First off, I know this will not be popular, but they have the same motors and you guys seem to really have some smart knowledgeable people here, exactly what I need right now....badly so full disclosure, it is a 2000 Astro, not a blazer.....82K miles, AWD, "W" motor. Now for full info to help get why I am so stuck.....

Now on to my problem driving me nuts. This vehicle gets little action as it is a utility vehicle for us for towing and dog hauling, but back in June we went on vacation and noticed that I could smell gas outside of the van when it was running. Could not see any leaks, so kept on using it since we were away from home. At the same time, out fuel gauge decided it would rear full to 3/4 full unless the low fuel light came on, then it would read empty. Also on the same trip I noticed that the van would really stumble, misfire and buck ONLY on the first take off after it was warm, when leaving a store parking lot after a quick in and out for example. This is the current problem.

It only does this once the van is warmed up and a short time being shut down. If I feather it lightly it will still stumble but not as badly, and clear up around 20mph or so and not stumble after that, not from a red light, not from a stop sign, not on the highway, ect.

So first thing I did was replace the cap and rotor since it was notorious for cold weather starting issues, and the cap was pretty corroded underneath. Plugs are a REAL pain in this van so left it for now. Cold weather starts seem to be fine now.

Read on here about possibly fuel pressure regulator dumping in the intake so I had taken the fuel pressure reading from the test port and did not write down what it was (stupid, I know) but it dropped something like 15lbs in 10 minutes. So I attached the fuel gauge (harbor freight special) to the fuel filter (again did not write down results so my memory is not to be trusted for hard data) and it went to something like 55psi and dropped 15lbs in 10 minutes. So I replaced the fuel pump with a AC Delco pump and figured worst case that it needed to be replaced anyways since the fuel gauge stopped working properly. New pump had one different electrical connector that needed to be wired in (included with the pump) and no external "sock". Tested again and pressure still dropped like before, but pump pressure was much higher. Figured maybe the gauge was leaking, but no visible signs of it, maybe bad quality, did not think the new pump would be bad out of the box, at least not a quality one....BUT still had same stumble.

Figured since I smelled the gas, and others had reported similar symptoms, and it is getting cold here I better just replace the fuel pressure regulator. Regulator was a Delphi, but looked a little different. The large black gasket was more like a top hat looking gasket (like two rubber washers of different size molded together), and the original had a nipple pointing down where this does not have a dot or nipple at all and was a very tight fit. I did not fully pull out the upper plenum since it is so hard to get at on these, but raised it more than enough to replace it with propping open the intake at the back (remember our vans have a dog house so this was not too hard). From what I could see, it did not look completely clean under the FPR, but did look lighter and was hoping that was the problem. Got it back together today to find the same stumble, but do not smell any gas anymore.

Read that someone had the same problem because of a sticky EGR, so removed mine, but it moved freely, but cleaned it anyways, still same problem.

Anyone else have this and found out the cause? Please help out even if it is not a Blazer, I am so sick of this, and know better than throwing parts at it, but I have very little time to work on it as I work tons, and it is getting pretty cold here in Minnesota.

thanks in advance to anyone who can help point me in the right direction, and sorry for the long post.

 

Okay, update since I woke up at 4:30am thinking about it and couldn't sleep, ugh......

Added fuel gauge tester to test port on back of motor. Put key on and shot up to 60 but as soon as the pump turns off (the usual 2 seconds or so) it goes down to 55 and drops one pound every few seconds or so down to 50 until I realized if I keep the key on my headlights stay on, so turn power off and it shoots back up to 60 and drops to 55 in a second. Weird. It seems to be holding much better, but key the ignition on again to see what happens, it shoots up to 60 again and drops to 55 when pump stops. Again it drops slowly. Five pounds in the first five minutes (so it goes down to 50) and then one pound the remaining 5 minutes, so from 55 to 50 in ten minutes.

Then I decided to see what happens when I start it, jumps up to 60, but drops back down to 53 and climbs 5 pounds when I rev it. Shut it off and it drops quickly like the first initial attempt down to 40 after 10 minutes.

I have a new fuel filter being delivered today since I need to unhook one side, I might as well see if I can get the supply side to break loose as a thought crossed my mind. This stumble happened on my vacation when the fuel gauge did not work and the gas got real low and maybe clogged up the fuel filter? Cheap maintenance needed either way. When it is installed I will take and record those readings.

Sorry for the long post but figured it would be better than the "Hey, my truck is running rough, what's wrong with it?" kind of post

edit: more info added
Decided I have time before church, so wanted to see what the fuel gauge did when driving. I drove it around with a regular 53 or so pounds of pressure, got it warmed up to simulate when the problem occurs. Shut it off for three minutes all the while holding the 55 pounds of pressure with no signs of dropping. Start it up (always start fine), but as soon as I try to accelerate it stutters and even backfired through the intake but the fuel pressure was just the same as on the cold drive....

Thinking maybe a crank sensor or something else not setting off an engine light? Once it is warmed up even before I park it I hear a slight ticking at what I am guessing above 1500rpm (no tach), but none at low rpm. Probably would not hear it if I did not have the dog house off.

thanks again guys/gals :/

 

would I get more responses if I buy a scanner and try to give data from it? would I be better off with a BlueDriver scanner that uses the phone, or something like the innoca 3040e? I assume it would be pretty hard to watch the scanner while I try to drive, so any suggestions?

 

I guess you've tried cleaning the mass airflow sensor? Sounds simple, but it made a huge improvement for me. No hesitation at all now.

 

WAS MEANT FOR DEBAGO 77 SORRY. My 4.3 was running fine and would rev in park/ neutral but became rough when load was applied- drive or reverse. I replaced plugs, cap and a couple other unnecessary things as it ended up being the rotor button. As soon as I replaced it the engine became smoother, quieter and more responsive than it ever was since I have had it. Just something to check, it an inexpensive part and could be the problem, good luck