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Why I Hate Car Computers

Started by mmd, May 24, 2010, 07:57:13 PM

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mmd

I work hard at keeping my car running.  Then the computer goes and it causes it to run lean on the left side and rich on the right side, causing the motor to really not run right.

I replace the computer, and what do I get, a rare model computer that can't even hold an idle.

http://www.youtube.com/watch?v=rfigEtt-L2o

I should give up and just put a carb on this motor, give up on this computerized stuff.
Brandon
Western Electric 302, 500

Dan/Panther

Sounds like a vacuum leak to me, or maybe a dirty PCV valve.
D/P

The More People I meet, The More I Love, and MISS My Dog.  Dan Robinson

mmd

#2
Quote from: Dan/Panther on May 24, 2010, 08:38:48 PM
Sounds like a vacuum leak to me, or maybe a dirty PCV valve.
D/P
Nope, engine is in tip top mechanical shape..  Before the old computer blew a sensor or something, the engine was great, tearing up the road wherever I went.

After this video, I verified with another 94 Caprice and used their $EE PCM, the one mine had originally, engine idled wonderfully.

This rare computer just, sucks..  No wonder GM only used it for 4-5 months then changed it quickly to a different revision..

If anything, I might be able to fix this computer though, adjust things like timing and fuel trimming, may help it..  My old computer that went bad was "tuned".

PCV is brand spanking new too..

http://img.photobucket.com/albums/v395/Evilweredragon/Car%20Pics/raiss3.jpg

(New PCV breather seen here)
http://img.photobucket.com/albums/v395/Evilweredragon/03-24-10_1347.jpg

(And valve here)
http://img.photobucket.com/albums/v395/Evilweredragon/03-24-10_1348.jpg
Brandon
Western Electric 302, 500

JorgeAmely

#3
mmd:

So many things have to happen right for a computer controlled engine to start and hold idle steady, that I doubt much that the computer is bad in this engine.

My car hunts for idle once in a while and the problem is the idle control valve, which controls how much air gets into the manifold. Perhaps if this engine uses something similar, you can inspect it for problems. This valve receives information from the computer to in turn control the amount of air the engine gets during idle. The throttle valve also sends a couple of signals to the computer:throttle closed and throttle fully open. Those are mutually exclusive. Something to look at also.

Is this a OBD II car? With a code reader you could check if some of the sensors are bad.

Good luck.

PS: If it wasn't for computers, we couldn't help fixing your phone.

Jorge

mmd

#4
Quote from: JorgeAmely on May 24, 2010, 09:30:57 PM
mmd:

So many things have to happen right for a computer controlled engine to start and hold idle steady, that I doubt much that the computer is bad in this engine.

My car hunts for idle once in a while and the problem is the idle control valve, which controls how much air gets into the manifold. Perhaps if this engine uses something similar, you can inspect it for problems. This valve receives information from the computer to in turn control the amount of air the engine gets during idle. The throttle valve also sends a couple of signals to the computer:throttle closed and throttle fully open. Those are mutually exclusive. Something to look at also.

Is this a OBD II car? With a code reader you could check if some of the sensors are bad.

Good luck.

PS: If it wasn't for computers, we couldn't help fixing your phone.


OBDI, and no codes whatsoever.

I am sure, it's the computer.  Installing another computer that is a rev C, the car starts idles great, and runs great.  It's these odd Rev B computers that just can't find idle correctly, and shakes a LOT when idling forward in drive.

GM knew there was something wrong with this computer and quickly released rev C..

I know how my engine works to know how it idles.  First it has the distributor, which has an optical sensor that reads camshaft position, tells computer, and computer uses it's MAF, MAP sensors to determine how much fuel to add via the injectors..  It guesses at this until the O2 sensors warm up, then the computer enters closed loop mode..

Now, right now I'm considering my MAF might be the problem, but other rev C computers idled fine with my MAF, which is from a 95 Camaro (the main computer is just programmed to use it though, the one that failed)..

I need to re-tune this rev B computer, or just see if I can update it's software..

EDIT:  This engine is very healthy:  http://www.youtube.com/watch?v=lwDA2CqzLy4

I know for a fact this is computer, and not mechanical..  My IAC is also new..  My engine has several new parts, including ignition..

EDIT2:  Oh and heres the big gem between these two computers, the one that worked, and the one that don't.

Stock PCM (Which is professionally tuned).
http://img.photobucket.com/albums/v395/Evilweredragon/Screenshot2010-05-24at93455PM.png

And this rare breed computer that won't idle right.
http://img.photobucket.com/albums/v395/Evilweredragon/Screenshot2010-05-24at93435PM.png

They are so different I can't even edit this rare computer because the numbers don't show up correctly.
Brandon
Western Electric 302, 500

McHeath

Car computers are surprisingly reliable.  It's rather uncanny really, if they were as buggy as our personal computers our cars would be needing to be rebooted all the time.  They also rarely go bad.

However, in the last 3 years I've had two cars with computers that both went bad.  What are the odds?  The first one I had a guy repair it, a cap had gone south and that led to a few other problems.  The other one I had to replace entirely, went used and it was still a pile of money for the computing power of a mid 90's PC.

Here in California you have not choice, you will not replace that fuel injection computer controlled set up period as it will not pass the biannual smog check.  Some people hate that, and I did when I was much much younger, but I do admit that the air today is a lot better than it was 25 years ago. You have to have a vehicle older than 1973 to start messing around with changing components on it, and there just are not many of them left. 

mmd

In florida im glad i can work on my car...  actually, my cars engine is so clean GM and the EPA allow removal of the emissions air pump, because they do nothing really..





The computer in my car is surely an interesting beast of work, has two flash chips, i wonder which one actually stores the tune..
Brandon
Western Electric 302, 500

Dan/Panther

#7
Have you checked also the air flow regulator module ?

I think Jorge and myself may be talking about the same item.
D/P

The More People I meet, The More I Love, and MISS My Dog.  Dan Robinson

mmd

trust me, i cant stress it enough, the engine is fine, and all of the sensors, its the computers tune that's wrong.

i'll make a video, swap computers in one shot, with one computer the car runs like crap, and another it runs great..

theres a difference in the revision of the software GM seems to used..  i looked at their firmware files, and several things are offset in memory..
Brandon
Western Electric 302, 500

stub

Hi mmd,
            Some of the older computers ,when they lost power, had to relearn the idle adj. Some had to be driven 20 miles or so. Anyway, good luck    stub
Kenneth Stubblefield

mmd

Quote from: stub1953 on May 25, 2010, 01:44:22 AM
Hi mmd,
            Some of the older computers ,when they lost power, had to relearn the idle adj. Some had to be driven 20 miles or so. Anyway, good luck    stub
Thats one thing i did think about, and it's a good thought.

when the car warms up, idle gets better thats for sure..  but as soon as it's turned off, and started cold again, bad idle..  it's like the computer has something in the programming that just isn't working with my car.
Brandon
Western Electric 302, 500

AET

a bubble caprice eh? Does that year have the digital speedo too?
- Tom

mmd

Quote from: AtomicEraTom on May 25, 2010, 02:27:54 AM
a bubble caprice eh? Does that year have the digital speedo too?
;)



The tach is installed by me, custom.  The check engine light was on because an O2 sensor failed when I took that pic.  Low oil light, well, yea, it was low, but I had put more in when that pic was taken, but never turned off the car so the light never reset.  Low washer, yea, I'm always low there.
Brandon
Western Electric 302, 500

mmd

#13
UPDATE:  I gave the computer the software from my old dead PCM (since I had the tune from it), and whattya know, pulling out of McDonalds onto the main road, I burn rubber and leave a nice 24ft trail.

Mind you it was by accident, I didn't expect it to be so aggressive in this humid morning.

I KNEW it was the computer, and not the engine, my engine is f.i.n.e. fine.

EDIT:  While I was flashing it.

http://www.youtube.com/watch?v=qNyObyp2m9Y
Brandon
Western Electric 302, 500

AET

If you ever come across an extra digital speedo, grab it, they're known to fail. 
- Tom