Blazer hard start when engine warm

[marshallblazer]

My Blazer is hard to start only when the engine is warm, when the engine is cold it starts fine. From about 10 min. after I shut the engine off, to about 4 or 5 hours later is when it has trouble starting. In this time period it takes about 3 to 5 sec. of cranking to start (a little less when hold down the gas pedal). When the engine is cold it takes a fraction of a second of cranking to start. This problem started slowly, and it's now been happening for more than a year. I thought this could be a problem with the intake air temp sensor or the engine coolant temp sensor, but I checked them and they are both working correctly. I hear the fuel pump turn on for 2 sec. when I turn the key to on, and I tried cyceling the key from off to on about 4 times before starting and the problem still happens.

I don't know if this is part of my problem, but about a month ago I started getting "random misfire" codes. I have replaced cap, rotor, plugs and wires, and I am still randomly getting this code. I don't know if these problems are related, but I figured more information is better than less.
I found another thread with the same problem, but it was never resolved. Here is the link http://www.automotiveforums.com/vbulletin/t395805.html

I would apprecieate any insight from anyone, I can't wrap my head around this problem.

1997 Chevy Blazer LS
4 Door, 4WD
4.3L CSEFI, Engine code W

[MT-2500]

What year and what engine?
If you are getting misfire codes you need to keep working on that end.
Does the scanner pinpoint what cylinder is misfiring?
But I would also run a good fuel pressure check on it.
Hook a gauge to outside of mirror or windshield and watch fuel pressure when running and when you shut it off and try to restart.
Post back fuel pressure readings and watch for a fast leak down when shut down.

[1996LTOwner]

Just a question MT, the spider injector fuel pressure regulator senses and regulates by the pressure inside the intake, could it be going bad and not properly regulating the pressure while it's warm? Bad pressure regulator could also cause the random missfire, couldn't it? I think if I had to "throw a dart", I might try the regulator. About $70 when I bought one a few years ago. Good time to inspect the injector hoses as well.

[MT-2500]

Originally Posted by 1996LTOwner

Just a question MT, the spider injector fuel pressure regulator senses and regulates by the pressure inside the intake, could it be going bad and not properly regulating the pressure while it's warm? Bad pressure regulator could also cause the random missfire, couldn't it? I think if I had to "throw a dart", I might try the regulator. About $70 when I bought one a few years ago. Good time to inspect the injector hoses as well.

The fuel pressure regulator controls fuel pressure but the fuel pump has to have good pressure for the regulator to control.
Around 75/85 lbs of full pressure at fuel pump
You need to run a fuel pressure test to see what direction to go.

Hard to start.
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.
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.
Post back fuel pressure readings.

[marshallblazer]

I gave my engine information in the first post it is a 97 Blazer LS, 4 Door, 4WD, 4.3L CSEFI, engine code W. The code they got on the scanner is P0300 - Random/Multiple Cylinder Misfire Detected, this turns on my service engine soon light for a few days, then it will go off for about a week, then it will come back. I am going to get my fuel pressure checked this week hopefully.

Also just to let you know I brought my car to a repair shop 2 yrs. ago and he said my injectors were leaking, and told me I would need a whole new rail (cost me $600, I wish I knew about the switch to MFI back then). The thing is I never had a starting problem before then, the starting problem happened about 6 months after that repair. I will post my fuel pressure readings when I can get them. Thanks for everyone's help so far.

[MT-2500]

Random misfire codes can be misleading.
Can be caused by a lot of things.
Here is a good one.
http://www.automotiveforums.com/vbul...play.php?f=589

If it is setting misfire codes you need to get it n a good engine capable scanner that will read out what cylinder is misfiring and how many times it is misfiring.
Also all other data that can cause a misfire.
Besides secondary ign problems Low fuel pressure and MAF sensor off is some leading causes of random misfires and camshaft retard setting off to and dirty injectors.
MT

[1996LTOwner]

How many miles do you have on it? I fought with a random missfire for a few years through plug changes, EGR valves, wire, cap & rotor changes, fuel pressure regulator change, O2 sensor changes, coil replacements, etc. The only thing I've seen/read on this site that fixed it on high milage engines was a timing chain replacement which I finally did and another person that forced a distributor adjustment. My initial fuel pressure with key on was 61 psi. Engine running was 57. After the timing chain replacement, engine ran great with those fuel pressures. The timing chain I replaced didn't show much slack, but apparently didn't take much. For more info, do a search for "Intermittant miss at light loads". You'll see what some of us went through trying to chase down this "Gremlin" that seems to plague the Blazer.

[marshallblazer]

Well I fixed my starting problem a few months after my last post. I know that was a few years ago, but I thought I would share what I found out in case someone else was having this problem. It turns out my fuel regulator was leaking into my intake manifold. This was causing some random misfires, and when I shut off the engine the leaking fuel would make the fuel mixture too rich. This would cause the starting problem, and after a few hours the excess fuel would drain (or evaporate) out of the intake which allowed the engine to start fine. I followed a post I found on this forum on how to replace the injectors (http://www.automotiveforums.com/vbul...d.php?t=559014) and chose to use the updated fuel spider. Thanks to the great post by JoshBarber it was pretty easy, although time consuming.

[Schrade]

Originally Posted by marshallblazer

Well I fixed my starting problem a few months after my last post. I know that was a few years ago, but I thought I would share what I found out in case someone else was having this problem. It turns out my fuel regulator was leaking into my intake manifold. This was causing some random misfires, and when I shut off the engine the leaking fuel would make the fuel mixture too rich. This would cause the starting problem, and after a few hours the excess fuel would drain (or evaporate) out of the intake which allowed the engine to start fine. I followed a post I found on this forum on how to replace the injectors (http://www.automotiveforums.com/vbul...d.php?t=559014) and chose to use the updated fuel spider. Thanks to the great post by JoshBarber it was pretty easy, although time consuming.

Too bad I didn't read the problem in 2007 when you posted - I'd have solved it the next day, like I posted last night, twice:

Originally Posted by cbec1999

GOOD DIAGNOSTIC WORK - CHECKING FUEL PRESSURE!

Your static pressure test indicates a leak in the line, or the regulator, or leaking injectors, or a weak spring in the FPR diaphragm (least likely).

You do NOT need to concern yourself with dynamic fuel pressure tests (motor running) at this time - only static tests.

First check, COLD motor = turn the key on. Let it prime the fuel rails, shut off, then turn the key off. Pull the vacuum line that goes to the fuel pressure regulator. If you can, pull it at the manifold, but if not, pulling it at the FPR is OK. Smell the vacuum line for gas.

If it smells like gas, or is wet, then the diaphragm in the FPR is ruptured, and extra gas will get drawn into the intake. (This will make for HARD hot engine re-starts).

If no gas is in the vacuum line, then disconnect the pressure regulator, and cap the line WELL. Connect the fuel pressure gauge. Forget PINCHING fuel lines - you'll damage lines that way. Test again, and have a pencil ready, and watch the gauge drop. NOTE THE PRESSURE BLEED-DOWN TIMES, in 5, or 10, or 15 second increments. Write them down, post that result back.

If it still drops quickly, the injectors are leaking, UNLESS there is a visible leak between the line from the tank to the injectors. You HAVE to check that, before pulling the injectors.

If no leak, pull the injectors, and repeat the test, WITH A MASON JAR UNDER EACH INJECTOR. This will show which injector is bad. Leaking injectors is like a water hose with no sprayer on it - it just runs out. Put on the sprayer, and it sprays fine mist.

If it does NOT drop after 5 minutes or more, the fault is AFTER THE injector rails, and the injectors of course don't leak. The spring in the FPR is bad. There's no place further down the line that matters...

EVERYONE - bookmark this post for reference!

... and here:

Originally Posted by cbec1999

READ THIS VERY CAREFULLY AND THOROUGHLY!!! I'LL cut through this horsewaste in short order. GUARANTEED.

Why do you say the TPS fails? The trouble code is Low Voltage. Go to a local mechanic, and get him to print out the PROPER diagnostic procedure from his computer for this code. Then do EXACTLY as the procedure says. You might have to pay him a few bucks.

You will need the harness pinout schematic for the TPS feed. NOT HARD TO FIGURE OUT by the picture.



The computer will relearn by itself after half a dozen OPEN LOOP (warmed-up) drive cycles. You'll know, because the transmission won't wind out each gear before shifting anymore. BUT, if there's a LOW Voltage problem, it will have a problem re-learning.





Most are not likely in your case.


Does this vehicle lope idle at all when warm? Surge at stoplights?


It will re-learn itself - see above.




COULD be. The vacuum supply to the FPR can draw gas into the intake, IF the FPR diaphragm is ruptured. BUT, you said fuel pressure HELD. So this cannot be.

The only way for fuel to flood into the intake/oil crankcase is leaking injectors, or ruptured FPR bladder/diaphragm. Double check your fuel pressure bleed-down time, and write it down til it goes to 0psi.

Also pull the vacuum line to the FPR, this way: COLD ENGINE, turn on the key, let the fuel rails prime, and then turn it off. Pull the hose and smell the line. STRONG gas???


There some GREAT pics of me backprobing a PCM connector in vette forums here post #68:
Automotive diagnostics at its BEST.



You CANNOT know this unless you see a data log that shows the injector pulsewidth (in miliiseconds), like so:

Notice the normal is 128. This is not just for vette, but for ANY car.



This could be EVERYTHING. A faulty temp sensor COULD make the computer think the motor is cold, and LENGTHEN the injector pulsewidth (MORE FUEL).

Why do you think THIS??? What was the voltage reading for the ECM pin for TPS signal supply???


NO NO NO


Need to see a pic. Could be ABS module?


Take back the ECM FIRST, since that was not the problem.

Let's start from square 1 - where are you now on it?


More good info; another post to bookmark uh HUH