Bad Computer Signs?

[JMac101]

I have a 2001 Dodge Caravan 2.4 Liter 4 cylinder. I have had a misfire code P0304 for going on about 7 months now. Tried replacing: plugs, wires, injectors, fuel rail, fuel rail wiring harness and all that good stuff. Even changed the coil pack and valve cover gasket and spark plug tube seals.

What I need to know is:
When I park my van and turn it off, You can hear a high pitch "wine" sound like a whistle coming from the computer. Today I put my ear to the computer and it is definately the noise maker.

The other symptoms I have are:
Wipers will be on a low setting and all of a sudden they will glitch to high then back to low. Air bag light comes on here and there every now and then and goes off on its own. Check engine light MIL on steady and blinking all the time. If I smell the computer region it doesnt smell burnt on the right side, but on the left side by were the wires connect I smell an exhaust fume smell.

Anyone think my computer could be faulty and causing a misfire code?
I have reset the code and it returns. I tried disconnecting the computer and plugging it back in and the code went away for 3 days and then returned.

Any input is appreciated.

 

[JMac101]

can a blown shot computer throw random codes or maybe the part that controls the signal to fire cylinder 4 is broken or burnt out? Van is mainly stock with 138,000 miles on it original computer.

 

[SLCraig]

I think I'd certainly be suspect if the computer itself was actually making noise... I can't say I've ever heard an ECU making noise before.

Have you tried to source a used ECU from a junkyard to try?

 

[J. A. Rizzo]

The misfire is detected by the crank position sensor IIRC. Has it ever died when you come to a stop? Maybe the reluctor ring is crudded up and causing a faulty signal to the CKPS? Have you checked compression on #4? Is there any gas smell in the intake or hard warm restarts?

The wipers probably aren't controlled by the ECU. Most cars have a separate body control computer that does those kinds of things. Same goes for the airbags. Is the P0304 the only code that ever shows up? When the MIL is flashing, that usually means the code is "current," or the condition causing the code is happening right now. Is it flashing when you turn the key to ON without the engine running? Does it flash at idle and constantly at all engine speeds? Are you sure it isn't misfiring?

Just a few things to think about. Hopefully a real expert will chime in for you here.

 

[dishdude]

I had a 95 Neon that the computer would whine after shutoff for a minute or so. There was a TSB put out that this was a normal condition - something about testing the o2 sensor after shutoff. I sold the car with 182k miles on it - had the original computer that whined for the 10 years I owned it.

 

[jim302]

Well, the computer can cause strange intermittent problems with nearly anything it controls which makes it very frustrating to troubleshoot. Intermittent codes like this are certainly possible.

Not smelling burnt just means the magic smoke hasn't escaped... it still could be bad. As just one example, bad memory or a number of other components can cause a bit flip (where a 1 becomes a 0 or other way around) which can cause issues.

The whine isn't necessarily a problem either... some electrical components inside can have a high frequency vibration that makes noise.

I would suspect a major computer problem to result in more random codes in more areas, maybe even some stalling. A wiring problem to a sensor, on the other hand, could cause intermittent problems with just a few codes. Even some internal faults could cause this.

The problem with the wipers and the air bag leads me to think maybe there is some other electrical problem. I doubt the wipers are controlled by the ECU/PCM (though maybe by the BCM). Usually, air bags have codes that can be read too... may be some useful information there.

Have you checked the voltage when it is having these problems to make sure the voltage isn't too high?

 

[BuickGN]

I would start with the battery and it's connections, primarily the ground and go from there.

 

[JMac101]

Never replaced crank position sensor so that is defeinatly a possiblity. Van has never died on me while driving, only in the winter on cold mornings it would start up stall and die. Warmers days are not a problem. I have not checked the compression is cylinder #4. There is a gas odor under the hood, but not near the intake it is more towards the right by the battery and such.
Yes the P0304 code has came up time after time after erasing it and also replacing many parts. A few weeks back I got a EGR code, I since then replaced the EGR and that code has went away.
The MIL light comes on Steady then while driving especially while accelerating hard starts to blink and the van shutters. Somtimes when I turn the key on but dont turn on the motor the MIL light blinks then as well. The MIL light sometimes blinks at idle but more while driving. IT started out staying steady with no blinking a few months back and now it blinks like crazy.
I dont think it is misfiring because of the parts I have replaced: plugs, wires, coil pack, injectors, fuel rail wiring harness, fuel rail, throttle position sensor, MAF sensor, EGR valve, Etc.
Thats why it is leading me to ask if a faulty computer could cause such a code and cause a misfire. I feel like I hit a brick wall with this one.

 

[JMac101]

I found a refurbished computer from a factory on ebay that program it to you VIN and mileage for $149.95.
I guess I will give that a try, that would be the easiest way but I would hate to throw a couple hundred more into parts I dont need. Im already like $500 in the hole and still have the code and rough idle.

 

[JMac101]

How would the battery produce a cylinder 4 misfire code?
Also could it be possible that a computer is partially burnt out or on its way out and produce some false codes but still produce some good codes?
Like stated before I have has this cylinder 4 misfire code for 7 months and no matter what I change it returns. I disconnected the harness to the computer and re installed it and the code went away for 3 days and the rough idle also went away.
now the code is back. Before that while I still had the misfire code for cylinder 4, I got a bad EGR code. Replaced the EGR and that code went away but the cylinder 4 code remained.

 

[J. A. Rizzo]

How about fuel pressure? Is cyl. 4 the furthest from where the fuel line comes in? The fuel pressure regulator can rupture, spilling gas into the intake and causing certain cylinders to run very rich. That could explain the gas smell, but you'd see and smell it in the intake. If you open up the throttle blade, clean it and the throttle bore while you're in there, and look for pooled fuel and a gas smell in the intake.

Do all the vacuum accessories work OK? Cruise control, HVAC controls, etc.? Any weird hissing sounds under the hood while idling?

As BuickGN mentioned, battery connections are important. Loose connections can lead to bizarre symptoms from computers. Ground connections loosen and corrode over time. Battery terminals get crusted up with gunk, etc. Check 'em out.

 

[mechtech2]

Bad computer grounds can produce all sorts of problems.
Get the battery cables shiny clean on BOTH ends, and where they seat. If there is an additional ground for the computer, make sure it is perfect, also.
Computers do go bad, but it is rare.

 

[Scott_Tucker]

I highly doubt the computer will fix it. I have seen computers get bad drivers but it is rare. Find the source of the misfire. That is what you need to do. Is there spark coming from the #4 coil. You can pull the coil pack and stuff an old spark plug in it and lay it on a good ground. Start the engine and if it is sparking, you have spark. Next move onto the fuel injectors. You can even just use a long screw driver while putting the tip on the injector and the handle against your ear. If injectors 1-3 click but the #4 doesn't you know the injector isn't firing. It doesn't mean the injector is bad but it is not working. You also said in another thread you were going to buy a compression tester but you haven't. I'm not trying to scold you because in the end it's your money but if you don't check the basics you're just going to keep throwing parts at it and wasting your money. Listen to the techs on the board, we have lots of experience with this kind of thing. I guarantee I could narrow down the problem in 15 minutes if I was working on it. Of course, I'm on the other side of the country so that won't work.

 

[JMac101]

money is tight so i havent picked up the compression tester yet.

 

[JMac101]

I checked all the ground wires and electrical connections today made sure everything was plugged in right and made sure grounds were clean and tight. I also made sure everything from the coil pack to the injectors were plugged in right. I went over the whole motor today top to bottom and everywhere in between. Injectors have been replaced twice and so has the plugs and wires. Coil pack replacement could be bad or have went bad your right. Im going to pick up the compression tester tomorrow like Tucker said I should.
Scott = If you dont mind could you please give me detailed instructions on how to perform a compression test?
Should I also check the fuel pressure like Rizzo said?

 

[JMac101]

Ok guys here's another update. I checked to see if I had spark and I do. I took plug 4 out of the plug port and held it over the crank case, I got spark and then the van stalled. I restarted the van and did the same test with the plug in the wire and again held it over the crank case and I got spark once again. I took the I injectors out and swapped the #4 injector with a new one. I reset the light and code and nothing returned yet but it still idles extremely ruff and it runs like sh!t. I think it is safe to say it is not the coil pack, injector, plug or wire. Well safe to say for bow anyway. I get paid tomorrow and I was thinking about picking up the compression tester then on my way home. Should I check fuel pressure as well since the number 4 injector is last on the fuel rail? Or should I stick to compression for right now? Can anyone give me detailed instructions on how and how not to compression test? Maybe some precautions?

 

[mechtech2]

If you want to go that route and check the compression:
A screw in type is easiest.
Unplug the ignition and fuel - connectors or fuses.
Open the throttle and block it open.
Test each cyl with 4-5 cranks. Note HOW it comes up, and the maximum. Is it 80% on the first crank, then a little more each time? Was it 40% and more each time?

Don't crank it 20 cranks to try and squeeze a higher compression reading - it is not valid.

At this point, I am jumbled up on what is wrong with your car.
I don't know the sequence or symptoms.

 

[JMac101]

Should I remove the fuel pump fuse and just unplug the coil back and remove the spark plugs?
Can I leave the fuel line plugged in and just remove the fuel pump fuse?

 

[JMac101]

*COIL PACK*

 

[mrkdk]

might need to check for voltage spike. it can clause miss firing and radom thing to happen. the limit for ac voltage for alternator is usely 500mv. need to use a true rms volt meter.