4.6L (1996-2004 Modular) MustangTechnical discussions on 1996-2004 4.6 Liter Modular Motors (2V and 4V) within. Sponsored by Cruizin Concepts
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I was hoping someone could give me some information on the returnless fuel systems. I have found the issues as to why there can be low fuel pressure but am struggling to find information on high pressure.
I have a 01 GT N/A that is is throwing some o2 codes intermittently. I hooked the car up to an Ethos a couple nights ago and performed a load test. I got these codes:
After seeing these codes I went to the live data to see if I could see anything that stood out.
This is the questionable data that I seen. All data was recorded at idle but car does have a rough fluctuating idle.
FUEL STATUS - CL
MAF(gm/S) - 8.44 (can someone help me out with the average on this?)
MAF(V) - 1.03
SPRKADV(*) - 14 (this is concerning because I watched it bounced between 10 and 30)
FuelLvlInp(%) - 54
FuelRailPrs(V) - 3.81
FRP(kPa) - 391 (56.7 PSI)
RPMDES - 848
FUELPW1(mS) - 2.8
FUELPW2(mS) - 8.8
O2S11(mV) - 662
O2S21(mV) - 105
O2S12(mV) - 98
O2S22(mV) - 573
LFTRIM 1(%) - (-25)
LFTRIM 2(%) - (25)
SFTRIM 1(%) - (-20)
SFTRIM 2(%) - (33)
Do you guys think this is going to be a faulty FRPS? I was under the assumption that since I was reading fuel pressure through the computer this number should always be within the 38-40 PSI spec as it is what the computer is trying to correct to.
Or could this issue be cause by something a little simpler like a stuck injector? I'm going to check my injectors tonight just wanted to get everyone's input on the subject.
Fuel filter is new and MAF has been cleaned. Fuel pump, injectors, and fuel lines are all stock.
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According to the code you're running lean on both banks, but looking at the fuel trims, it looks like bank 2 is experiencing the most lean condition. The huge + for the SHTFT indicates that the system is trying to give more fuel to that side. This could cause your increase in fuel pressure. The rich code on Bank 1 could be a result of the engine trying to give more fuel. In an attempt to reduce the lean code on bank 2, it overcompensates on bank 1 causing excess fuel to be dumped, resulting in your rich condition.
Feel around some of the hoses for them to be pinched or sucking air. You could have a bad gasket somewhere as well. Those things are a little bit harder to troubleshoot, but you could always take a bit of carb cleaner and spray in certain areas to see if the engine RPMs rev up. You don't need to spray much, just tap the nozzle. Use this with caution as carb cleaner is obviously flammable.
My guess would be intake manifold gaskets need to be replaced. Have you done any head work, or intake work recently? If so, there could be a torn gasket.
Short Term Fuel trims should fluctuate around +/- 5-10%. Think of fuel trims as current and average fuel needs of the engine. Short term is what the engine needs right then. Long term is an average of what it has needed for several cycles. To be honest, I can't remember the "acceptable" percentages for long term. I always used 15% as sort of the breaking point when I was a tech. It probably changes from vehicle to vehicle, but I can say that 30%+ is way too much.
Thanks for the response, I've checked for vacuum leaks and was not able to find any. I replaced the PCV valve just yesterday because I noticed a lot of oil passing through into the intake. It helped for a few hours then slowly went back to the way it was.
The short term and long term fuel trims will stay stuck at (25%) for bank 1 and (-25%) for bank 2
I should probably mention that all those codes only appeared when a load test was performed using the ethos. Just driving normally I will only receive P1151 and P1137.
What is really throwing me off is when I look at my o2 sensor voltage it seems that they are completely off where they should be.
o2-11 and o2-22 will read rich but o2-21 and o2-12 read lean. I know there is an x pipe on the car but I still don't feel like that should be the case.
These are not real numbers but it is about average for what I have been seeing:
o2 11 - 0.88v
o2 12 - 0.11v (sometimes averages about what 11 and 21 average)
o2 21 - 0.05v
o2 22 - 0.79v
The other weird thing that I noticed is the HEGO voltage will go crazy. This is what I was seeing after I replaced the PCV.
o2S11SV (V) - 63.00
o2S21SV (V) - 0.8
In this case .5 would be stoichiometric and they should never be above 1V but when it was reading 63V's the car was actually idling correctly. When I gave it some throttle it was think for a few minutes (run extremely rough and read .4V like it was trying to readjust fuel trims and then smooth out and jump back to 63v)
At this point I'm almost thinking that I have a lazy o2. I am going to attempt to take both upstream o2's out and clean them then change banks with them to see if my codes thrown switch banks.
Do you happen to know what the average gm/s of flow should be on the MAF? All my readings are indicating that it is getting the correct signal and the voltage increase with throttle is moving like it should with no jumps but I want to make sure I can completely eliminate it from a possible causes. I also don't want to be spending over $100 for a new MAF if mine is still good.
One other thing I'm curious about that I don't know too much on is the EVAP system. Is there anything I can be looking for in the live data that will indicate if I have an issue in that system?
Have you made sure that the post-cat O2 sensors aren't swapped? It's possible that they were swapped during the x-pipe install, causing some confusion. They are color coded, but I can't remember which one is bank 1 and which one is bank 2. Take a look at how the harness is on the transmission crossmember.
That 63V is alarming. Like you said, it shouldn't be above 1V, as that's all the PCM will give it. Could be a good indication of a problem though.
If your diag device let's you view the waveforms of the O2 sensors (and if you're using the Snap-On Ethos it better or return that thing!) pull it up and watch the pre-cat O2. Under normal conditions, they should fluctuate between hi and lo (.1V - .9V) in a sinusoidal fashion (up for some time, then down for some time). On the lean side, it will probably hover more towards the low voltage. If you could monitor this, spray some carb cleaner around in the intake manifold and other intake components and see if the O2 jumps up to high voltage.
As for the MAF sensor, I would maybe lean towards that if both banks were always calling lean codes, but in your case, it seems to be one bank mainly. I don't remember the gm/s. We would normally just use the voltage, as gm/s is calculated via the voltage.
EVAP is a possibility, but I kinda doubt it.
Right now, my guess is the post-cat O2s are swapped and it's causing some serious confusion. In fact, it could be the whole problem if that's really what's going on.
I apologize, I probably should have stated in a previous post that the rear o2's and EGR have been shut off with the a tune. So I am not worried about those two things as being a cause of the issue.
I was unable to get to the shop last night to switch out the o2's like planned. Since I didn't make it I also did not get a chance to hook back up to the Ethos. I did pull some graphs with my tuner. I was pretty limited with this though. o2's didn't show any fluctuation. They pretty well all just stayed right around where I posted previously.
I should probably also clarify why I was wanting some information about the MAF. Going back I noticed that my barometric pressure was holding steady at 28hz. (yes I know this is a issue because it is MUCH lower than it actually should be) However the voltage to the MAF holds strong at about 0.9 volts at idle and rises steadily with no issues as RPM's increase. That is why I was wondering what the gm/s should be. Trying to get all the readings for the MAF possible.
I really don't think the boro pressure is the issue though. I think it is just a symptom. It doesn't make sense to me that the MAF is bad but it is only affecting one bank.
Another note: I have started to smell the odor of gas on a full fill up. Which leads me to believe that I might have an issue with my evap system. I'm not really leaning towards any leaks or issues with the purge valves and sensors since I am not getting any codes for it. However is there a way to easily check the charcoal canister using live data? Never had to diagnose an issue with the evap system and I really want to avoid paying a shop to do a full smoke test if I can.
The BARO reading 28hz is definitely an issue. The chart below is a good baseline for Ford BARO sensors. Even with the voltage looking good, the baro being off can cause some issues. Also the gm/s chart I attached is for a 96 Mark8 off of autozones website. For a ~9gm/s flow, 1V looks dead on.
I've seen more than once where an older couple would go up to the mountains and come back to town (which was close to sea level) and get CELs due to the baro being off.
Have you reset KAM to see if that resolves it? 3 WOT is should also do it, but I've always had to do a KAM reset in my experience. If you did KAM reset and BARO still reads 28Hz, I would start to think the MAF is contaminated. I know you mentioned you've cleaned it, but I've always seen that be hit or miss on the results.
Have you asked the person who did your tune if they know of any problems like this that it could cause?
There is one other thing. Your original post mentioned that you had some higher fuel pressure. It is possible that the fuel pump could be causing some issues or you have some injector issues. The FP may try to boost the pressure if it's seeing a lean condition. Have you put a gauge on the fuel pressure tap and drove it to see if you're getting a pressure loss under load?
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