Poor idle, NO power

[2000StreetRod]

A different throttle body should not make a significant change in AFR at 2,500 rpm. The MAF sensor measures the higher air flow (if any) and the PCM compensates. The AFR might be lean above 5,000 if there is enough increase in air flow to peg the MAF sensor.

The PCM cycles the AFR between slightly rich and slightly lean from optimum. This is reflected in the short term fuel trims (STFTs). The pre-cat O2 sensors should cycle between about 0.2 and 0.8 volts. The long term fuel trims (LTFTs) should be fairly constant at less than + or - 5%.

It is desirable to have reliable performance before loading a tune.

 

[JW]

OK, did some more testing. Performance seems to be inversely proportional to throttle position. At part throttle, it works as expected. But anything more than about half open and it goes nowhere. Lots of intake noise but no power. Long term fuel trims are generally around 7-9% with spikes into the 10-12% range (steady at 7 or so at idle, and consistently higher on bank 1 vs bank 2 by about 0.5%). Short term is jumpy between -2 and 4 at idle. Idle RPM is around 800.

 

[2000StreetRod]

Fuel trims at idle are not very useful because there is very little load on the engine. 0.5% LTFT difference between banks is inconsequential. As I recall the PCM will adjust the LTFTs to keep the STFTs within + or - 30%. Is the vehicle drivable? If so, I suggest turning off the O/D and driving at a constant 1,800 rpm or so and check the fuel trims. It may take two people in the vehicle to do it safely. If the LTFTs are greater than +5% then the engine is running lean. Does your engine have a crankcase breather that vents to the atmosphere? If so, then unmetered air (not measured by MAF sensor) can indirectly enter the intake system resulting in a lean condition. I noticed that you live in California. Autos produced to be sold in CA frequently have lower than standard flow fuel injectors to meet the stricter CA anti-pollution requirements. If your PCM is programmed for 19 lb/hr injectors and you have 13 lb/hr injectors the engine will run lean - especially after mashing the accelerator (tip in) or under load.

 

[JW]

It is drivable, and I discovered last night that my OBD app will log to a CSV file any parameter the PCM will output. I'm about to go take it out for a bit, so the test criteria is very helpful. I'll post the test results when I get back.

I believe it has the 19 lb/hr injectors (orange).

No breather to atmosphere. I have the PCV connected to the Trick Flow intake with a rubber hose, and the driver's side vent is connected to the intake tube the same as stock. PCV isn't stuck.

 

[JW]

Data is on my Google drive. There are several options for logging short term trims, so you'll see what look like duplicate columns, but with different data. Not sure which is correct. I went with the standard PIDs wherever possible.

https://docs.google.com/spreadsheets/d/1MGKWxEHvY6Z5ogPhefcyMoG5qb7pVm8NIBN4nVzDIgE/edit?usp=sharing

Again, at part throttle, it seems to be fine. At anything more than about 35-40%, it starts to bog and sounds like a diesel with the jake brake engaged.

 

[2000StreetRod]

Your pre-cat O2 sensors are good. Bank 1 sensor 1 varies between 0.06 and 0.86. Bank 2 sensor 1 varies between 0.05 and 0.855. On my PCM strategy if the PCM determines one bank sensor is bad it will utilize the one good sensor for both banks. It is obvious when this happens since the STFTs for both banks will always be identical.

The PCM primarily uses the MAF sensor airflow to calculate load. For your data log the load seems to be proportional to the MAF sensor reading. In general the MAF sensor reading increases and decreases with engine speed and with TPS voltage.

I think the significant issue is that both bank LTFTs slowly change but increase significantly with load but the STFTs rapidly change a small amount. This puzzles me. I'm considering there may be a sensor wiring error. I suggest that you disconnect the sensor connector that is easiest to access. The PCM should detect a sensor heater voltage error and set the corresponding DTC. Read the code and see if it corresponds to the sensor that was disconnected. Remember that bank 1 is the bank that contains cylinder 1 (engine front/passenger side in USA). Sensor 12 is the bank 1 post-cat sensor and sensor 21 is the bank 2 pre-cat sensor.

 

[N4YLOR]

I know you said you took readings on the MAF and swapped it with a non motorcraft one, but I have a quick story anyway.
Years ago I had a 99 super duty with a 5.4. I was driving along and all of a sudden the truck became gutless, would never stall, but I would put my foot right to the floor and it just wouldn't go. The check engine light flashed while this happened and then it would just clear up and the truck would be happy again. It wasn't long and it would happen all the time. It was so frustrating not having any guts to keep up with traffic and I would throw it in neutral and roar that truck thinking maybe I'd clear out some restrictions but nope.
Went to the parts store and had them scan it for me. Came back as whatever the code is for possible MAF issue. Asked the kid at the parts counter to look it up for me, 100 bucks. He goes dude, save yourself some money and clean it with this stuff (CRC MAF spray). Gave it a shot and it didn't really do anything. Brought it to a local garage and they said 'your shift sensor is toast, we can swap it out right now, 250'. So I went with it. Left with the truck and it was okay for a couple days, then the issue came back. Went BACK to the garage they scratch their head and say leave it overnight. Call me up a few days later and say 'what have you been doing to this thing, the catalytic converter is all stuffed up no wonder it's got no guts!! Temp readings through the roof before the cat!' $700 for cat and new exhaust behind it.
2 miles down the road, you guessed it. I start thinking and go back to square one and ask the garage 'you think it could be my MAF after all?' He says No way, not a chance, we checked the readings it was within spec blah blah blah(kind of like my story). So I said okay, if you're so sure then let's make a deal. You replace the MAF with a motorcraft. If that solves the problem, you pay for it, for bending me over on all these un-needed repairs. If it doesn't work, I pay for it. He said deal and guess who only had to pay 950 for a 100 dollar repair? Anyway the moral of my story is, your symptoms sound a lot like the MAF problem I had. Is it possible it really is faulty, and the car just doesn't like the aftermarket MAF you replaced it with? Could you try out a Motorcraft one and return it if it doesn't fix the problem?

 

[boominXplorer]

Check your o2 sensor wirering side to side for the front o2s. Make sure you don't have the banks switched. It's easy to do since both o2 sensor wires come out near each other in the harness and have pretty long pigtails.

 

[JW]

boominXplorer - O2s are definitely not crossed over. Replaced them one at a time while the engine was out, so they were easy to trace.

N4YLOR - still running the factory MAF and housing. I temporarily swapped in an aftermarket MAF and got the same results, so I went back to the original. (Not saying it's not *a* problem, but it doesn't seem to be *the* problem.)

2000StreetRod - are you saying the LTFTs are not *proportionally* increasing with load? Does a higher percentage indicate rich or lean? (I think I've answered that with some research - lean.) And you're talking about disconnecting an upstream O2 sensor, correct? Do the downstream sensors play any role in tuning the engine?

Also, I re-read an earlier post of yours while reviewing my datalog. You stated that anything over 5% indicates a lean condition. Most of my LTFTs in the log are well over 5%, except on the driver's side.

 

[corignelson]

Not sure if the issue is resolved(almost a year old), but it sounds like an intake manifold leak. Or a timing chain issue. The fuel trims indicate unmetered air in the exhaust stream and smoothing out with the throttle cracked supports that.

 

[corignelson]

Especially if it’s a plastic manifold, they tend to crack.

 

[JW]

Turned out to be a blown driver's side cat, which sent debris downstream into the secondary cat/resonator/whatever it is.

 

[corignelson]

That’s good info to have. I just bought a 99’ 4.0 sohc that needs a timing set at a minimum. If, after the rebuild, I experience these symptoms I will definitely take a look at the cats.