1999 Chevy S-10 S-10 4.3L easy cold starts, difficult warm s

Tiny
COASTY
  • 1999 CHEVROLET S-10

Engine Performance problem
1999 Chevy S-10 6 cyl Two Wheel Drive Manual 110000 miles

I've noticed recently that the truck always starts up immediately if the truck has been sitting a while and is cold, especially over night. If the truck is shut off and restarted a few minutes later it starts just as quickly, however if it sits for longer than that it can take 5-7 seconds to restart. I have a new coil, wires, plugs, cap, rotor, fuel filter, air filter. Its been quite a mystery, i've had no trouble codes so i'm not sure where to go with this.

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Wednesday, October 29th, 2008 AT 10:16 PM

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Tiny
MERLIN2021
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5-7 seconds seems unreasonable? You may spend a small fortune to fix it. Most of the time it;s between the cluster(instrument panel) and the harness(wiring) and the security module, and will take some time to diagnose, or as simple as a 20.00 dollar ECT(engine coolant temp) sensor.

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Thursday, October 30th, 2008 AT 4:58 PM
Tiny
COASTY
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Well, I may be a little conservative with the 5-7 second estimate. But stare at your watch for 7 seconds and you can see that the engine is turning for longer than normal. What concerns me is it seems as though the time it takes to start warm is increasing ever so slightly as the months tick by. Plus, there's that embarrassment of the truck not starting up right away, or even taking several attempts to crank. Maybe its just injured pride because people know I take pride in the care and maintenance of my vehicle. But, I understand that there are only a few clues that i'm providing here.

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Thursday, October 30th, 2008 AT 7:27 PM
Tiny
MERLIN2021
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First thing to check is that ECT I mentioned, when cold resistance across the sensor should be 10,000 ohms or more, warmed up it should be 177 ohms at 194 degrees, check that and get back to me.

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Friday, October 31st, 2008 AT 10:57 AM
Tiny
COASTY
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This may be a stupid question, but if the temperature gauge is indicating inside the truck does that mean that the ECT sensor is good? Is it possible for the ECT sensor to be bad if its still indicating a correct temp on the instrument cluster? I tried to do the resistance test and I was getting open circuit when the engine was warm and cold, however like I said the temp gauge is still functioning normally. This doesn't make sense to me. Its pretty tight in there, maybe its possible I didn't get the probes positioned properly on the two pins?

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Saturday, November 1st, 2008 AT 1:20 PM
Tiny
MERLIN2021
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The gauge is operated by the temp sender, not the ECT.

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Saturday, November 1st, 2008 AT 2:32 PM
Tiny
COASTY
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Forgive my ignorance, but where is the ECT on a 1999 S10?

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Monday, November 3rd, 2008 AT 9:15 PM
Tiny
MERLIN2021
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If I recall correctly, it's on the driver's side on the side of the cylinder head.

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Friday, November 7th, 2008 AT 3:10 PM
Tiny
COASTY
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Right, that is the one that I tested, and also sends input to the gauge. I think it might be combined for this year of the S10.

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Saturday, November 8th, 2008 AT 8:05 AM
Tiny
MERLIN2021
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I show the gauge sender on top rear of the engine.
The other possibilty is the fuel pressure regulator or an injector may be leaking...test fuel pressure and leak down.
http://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
You can rent the test gauge at Autozone.
Or buy it here.
http://www.2carpros.com/affiliate/uid/merlin2021_1
4.3L, 5.0L, 5.7L & 7.4L 1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step. 2. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Using scan tool, command fuel pump on. Bleed air out of fuel pressure gauge into container. Monitor fuel pressure with fuel pump running. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI system. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 8 . 3. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds. Observe fuel pressure after fuel pump stops running. After fuel pump stops, fuel pressure should stabilize and remain constant at 55-60 psi (3.9-4.2 kg/cm 2 ) on CSI system and 48-52 psi (3.4-3.7 kg/cm 2 ) on SFI system. If pressure is within specification and holds, go to step 5 . If pressure is not as specified, go to next step. 4. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Disconnect fuel filter. Drain any remaining fuel from fuel pipes into container. Install appropriate fuel line shutoff valve in place of fuel filter. Open shutoff valve. Using scan tool, command fuel pump on. Check for leaks at shutoff valve. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds. Turn ignition on with engine off. Using scan tool, command fuel pump on. Wait for fuel pressure to build. Close shutoff valve. Fuel pressure should remain constant at 55-60 psi (3.9-4.2 kg/cm 2 ) on CSI system and 48-52 psi (3.4-3.7 kg/cm 2 ) on SFI system. If pressure is as specified and holds, go to step 12 . If pressure is not as specified, go to step 6 . 5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to step 27 . If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step 26 . 6. Check fuel feed line between shutoff valve and fuel pipes. If fuel feed line is faulty, go to step 25 . If fuel feed line is okay, go to next step. 7. Open shutoff valve. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install appropriate fuel line shutoff valve in place of fuel return pipe union. Open shutoff valve. Using scan tool, command fuel pump on. Check for leaks at fuel shutoff valve fittings. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds. Turn ignition on with engine off. Using scan tool, command fuel pump on. Wait for fuel pressure to build. Close shutoff valve installed on fuel return pipe. If fuel pressure remains constant, go to step 22 . If fuel pressure does not remain constant, go to step 29 . 8. Turn ignition on with engine off. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds, and then turn off. Observe fuel pressure after fuel pump stops running. If fuel pressure is present, go to step 13 . If fuel pressure is not present, go to next step. 9. Using scan tool, command fuel pump on. Listen for operation of fuel pump. If fuel pump operates, go to next step. If fuel pump does not operate, see appropriate FUEL SYSTEM ELECTRICAL CIRCUIT under NO START DIAGNOSIS . 10. Check for restricted fuel filter, fuel pump strainer or fuel line. If a problem is found, go to next step. If no problem is found, go to step 12 . 11. Repair or replace as necessary. After repairs, go to step 30 . 12. Replace fuel sending unit assembly. After repairs, go to step 30 . 13. Turn ignition on with engine off. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is greater than 66 psi (4.6 kg/cm 2 ) on CSI system or greater than 62 psi (4.4 kg/cm 2 ) on SFI system, go to next step. If fuel pressure is not as specified, go to step 15 . 14. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Disconnect engine compartment fuel return line. Attach a flexible hose to fuel return line. Place other end of hose in container. Using scan tool, command fuel pump on and observe fuel pressure within 2 seconds. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI system. If fuel pressure is as specified, go to step 16 . If fuel pressure is not as specified, go to step 17 . 15. Turn ignition on with engine off. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is less than 60 psi (4.2 kg/cm 2 ) on CSI system or less than 56 psi (4.0 kg/cm 2 ) on SFI system, go to step 19 . If fuel pressure is not as specified, go to step 30 . 16. Locate and repair restriction in fuel return line. After repairs, go to step 30 . If fuel return line is not restricted, go to next step. 17. Check for restriction in engine fuel return outlet pipe at point where fuel line was disconnected. If fuel return pipe is restricted, go to next step. If fuel return pipe is not restricted, go to step 22 . 18. Replace engine fuel pipes. After repairs, go to step 30 . 19. Inspect in-line fuel filter and fuel line for restriction. If restriction is found, go to next step. If restriction is not found, go to step 21 . 20. Repair or replace in-line fuel filter and fuel line as necessary. After repairs, go to step 30 . 21. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install appropriate fuel line shutoff valve in place of fuel return pipe union. Open shutoff valve. Using scan tool, command fuel pump on. Bleed air out of fuel pressure gauge into container. DO NOT allow fuel pressure to exceed 75 psi (4.5 kg/cm 2 ). Excess pressure may damage fuel pressure regulator. Slowly close shutoff valve installed on fuel return pipe. Fuel pressure should increase to greater than 66 psi (4.6 kg/cm 2 ) on CSI system or 62 psi (4.4 kg/cm 2 ) on SFI system. If fuel pressure increases as specified, go to next step. If fuel pressure does not increase as specified, go to step 23 . 22. Replace fuel pressure regulator. After repairs, go to step 30 . 23. Check for the following conditions: Low fuel pump voltage due to high resistance connections. High fuel pump voltage due to internal pump binding. Poor fuel pump ground. Partially restricted fuel pump strainer. Incorrect or faulty fuel pump. If any of the listed conditions are present, go to next step. If none of the listed conditions are present, go to step 12 . 24. Repair or replace as necessary. After repairs, go to step 30 . 25. Replace fuel feed line. After repairs, go to step 30 . 26. Start engine and allow it to reach normal operating temperature. Open throttle quickly. Observe fuel pressure. Fuel pressure should increase to near 66 psi (4.6 kg/cm 2 ) on CSI system or 62 psi (4.4 kg/cm 2 ) on SFI system. If fuel pressure increases quickly, see appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure does not increase quickly, go to next step. 27. Check for the following conditions: In-line fuel filter for restriction. Fuel feed pipe for restriction. Mispositioned or damaged fuel pump strainer. Fuel pump flex pipe for leaks. Vehicle is equipped with correct fuel pump. Fuel pump electrical wiring for high resistance. If any of the listed conditions are present, go to next step. If none of the listed conditions are present, go to step 12 . 28. Repair or replace as necessary. After repairs, go to step 30 . 29. Locate and replace any leaking injector(s). After repairs, go to next step. If all injectors are okay, go to FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. 30. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional DTCs are present, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not present, system is okay.

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Saturday, November 8th, 2008 AT 9:49 AM
Tiny
COASTY
  • MEMBER

I'm going to go ahead and do that fuel pressure test next weekend probably. But just as a little experiment, when I pulled the plug on that temp sensor on the left rear (driver's) side of the engine, the temp gauge inside the truck fell off to full cold. And when I plugged it back in, it started indicating again. I don't see another temp sensor on the engine. I think that 1999 and up s10 temp sensor/senders may be integrated somehow.

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Saturday, November 8th, 2008 AT 10:36 AM
Tiny
COASTY
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Just completed the fuel pressure test, (or most of it). When I turned the key to the on position, the pump ran and the pressure was 54psi (I have the CSFI engine so it should be between 56-62psi).
Once pump stopped the pressure is supposed to stabilize between 48-52psi, mine immediately dropped to 46, and over a few minutes continued to drop to nothing.
I started the engine and warmed it up. The pressure was 52.5psi with a vibrating needle of +/- 1 psi. When I revved the engine it increased up to the required 62psi, then dropped to 50 and then began to vibrate again with an average of 52.5psi.

From what I gather it looks like I have a faulty pressure regulator and/or one or more leaky fuel injectors. My fuel pump is also putting out just slightly below the required numbers, so I don't think that is the culprit, but will likely need replacing eventually. Would you agree with this?

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Monday, November 17th, 2008 AT 2:01 PM
Tiny
COASTY
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Just wanted to see what you thought of those numbers.

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Monday, December 1st, 2008 AT 6:53 PM
Tiny
HSTECH2003
  • MEMBER

Coasty, I seem to be having the exact same problem with my truck. It started a few months back. First start of the day and its fine, but after it gets to temp its very hard to start.

I searched countless message boards about this problem and it doesnt seem very common. Most people say its the pressure regulator. Others have said that they had an aftermarket fuel pump that somehow starts leaking after it runs awile. Could be either.

If you have any success I would sure appreciate it if you kept us posted, and I will do the same.

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Thursday, December 4th, 2008 AT 10:45 PM
Tiny
COASTY
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Yeah, i'm pretty sure whats happening is there is one or more leaky fuel injectors dripping fuel into one or more cylinders essentially flooding the engine. If it were the pressure regulator dripping fuel into the return line the system would repressurize when the key was turned on, energizing the fuel pump, and in theory start normally. I've decided to wait on pulling the top end of the engine apart until it gets warmer in the spring, or if it does get worse I may do it this winter. I'll keep you posted. And if you decide to tackle it let me know how you pan out.

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Friday, December 5th, 2008 AT 8:00 AM
Tiny
HSTECH2003
  • MEMBER

By any chance, have you tried the coolant temperature sensor yet? Ive been told that if this sensor is faulty it will send the wrong temperature to the ECM and therefore it will flood the motor when its warm. I was planning on trying this in the coming days because its about a 10 dollar part and its easy to get to..

edit-- just read your other posts. Looks like you did test it. Are you sure it wasnt the sender and not the sensor? Here is a picture:


http://www.2carpros.com/forum/automotive_pictures/281635_wl2su109003_1.jpg



I think its near the thermostat..

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Friday, December 5th, 2008 AT 9:33 AM
Tiny
COASTY
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You know, I did can not say for sure. I tested the one that looks exactly like that. It was on the driver's side cylinder head down by the exhaust manifold. When I unplugged it the temp gauge in the cab went to zero, so I know its feeding that gauge, but I couldn't find another sensor on the engine. I have a 1999 so I was wondering if maybe that year the two were integrated somehow. The 2carpros guy told me that the one I tested (on the driver's side head) was not for the gauge, but I can say without a shadow of a doubt that it did feed the gauge. Do you happen to know if there were 2 sensors on the 1999 4.3L engine?

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Friday, December 5th, 2008 AT 9:53 AM
Tiny
HSTECH2003
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From what Ive heard- haven't actually looked yet- there are 2 sensors. One is a sender that feeds the gage and the other is a sensor that feeds the computer.

The Sender is supposed to be on the left side cylinder head and the Sensor is supposed to be near the thermostat. The sensor is the 2 wire plug (like the picture). I know Ive seen this on my truck before and Im pretty sure I saw it next to the thermostat. I have not noticed the sender yet. Could it be possible that both the sender and the sensor look exactly the same but are in 2 different places?

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Friday, December 5th, 2008 AT 12:19 PM
Tiny
COASTY
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This does seem to be quite the confusing issue, i'll take a look near the thermostat for this tomorrow. But either way, my readings from the fuel pressure test do indicate that I have a fuel problem. If I do find another sensor I'll check it out too.

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Friday, December 5th, 2008 AT 10:50 PM
Tiny
HSTECH2003
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Youre right. There is only one sensor. I can see where the other sensor USED to be on the older trucks (there is a plug there now).

Like you said before, it could be possible that its giving the right reading for the gauge and not the computer, so I am going to try to replace it anyway since its only about 10 bucks.

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Tuesday, December 9th, 2008 AT 7:11 PM
Tiny
COASTY
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Cool, I knew I wasn't going crazy! Let me know how it goes!

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Tuesday, December 9th, 2008 AT 7:25 PM

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