This is my first post, and I am sorry for this being such a long one. I have been reading a whole lot on here and trying out what I have read. I have a 2001 LS 4.3l with 117000 miles. I'm not an ASE certified mech, but I can usually figure things out for myself. But this thing has got me scratching my head. It started and ran fine all summer long. It has just began giving me problems since the cold weather set in. It will turn over, and over, and over when it is cold out but it doesn't want to start...... Most of the times.
Once it finally starts, I usually don't have a problem starting it the rest of the day. When it is running, it runs like a champ. First I changed out the fuel filter. No change. I have done the fuel leakdown test, which lead me to change out the spider assy. When priming it would hit the high 50's and then leak down to the 30's within 5 mins. Since changing the spider, it hits 60 priming, and anywhere between 51-58 while cranking. If it is below 54, it will not start. It drops down to 45 when I shut off the engine. It drops down to the mid 30's within 5 mins after shut off. I got those numbers from the test port. I glanced into the plenum and did not notice any washing. I also changed out the dist cap and rotor. The plugs were changed at 90000 miles and the plug wires look really good.
I checked the dead end pressure at the filter. It hits in the low 80's when priming and doesn't drop below 60 after that. I sat and watched that for 10 mins.
My ignition switch is a little weird. Once it has been running, if you turn the key all the way, it won't start. But if you turn the key just enough to engage the starter, it will fire right up. Now when it is giving me a fit and won't start, it doesn't matter how little or how much you turn the kay, it just won't start. I have also noticed the voltage gauge while trying to start it. I have good voltage (14) when priming. When I try to start it, if they drop just a little, it will usually start. Sometimes they drop down below 9 and it won't start. It may or may not have any bearing with my issues. Just wanted to give you all everything I could so I can get some valid advice. Thanks in advance for your help.

 

Take a look at this link and read Captain Hook's post (second from the top) https://blazerforum.com/forum/2nd-ge...d-75428/page3/ It's the third page in a thread, so you might want to even go back to the beginning of the thread because it may be similar to your problems.

I have a problem with my lock cylinder and bought one to replace it. Does yours feel loosy-goosey in anyway? Even though the ignition switches apparently are common problems, from what you are describing, are you sure yours might not be the lock cylinder instead?

 

I had a very similar problem to you in my '96. In the summer it would start fine, but once it started getting cold it had problems starting. After changing batteries it worked better but would still sometime crank a long time when really cold before it would catch. It even got so that when it was below -25*C it wouldn't catch unless boosted from another vehicle. I finally narrowed it down to a slowly failing fuel pump. The pump wouldn't hold pressure when the vehicle voltage dropped while cranking, and the cold makes your voltage drop more (for a number of reasons). As soon as I replaced the fuel pump (only use a Delphi or AC Delco) it fires right up first try, even when it's -30*C. It already sounds like you've replaced everything but the fuel pump so that may be your next step.

 

On your 2001 there is a vacant terminal in the underhood fuse panel:



With the fuel pressure tester connected, connect a fused jumper wire to the positive battery terminal. While watching the pressure tester, touch the other end of the jumper to the pump prime terminal several times. Pressure should immediately indicate the same pressure each time, 60psi to 66psi. Then test leakdown pressure after 10 minutes, and post your results.

If it passes those tests, (which it probably won't), here's an idea:
The pressure from the pump at 80psi is low but still within specs, (should be 73psi to 108psi) most pumps usually produce closer to 100psi. Holding above 60psi after 10 minutes means that leakdown in the pump is within specs. Using the data from those tests.... The regulator is receiving ~80psi, which is more than necessary to diagnose regulated pressure. Your regulated pressure in the high 50's is too low, (must be 60psi to 66psi) and leaking down to the 30's means there is excessive leakdown in the plenum, (must remain above 55psi). Assuming, (which can be dangerous) that the injectors and lines are OK, the pressure regulator has a problem, most likely leaking internally.

 

I had the same exact problem with 00 Sonoma 4.3. it drove me nuts for 3 months, took it to 3 different mechanics and they could not figure it out. I changed the starter twice thinking that was it, but it wasn't. I read the solution online by a chevy mechanic. He said to change both battery cables even if they looked good, his reasoning behind it is that the cables may look good but if they are older than 10yrs they get corroted inside and don't give the starter the minimum voltage to crank in cold weather.. I changed the cables, got the good ones from Napa and problem solved, never had any problems again. Not sure if your having the same problem because you don't mentioned if your starter turns or if it makes contact at all. mine did nothing when I turn the key , once the temperature rose over 50 it would crank and star perfectly. Hope this help.

 

OK. I have done some more checking. I used the jumper wire to prime the pump. It immediately went to 60psi while priming and held steady at 52psi. The Blazer will start with the pressure reading at 58psi, so maybe it is possible that the guage is not totally accurate. It will not start when the pressure reads 52psi.

The volts are concerning me a little. If I turn the key all the way, they drop below the 9 on the guage and it will not start. If I turn the key just a little until the starter engages AND the volts stay above 9, the fuel pressure stays above 55psi and it will start. If I turn the key a little until the starter engages AND the volts drop below 9 on the guage, the fuel pressure drops below 53 and it will not start.

If I have the batt charger hooked to it, the volts stay good and it will start. Should I be looking at the batt, ignition switch, or fuel pump with these problems? I am getting ready to run my batt into town and have it checked and I am hoping to drop the tank today and check the pump connections. I did check in the plenum and saw no washing. Could the fpr be leaking and not cause any washing even though it is new?

 

Have your battery and charging system checked. Most battery places will do it for free. Do you have corroded contacts on your battery or grounding points?

It could still be your fuel pump. That's exactly the same behaviour as I was experiencing. My truck would turn over fine, and would crank for minutes on end if I wanted to. What I found to be happening is exactly what you described: When the voltage dropped while cranking the engine, so did the fuel pressure and it wouldn't start. If I had a charger on it, or boosted it with a spare battery the voltage woudn't drop as much and it would start fine. After changing my fuel pump I've never had another problem with it starting. It's going on 6 months for me, with the last two months being all well below freezing temps.

 

When available voltage/amperage at the fuel pump drops, so does fuel pressure. In other words, if there's a poor connection causing high resistance in the fuel pump circuit, fuel pressure will be low; your pressure at 60psi is at the lowest allowable spec. Checking voltage at the pump may test fine but, it will not tell if there is enough amperage available at the pump. For that, you need to do a voltage drop test, and check amperage draw of the pump motor. Voltage Drop Testing

 

Thank God it's fixed!!!!! After much scratching of my head, I finally decided to listen to my wife and look into the ignition switch. I unplugged it from the key cylinder and took the cover off the contacts. Two of the 3 were bright and shiny while the third was dull. Upon further inspection, the contacts were burnt and caked with what looked like a carbon build-up. All I did was to wire brush them clean and now the thing starts the first time every time. It even starts when you turn the key all the way forward. Thanks for all the help and suggestions everyone. I learned a lot about the Blazer through all this.

Long story short, if you are having problems with your Blazer starting and you have good fuel pressure but intermittent spark, don't count out your ignition switch. Also, humor your wife if she has an idea, it just might work and save you lots of time and frustration!!!!!