Symptoms? signs?

getting clogged/dirty...what is seen on the data-logs.

Trying this question from a new angle since no one seems to be able to answer the question fo how do I know if my injectors need replacing since I think I've eliminated every other option and not wanting to burn $300 on a fix if it may not really fix it.

 

You can pull the fuel rail off with the fuel lines still connected and hit the key to prime the pump. That will show you if you have any leaks. If you have a dead injector, it will cause a misfire, but I don't think the OBDI computer will pick it up..

 

perhaps I should rephrase the question.

How does the vehicle, or the PCM act/detect when there are no leaks, the injectors are simply really old, and one, two, or more seem to be unable to keep up with the duty cycle required at full WOT/RPM.

 

The PCM only knows if the injector electrical circuits (left and right bank) are correct. There are no other direct monitors of the injectors.

A worn out or dirty injector will not spray as much fuel as the PCM thinks it will. That causes a lean condition on the bank of the engine with the weak injector (s), and that shows up in the O2 sensor. The PCM increase fuel to the entire bank, on the assumption its running lean. Now you have one cylinder (or more) running slightly lean, and three cylinders (or less) running slightly rich. Power and fuel mileage will suffer.

Other than looking at the long term fuel corrections for both banks of the engine, there's nothing that's going to jump out and say "worn injectors". Even looking at the long terms is not going to be conclusive.

If the problem only shows up at WOT, you can only look for signs of leaning out on the O2s'.

Checking for leaks by pulling the rails is a good idea, since a dirty injector may leak. Again, not conclusive, just another piece of data for the puzzle.

 

I appreciate the info.

I have in fact pulled all the injectors, left them in the rail and pressurized the system, no leaks.
The indications that there is a problem are:
A. progressively lowering RPM's (1 month ago it was starting to *cut-out* at around 5500 RPM, right as I shift, now it is typically in the 4800RPM and above region, sometimes dipping as low as 4500RPM) as a failing condition.
*cut-out* means the engine bogs, its as if its running rough, or missing on several cylinders at once, like a lean fuel condition.


So two follow-up questions.

1. Datamaster logs show the stock o2's reporting brief (tens to hundreds of milliseconds) o2 sensors going from their typical 880mV to 60-80mV....I thought o2's would report their maximum value during a maximum lean condition (1500mV) and a minimum value during unheated/rich condition (100mV)

2. I have checked fuel pressure at all times, replaced the coil and opti with no change.
The only indications that I have a problem are that the engine bogs at high RPM's and at WOT only (for the most part), and the datamaster logs showing erroneous spurts of o2 weirdness.
The only point of failures I can think of are the injectors (150,000 miles on them, worst they've ever been put through is 80% duty cycle, and been running on this engine upgrade for 11,000 miles now) and the spark plugs need to be changed out, getting worn.

I can't see the spark plugs being the cause of the problem, if there was an issue, it would be happening across the board, because the engine runs strong and pulls hard just as it did before at all other times.

I can MAYBE see how the injectors could be the cause of the problem, (aka, unable to reach more than 75% duty cycle due to clogging), and the PCM is correcting for it by incresing the duty cycle during the engines other operating points, but just can't go up high enough during high RPM/WOT.

I've got a baby due in 2 months, working two jobs and 60 hours a week to make ends meet, I just want to know that I'm not buying a nice new set of Ford SVO 36# injectors only to install them, and not have the engine running right.

 

If it was the fuel system, you would see dropping O2 values at wOT. Misfires should also show dropping O2 values.

You lost me completely on that one. 880mV is rich. 60-80mV is very lean. They seldom go over 1,000mV (rich). When they are cold, they don't generate any voltage at all, and the PCM will "see" its own bias voltage on the circuit and indicate ~450mV.

If your O2's are indicating 880mV in PE mode (WOT), and drop for an instant to 80mV, something is cutting the fuel off for an instant.

Fuel pressure will not drop with lazy or dirty injectors. The fuel just won't flow through the injectors.

Could just be the ignition breaking down at max rpm, weak valve springs (although 4,500 would be extremely low for valve springs to allow the valves to float), etc.
"Duty cycle" is a calculated value, reflecting the engine RPM and the injector pulse width. The pulse width is what the PCM "thinks" will provide the required fuel. It has no way of knowing the injector is not supplying the fuel in open loop.


Disagree. The high rpm, WOT condition requires the highest voltage to fire the plugs. If there is any weak component in the ignition system - Opti, IC Module, coil, wires, plugs - that's exactly when its going to show up. You might also try lugging the engine at low RPM in overdrive. Misfires under those conditions would show up an ignition system weakness.

The PCM does not set, calculate or control the duty cycle. That is an "after the fact" calculated value. The PCM can only look at the mass air flow, divide the mass air flow by the desired A/F ratio to get the required mass of fuel, correct that fuel mass using the long term fuel corrections, and set the injector pulse width at the length required to supply that corresponding mass of fuel.

DC = (injector pulse width in millisec X RPM) / 120,000

And, DataMaster DC calculations appear to be "off", because I see injectors approaching 100% DC in engines that can't possibly require that amount of fuel.

 

Bingo, that's what I needed to know. Need to put in new plugs (given) and new injectors and that should clear up the problem....absolute worst case scenario I need to pull my valve covers and ensure I'm not running into the of late common problem of poorly manufactured lifters and ensure they are all providing full lift still and not of my springs look to be worn.

Thank you very much for taking the time to answer this fully, I think I understand how the symptoms lead to the problem in this case.

 

Figured I'd post the end result, so others can see how it was resolved.

Installed new fuel injectors...problem solved, old ones didn't leak and I had run tons of pure injector cleaner through them on the bench...guess it was just their time, or the miniature relay/whatever electro/mechanical device was failing.

so, short-band o2's showing minute bursts of low mV during WOT in this case = injectors failing.


So, the WOT seems to be around 880mV, I will dyno tune that some year from now when I get within 200 miles of an actual dyno...

my cruise STERMs and LTERMs are high, 130-150, and staying there, not sure how long it takes the PCM to correct all that stuff, but I'm tempted to believe that the formula sqr(43.5/39)*36 = 38.02 for the injector constant since these are ford SVO's is off by a bit, assuming my fuel pressure gauge was correct, 41-42psi operating fuel pressure, that should be more like 36....now sure off the top of my head if that will change what I'm dealing with "lean" to a more rich mixture or not, I'll sit down and contemplate it when I have time...

 

I am having an issue that is leading me to believe that my injectors may be going out as well..

scenario:

1500-3000 rpm, 0-10% throttle ...I feel what seems to be a stumble, & it sounds like a miss.

while on the road, the car feels like it is tugging at me.

50% - WOT, full power, no problems. Pulls hard all the way to 6400 RPM.


My initial thought was that this was ignition related.

I changed the coil, ICM, plugs, wires, & Opti. Results are the same behavior.


with 130k on the car, and 50k since my heads cam build, I am begining to suspect the injectors as being the culprit.


Any input from the folks involved in this thread? Any help is appreciated.

Adam

 

I am researching some Ford injectors and found this one to be of great value while reading it. I am about to replace my current stock injectors and get some 42lb injectors and it appears this could be a lot of the problem i am having. I am doing this because i want to eliminate the fmu and go with bigger injectors for my setup. I have the classic 1500-3000 rpm stumble that i have seen so much on here we will see how this turns out. My car when it reachs higher speeds seems to loose power so i hope the tune and new injectors help out. Glad to see the authur came back and shared his experience. The weather sucks here and it makes working on my car nearly impossible. Besides the money issues that keep coming up everytime i get close to buying the parts.