I will look at the O2's. I'm going to hook up a hose to extend my fule gauge to make sure I am maintaining fuel pressure. I have a brand new aeromotive EFI tank and a Aeromotive tank. New FPR and filter. maybe only 100-150 mile on my set up so I doubt that I would have a clog just yet, bet nothing is ever out of the question. So if the MAF is functioning correctly, the Hz will continue to increase? It is after and while holding 100% throttle. Will fall flat on its face and then recover or I will feather the throttle and it will recover.Also, it I feel like shes a little down on power and when accelerating, not wot, I feel a hesitation and recovery although not as pronounced. Tranny is shifting properly as far as I can tell.

 

So the car wil still be steetable with a bad MAF?

 

It really "sounds" like it's a fueling issue, however it's always important to check the basics first. It's hard to diag something over the internet. There's a dozen different things it could be but I'm speaking in general terms of what it could be.

The first thing I would do is;
1. check for DTC's(but don't clear them!!!)
2. STFT and LTFT at idle, 1500, 2500 and 3500 in park
3. I would log and see what the narrowband 02's are doing when it's bogging. At WOT your 02's should be 900mv or more. You will see them go lean after the hit but "should" quickly go rich, 900mv or more after a second or so. On a WOT hit the PCM see's the lean condition, throttle input, MAP and several other things and opens the injectors up all the way(depending on the setup and size of injectors).

Again check the basics. It could be any number of things.

 

Thank you. I will work my way through he list. I know it is something simple. It's just a matter of tracking it down. Excuse my lack of knowledge but what is STFT and LTFT?

 

Where in SoCal are you...?

 

Hey there sir. I am in the Fullerton/Anaheim area

 

I'm in GG (near the 405/22/605 interchange), I'll have to see how my schedule is...

 

Oh your not far at all. That would be awesome! I don't have any LS friends or know anybody with LS experience so it's just usually me and the internet lol

 

No worries.

STFT are short term fuel trims
LTFT are long term fuel trims

STFT job is to keep the 02 sensors switching at stoich which is 14.7:1(actually it depends on the fuel but most people use 14.7) "Approximately" 450mv is the switch point. Anything higher than 450 is rich and anything lower is consider lean. Let's say your 02 voltage is 300mv, the PCM sees this as a lean condition and adds fuel. Then the 02 voltage goes to 800mv and it sees it as rich so it takes some fuel out. The 02's are constantly switching back and forth. If everything is in working order the STFT should be +/- 5%

LTFT job is to keep STFT at or near zero. Let's say your car has a vacuum leak so the 02 sensors are "seeing" a lean condition constantly and the STFT are adding +15% more fuel all the time. The LTFT sees this and will add the 15% on it's own(for lack of a better explanation the LTFT is adding additional fuel to the tune in the PCM) When the LTFT adds the 15% the STFT doesn't have to anymore and the STFT will go back down to zero.

Think of STFT as short term memory and LTFT as long term memory. The STFT react instantly to the 02 voltage and the LTFT learns from the STFT.

Since STFT act instantly, if there is a big enough swing, adding/subtracting fuel, you can actually feel it while driving. It kinda feels like a surge but the STFT really have to be swinging wide +/- 25 in my experience to feel it.

There is also total trims which is when you add the STFT and LTFT together. For example if your vacuum leak is really bad, the LTFT are +25 and your STFT are +25, the PCM is adding an additional 50% fuel, which is A LOT.

A narrow band 02 sensor only reads in closed loop(when the PCM is controlling fueling)after it reaches a certain temp(I think it's 650 degrees but don't hold me to that) It also doesn't control fueling at WOT(the PCM goes back into open loop and fueling is controlled by what's in the tune) Reason is a narrow band 02 sensor is only accurate at/around 14.7 and that's the only thing it cares about.

You can't decipher what your AFR is from a narrow band(I know I'm going to get flamed for that but that's my .02) because once it gets away from 14.7 it's not accurate. At WOT the narrow band 02 sensor isn't controlling fueling but it still sees whats going on in the exhaust. So if you go WOT and it bogs and your 02 voltage isn't 900mv or more there's not enough fuel.

Newer engines like the Coyote Mustangs come factory with wide band 02 sensors which read the AFR, it actually reads Lambda but most people view it as AFR. On the Coyote engines the 02 sensor after it's warmed up controls fueling all the time even at WOT and will make corrections at WOT.

 

My schedule is all over the place... it will be easier to swap phone numbers by pm.

 

Wow you seem to be a resource of knowledge. I love this forum already! That actually makes a lot of sense to me. The only thing I'm unsure about is the wide band and narrow band O2's. I understand on oem setups they have a front and rear set. I'm running mine in a 55' Chevy with an aftermarket psi harness and one set of O2's deleted. I remember when I was doing the install I picked up a front set of O2's and they used a different connector than my harness. I ended up buying the rear O2's and they worked. Now are the rears narrow or wide band and how does running the system off of only 2 instead of 4 effect it?

 

The factory O2 sensors were all 4 narrow band sensors. The front 2 were used for fuel corrections and the rear 2 were only used to verify catalyst efficiency (placed after the catalytic converters).

You only need the front 2 if you are not trying to be emissions compliant, and it doesn't matter which o2 sensor (front or rear) because they would all be the same narrow band sensor with a different plug.

I believe the square plug used on trucks for the rear o2 sensor is the same plug used on the front o2 sensor on Camaros, which is what most aftermarket harnesses are duplicating.

 

That makes a lot of sense now. I didn't understand why they used the plug that they did before and did not realize that they were all narrow band O2's. Thanks for the info. So how do guys run wide band gauges on these motors? Anothe set of O2's and standalone computer?

 

Also, I would like to acknowledge how kind and helpful Joecar is. He has reached out and offered his help. Spoke with him on the phone yesterday and he is very knowledgeable. he is even going to let me come over and he is going to go over my system with me. Very stand up guy! Thanks Joe!!!!

 

An aftermarket wideband would be used for logging and tuning only so you can either weld an additional bung in the exhaust or remove a factory o2 and insert the wideband while you are tuning in open loop.

The wideband will not communicate with the factory computer, it is only used to provide data via the tuning software to make corrections to the factory tune.

There are some aftermarket computer systems that can use wideband and will make tuning corrections on it's own, but for stock pcms, you need the tuner.

 

Would one be sufficient or would I weld a bung on each side and run 2 O2 sensors?

 

Thanks for the kind words.

Let's aim for Wednesday after work while it's still daylight...

 

So, the problem started happening after the fixed transmission was installed...?