Bman2000

so people with tech experience are welcome to give me advice. But i dont know what ive said on here about all my issues. I know i mentioned my fuel issue which i have decided to solve by going return style and bigger injectors. But part of the problem that raised after my track outing, i had a few misses that set off the cel at the strip, but its what i thought was my cop issue, since i used 2 old once when i broke my new ones. Long story short i sent them out to be fixed, they came back and now the issue is worse and worse every time i get in the car.

But always number 3 misfire with a bank 1 lean. So i started by swapping the cops around to make sure, misfire on 3, then moved the injectors across, misfire 3, then i move spark plugs around, misfire on 3, then i tightened the injector plug in thinking that it was loose, put it back on, misfire on 3, put a noid light on the injectors, and it seems to be working fine. checked compression today to be sure, all of them checked good 155-165 psi 6 of the cylinders were actually at 160.

So now im just stumped, i do know when i unplugged the injector on the cylinder the car didnt seem to run alot worse only a little, but when i unplugged others it seemed to be much worse. So i have a feeling its bad wiring? but so far everything seems to check fine. most of the miss isnt at idle or low throttle(although you can sorta hear a minor miss at 2000rpm in neutral), comes on really strong when i have load and boost. any ideas? i need to have this fixed before i swap the fuel system, i cant afford to go up to the dyno with this issue it would just be a waste of my money.

69MustangCoupe393cid

I had a ghost misfire in one of my old cars, nothing fixed it. Ended up being a bad ECU. Soon as I swapped it problem went away. This was on an OBD1 car but I assume OBD2 could have the same issue. Especially if you've flashed your computer a bunch of times; I have head that can mess the computer up, so maybe you're computer it at it's life?

cliffyk

This is a valid suggestion, however I doubt it is related to any practical limit as to how many times the PCM has been flashed; I have also heard that concern expressed, however it is quite unlikely.

The flash memory used in the EECV PCM is an Intel 81C65 PLCC chip with a P/E (Program/Erase) rating of 100,000 cycles. This would be the equivalent of flashing the PCM 10 times a day for 27 years.

A more likely cause lies in that the COPs are fired by the PCM controller turning on and then off a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The transistor behaves as a switch that is first turned on to magnetically charge the coil's core (by switching the negative primary winding to ground), and is then turned off causing the magnetic field to rapidly collapse (much more rapidly that it could be charged). This generates a high voltage in the coil's secondary winding--and the plug "sparks".

The MOSFET performs the same function as do the "points" in a conventional ignition system, and like the points is subject to wear--but wear of a different sort. Points could erode and burn, the MOSFETs can become overly resistive and/or sluggish which of course affects the current and voltage applied to the COP creating a weak spark.

The only way to diagnose this is with an oscilloscope, to observe the waveform generated when the PCM tells the MOSFET to turn off and let the magnetic field collapse. Thirty seconds on a diagnostic 'scope will determine if this is the problem, and at the same time very likely reveal whether the misfire is ignition (or even poor compression or fueling) related--it's worth hours of swapping parts and hoping to get lucky...


This is what the normal COP primary circuit waveform looks like, this from my '03 GT at idle (on our cars the PCM fires each plug three times in rapid succession at idle and up to 1200 RPM or so):

Bman2000

Thanks cliff. Correct me if I'm wrong please, but if I'm getting a misfire, and a lean on the same bank as a misfire, isn't it more likely a fueling issue to begin with? The only reason I kinda removed the possibility of it being a cop right now is because of the lean signal, also one of the times I pulled the plug it was a bit blistered, of course this was when it wasn't so bad I could t drive it, now I can't do much more than a short drive to diag or see if I fixed or moved it. The last question I have is if it is from a cop due to what your talking about, the bottom line would still be a PCM problem correct? I didn't know the PCM could have a failure of just one cylinder. Oh and I did the compression check so I know engine wear is t the issue. Thanks again cliff.

cliffyk

The fuel system (other than the injectors) is common to both banks and all cylinders, therefore it would not be my first suspicion in tracking down a consistent single cylinder misfire.

A gasoline IC engine needs three things to fire:

• A combustible fuel mix (air and gasoline in proper quantities);
• Compression sufficient to accommodate rapid combustion of the fuel;
• A spark to ignite the compressed fuel at the proper time;

That's it.

So what would make one cylinder misfire?

• Lack of a combustible fuel mixture--bad injector, bad wiring or bad PCM¹, everything else is shared;
• Lack of sufficient compression--you have already ruled this out;
• No (or a weak) spark--bad plug, bad COP, bad wiring or bad PCM¹, everything else is shared;

You have already swapped injectors, plugs and COPs; this leaves just bad wiring and/or a bad PCM¹.

Getting it connected to a diagnostic 'scope will sort out the problem in 30 seconds--less time that it took me to type this message...

----------------------------------------------------------
¹ - The injectors and COPs are triggered individually by the PCM using MOSFET transistors operating in a fully saturated mode as "switches"--there are eight of these for the injectors, and eight for the COPs. The PCM turns on the MOSFET switch to connect the device (injector or COP) to ground thus completing the electrical circuit (the injectors and COPs are connected to +12V whenever the key is on).

In the case of the injectors the switch being on causes it to open and inject fuel, for the COPs the switch being on cause the iron core of the coil to build up a magnetic field.

Bman2000

I knew there was a reason I like talking to you haha. I need to find someone with a scope. The only access I have is to big handheld units, is there a way for me to check the PCM that way? Because otherwise ill have to pay money and hope the person knows how to use it, where I can use the handheld without paying.

Bman2000

Oh also was wondering, I only ever used a scope once, but there's a possibility that it won't miss at idle but I can get it to sort of miss lightly at around 2000-2500rpm without load. Otherwise it only misses hard under load. Scope should still pick that up right? Cuz I know scopes aren't driving tools

Bman2000

Looks like I got confused must be the older scopes I was thinking of. So then what type of signal would I be looking for? What would tell me bad PCM vs bad wires?

cliffyk

You can use any oscilloscope, just make sure you use a 10:1 or 20:1 probe and a high vertical V/div setting; 2V/div or better (which will actually be 20V/div with a 10:1 probe).

This trace of the triple-strike spark at idle:



was captured using my Owon HDS1022M-N 20mHz handheld scope (a great automotive diagnostic tool BTW):



The probe's tip is connected to the non-red "other" wire at the COP (the color is different at each COP), the ground lead to ground.

Bman2000

thanks cliff, getting a scope available this week i hope to check this stuff out. I do have another question, i was messing around with the wires on the injector of number 3, because after my compression test when i restarted the miss was less severe. Well long story short it got worse, and set off a whole slew of codes, none related to number 3 which is the only place i was messing with stuff. got a lean bank, number 4 misfire, po1233 which somehow it set off even though its usually a code that means the car wont run? so im totally confused now.

So i had a thought, is it possible at all that the ccrm may be bad? is there a way that could be causing any of these problems ive been having? because ive had the fueling issue since i put the supercharger in with the pump not being able to supple enough flow up top even though the pump should be good for more power than i have, and the only thing left in the system besides the pcm that i didnt replace was the ccrm?