I'm going to ry one more thing before I break down and take it to the shop.2003 2WD Blazer. Just turned 130,000 miles. Recently I changed the oil, plugs (AC delco) wires Dobule plantium) rotor (AC), Dist cap (AC) although I thought I had a problem with the cap installation (another thread on here, but things seem to be O.K.) new fuel filter.

I recently use MAF CLeaner and cleaned the MAF, however I could not get the MAF in half, two of the bolts would not loosen, so just sprayed where I could. Also, new air filter.

Yesterday, I was so excited the way the truck was running. I went up a hill and for the first time, when I gave it gas, it shifted fine and the power increased. However, on the next hill (about 200 feet away) it started to hesitate when I gave it gas and I was not sure that I was going to make it up the hill, let alone to my destination. On the way home it was stuttering and had the same problem. I had about a 1/4 tank of gas. Filled it up to about 3/4 of a tank and made it home, no stuttering, but I could not go above 65 MPH and pressing on the gas pedal did nothing to increase my speed. No stuttering after taking off from stop signs or lights as before.

I have yet to have the timing adjusted (will have to take it to the shop for this) as I am not a mech.

So for the long post, but I have done a search and found some posts which make me think it could be the MAP sensor.

Two other questions, if I may. Could a partially filled tank cause any of these problems?

Also, I know it could also be the Cat and somebody said that I should drill a hole in the Cat to let things blow out. I know this is against the law but so is robbing a bank, which I will have to do so the keep replacing things.


Many, many thanks for any input....

 

Having read your thread on the dist cap, { https://blazerforum.com/forum/2nd-ge...ist-cap-64560/ ] I hate to tell you this but first thing I would do is pull it and look for fine metallic dust and wear grooves on cyl contacts. To be safe dose it good with wd40 to clean it and see if that helps. Caps dont have to be far out of registration to eat their contacts up. While you have the cap off, check the rotor shaft for any slop. A little up and down may be alright, but no sideways slop.
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FIRST pull any codes with a scan tool, see if any are related to that sensor. 'Out of range' is a giveaway.
- Obviously you want to pay attention to all codes stored. They may tell you more than you would suspect.

O2 rich or lean symptoms, you should pay attention. Esp if they are the only ones showing.


Generally speaking there are sensors you can replace without adding problems and some you cant.
MAP is one you can 'generically' replace. To find out which applications use the same sensors, go to rockauto and find the one for your car, then click on the part #. It should list a lot of vehicles.
Then go to a salvage yard and get a used one. If it's a pick and pull, obviously you want one off a wreck that has apparently been well maintained. However in the case of a MAP they really dont fail all that often. However, if you see 'Wells' label on it, go on to next car.
One way of findng out if it's your MAP is to unhook the MAF before starting and seeing how the engine performs.
Sounds illogical but what happens is the PCM then runs in 'Speed Density' mode.. like the old days before the MAF. Key element to that is the Manifold pressure and TPS.
{ Note: I say that academically, having been 'raised and learned' on Ford EFI where they do things logically. I assume GM engineers are not totally brain dead}

LSS: If the engine runs worse with the MAF disconnected then you have problem with either the MAP or the TPS and if you didnt have shifting problems prior, it's probably not the TPS.
- sidenote: The TPS is, along with O2, the only sensor that 'wears out' with use. I note there's more problems with GM MAP's than I would suspect, so their construction MAY put them in that category as well. As a ford guy who had a lot of Mustangs in the day, I sorta collected MAPs whenever I junked a donor car. Never had to use any of them. Unlike the TFI ignition modules


If the truck runs better when you start without MAF, then that tells you MAF.

As far as effect of tank fuel volume, I would think there would be evap codes present. Which should not affect performance that much, anyway.

Your problem definitely COULD be a clogged cat. I've followed cases where that was the problem once engine was warm for a while, power fell off a lot. I've also followed many cases where cars passed tailpipe emissions test with hollow cats. But there has to be a problem with the fuel, fuel metering and/or ignition for a cat to fail, anyway. And generally your secondary O2 sensor will pick up a problem with a cat.

 

Thanks so much for your reply. I forgot to mention that the SES light did come back on, on the way home. I also heard the mysterious clicking noise that I have previously posted about, right before the SES light came on. I have had the code check 3 times and has always be 0455 Huge EVAP leak, but it would go away by itself. I am on my way to AutoZone right now to have the code read again.

Also, when you say to remove the MAF, should I drive the truck, or just listen while in park? Thanks for all the info and hope I don't appear to stupid.

UPDATE: Went out and started the truck to move it closer to the garage. Started fine and SES light was on as well as the GATE AJAR. Got out and closed the hatch, thinking some body tried to get into it overnight.

Shut it off and came inside for about 10 minutes. Got back in and started it up. Hesitation beforeit started. SES light was out, clicking noise came back and GATE AJAR on again. Reshut the the hatch and tried to pull away. Soon as I put it into reverse, it wanted to stop running. Had to sit there with my foot on the pedal to keep it running. Ran down to the local store to get some beer, (knowing it was going to be one of those days) Had to sit outside with my foot on the pedal for about 5 minutes before it would stay running without shutting down. I also noticed the the fuel gauge was bouncing back and forth from 1/2 tank to 3/4 tank.

I am losing it here. Just for the heck of it, since it's pouring down rain, I brought it into the garage and will remove the MAP sensor and spray it down with MAF cleaner. Crawl under it and look for and bad/bear wires going to the back and check all the fuses.

i will also remove the dist. cap again and check like was said above.

Thanks guy's and look forward for more suggestions, other than buy more beer, but that's not a bad thing either.

 

UPDATE Posts by edit, not adding posts

No.. sorry. Just disconnect MAF wiring connector before starting engine and drive it.

Spraying MAP port with MAF cleaner probably wont help .. it uses a diaphragm.

Clicking AND 455.. find your purge valve solenoid. Otherwise loose gas cap is majority of problems when it happens.
You didnt recently drop the tank and damage the vent nipple, didja?

Was the gate actually part open or not? That could be important. Which way was the fuel guage reading wrong. Does it likely have 1/4 or 1/2 tank?

 

Thanks for the info regarding updating. Just replaced the gas cap when I first got the 455 reading, about two months ago. Did not do anything with the tank.

The gate (window) was actually down, just not latched. Both times. I don't think there is a way that I can remotely raise the hatch/window, although I have read that this appears to be an option,''

The tank gauge was moving between 1/2 tank and 3/4 tank, I probably had closer to 3/4 tank.

Thanks so much and I owe you one of my beers for your help

With my luck recently, I have a feeling that it will turn out to be a costly thing, like the fuel pump.

Oh yea, what should I look for when I find the purge valve. i think I know where it is already.....

 

I was thinking of it in reference to the clicking sounds you heard. There's also a vent valve solenoid but -I think- it's back near the tank.

Here's some diags from a 99

Note there's a ground connection in common between Fuel tank press and fuel level in the one diag. Splice pack 423 also grounds the fuel pump. I'd trace from the MAP gnd to local splice then the black wire that goes to connector to the rearward harness, pin D where other side it is black/wh. You COULD unplug the PCM and measure resistance to chassis GND

Splice pack 423 grounds to chassis at G 402, wherever that is.

Or does it.. Damn you Alldata!
Anyway.. guess what a search turned up:
https://blazerforum.com/forum/2nd-ge...k-243-a-48712/

Also - amazingly- hi i have a 2000 chevrolet blazer 2 door 4x4 4.3L and i was - JustAnswer
MAY just be your answer!!
UPDATE, AGAIN:

Everyone who has a similar problem should read this entire thread:
https://blazerforum.com/forum/2nd-ge...problem-42968/

Actually Rifleman 308 found TWO problems. We should be thankful for his tenacity.

Remember if search doesnt work and you wonder if you came in the middle of something, search 'all posts by' on the author of the 'orphan' thread. That's how I found the last one.

Here.. btw is that stupid Sp 423 G402 location. Like Rifleman noted, I cant think of a dumber location designed by Michigan Engineers.

 

Once again, many thanks for the great info. Looks like I got a few things to do today.

In regards to the clicking noise, it is definetly coming from the rear, kind of sounds like it's on the pass. side.

Also, in regards to the alt. I had just replaced the old one with one from the junk yard about a month ago.

I am going to due a fuel pressure test today and have AZ check the alt, but I will probably just buy a refurb AC Delco and not worry about itbut funds are tight and I don't recv. my disbility check until next week, so it might have to wait.

I will keep you posted. Thanks