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Please Help with starting issues.

06-14-2010, 03:10 AM
Okay. Here goes nothing.
I drive to work at 5 in the afternoon and work 12 hours. Get in my truck at 6:30 and it will not start.
Acts as if it is getting no fuel or ignition. It will turn over and over but not start. I can turn the key on try to start then turn the key off again and after about 2-5 minutes of cranking it, It starts. Once it starts it runs great.
When I get home 20 iles later it starts as if nothing ever happened.
It does this every morning.

Can the MAF Sensor cause this?

I have no CHECK or SERVICE engine soon lights coming on.............

Thanks in Advance

06-14-2010, 02:37 PM
What year, make, model, engine?
Have you checked fuel pressure and leakdown?
Have you checked for spark?

06-14-2010, 02:46 PM
98 S-10
4.3 v-6

Have no way to know for sure about fuel. Shops prices are too high. IS there a cheap way to check for fuel or spark while doing this alone?

As for leakdown? If I wait 12-13 hours and can start it during the daytime hours without incident but it has a hard time starting early in the mornings after I get off work, would that give a clue to anything?

I'm no mechanic. A friend suggested the MAF sensor due to him having a similar issue.

06-14-2010, 03:24 PM
Extremely doubtful on the MAF sensor, save your money. A quick easy way to check for loss of spark is pull the coil wire off of the distributor and rest it, (don't hold it) about one half inch away from the engine, (ground). Have someone try to start it and watch for spark at the wire jumping to ground.

Checking fuel pressure and leakdown requires a fuel pressure tester. This is a more likely cause than loss of spark, so it might be worthwhile to invest in a tester. Harbor Freight has one for under $20. It's not professional by any means, but it'll do the job. Key on, engine off and cold, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the pump shuts off.

06-14-2010, 09:34 PM
I am a little confused at how it only does it in the morning but starts right up in the afternoons. 12 hours between starts and it only happens in the mornings.

06-16-2010, 08:03 AM
Cold start you need full fuel pressure to squirt injectors.
That is why you were told to run as fuel pressure test.
There is no easy button.
We can not help if you do not follow instructions and run proper testing.
Some parts places like AZ also loan rent or sell fuel pressure tester.

Post back fuel pressure for help.

06-16-2010, 09:38 PM
Sorry, old_master sent me a link on how to do the test. It was not posted here. He sent it to me privately.
The test was normal and that is why I asked why it only did it in the mornings.
I let it set for 24 hours and cranked it at 4 P.M. yesterday afternoon and it started right up. I went out at 6 A.M. this morning and I had to crank it awhile before it would start.


I was looking at my vacuum lines for my a/c and when I replaced the lines there were 3. 1 was 5/32 and went into the fender well where the vacuum /box/ball whatever is located and one runs under some wires. The 7/32 hose runs from the connector you see to what I assume is the top of the FUEL PRESSURE REGULATOR.

I will try to see if the vacuum lines help the issue.

It fixed my vents that use to only blow out the front and not the defrost and floor.... woohoo
See photo:

06-16-2010, 09:49 PM
The larger line on the black side of the check valve goes to manifold vacuum. It is the vacuum supply for the HVAC system and the 4WD. The fuel pressure regulator in inside the plenum and does not have a vacuum line connected to it.

Connect your fuel pressure tester, then restart to pressurize the system. Then shut the engine off for the day.... When you try to start it the next time, notice what the fuel pressure is before you turn the ignition on and while cranking.

06-16-2010, 10:01 PM
Guess I was about to buy the wrong fuel pressure regulator. Dude at the dealership showed me one where the fuel return line and vacuum line plugged in?

Also, I removed the air plenum from the top of the motor to access the vacuum line and forgot to reattach the big tube that plugs into the back of it. My SES light came on and I scanned it. Codes P0171-P0172 came up. That covers about 5 things to check. Including fuel injectors.

OH, Do you happen to know how to get to that canister in the fender well? My hands way to big.

Guess I am really lucky to have you guys around.
Thanks again.

06-17-2010, 02:00 PM
The fuel pressure regulator attaches to the fuel injector housing. It has a nipple on the back end of it that a hose could fit onto.

It doesn't need one because the entire inside of the plenum is exposed to manifold absolute pressure, which is what operates the diaphram inside the regulator. This holds true on both the CSFI and the CMFI engines.

06-17-2010, 03:07 PM
Okay, I see how that fits now. He did not know exactly what he was looking at apparently. He told me the vacuum line went to the fuel return nipple. I asked a mechanic and he explained it to me.

Now, any photos of how to remove and install it?

I will try to start it again in the morning. I will be working tonight.

I think that if the fuel system is the problem then I should start cheap.

However, I did install a new fuel filter about a month ago and I had problems getting it to snap in on one side. I had to wiggle it around until the one tab snapped in place.
I'm guessing that would not be an issue.

06-17-2010, 03:29 PM
Pressurized fuel comes from the pump, through the filter, past the service port and directly to the injectors. The green arrow going into the regulator is downstream, (after) from the injectors. Spring pressure on the diaphram is what allows the pump to build pressure. The arrow going out of the regulator is the fuel return line back to the fuel tank. The regulator is pretty simple and rarely fails, don't start throwing parts at it before diagnosing the problem.

06-17-2010, 04:22 PM
What steps should I take if all the fuel pressures come back normal?
So far the pressure have been around 62-64 give or take. The onlt thing I'm not comfortable doing is using the shut off valve.

Cannot see any visual fuel leaks or signs of leaked fuel like some say they are able to notice.

It has spark at start up and it does not hesitate, backfire, or miss.

06-17-2010, 04:56 PM
If pressure and leakdown check out when it's acting up, the next step is to see if ignition is being lost.

No external leaks is a good thing! The problem could be an internal fuel leak in the plenum or in the tank, and that will show up as excessive leakdown. If that's the case, the ONLY way to tell if it's in the tank or in the plenum is with the shut off valve. Without the valve, you're guessing, and guessing gets expensive.

Ignition failures typically occur when the engine is hot, not cold. Fuel delivery problems typically occur when the engine is cold, not hot. Any way you look at it, it's got to fail when you have test equipment connected in order to find which system is at fault.

06-18-2010, 06:50 AM
Well it did it again this morning. My last 4 days off it started for me but I guess it does not like where I park at work. :runaround:
I just hope it continues to start until my next days off.:rofl:

06-18-2010, 01:22 PM
Did you have the fuel pressure tester connected? These things are just like kids, they won't act up if they know you're watching them!

06-19-2010, 06:50 AM
Nope. I can't really play with it at work. I work for the state and they don't like us playing shadetree mechanic at work. LOL
Will it hurt to install it and leave it on and drive it to work and the check it before I start it up?

06-19-2010, 07:12 AM
That's the only way you'll be able to see if fuel pressure is the problem. No, it won't hurt it a bit.

06-21-2010, 07:23 AM
Wow. I think I have gremlins.
Okay, I was on the way home and my truck suddenly started overheating. Did not see any visible signs of fluid leaking anywhere but when I checked the water it was low 1 1/2 gallons. wow
Well I decided to install a new thermostat and see if that helped. When I added water and got it to normal temps it did fine. I thought well that was easy.
Then I began to hear a hissing sound and I noticed some water dripping from what I want to say will probably be the water pumps seep hole.
Before I could get it on the ramps it stopped.

Okay, long story but odd story short. I went to start it up this morning and guess what? No issues with the starting????????????:eek7:

Could it be water was leaking while driving and shorting something out?
Dunno. I'm off for 4 days so it will be interesting.

06-21-2010, 02:05 PM
If the weep hole on the water pump is leaking coolant onto anything that would cause a no start condition, it would be the crankshaft position sensor. If that happens, it's possible the sensor would not work properly. The sensor creates a very low, pulsed, AC voltage signal that tells the ECM where the crankshaft is in its rotation. The ECM uses that signal to supply the ignition module with a ground pulse to fire the ignition coil. In short, if the crankshaft position sensor fails, there will be no spark from the ignition coil. There may or may not be a DTC set in memory, and the SES light may or may not be on. Pull the connector apart and inspect it, very carefully, for damaged terminals, corrosion, traces of coolant, frayed wires etc. Don't replace the sensor unless you can confirm that it is faulty. Replacement of the crankshaft position sensor requires a re-learn for the ECM which requires a capable scan tool. The average, run of the mill code reader is not capable of initiating the re-learn process. Back to the basics, you need to determine, for certain, if it's losing ignition or fuel pressure.

06-25-2010, 01:51 AM
Well, the leak is at the top of the water pump and it sprays a thin stream of water right on top of the EGR valve. Don't really think that would cause the issue.
I am fixing that later today.

I hooked the fuel pressure gauge up and let it stay on while I drove to work. After about 15-20 minutes of sitting in the parking lot it went from 63 to between 60-58. The only thing is I left it connected while I was at work and the next morning it was between 0-5. After I turned the key on a couple of times it primed back to 65. And again it leaked down between 60-58 after about 15-20 minutes.

So i am still not sure. I will try the fuel pump pressure after I buy the fittings to do it with.

06-25-2010, 02:52 PM
No matter how far the pressure drops, it should prime between 60psi & 66psi before the ECM shuts off the fuel pump, (approx 2 seconds). Did the engine start? You need to check the fuel pressure when the engine will not start... you need to keep the tester connected until the no start occurs so you can determine if it's a loss of fuel pressure that's causing the no start condition.

06-28-2010, 11:48 PM
Okay. I was gone for two days. Went outside and hooked up the pressure guage and it went to 40. The I tried to start it and it just turned over and then I cycled the switch 3 more times and the pressure went to 50. Then it started.

Once started the pressure hovered around 55-58. I turned the engine off and the gauge was at 60. It dropped to around 55 after 20 minutes.
I really think it's the fuel pump but can't be 100% sure.:runaround:

06-29-2010, 08:35 AM
Okay. I was gone for two days. Went outside and hooked up the pressure guage and it went to 40. The I tried to start it and it just turned over and then I cycled the switch 3 more times and the pressure went to 50. Then it started.

Once started the pressure hovered around 55-58. I turned the engine off and the gauge was at 60. It dropped to around 55 after 20 minutes.
I really think it's the fuel pump but can't be 100% sure.:runaround:

Your pressure is low.
Could be fuel pump or pressure regulator or fuel leak or other.
Before throwing fuel pump at it do the full fuel pressure test to find the real problem.
And if it is fuel pump only replace with a Delphi pump even if parts place has to special order it at 25$ extra.

Airtex and after market are junk.

Go with Old Master is telling you on your problem.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

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