S10 no start condition - please help!

[johnw48]

Hi guys. I'm new to the forum. I spent a few hours reading threads that seemed similar to the problem I'm having with my S10 and, from what I've read, I believe the problem lies within the circuit involving the FP relay and OP switch, but I'm not sure, and that's why I'm here looking for help. 1996 S10, 4.3 vortec with spider injection system, Automatic, 2WD, Ext cab. Here are my symptoms: Returned home yesterday from a 2 hour errand trip around town. Shut it off, and when I tried to start it about 1/2 hour later, it would not start, Just turned over, but no start. Let it sit for a few hours, same condition - turn over-no start. Loosened clamp and peeled back intake hose enough to spray starting fluid into intake. Replaced hose and it started right up. I expected it to run for a few seconds (off the starting fluid) and then die. But to my amazement, it stayed running and ran fine. I then ran it for a few minutes, shut it off. Waited a few minutes and tried again, started right up and ran fine. Shut it off for the night. This morning, same condition - turn over-but no start. I did the same procedure with the starting fluid and it started. I took it on a short trip around town (went into a store but left it running- afraid to shut it off)--- came home. shut it off-waited a few minutes- tried again and it started--waited 1/2 hour--tried again and it started Waited 2 hours- tried again and it started. that's where I'm at now. It's very confusing and I hope someone can help me out. By the way, i live in a cold climate - South of Boston, Mass. thanks

[j cAT]

Originally Posted by johnw48

Hi guys. I'm new to the forum. I spent a few hours reading threads that seemed similar to the problem I'm having with my S10 and, from what I've read, I believe the problem lies within the circuit involving the FP relay and OP switch, but I'm not sure, and that's why I'm here looking for help. 1996 S10, 4.3 vortec with spider injection system, Automatic, 2WD, Ext cab. Here are my symptoms: Returned home yesterday from a 2 hour errand trip around town. Shut it off, and when I tried to start it about 1/2 hour later, it would not start, Just turned over, but no start. Let it sit for a few hours, same condition - turn over-no start. Loosened clamp and peeled back intake hose enough to spray starting fluid into intake. Replaced hose and it started right up. I expected it to run for a few seconds (off the starting fluid) and then die. But to my amazement, it stayed running and ran fine. I then ran it for a few minutes, shut it off. Waited a few minutes and tried again, started right up and ran fine. Shut it off for the night. This morning, same condition - turn over-but no start. I did the same procedure with the starting fluid and it started. I took it on a short trip around town (went into a store but left it running- afraid to shut it off)--- came home. shut it off-waited a few minutes- tried again and it started--waited 1/2 hour--tried again and it started Waited 2 hours- tried again and it started. that's where I'm at now. It's very confusing and I hope someone can help me out. By the way, i live in a cold climate - South of Boston, Mass. thanks

COULD BE THE COOLANT SENSOR on the intake manifold that sends temp info to the computer. if the sender is telling the computer the engine is warm when the engine is cold the mixture will be too lean for a cold start. If this is off ,, will not throw codes , and cause a poor cold start. the engine when warm will act normal. check connections first.

[johnw48]

thanks, is there a reliable way to check the coolant sensor during the no-start condition?

[jamesslcx]

johnw48, yes check resistance cold then warm with a multimeter. Have you serviced fuel filter lately? Checked fuel pressure? Ran a fuel system cleaner through recently?

[johnw48]

jamesslcx, thanks, I will do the multi meter check tomorrow. Just a quick update on the problem.... I used the truck 3 or 4 times today, with a 2 to 3 hour cool down period in between, and it started right up each time. I'm waiting to see what happens in the morning after it has been sitting all night in the cold. I replaced the fuel filter about 6 months ago. I haven't done a fuel pressure test yet and I haven't used any fuel system cleaner. I will try to get a pressure test done tomorrow. Is there any particular fuel system cleaner you recommend? thanks

[j cAT]

Originally Posted by johnw48

thanks, is there a reliable way to check the coolant sensor during the no-start condition?

get a new sensor. do not install new sensor ,,,just disconnect connector on engine mounted sensor and plug in the new one you purchased. if the problem is gone then install the new one into the engine.

they cost 20.00 approx.

when these sensors are cold like 25-30 deg the resistance is about 3500 ohms.. when at the operating temp of 190 deg f about 200 ohms.

if the wire is open to sensor this would be minus 40 deg f.

[jamesslcx]

johnw48, Chevron Techron fuel system cleaner is a good one. Massachusetts is a beautiful state and the people are great but it surely does get cold there! Best of luck. Let us know.

[johnw48]

Thanks j cat, hi neighbor! Are you saying if the circuit is open between the sensor and the computer that the computer thinks it is 40 below zero? And if so, what does the computer do in response to this information? Also, it has been suggested to me that this problem could be caused by a bad oil pressure sensor. Is this true? And if yes, what is the testing procedure for that one. Is it the same as the coolant temp sensor? thanks

[johnw48]

jamesslcx.... Thank you for the kind words. I've visited Tennessee one time about 10 years ago and I think it is much more beautiful than Massachusetts. And yes, it certainly is cold here, I hate the winter months. Anyway, I'll continue to update the progress, or lack of, with the s10 problem. thanks again

[johnw48]

I should mention that the coolant sensor was changed about a year ago when i was having a rough idle situation-also changed the EGR valve. About 6 months ago, I installed new fuel filter, plugs, wires, coil, cap, rotor, and pcv valve. Question: If the coolant sensor is causing the cold no-start situation now, why would the engine start and run fine immediately after shooting some starting fluid into the intake? I believe this is why someone suggested that the fuel pump is not supplying fuel until it sees oil pressure???

[old_master]

An open circuit in the ECT sensor will cause the PCM to provide a maximum rich mixture. If the engine starts using carb spray, (don't use starting fluid) your mixture is lean. A faulty oil pressure sending unit will not cause a no start situation on your vehicle*. Your symptoms are a classic example of low fuel pressure. Check fuel pressure and leakdown: Key ON, engine OFF, fuel pump running, fuel pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. Post your results.

* If the OPSU shorts to ground, fuse #9 will blow and the fuel pump can not be energized. The fact that you can get it to run says fuse #9 is good.

[johnw48]

old master.... thank you for the info.... I will definately get a fuel pressure test done tomorrow, and post results. Is this "low fuel pressure" problem you mentioned usually the result of a faulty fuel pressure regulator? Why should I not use starting fluid? thanks

[old_master]

Low fuel pressure can be caused by several things from a poor electrical connection somewhere, a faulty regulator, weak pump, internal fuel leak, etc etc. Checking fuel pressure and leakdown will test many things all at once. If it fails either part of the test, it only tells you there's a problem and further diagnosis is necessary to determine where the problem is.

If you use starting fluid, and the engine backfires through the intake, (called induction) it can do some serious damage. I have seen rocker arm covers and intake manifolds blown clean off an engine... not a pretty sight, not to mention dangerous to anyone nearby.