so, on average you have 1.75 difference between the banks and up to 3 between individual injectors
this is around 9% and 15% putting things in perspective
I’m not sure it would be enough to cause you some grief
In Eric’s video above, it was 20% difference what made his customer truck to have bad operating issues, so your 15% may be not that far from that
also, in Eric’s video his starting fuel pressure was substantially higher than yours, something in ballpart of 55 psi, while you report 45-46.
AFAIK he was troubleshooting exactly the same engine.
Do I need to retest injectors? I ask because I heard they should all be within 1.5 psi? Could a slightly rich condition (1psi more) on #2 cause it to misfire on occasion? Or am I stretching? I know anything is possible but is it logical?
I am not sure about the 45 psi start. When I turn on key and/or short pump relay pins and it comes on the pressure jumps to 50 psi but then drops to 46 psi when pump stops. Also if I let it sit that way for 20 minutes the pressure drops down to 42-43 range. It’s a new pump and new filter. The regulator is not leaking and 1 year old. When idle it runs at 43-44 spec and removing the regulator vacuum line it jumps to 50 which it should. Thoughts? BTW my emissions Evap is never passing or getting to ready but I have no Evap codes. I am replacing the gas cap because it’s 15 years old. But could a evap issue cause the slight pressure drop?
Spark Tester - I placed an in-line spark tester between the coil and plug on #1.
It lights up when spark occurs. I notice that the light blanks out on occasion and seems to be in sequence with my ears hearing the misfire but to be honest my skills are not honed enough to be sure. What is for certain is the firing is not consistent and blanks on occasion. So after thinking about it is below thought correct?
a. The coil firing is between coil and ECU and a good wire and spark plug. Regardless if fuel/air mixture combusts in chamber I should never see a spark blank out. Correct?
b. If true then it appears the misfire (spark blanking out) is caused by the coil not firing on occasion. The coil appears good since I have swapped it with other coils. The same for plugs and cable. So I need to figure out why is the firing blanking out? If not coil it has to be the firing/ignitor signal correct? How can I test? Can I use T-pins and another test light to see if the ignitor signal is blanking out on the #1 ignitor input signal?
c. Noting I have a new bank coil harness that splits to each coil and attached to main bank connector and that has been eliminated.
d. What is more logical? A intermittent continuity problem on 1 wire? Or an ECU that is failing to fire properly?
I watch one guy on youtube who is into diagnostics a lot, and he posted quite the interesting case few months back, where he had weird situation when car (manual transmission) would not start off starter unless it is hot, but would start cold if “pushed”, even a little bit, but would misfire until warm.
He made all the experiments with swapping coils, plugs, etc… and consistently received troubles on one cylinder, although on 4-banger it was way easier to detect misfires and blanking out.
He even swapped coils to another car of similar model, which was in his shop at the moment, rececing all sorts of confusing results in between.
So… more and more his confusion was leading that symptoms were different, but they all rotated around one cylinder, so he pulled a trigger and tried swapping ECU to the junkyard unit, which worked, but then he figured that “new” unit was from the different engine generation, so he’s got some idle issues and such.
Finally, he disassembled both ECUs and swapped transistors from the “new” ECU into the misbehaving channel of the old/original ECU, and it was the magic, car ran great.
So, if you really have “blanking out” time to time, it may be ECU, one channel, but to really pintpoint it, you would need a good recording oscilloscope, like Pico or such.
It seems you have spent a lot of time and perhaps money also trying to find out if the trouble is or isn’t with the ECU. There are many used ones for sale on Ebay. Here is a link to just one of them. It may be worth the money to just purchase one and see if that corrects the issue. If it doesn’t work, well then you at least have a spare unit on hand if it is needed later on.
I would expect the pcm needs to be married to the vehicle
not sure that’s possible with a used module
I’m mentioning this based on the model year of the vehicle in question
On older vehicles it was possible to just plug and play
After a certain time point, that was no longer possible. Once married to a particular vehicle, the module was only good for that one, and a paperweight for all others. And “marrying” would occur on its own after a set time period had passed, even if you didn’t initiate it
A shop that rebuilds/repairs modules might have other options, though
As far as spending on parts it’s ok because I am having a blast. I have never got to work on cars much (I am 53) but since this car is paid for and in good shape I need it to run another 100K because my son is in college.
The plugs, cables were needed. The throttle body and fuel regulator went bad last fall. I had a manifold leak so rebuilt it myself and built my own homemade smoke tester to boot. Also while it was off went ahead and changed CAM sensor for $30 because it’s hard to get to unless the intake is off and it was on list for possible misfire issue. The Crank sensor did go bad and I had to replace it. The o2 sensors were 15 years old and I had strange fuel trims so got a pair for $40. The fuel filter needed replacing. Probably the 2 things not 100% needed was fuel pump ($180) and injectors ($120 Amazon), but at the time a lot pointed that direction… so she still runs pretty good and I invested about $500 in parts and tools but have learned a lot and have tools to reuse…
ECU - ok I do have another ECU. Knowing vehicle is getting old (15 yrs) 2 months ago I looked and on Amazon a company sells refurbs or ones from scrap yards. They test them and they program your VIN into them before mailing it. It cost me $99 but I got it for free because I opened an Amazon card that I will rarely use anyway. The issue with ECU swap is 1) it scares the crap out of me to try it, and 2) I will need a relearn initiated by technician. I do know a guy with an scanner who charges me $40 if I need it.
My next step is to insert some T pins into the coil connector input (ignitor pin) and see if it will light a test light? Not sure if it’s 5 volt signal only? I want to see if the light blanks out the same as it does on coil output. If it works I will film it and slow it down. Also compare it to a good cylinder…
I have the ECU in my pocket for after I have exhausted my ideas.
Oh and yea I wish I had a Pico Scope to pull signals but that’s out of my $budget.
I also have a 2007 Silverado with 4.8L and it’s fuel pressure spec is 62 key on, and around 55 idle. I did the same test where I turn on key ( no crank) and pressure jumped to 62. I turned key off and over about 30 minutes the pressure slowly dropped down to 40. My truck runs great with no issues. Thus it must be normal for fuel pressure to slowly slip down when key is off. So I am eliminating fuel pressure issues altogether…
Ok here is my plan. I ordered an 8 channel scope for $100. It’s not a pico but those are $140 for 2 channel only. It appears per reviews if I get the correct drivers it will work great. I want to watch all coils per bank together and compare waveforms.
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The switch internal to the PCM (or ICM/points) closes. Current rushes into the coil and begins to build, which is why voltage drops close to ground and essentially remains there until the firing spark.
The coil is now saturated with electricity, as indicated by the jump in voltage. The coil is no longer charging up thanks to the ICM/PCM.
The PCM switch opens, unleashing all the built-up current. Amps drop like a rock and voltage skyrockets.
The spark line indicates the length of the spark event at the plug.
When not enough power is left for the spark, remaining power is rung out and the event begins all over again.
Interestingly enough, the trouble was in the aftermarket distributor cap and he found it on oscilloscope, but only after some old-style “water spray bottle” motivation was added to the mix.
