Engine computers

engines
computers

#1

can anyone tell me what the symptoms are for a failing main computer?I have a 1995 Subaru Impreza with 168,000 mile son it & have had intermittent starting problems & have had it suggested that the main computer could be failing. Any more thoughts on it would be a great help. Thanks


#2

Computers rarely go bad. For now, forget about replacing the computer. Describe the problem in detail. Give symptoms. Give reactions (the car’s, not yours). Weather conditions, etc.


#3

Have any other diagnostic tests been done to try to solve the starting problem? Replacing the computer is a LAST resort, not a first attempt. More information, please.


#4

Most of the time it’s NOT the computer…it’s one of the sensors. The computer is probably the MOST reliable part on your car.


#5

The problems started about a year ago. The first time I started the car in the morning, moved it out of the driveway so my kids could play basketball & shut it off. When I went out a few hours later, it would not start, it cranked and cranked, but wouldn’t turn over. I had it towed to town (not a quick deal, i live about 40 minutes from civilization) and it started right up at the shop…my mechanic told me he thought it was because I did not allow the engine to fully warm up and that was the cause of the problem. So I have allowed the car to fully warm up at all times, unfortunately the problem has gotten worse. If the car is warm & I go out to start it sometimes it cranks right up, others it cranks and cranks and won’t turn over. My original mechanic tried replacing the ignition module, that was not the problem, he also supposedly checked connections and things along that line and has declared it to be the computer. I took the car to a second mechanic and he said that one of the sensors was very erratic and he replaced it and said that it still wasn’t reading correctly, but it was better. That was about 3 weeks ago he replaced that and has been out of town and will be out of town until November, so just yesterday i went to another mechanic. He had the car all day, drove it around and tried to get it to reproduce the problem, which of course did not happen. One factor that I have recently noticed is that damp, cool weather affects it. I was shown how to check for spark & one time when it wouldn’t start it had spark and once it did not!!! So…hope that helps you to help me!


#6

The problems started about a year ago. The first time I started the car in the morning, moved it out of the driveway so my kids could play basketball & shut it off. When I went out a few hours later, it would not start, it cranked and cranked, but wouldn’t turn over. I had it towed to town (not a quick deal, i live about 40 minutes from civilization) and it started right up at the shop…my mechanic told me he thought it was because I did not allow the engine to fully warm up and that was the cause of the problem. So I have allowed the car to fully warm up at all times, unfortunately the problem has gotten worse. If the car is warm & I go out to start it sometimes it cranks right up, others it cranks and cranks and won’t turn over. My original mechanic tried replacing the ignition module, that was not the problem, he also supposedly checked connections and things along that line and has declared it to be the computer. I took the car to a second mechanic and he said that one of the sensors was very erratic and he replaced it and said that it still wasn’t reading correctly, but it was better. That was about 3 weeks ago he replaced that and has been out of town and will be out of town until November, so just yesterday i went to another mechanic. He had the car all day, drove it around and tried to get it to reproduce the problem, which of course did not happen. One factor that I have recently noticed is that damp, cool weather affects it. I was shown how to check for spark & one time when it wouldn’t start it had spark and once it did not!!! So…hope that helps you to help me!


#7

I forgot to mention that sometimes the car wil start after a few minutes, other times it is the next day.


#8

OK, new mechanic could not get the car to not start. He tried spraying the engine in certain areas & says he thinks it’s the computer also. But I still don’t know what the symptoms of a failing computer are…


#9

It sounds like your mechanics are wild guessing here. Spraying the engine in certain areas is not a real scientific approach and as mentioned, the computer is the last thing to be suspect.

Ideally, it needs to be determined when the car will not start if the problem is fuel or spark related.
When it will not start, try spraying some aerosol carb cleaner into the air intake. On an erratic problem this may not be 100% definitive, but could help.

If you think cool damp weather is the problem, then try spraying the ignition coils down with WD-40 and see what happens.
Another sometimes overlooked problem can be the electrical part of the ignition switch. These can be an on again/off again type of thing.
At this point, forget the bad computer business. The computer is often the fall guy for someone who has no idea what the problem is. The fall guy’s twin brother is “bad gas”.


#10

Click on this ebay web page: http://cgi.ebay.com/ebaymotors/NEW-4PC-INLINE-IGNITION-SPARK-PLUG-HT-TESTER-TOOL_W0QQcmdZViewItemQQcategoryZ43989QQihZ013QQitemZ230189645033QQrdZ1QQsspagenameZWDVW. Click the X in the upper right hand corner of that page to come back here. I like to use these because they are easy, simple, to use. Pull the spark plug off the spark plug. Put this test light into the spark plug wire and snap onto the spark plug. If there is spark, they will flash AND the spark STILL goes to the spark plug and the cylinder still works. I suspect the ignition switch. The ignition switch, which has wires attached (NOT the key and lock part), is about $30 and fairly easy to change. It’s a bit more difficult to test. The mechanic would have to be able to read a wiring schematic and use a voltmeter.