Hesitation in acceleration

What's been done? (In order of doing, all since August 2005)
New Air Filter.
New Fuel Filter.
New Fuel Pump (actually 2).
New EGR valve.
New Nut Kit/CPI unit.

New AC Delco Plugs.
New Wires.

New (Used but dyno tested) Engine.
New Cap and Rotor.
New Fuel Pump Relay

Tested Iginition Coil.

New Cat Converter.
Back Pressure Tested twice, (remains in green zone) Once before new cat and once again after.

Whats happening now? Hesitation or (perceived) loss of power when giving gas. The jerking at cruise speed (symptom before replacing cat converter) is gone for now, at least it seems to be.

Also a rotten egg smell is noticable now with new cat. Didn't notice it before...

Latest scenario was: After taking it back to the mechanic and he can't find any cause, he does feel the problem, he suggested plugged cat. I replaced the cat after finding it was just crumbs in the bottom. Still didn't drive good so I went to dealer. They said go back to exhaust and have back pressure tested again (it would be cheaper). Back pressure is within range. Dealership said if they didn't change the muffler then it could be full of all the debri from the cat. The cat guy says he remebers that the honeycomb was on broken on the engine side, meaning no debri would have gotten past the other end and on into the muffler. But, we still only checked the back pressure, we didn't pull the muffler off and shake it or anything to see if there is loose material inside. So cat guy says he thinks it's a lack of fuel getting completly burned up that causes the smelly rotten egg smell I'm now noticing.

I'm thinking it's time to go back and recheck the plugs and possibly pull the egr valve and check (or at least put a screwdriver to it and listen for clicking??). I've read and searched and I'm not really finding any solutions other than maybe possibly the TPS or IAC's heck maybe even an O2 at this point. But I'm not getting any codes thrown.

When you replaced the CPI Nut Kit, does that come with a new fuel regulator?
Have you checked the plugs since you replaced to see that they are not fouled in any way?

When you replaced the CPI Nut Kit, does that come with a new fuel regulator?
Have you checked the plugs since you replaced to see that they are not fouled in any way?

I understood that it was all one piece and I replaced the entire spider unit...

I have not rechecked the plugs. I will be tonight or this weekend as I go back over this thing again.

Definitely seems like the fuel is being incompletely burned. Do what you said and recheck plugs, wires, and nut kit.

Definitely seems like the fuel is being incompletely burned. Do what you said and recheck plugs, wires, and nut kit.

egr valve once again clogged with carbon pellets...Damn I'm getting tired of this. Where can I get the gasket with the screen for this thing? I'd rather clean it with each oil change than keep on having it get a carbon chunk lodged in it.

Where is the carbon pellets coming from, how do I stop them. Don't suggest any foreign liquids, I've done that and I paid out the @$$. I thoroughly cleaned the upper intake plenum and all? What is causing this???

egr valve once again clogged with carbon pellets...Damn I'm getting tired of this. Where can I get the gasket with the screen for this thing? I'd rather clean it with each oil change than keep on having it get a carbon chunk lodged in it.

Never mind, I got one overnighted to Advance Auto as they sell them but didn't have one in stock. Did a google search and found the name to be Klean Screen from Tomko. There are other ways of getting one I'm sure. It was 11 dollars.

So far the engine hasn't sputtered or hesistated, but I'm still very cautious. Unless I write again here the answer is this gasket. I will be checking it periodically for carbon build up and all. I also read where this is a pretty well known problem with these vehicles so if your getting the carbon pellets in your EGR like I am you may want to try the screened gasket.

I hope that you have found the problem. Good Luck.

Never mind, I got one overnighted to Advance Auto as they sell them but didn't have one in stock. Did a google search and found the name to be Klean Screen from Tomko. There are other ways of getting one I'm sure. It was 11 dollars.

So far the engine hasn't sputtered or hesistated, but I'm still very cautious. Unless I write again here the answer is this gasket. I will be checking it periodically for carbon build up and all. I also read where this is a pretty well known problem with these vehicles so if your getting the carbon pellets in your EGR like I am you may want to try the screened gasket.


Also for your consideration if the problem doesnt seem to fix after you do that i think you should check your MAF sensor, i had some long painful experience with a bad one. Replaced all the above that you did. Checked fuel pressure, check fuel pump, etc you name it i either checked it or replaced. But after my friend mentioned that i may have a bad MAF, (who just happens to own a blazer as well) i plugged his into mine and low and behold, worked like a million bucks. I had given up hope that it was a bad MAF because i tested it and it was electronically sound, it was an intermitten thing im assuming. If you can get your hands on one to test it you wont be sorry, in fact i will give you a 75% chance that this is your problems. If you can get a loner to plug in as well you cant lose. Good Luck

Also for your consideration if the problem doesnt seem to fix after you do that i think you should check your MAF sensor, i had some long painful experience with a bad one. Replaced all the above that you did. Checked fuel pressure, check fuel pump, etc you name it i either checked it or replaced. But after my friend mentioned that i may have a bad MAF, (who just happens to own a blazer as well) i plugged his into mine and low and behold, worked like a million bucks. I had given up hope that it was a bad MAF because i tested it and it was electronically sound, it was an intermitten thing im assuming. If you can get your hands on one to test it you wont be sorry, in fact i will give you a 75% chance that this is your problems. If you can get a loner to plug in as well you cant lose. Good Luck


I will look into it as well thanks. So far all seems well...
What about a code though, did you not get a code indicating this was your problem area? I finally received another code 32, but not since installing this klean screen gasket...

I will look into it as well thanks. So far all seems well...
What about a code though, did you not get a code indicating this was your problem area? I finally received another code 32, but not since installing this klean screen gasket...

I show a MAF sensor as not required on Autozones shopping site. It references to a MAP sensor. Are these one in the same. A pic of a MAF sensor in someone else's thread (maybe yours) shows a different part than what is inserted in to my intake tube from between the air filter and the intake. I must be looking at the wrong part.

Where is it and if I need to where do I buy one?

{What's been done? (In order of doing, all since August 2005)
New Air Filter.
New Fuel Filter.
New Fuel Pump (actually 2).
New EGR valve.
New Nut Kit/CPI unit.

New AC Delco Plugs.
New Wires.

New (Used but dyno tested) Engine.
New Cap and Rotor.
New Fuel Pump Relay

Tested Iginition Coil.

New Cat Converter.
Back Pressure Tested twice, (remains in green zone) Once before new cat and once again after.

Whats happening now? Hesitation or (perceived) loss of power when giving gas. The jerking at cruise speed (symptom before replacing cat converter) is gone for now, at least it seems to be.

Also a rotten egg smell is noticable now with new cat. Didn't notice it before...

Latest scenario was: After taking it back to the mechanic and he can't find any cause, he does feel the problem, he suggested plugged cat. I replaced the cat after finding it was just crumbs in the bottom. Still didn't drive good so I went to dealer. They said go back to exhaust and have back pressure tested again (it would be cheaper). Back pressure is within range. Dealership said if they didn't change the muffler then it could be full of all the debri from the cat. The cat guy says he remebers that the honeycomb was on broken on the engine side, meaning no debri would have gotten past the other end and on into the muffler. But, we still only checked the back pressure, we didn't pull the muffler off and shake it or anything to see if there is loose material inside. So cat guy says he thinks it's a lack of fuel getting completly burned up that causes the smelly rotten egg smell I'm now noticing.

I'm thinking it's time to go back and recheck the plugs and possibly pull the egr valve and check (or at least put a screwdriver to it and listen for clicking??). I've read and searched and I'm not really finding any solutions other than maybe possibly the TPS or IAC's heck maybe even an O2 at this point. But I'm not getting any codes thrown.}



I did most of these things too. I would be more than excited to find that it is the MAF sensor. I thought for the longest time that it was the tranny that I replaced last year. But now, after reading this post,
I have new hope that it's not. Except for the fact that is sounds like it's running heavy.

Where is your MAF sensor located on a 95 4.3L Vortec? The one inserted into large plastic air intake hose that is attached to the manifold? Looks like a single probe looking device probably just reading the air as it goes by from the air filter and it is engine side of the vacuum hose that is attached to this same intake hose.

I don't see anything like a three filament wired sensor device that I thought I was looking for. But, once again, maybe I'm not looking at the right thing.

For the MAP sensor my haynes manual seems to be talking about the little black rectangular device sitting just on top of the intake mainfold near the front right side of the black plate with vortec written on it (looking from front of vehicle). I see no vacuum hose attached though, it said to remove it and the electrical connector when removing...is this what everyone is referring to or is there something I'm not getting???

Where is your MAF sensor located on a 95 4.3L Vortec? The one inserted into large plastic air intake hose that is attached to the manifold? Looks like a single probe looking device probably just reading the air as it goes by from the air filter and it is engine side of the vacuum hose that is attached to this same intake hose.

I don't see anything like a three filament wired sensor device that I thought I was looking for. But, once again, maybe I'm not looking at the right thing.

For the MAP sensor my haynes manual seems to be talking about the little black rectangular device sitting just on top of the intake mainfold near the front right side of the black plate with vortec written on it (looking from front of vehicle). I see no vacuum hose attached though, it said to remove it and the electrical connector when removing...is this what everyone is referring to or is there something I'm not getting???

I may have answered my own question with a search on AZ for a different year. Maybe mine didn't have a MAF sensor...

I amy be wrong, but after looking into it I don't think that the '95 4.3's with the CMFI engines have a MAF sensor.

On the '96 and later CSEFI engines it is located in the air intake duct just after the air filter box. It is a hardened plastic box between two sections of the duct with an electrical connector coming out on the side of it. When removed you can clearly see the wires and a mesh screen in the sensor.

I amy be wrong, but after looking into it I don't think that the '95 4.3's with the CMFI engines have a MAF sensor.

On the '96 and later CSEFI engines it is located in the air intake duct just after the air filter box. It is a hardened plastic box between two sections of the duct with an electrical connector coming out on the side of it. When removed you can clearly see the wires and a mesh screen in the sensor.

Thanks for description...
Mine isn't set up like that. I have a smaller probe like device (that I've cleaned) inserted into the side of the duct just prior to entering into the manifold. It is the only thing electrically connected to the air duct or filter area...

No problem with the help, I know I've used a lot of help from this forum.

I think the probe you are talking about is the IAC valve. If it is it's located just at the front of the Plenum and above the coolant temperature sensor.

I will look into it as well thanks. So far all seems well...
What about a code though, did you not get a code indicating this was your problem area? I finally received another code 32, but not since installing this klean screen gasket...


Yes i did actually a MAF code, Like i posted earlier i even cleaned the MAF and it helped for like a day and kept the MAF code from coming on, but i stil experienced everything you did. Only after i replaced it did it finally run normal

Well sorry to get your hopes up, i didnt realize you had the CMFI engine. But i swear the symptoms your describing mimiced mine in everyway. Look into the sensor that monitors air flow, i think you said earlier the Manifold Absolute Pressure sensor. Find a way to test that and see whats up. you may have noticed on their site, that auto zone gives repair info. See what happens.

Hello i'm new to this site.Heres my problem.I have 1992 S-10 blazer with a 4.3 "W" code cpi. It has 154,000 miles on it.It seems to be giving me trouble these days.I just tuned it up and put a new o2 sensor,checked fuel presure and ran it on the scanner and everything checked out ok.The cat is ok too.Not pluged at all.It seems the warmer the outside temp.is,the worst the truck runs.i.e. bucking spuddering etc.Usally when taking off and part throttle like it's being held back.I'm also smelling a stong lean oder from the exhaust it almost makes my eyes tear.Is there some kind of sensor that detects the outside air temp that could cause this to happen?I had to a meachinc and he couldn't figure it out.Thanks for your help.

Hello i'm new to this site.Heres my problem.I have 1992 S-10 blazer with a 4.3 "W" code cpi. It has 154,000 miles on it.It seems to be giving me trouble these days.I just tuned it up and put a new o2 sensor,checked fuel presure and ran it on the scanner and everything checked out ok.The cat is ok too.Not pluged at all.It seems the warmer the outside temp.is,the worst the truck runs.i.e. bucking spuddering etc.Usally when taking off and part throttle like it's being held back.I'm also smelling a stong lean oder from the exhaust it almost makes my eyes tear.Is there some kind of sensor that detects the outside air temp that could cause this to happen?I had to a meachinc and he couldn't figure it out.Thanks for your help.

Well, I'm only guessing but have you looked at the EGR valve to see if it may be clogged. Assuming you have a decent tool set it's relatively easy to get to. At least on my 95, don't know much about other years. If it's got carbon pellets it will effect driveability... I'm still in 'test drive' mode on a new gasket I installed to prevent more pellets from entering the EGR. Jury is still out if that was the fix or not. However I haven't had any engine codes thrown since installing. Usually you get a code, but it took a while for my to throw it this time around...even though I already was feeling the drive problem...

gmyoyo, just wondering how the Klean screen has worked out for you. I have a 96 Blazer that keeps throwing an EGR code and I'm hoping that this might be the answer.

well gang, try this on for size... similar issue- sputter, stummble backfire at low throttle/cruise low speed. code 43. (1992 w/94 engine both vin w) now getting a code about ground at egr. sorry, paper is in truck with the woman right now. anyway, start up, a little rough, but snappy. hit it and goes. but after a few minutes, like a switch, stumbles, pops. stomp it, gets it on.. i have noticed when coming to stop on a exit ramp, let of gas and sometimes it is smooth. other times, popping in exaust, like glass packs. when it does that, i know its not gonna take off well, when it dont, takes off fine. knock sensors light up test light when running. both. slow blink at idle, fast at high rev. esc/est module prob? code 43. egr is clean. and by the way, if the screen is blocking carbon, wont that essentially "block off" the egr? and maybe eliminate the egr all together? heres my computer #'s if someone has a spare memcal unit they wanna send me (for free) sorry, ima broke sucker ownin this thing, lol. serv # 16156647, 866521, m220287721, chip is bawp 6600, the white chip inside the unit has #5122069, other chip numbers i found 16045915, ad27c256, and v147001mc all located in the memcal unit in the ecm. email if ya gotta spare just layin around and wanna try to help me out. i suspect it is the cause, resulting in carbon buildup also. dont need ecm, changed that with a 2.2 (or 2.5 i forget what one it was, same unit, diff chip) with my chip, same results. they didnt have a chip for mine at junkyard. i imagine ya could mail that chip. [email protected] if ya wanna get ahold of me.:banghead:

Ha, funny you should ask, or more to the point, funny you should ask when I came in today back with blazer problems.

As far as the kleen screen, it seems to be doing it's job, there were not carbon pellets in the egr or screen or even the hole coming from the engine to the egr. (While I agree with what the other person thoughts/questions about the build up, mine is simple enough to get to to be able to treat it like a fuel filter or even an oil filter change....)So I think it was worth the purchase to stop the pellet problem...

But, all the sudden (so my son says) the car has started doing it again. So I got it from him this weekend and yes, it seems to be running rough. I haven't had time to get under the hood but plan on it in the evenings this week.

It is a long history, but where I'm at now is dumbfuddled. It doesn't seem to want to run smoothly once it's warmed up. Sputtering on acceleration from stops, missing feeling when at speed. Seems to idle great though...

Hey all! I really hope somebody can help me. I have a '96 Blazer LS, 4.3L Vortec, "W" VIN, with 163,000 miles. I got it back from the shop today, hoping this hesitation problem was fixed. I got to work (30 miles away) fine; it ran great (for a change). As I was coming home at 1 o'clock in the morning, however, it started hesitating again. I heard a clicking-type sound coming from the front passenger side everytime it sputtered, almost like a rock was stuck in something. Then, the "Service Engine" light came on, the "charge" light came on, she decelerated and died, in that order. While waiting for the Triple-A tow truck to come, I decided to see if it would start, and it did; no clicking sound. The "Service Engine" and "charge" lights went off by themselves. Even once we got her home, I turned the key. It had some trouble turning over at first, but I gave it a little gas and it started enough to get in the driveway. I plugged in my code reader, but got nothing. What do I tell my mechanic to look for when I take it back tomorrow?

Oh, the things that I recently had fixed/replaced: heater core, ignition switch, full tune up, fuel filter, radiator flush & coolant, oil change, several seals 'cause it was leaking major oil, and front wiper motor and assembly (I know that has nothing to do with it, but just thought I throw it in there anyway).

Simply a guess, but the clicking sound from the passenger side may have bee a couple of things. One, the battery has a loose connection. Two, the relay located in your glove box that runs the fule pump is going south.

Check your battery connection. If that's not it, look in the glove box behind the relay panel, there is probably two but maybe three relays, you might try to just switch them to see if the problem persist, but that may not be the best answer as I'm not completly sure what the other one does (controls). But I beleive the middle slot is for the fuel pump. If it cuts out, then your car would die out.

I just realized your relays may be under the hood on the firewall on the passenger side, but I'm not sure as I actually on a '95. It just looks body style like the 96's and later, but it has a 95 computer. So it's more like a 95.5

I'm curious, when you plugged your reader in, what did it say? Anything like it couldn't read or make the connection or initialize, or did it just not return any trouble codes?


Oh yea, don't really know what to say to the mechanic other than telling him same thing you said here...

The code reader didn't spit out any codes. I'm thinking the "Service Engine" and "charge" light came on because the engine was shutting off (like when the lights come on automatically when you first turn the key). I first thought it was the fuel pump because it started whining like crazy, but that was also when it was "dying".

So, you think if I just replaced the relays and fuel pump that should do the trick? What about the MAP sensor that I've been reading about? How can he check that just for good measure?

No one said replace the fuel pump yet. It seems to be working fine, it sounded to me like the fuel pump relay might have acted up though, very inexpensive and it's just a plug so you can do it yourself. But, once again, I'm not saying it is or isn't the relay, I'm just guessing. If you turn your key to the on, but not start, and can hear your fuel pump whine for a couple of seconds, then I wouldn't go messing with that at all.

I'm not sure, but I don't think a MAP sensor would have caused your car to just shut down like that. But then again, my status on this forum should be indicative of my knowledge, I'm a newbie too.

Thanks for your help. I'm on my way to the shop right now. Wish me God-speed!

:crying: The mechanic said the fuel pump was going and it was hesitating because the transmission was going (although it was fine as I drove it to work). I was looking at over $2000 worth of work. I only paid $500 and already put about $1500 into it. Anyway, I left it at the the shop for the parts to be sold off. Some guy already need the rear suspension system from it. I'm a little sad right now. I don't know what I'm gonna do. I don't have a car! :disappoin

GMyoyo,

No MAF on a 1995, yours is s speed density system, not a mass airflow system introduced in 1996.

The hesitation, when does it come into play? Off the line or somewhere else?

Also, how old are the O2 sensors?

Well, typically it seems to only begin to occur after the car has warmed up. Once it's warmed, I start to just every now and then feel a jerk, or miss feeling, when at cruise speed. Can't 'kick it' when cruising and wanting to accelerate because it causes a sputtering, but it does increase speed, it just doesn't feel heatlhy the way it's supposed to. Other times it goes, but you can definitely feel the sputtering/missing. Then you start to feel a little miss when sitting at a stop sign or such. Try to accelerate from stopping and I get that hesitation/sputtering while getting up to speed.

It's been sitting for while now as I've had other things to attend to, so I haven't even been able to pull the plugs and re-inspect. As of right now it is definitely my weekend 'thing to do'.

I've read all the posts dating back to the engine replacement.
I am just going through the same steps myself with a new used engine going in as I speak m.... main bearing problems from a rear intake coolant leak ... or so I'm told.

I have had the problem similar to what you describe. Small jerking like a miss or partial miss at cruising speed. I say partial miss since I never had the rough accelleration, but at cruising speed I got these subtle bumps from the engine that seemed like a misfire.

My fuel pump is getting long in the tooth "a little noisy but still appears to work fine. I would direct my attention to the fuel filter. Restricted flow could lead to "engine side" partial decreases in preasure at cruising speed and the odd injector missfire. Just a thought. Also could be a marginal partially fouled injector. Not bad enough to cause 100% failure but bad enogh to cause the odd bump hear and there.

I have the same symptoms plus HORRIBLE gas mileage. Like half a tank in a day of normal driving. Do you have horrible gas mileage? Whats your fuel pressure?