Perplexing start issue

start
intermittent

#1

My car always cranks just fine and usually runs good too but sometimes (maybe 10%) does not want to start or starts and runs extremely poorly and stays that way until I turn the key off. This 10% seems to run in spurts, maybe I try 10 or 20 times to get a normal start. When it starts normally it will continue running normally, even for hours, until it is shut off. In other words it never transitions from “bad” to “good” or vice-versa while running, only between start attempts. I am hoping some of you reading this will be able to interpret this fact as a clue and suggest where I should focus my troubleshooting efforts. My car is a stock 1989 Nissan 240sx with 250,000 miles on it. Tomorrow I plan to look for OBD codes, but again I would appreciate your suggestions.


#2

If the ODB-I system in this car is like my '88 Supra, it is generally worthless as a diagnostic tool. I’m not too familiar with the inputs this ECM uses, or the programming cues, but it would seem like there is a sensor on the verge of going bad, and sends a false initial code to the ECM when you start the car. If you turn it off, then restart, you get a good initial code, and the car runs fine. The sensors that are used on start up that let the ECM ‘initialize’ itself with the engine are crank sensors, cam sensors, IAC motor, and TPS. If any of these sensors sends a wrong initial code, and therefore get calibrated incorrectly, then it will make the engine run rough.


#3

The problem has gotten worse. Won’t fire at all now. Plugs are sparking. Tried spraying carb cleaner in intake while cranking - no sign of combustion. Only code from ECU is 13 which is temp sensor. Factory manual does not give typical example of temp sensor failure but I am sceptical. What do you guys think? I bought a used distributer (contains the crank angle sensor). I am a little bit afraid to swap it for fear of messing up timing. A little how to about that would help me. Thanks.


#4

When you turn the key off and then on again, you may be rebooting the computer. This doesn’t happen with a working computer but it could be what’s wrong with yours. There are many other probable causes, like where is the new car?


#5

So, check the wiring to the engine coolant temperature sensor, and change it. Click this link for a picture and price: http://www.autozone.com/N,15900113/shopping/partTypeResultSet.htm