LS6427

iTrader: (2)

So, I've been telling people for about 14 years that all PCMs are NOT created equal, they all have their little weird personalities. (EX: Mine will not operate with Bosch 02 sensors)

Another thing I've been saying.....nobody, including the engineer at GM that designed the computer fully understands how it works and what it can do.

So listen to this crazy stuff:
About 2 1/2 months ago I noticed my oil pressure gauge on cold start go up to about 60psi (normal).....but then after it warms up and I start driving around....it basically stays there and just moves up and down about 3-4 psi the entire time I drive, no matter how long I drive it. So...I figured the OPSU was failing. Its been 2 1/2 months and I still have not change the OPSU......

I drive to Orlando, from Lauderdale, this week. About 30 miles from reaching my destination in Orlando my SES light comes on. So I pull into an AutoZone and get the code read. Code was for a bad MAF. The guy also has an OBDII scanner in his car and offers to scan it further. He see's that the MAF is reading something, so we figure it just needs to be cleaned.
I got some MAF cleaner and cleaned it.

Code went away.....and my oil pressure gauge now reads normal. It jumps to about 60 psi on cold start, but then as it warms up it comes down like it used to do. Moves completely normal now.

Who would have thought a dirty MAF, can tell the PCM to give wrong readings on the oil pressure gauge.

Just an FYI...............PCMs are some pretty complex components.

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wssix99

iTrader: (5)

I think its more likely that you have a shorting wire somewhere and when people were messing around in the engine bay, they cleared the short.

I'll bet that the problem will come back...

There's no voodoo that goes on in the PCM, but there is a Medusa's wig of wires in the engine bay (a hostile environment) that can send a bunch of mixed signals to the PCM, which just reports what it "sees."

I'm surprised that with a 3-4 psi reading, you didn't get a check gauges light?

LS6427

iTrader: (2)

No.....after my cold start it would jump right to 60psi like it always does when its cold. Then all day long driving, engine hot....it would only fluctuate 3-4psi up and down from that 60psi mark. So it moved slowly when on and off the gas driving around.....56-64psi.....very slight movements of the needle all day long. Basically, stuck way up high around 60psi all day....not a correct reading.


And nobody touched anything under my hood. I popped the hood, unplugged my MAF, removed the MAF....cleaned it and put it back on.

As soon as I started it up, no SES light. Then the next day, yesterday, I drove 3+ hours home and no SES light. Oil pressure gauge reacting normally again. 60psi on cold start like normal, but now it comes on down to around 42-45psi aftert its warmed up and then moves normally with throttle inputs and going WOT, and idle psi.

Its fixed now. All I did was cleaned the MAF.

And there is no question that PCMs act differently then others. Like I mentioned, my PCM will have nothing to do with a Bosch 02 sensor, my engine will hardly stay running with one, no way you can put it into gear and drive, it will stall out. Pop in a Denso and bam....perfection.
Same with a friends Camaro....his car (1998) like mine will run just fine without a Coolant Temp Sensor plugged in....My engine will not stay on at all, it will start, then it will sputter, misfire and backfire, then stall. Plug it in and it runs perfect. Thats why I have a spare in my car with me.

PCMs are different.....

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LS6427

iTrader: (2)

I have a bunch of stuff to do tomorrow, I'll report back if day two of driving around all day creates an SES light.....

Going to the gym right now too.....I'll see now if its still ok.

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LS6427

iTrader: (2)

Gym and back....maybe 7 miles one way. Working normal. Didn;t get to full operating temp, only about 10-15 minutes driving. But it already came down to about 50psi at idle.

No SES.....

Video 1....cold start
Video 2...After 7-10 minutes of driving......Past 2 1/2 months....it would be stuck at 60+ for 15-30 minutes before anything changed. And again, it was pretty much stuck near 60 all day long.

....EDIT....Great, videos won't upload from my iphone.......

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RPM WS6

iTrader: (3)

MAF doesn't report anything regarding oil pressure. You can unplug the MAF entirely and the oil pressure will continue to show a reading. Cleaning it won't change that. Intermittent short in the harness as mentioned by wssix99 is likely, perhaps in unplugging the MAF you jarred something in the harness.

Overall, your setup is pretty extreme and has probably undergone many custom tunes over the years. Do you still have the factory original PCM? Lots of reflashes from different sources may have led to some weirdness or sensitivity, and/or just the extreme nature of your setup causing a lack of tolerance for certain sensor activity/inactivity that might be passable for a more stockish setup (regarding the ECT and O2s.)

Having said that, I've had a few odd PCM related things happen with my various LS1s, things that were extremely intermittent and that extensive diagnostics couldn't determine, even when stock. In those cases, the factory service manual recommends PCM replacement - but none of these concerns have ever been serious enough to make me feel that such was necessary.

wssix99

iTrader: (5)

As a general statement, this violates the whole point about having a computer, but... being a '98 and the first year of a mild design change and power-train change for the car - it would not surprise me if there were different parts flowing through production that year.

Did you ever see the movie Gremlins? We are driving imports, you know... (Regardless of the cause, I think this is definitely a true "gremlin".)

[grem-lin]

noun
1.
a mischievous invisible being, said by airplane pilots in World War II to cause engine trouble and mechanical difficulties.
2.
any cause of trouble, difficulties, etc., especially in a mechanical, electrical, or other system.

LS6427

iTrader: (2)

My tune is the only one its had....a new 98' PCM went in along with this new 390ci. Wiring harness was all checked and its perfect.

2 1/2 months....no oil readings basically. I sprayed my MAF and oil readings are back to normal instantly.......something happened within the PCM, has to be. The new fresh signal from the CLEAN MAF....did something.

I know its weird...and I know GM didn't plan for the PCM to have any relationship with oil pressure and a MAF......but nothing was moved or touched in my harness. I touched the MAF plug to unplug it....then plugged it back in.

Thats why I posted this......its not the first weird things these PCMs have done over the years. Like mine will not run on Bosch 02 sensors....explain that.

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RPM WS6

iTrader: (3)

So then both your original factory PCM and the current (new-to-your-car) PCM won't run on Bosch O2s? If both PCMs reacted this way, then it sounds more like a problem with the operation of those O2 sensors and the fact they may be marginal or totally inadequate for certain non-stock setups/placements such as yours. If not, then which PCM had the issues? Original or current?

But how do you know that the issue isn't with the cluster, or the sending unit? I know that sounds coincidental, but such is equally true of the MAF cleaning since it's totally unrelated to oil pressure readings. What about the scanner that was used to check the codes prior to cleaning....was it used to clear the code from the PCM (i.e. PCM reset)? Was it a read only scanner or was it also used to give commands during diagnostics? What about unplugging and re-plugging the MAF connector....how could you possibly do that without at least minimal movement of the harness?

wssix99

iTrader: (5)

If the check gauges light was not on - I would think that's an indication that the signal to the cluster is good and the gauge is bad.

LS6427

iTrader: (2)

No, the Bosch 02 sensors never worked with my original PCM from 1998-2013. I tried a few times over the years, they would never work. Only AC Delco or Densos would work.



The cluster has operated flawlessly since I installed in 2002. Those lights have all been on permanently for like 8 years. Mike Norris was supposed to fix it but I never took it back up to Orlando to do it.

He only scanned it to see if my MAF was reading something....thats how we knew it was just dirty. He did not clear the code. I drove about 1 mile to my destination and parked. The next day I woke up and cleaned the MAF. Started it up and there was no more SES light......first drive we took oil pressure was back to normal and no more hard starts when it was cold. Ran normal.

Its a weird one.....lol

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LS6427

iTrader: (2)

Well, I leave for the Middle East next Thursday. I get home in 4 months.....car is going on a lift and taking the engine out to install my BMR turbo K-Member along with my Huron Speed turbo kit.

So all this stuff will be fixed in the process.


BUT....if you look in the PCM/Diagnostics section.......look at my little gremlin of a surprise that started tonight. More weird stuff........

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