When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am going to be away from my computer until late tonight so I am going to assume that the chart you posted are the freeze frame values at various freeze frame captures during a P0102 DTC set.
This is a fairly global problem, one that does suggest an engine computer more than most problems here but I am still not convinced. No events occur at idle which suggests an issue specific to speed/vibration/engine load/electrical load. Its not likely a regulated voltage problem because of as a minimum, the O2 sensors. The issue is transitory and extremely brief because of the "millisecond" factor. You have a new computer on order so that will get proven soon enough, or not. In the meantime I would look at:
The alternator output, especially at higher rpms. Is it stable
The engine block grounds
The stability of the voltage to the PCM at the pins (to PCM pin ground
The PCM connectors, pins, wires
The wiring harnesses in general. Block the rpm to 2500, watch your scanner and move every cable and connector, especially to the PCM, the wonky sensors and the main cable going under the fuse box
Look at the fuses for corrosion, weak blade connections
MAF net power and ground backprobed at the connector, moving everything around, and the resistance of the isolated signal wire back to the PCM. Do you still get this behavior with the MAF unplugged?
Are there any new and poor quality parts installed just before this all started?
the data dated sept 25, is recorded data, not freeze frame. This obdii reader will store 20 samples then stop. I believe it has a slow sample rate to cover about 1 minute of engine data. I don’t know how long it will record data,but it is memory limited.
no I was asking about measuring the heater only current on the ho2’s because if they are powered by reg 12 volts and if I can see one drawing excess current then it may be worth replacing it. It might also indicate that the reg 12 v supply is being pulled down by a bad/low R load. But your reply about the heaters being powered by raw bat tells me that it won’t answer any of my questions.
the column heading on this last page, sept 25, are the sample events starting at the beginning of the trigger point continuing until the 20th sample has occurred. As you can see by the data the maf fault occurs for very short times, and this added data is now pointing to other issues like power supply problems or as you point out something loading down them. My next thought is maybe an intermittent short like a wire that has been heated enough to melt its insulation and may be bouncing on and off a frame part; inside the engine compartment all wire bundles are covered with that corregated plastic covering/conduit so I wouldn’t think it would be there.
The data dated sept 24, is confusing because I goofed, it starts in the middle of the sampling process, thus frames, trigger through 10, are after the trigger point and then the next 10 are before the trigger point thus labeled negative frame number. I apologize for the confusion.
I’m answering one of your questions before I do more testing. This problem started about June, maybe1st or 2 week. During the month of may I did two major jobs on the truck. I bought a kit to replace front ball joints, front bearings, and steering linkages, so I spent time under the truck. Then I replaced the emergency brake because the ratchet wouldn’t hold. Here is where there must be. 50 wires that could have gotten pinched, but I tested everything to make sure they worked, lights,horn, flashers, turn signals, backu.p lights, etc. Everything work normally. The obdii tester was put on the dlc and there were no dtcs showing as of Jun1, and there is a green light on the tester which indicates it will pass smog ,if it is lit— it was on.
I just went and tested voltages with my Dso—digital storage oscilloscope—it has super features like it will display period or frequency while displaying the signal waveform. First the alternator looked great, 14.0 to14.2 v. Until the engine warmed up, then 13.7v exactly after warm up.
so I decided to go back and look at the maf signal lead again. Guess what, it looked great freq = 2.2 KHz at idle, then I ran it up to maybe 3000rpms, no change in waveform shape, freq just went up to maybe 3.5 KHz, then I just kept doing it about 20 times, and then it happened.
It jumped up in frequency to 27 kHz and the waveform changed to a more triangular shape.
Is there any possibility that the pcm can cause this or is it strictly dependent upon the maf? I now suspect that a brand new maf is bad!! But this problem started on my original maf that came from the factory before I dropped it thus making me buy this new one .
vic
I forgot to add that it returned back to normal after just maybe one second, I did this several more times and got it do the 10 times normal frequency one more time. Then I must have tried it 10 to 20 more times with 0 failures.
Last edited by Vicjordan; Sep 27, 2023 at 07:38 PM.
Reason: Forgot more info
Of course the MAF can be faulty but you are saying that three MAF sensors have all given the same "results", right. That is statistically improbable. Monitor the net back probed voltage at the MAF and also see what live data reports on your scanner when this happens. You can also monitor the output at the PCM pin and see if you get the same result. I don't think that the PCM can cause the MAF to report wildly out of range frequency values. The triangle waveform may just be a limitation in maintaining the rise and fall times at those frequencies. Wiring could also perturb the waveform. The PCM might be able to deform the waveform.
I have only had 2 maf’s, not 3. The problem started in June, the original maf was in place, the problem was extremely intermittent, like once every 2 weeks or so. Then by Aug it was getting worse and the P0102 code would not clear, so I couldn’t get a smog check. SoI started trying to solve the issues by cleaning the maf— original one—I accidentally dropped it while cleaning it so I bought a new one. This is the one that I just tested to find the problem of the freq jumping up to 27KHz in freq. so only 2 total maf’s.
The maf did not display this problem on my first testing it with my DSO, probably because I didn’t run the engine speed up to 3k rpm’s as many times as I did today.
I’m returning it and will replace it with a better one sometime next week.
l bought a 3rd MAF sensor and installed it today. The 2nd one which was brand new out of the box was causing the intermittent operation.
So your intuition about the problem NOT being the pcm was correct!!!
As soon as the 3rd MAF was installed and the pcm DTC’s reset, everything has started to settle down. I’ve driven about 50 miles, no dtcs have popped up, all I/Ms have set except cat and htr. I think they will set in a few more miles then I can get the smog check done, then pay registration.
thanks for your help, it’s been a frustrating problem being so intermittent. If you get out west, my wife and I are willing to take you out to dinner here in the Reno—Carson City area.
With my maf problems, you mentioned you knew PIN numbers for several pcm pins. I assume you have access to schematics. Would you be able to supply me with a source for purchasing schematics and service manuals for a 2001 model? I’ve tried various places and most only have e manuals— I’m so old fashioned that I need paper— still love my old text books and just about any thing written on paper.
also, for some lucky reason I got a pass on my smog check, then 2 days later, a new maf installed, I’m showing p0101 single dtc codes, which clear after a2nd key start. Want to help with that problem when I start a new thread?
