98 Blazer won't start when cold
 

I have a 98 S10 blazer with a 4.3 engine. When the temperature is above 20 degrees, the blazer starts fine and runs like a top. When the temperature is below 20 degrees, it is had to start and sometimes will not start at all. Once started, it runs fine like nothing was wrong. I have changed the temperature sending unit, crank sensor, air sensor and other things and nothing has helped. Any creditable information would certainly help. Thanks

Guessing parts to change is usually a pretty expensive and un-fruitful way to go. Need to go back to the basics. Forget sensors and computers at this point and don't let the fuel injection system intimidate you.

Engine needs compression, spark, and fuel to run. Engine has to be very shot to not start at cold temps because of compression. I had a 289 Ford during high school that had too low of general compression to start in below zero weather (40-60psi on all cyl), but the rings were very shot and it had tons of blow-by. Doubtful that compression is the cause of no start, if it starts and runs good at a higher temp.

Hook up loose spark plug to a wire and ground it. Got spark during no start? If so move on. If not, fix it.

Check fuel pump pressure during no start, and ability to hold pressure with key off. I think you will probably find the problem here somewhere. If not, come back to report and get more help. You can borrow a gauge from Autozone or Advance Auto Parts or others with deposit.

If required, for further diagnosis it may (or may not) be worth your while to in invest in a wireless OBD2 reader. Then you can know what those sensors are reading. The bluetooth OBD2 reader from BAFX products on Amazon is one of the best OBD2 reader clones (I get about 20 scans/sec), but requires an Android device. I highly recommend Torque Pro Software for the Android. Total cost is about $30 if you have an Android phone or tablet.

I also have a cheap Wifi clone for my iPhone but it is only 3 scans/sec on both the Blazer and my 2008 Ford Ranger - and I think it may have damaged the ECU in my 2006 G6 when trying to connect, as the car will no longer connect with any reader (even the reader previously used with this car at Advance Auto Parts). When this Wifi clone was first connected, it lit up all kinds of odd dash lights on the car (now it doesn't do the same anymore). Seems the ECU diagnostics on the G6 are now inop, but the car still runs fine. It's apparently not a fuse. If I ever have to diagnose anything on it, I suppose I'll have to deal with things then. Moral I suppose is to beware of hooking up just any cheap crap out there to your ECU.

Good luck,

Les

I have had the fuel pressure check by a mechanic (in fact 2) and they all said it was normal. I have the OSB2 and the software Torque Pro. There are no codes that show up when connected to my Android phone. Sometimes when it is below 20 degrees and don't want to start, if I keep holding the key in start position, it will finally start for a few seconds and then shut off and sometimes it will keep running like normal. I would think that if the spark is there once the engine runs it would not be due to spark, but I may be wrong. I would have thought the mechanics would have checked this also. I sure am baffled at this. I don't mind fixing things, but I hate to pay for something a mechanic tells me to fix, and then that does not fix the problem. When this first started happening, if I put a charger on the battery, it would start, but it will not start that way now for some reason.

I forgot to tell you that I can hear the fuel pump running when I first turn the key on, but sometimes it will not start in colder weather.

If there are no DTC's in memory, and no SES light on, the problem is something that is not monitored by the OBDII system. Fuel pressure and leakdown are not monitored. I realize you had 2 guys check it, but, your symptoms are classic for low fuel pressure and/or excessive leakdown. It will cause hard/no start in cold weather if it is not within specs. Fuel delivery is critical on this engine. Most auto parts stores loan/rent the tester for free, and sell them for ~$40. Very easy to test it, and it only takes about 15 minutes. Let us know when you have a tester and we can explain how to do the tests.

BTW, after replacing the crank sensor on this engine, the crankshaft position sensor relearn MUST be performed, (not optional). It is done ONLY with a scan tool capable of initiating it, (usually a high dollar scan tool). If the relearn is not done, the engine will start and run, but ignition and injector timing will be incorrect, guaranteed.

Check your battery, ive seen many cars, all makes and models sound like they are cranking ok but they can have as low as 50 CCA and still crank the engine over, also you can have plenty of cranking amps but have a bad cell and not even know it, if the voltage is too low to begin with then when you start cranking it drops even lower, too low for the computer to function. There may be enough for the fuel pump to run at key on but that doesnt mean that there is enough voltage left for the computer to do its thing during cranking. Check battery voltage during cranking and rule that out before you chase your tail for too long(been there before). It should stay above 10.5 volts, the computer needs a bare minimum of 9 to function. Also your comment about the charger helping points at the battery too, it probably just cant the amps anymore, unless you have a 200 amp boost mode you cant really get enough juice into it all at once. Maybe as a cheap test swap a battery with another vehicle if at all possible or maybe your local auto parts store has a tester and they can check it?
Let us know what you find.
Good Luck!