92 C1500 4.3 Starting problems

[Underwood95]

Well, I have a 1992 Chevrolet Cheyenne W/T1500 4.3 V6,139xxx miles, and im having odd ignition problems. I have crank, fuel pump & throttle body is good, battery and alternator are good, but for some reason it takes a few cranks on a cold engine to get it to fire up. Now, when the engine is at temp, it will turn over perfectly, unless I turn the key over too first and misfire. If I do that, it will not start for a while.

I just noticed today that it has a small amount of coolant leaking from the upper hose, where it meets the engine. I do not believe that is causing the starting problems though, but it may be, I'm not sure. But I am also having idle/compression problems. When the engine is at temp, and i come to a stop, accelerate slowly, or reverse, the oil pressure drops really low. Now get this. I did the math on my mpg the other day, and I'm getting roughly 9 city, about 11-13 highway. I've been trying to find out what this problem is for a while. Service Engine light has come on maybe 2 times since the problem has begun, but it dissappears in a few min. What could this be? I'm so confused on what it could be.

[Jsdirt]

If it has low compression, the only fix for that is a rebuild or replace.

 

Usually hot start issues are caused by a rich condition. Those injectors can dribble quite a bit of fuel instead of spraying. Good thing is, you can watch while someone cranks it over to rule that out. Quick and easy visual check. Sometimes heat can cause a coil to break down - sometimes they fail completely and become a no-start, other times they fail partially, and misfire like crazy.

 

Lots of times I've just thrown parts at those year trucks, and replaced the o2 sensor & coolant temp sensors (since they USED to be cheap) and got mileage back - went from 11 to 18 on my '91 S10 Blazer just changing the o2. Now that I know how to test the damn things, I'd have probably done that first, and found it stuck rich. If you can get a multimeter lead into one of the o2 signal wires, you want to see them switching rapidly from near 0 volts to about .9 volts. Never tried with a multimeter, so not sure if it will be fast enough to capture the switching - an analog meter might be better suited for this. If the needle stays in one spot (when warmed up of course), pitch the o2 and install a new one.

 

Temp sensors are easy to test too. Just 2 wires (if there's only 1 wire, then you're on the sender for the dash gauge) - one is a 5v reference, other is ground back to computer - the sensor will pull the 5v reference down closer to ground the hotter it gets. If you're reading close to 5v on a hot engine, pitch the sensor and grab a new one. Same if your reading 1 volt on a cold engine. In that case you can unplug the sensor, and you should read 5v (or very close to it). This also verifies that the computer, and wiring associated with the sensor is all good. If you unplug it and the voltage stays low, you've got some wiring issues.