Loss of top end power

OK here we go. 1998 Blazer LT 4 Door 4X4 W 4.3. 137K miles. Recently changed plugs, wires, cap and rotor. Changed the fuel filter about 15K miles ago and I cleaned the throttle body about 5K miles ago. I run Mobil 1 5w-30 and I ran a bottle of techtron and 93 octane through to clean a little better. Basically at 60 miles an hour or higher if I floor it or give it a good amount of gas It kind of surges up to speed. The tach will hit like 3K RPMS and then surge upwards sometimes slow and sometimes fast, almost like it is bogging down as if a carb was out of sync, I know my truck is fuel injected I:evillol: have not cleaned the EGR, is that my next step? Oh and it is not throwing any codes. It was misfiring before I did the tuneup but that seemed to take care of it. Also, sometimes it starts rough like it is not getting enough gas until I give it some and then the shaking and shimmying stops and does not come back until restarted. Right before the tuneup it was running terrible, for a week after the tuneup it ran perfect, and now it is just running a little funny with the surging and with the idling rough. One more thing that has gone wrong recently is the gas gauge goes crazy sometimes and bounces all over, I have heard that could be a sign of a failing fuel pump and a bad sending unit. Thanks Everyone.

sounds to me like a possible fuel pressure problem.

OK here we go. 1998 Blazer LT 4 Door 4X4 W 4.3. 137K miles. Recently changed plugs, wires, cap and rotor. Changed the fuel filter about 15K miles ago and I cleaned the throttle body about 5K miles ago. I run Mobil 1 5w-30 and I ran a bottle of techtron and 93 octane through to clean a little better. Basically at 60 miles an hour or higher if I floor it or give it a good amount of gas It kind of surges up to speed. The tach will hit like 3K RPMS and then surge upwards sometimes slow and sometimes fast, almost like it is bogging down as if a carb was out of sync, I know my truck is fuel injected I:evillol: have not cleaned the EGR, is that my next step? Oh and it is not throwing any codes. It was misfiring before I did the tuneup but that seemed to take care of it. Also, sometimes it starts rough like it is not getting enough gas until I give it some and then the shaking and shimmying stops and does not come back until restarted. Right before the tuneup it was running terrible, for a week after the tuneup it ran perfect, and now it is just running a little funny with the surging and with the idling rough. One more thing that has gone wrong recently is the gas gauge goes crazy sometimes and bounces all over, I have heard that could be a sign of a failing fuel pump and a bad sending unit. Thanks Everyone.


Here is a good thing to check or a place to start..
Hard to start cold or lose of power.
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.
MT

I can try that, not sure when but soon. Would loss of fuel pressure throw a SES? Thanks by the way

I can try that, not sure when but soon. Would loss of fuel pressure throw a SES? Thanks by the way

No it will not set any direct codes.
The computer has no way to tell what the fuel pressure is.
But fuel trim and other senser reading may point to low fuel pressure.
MT

Sounds normal to me.

This engine doesn't start to produce power until after 3000rpms.

The air resistance at that speed is what is holding it back.

WEith my CPI, when I hit 3000rpms and the IMTV valve kicks in, it is like a mini-turbo spooled up and the engine really takes off.

But it never did this before. :)

Sounds normal to me.

This engine doesn't start to produce power until after 3000rpms.

The air resistance at that speed is what is holding it back.

WEith my CPI, when I hit 3000rpms and the IMTV valve kicks in, it is like a mini-turbo spooled up and the engine really takes off.

What brand of spark plugs did you put in the blazer?

AC Delco Plats all the way

Have you lately reoiled your air filter?

Begining of last summer

Info I've read on fuel pressure was minimum 60 psi cold start and 54 running.
If the gauge is bad time to change the pump anyway (1 piece on these). As above on oiling, clean the MAF sensor. Rough idle can be caused by injection poppet problems. If this does not occur while reving while parked, what about the trans converter slipping.

Begining of last summer

I would clean your MAF again.

Sounds like it is not able to detect the air flow at higher rpms.

Would make sense. I may have over oiled the filter, so I let it sit in the sun for a while the other day and now it looks like it did when I first got it. I will clean the MAF again. Thanks

Remember to use brake cleaner and a gentle toothbrush.

Be REALLY gentle and massage the gunk off the filament wires.

Brake cleaner or electronics cleaner used to be the best choices for cleaning the MAF, but now there's a better (safer) alternative:

http://www.midwayautosupply.com/images/crc/05110_3X.jpg

Well well....

Good one bud.

Even though the MAF cleaner is safer, I'll probably still personally use brake cleaner because it's half the price and I've never seen anyone have problems as long as they were real careful.

I know this sounds dumb but Im an IT tech, and I know that just out of the blue, cables will come loose, so try checking all your wire connections.....It never hurts to check...also you may want to make sure one or more spark plugs are not loose...sometimes its the obviouse that stumps us.

well put nickledimed

Have you lately reoiled your air filter?

Excellent question!

I was scrollling for it after seeing his first mod in his list...


EDIT:...

That MAF filament is fragile, and ain't cheap. Maybe instead of a toothbrush, use the previously recommended fluid cleaner, and a [new] paintbrush. The bristles might be a little finer. Then put the vacuum to it, with your PC keyboard vacuum attachment brush to the filamant. That one also is fine-bristled...

PROFILE EDIT:
Nothin' like the smell of NAPALM in the mornin', huh Blazee!!!

mmmmmmmMMMMMMMMmmmmmmmmmmmm! yum!

PROFILE EDIT:
Nothin' like the smell of NAPALM in the mornin', huh Blazee!!!

It smells like victory!

ive been following this thread, cuz ive noticed mine kinda of dogs on the high way and above 3000, anything above that it just makes noise, under 3000 though it takes off. But i dont normally let it go past 3500. I went to clean my MAF, and it was dirty like it was its job. I was trying to figure out why so dirty. I went to clean my cone filter(i have a CAI), where rubber top part of the filter meets the metal part of the filter was complety ripped off underneath, out of sight:banghead: soo i ran out and got a new cone and started it up there is a improvement. I was supprised something like that can make that kind of differnce.

1997 4dr ls

One question though, of the MAF i know it has to face one way. screen towards filter, but as how it sits, the the large plastic part w/ the wire harness click in, I have mine face the drivers fender. Does it matter how it sits?

ive been following this thread, cuz ive noticed mine kinda of dogs on the high way and above 3000, anything above that it just makes noise, under 3000 though it takes off. But i dont normally let it go past 3500. I went to clean my MAF, and it was dirty like it was its job. I was trying to figure out why so dirty. I went to clean my cone filter(i have a CAI), where rubber top part of the filter meets the metal part of the filter was complety ripped off underneath, out of sight:banghead: soo i ran out and got a new cone and started it up there is a improvement. I was supprised something like that can make that kind of differnce.

1997 4dr ls

One question though, of the MAF i know it has to face one way. screen towards filter, but as how it sits, the the large plastic part w/ the wire harness click in, I have mine face the drivers fender. Does it matter how it sits?

I don't think so.

Just don't overoil that filter.

And having a 1997, be mindful of a possible ignition switch module replacement in the near future.

I haven't posted in a while, But there is one more thing to check. Look at the vacume tower located on the intake plenum just follow the vacume booster brake hose back to the plenum, that thing with the multiple fittings on it is temperature activated, has a real effect on performance if its bad replace it. Night and day difference!

I don't think so.

Just don't overoil that filter.

And having a 1997, be mindful of a possible ignition switch module replacement in the near future.


the switch was acting up a while ago, but now that its warm im not having any problems so well see i probly should just replace it any way once i get a lil extra change though its not fun sitting on the side of the road wating for AAA to come

But i tested the MAF cleaing again, it does have a bit more power all over, and i gave it all she had till about 75 it picked up alot better but i smelled oil buring for a few secs, so i packed off real qucik and babied it home and looked at it, engine and tranny levels were fine and no sings or a leak but i wont be doing that again any time soon

It smells like victory!

You're close, blazee...


It smells like ... ??? ... [look around for insight] ... victory!

the switch was acting up a while ago, but now that its warm im not having any problems so well see i probly should just replace it any way once i get a lil extra change though its not fun sitting on the side of the road wating for AAA to come

But i tested the MAF cleaing again, it does have a bit more power all over, and i gave it all she had till about 75 it picked up alot better but i smelled oil buring for a few secs, so i packed off real qucik and babied it home and looked at it, engine and tranny levels were fine and no sings or a leak but i wont be doing that again any time soon

NICE PIC, Esl!...


More than mine will do. BUT are both ends of the rear axle turnin' equal???:wink: :wink: :wink:

And if you go with front lock-up, what'll happen?

NICE PIC, Esl!...


More than mine will do. BUT are both ends of the rear axle turnin' equal???:wink: :wink: :wink:

And if you go with front lock-up, what'll happen?



haha no one wheel burners :frown: i wanna get a limited slip sooo bad in the rain if im on any type of hill or if im on the white lines on the road, that wheel just keeps breaking lose it gets old quick, id rather have the back end slide then one wheel takin all the power and i know its bad for the diff on one wheel spins oh well if i want a hot rod, it get a maro or a stang but this is getting off topic

Having a cold air intake system, how often should i clean the MAF? I do use a light pressure washer about every other, or every weekend on the engine when i wash my car its kind of hard to to get the filter soaked im sure some mist gets sucked up after that

haha no one wheel burners :frown: i wanna get a limited slip sooo bad in the rain if im on any type of hill or if im on the white lines on the road, that wheel just keeps breaking lose it gets old quick, id rather have the back end slide then one wheel takin all the power and i know its bad for the diff on one wheel spins oh well if i want a hot rod, it get a maro or a stang but this is getting off topic

Having a cold air intake system, how often should i clean the MAF? I do use a light pressure washer about every other, or every weekend on the engine when i wash my car its kind of hard to to get the filter soaked im sure some mist gets sucked up after that

Gosh! I wouldn't play around too much with the MAF filament. It ain't cheap. With a K&N, as I have, I'd go light on the oil, and let any excess pull thru. Even then, Gordon Killebrew, the C4 [corvette] guru, said you can get away with pulling the MAF screen, but in fewer years, your filament would take the hit.

Even the old C3 vettes had w/w fluid on the intake, for cooling, however, that was before EFI of any sort.

The MAF is the vehicle's FIRST calculation in air/fuel mix, so use caution...

Gosh! I wouldn't play around too much with the MAF filament. It ain't cheap. With a K&N, as I have, I'd go light on the oil, and let any excess pull thru. Even then, Gordon Killebrew, the C4 [corvette] guru, said you can get away with pulling the MAF screen, but in fewer years, your filament would take the hit.

Even the old C3 vettes had w/w fluid on the intake, for cooling, however, that was before EFI of any sort.

The MAF is the vehicle's FIRST calculation in air/fuel mix, so use caution...



I wasnt plaing on touching it again...... for ever it has almost 120,000 miles on it i figuerd it was fine, but just thought to ask, and the screen after many conclusive proof from blazerlt and some other guys it can only hurt it, i wont get any gains, so that stayed.
thanx for your input

Yeah, but definitely check Fuel pressure with a gage. I was having wierd surging and lunging at highway speeds all over the RPM range when trying to get a little boost to climb the hills out here until the fuel pump quit. Replaced it with an O.E. Bosch, rather than a Delphi or Cardone replacement and She starts like a firecracker when cold. (64 PSI) She drops and levels off to about 57 PSI when idle. But after that, a new in-tank sock and a new Deustch fuel filter, she feels like she can haul the rock of Gibraltar and still pass on inclines. :D

Ok so I cleaned the MAF and the throttle body, truck ran fine for a few days then back to acting up. So I disconnect the the MAF and everything runs better but of course the SES light is on. Think I ruined the MAF by over oiling the K&N Filter??? :(

That could have happened and removing the wire puts the truck in limp home mode which is rich.

MAF's are actually quite cheap at Advance auto parts.

Still trying to figure out why when I give it some gas it kind of rocks the engine and then idles smoothly or revs smoothly at that point. This does not happen all the time but is getting more frequent and quite a pain in the ass at this point. I am losing power somewhere and I have yet to have a chance to check fuel pressure, I was thinking of replacing the pump since the sending unit has gone bad. Tuesday my truck goes in for some body repair and after that I will concentrate on fixing my engine issues.

Still trying to figure out why when I give it some gas it kind of rocks the engine and then idles smoothly or revs smoothly at that point. This does not happen all the time but is getting more frequent and quite a pain in the ass at this point. I am losing power somewhere and I have yet to have a chance to check fuel pressure, I was thinking of replacing the pump since the sending unit has gone bad. Tuesday my truck goes in for some body repair and after that I will concentrate on fixing my engine issues.

I wouldn't replace unneeded parts when you are saying that unhooking the MAF has the engine smooth out.

Don't start throwing parts at the truck in hope that it will fix your problem.

Well if your sending unit goes bad isn't that sometimes an indicator of a fuel pump going bad? Also unplugging the MAF seemed to smooth things out, waiting for some better weather to test it out as it has been poring again for 3 straight days. Why am I not throwing an SES when i is running shitty? I am planning on doing some major work to my truck this summer after I get married. Another one bites the dusts :)

Last time I saw a contaminated MAF meter, it gave me a P0171 code. Didn't need to touch it with any kind of brush either, just cleaned it by spraying with non-residue electronic spray cleaner from NAPA. Code went away.

Now if I turn the wheel to lock in either direction and then give some gas it shakes and shimmies like it wants to stall but doesn't. This is killing me!!!

When you put a strain on your stearing like that it puts a strain on your engine, this is normal, but its not normal to strain your automatic steering system, this will make it wear out quicker, you should never turn your steering wheel like that unless you absolutly need to.

I agree but I did have to, what is happening with my truck is not near normal, unfortunetly

Truck is in shop for at least a week getting body repair done so I will be driving a 2001 blazer that I have been thinking of scavenging parts from :)

Getting my truck out of the body shop today and they are going to slap a sticker on it and hopefully they will do what I asked, which is take it for a ride and throw the computer on it and find out whay it is acting funny. God I want her running right!!!!!!!!!!!!!!!!!!!!!

So I talked to the dealer and my baby is all fixed, body wise anyway. The mechanics are going to scan it for codes but they want to charge me $95 to hook the computer up and take it for a ride to see what she is doing and why she is running funny. Does that sound right????

So I talked to the dealer and my baby is all fixed, body wise anyway. The mechanics are going to scan it for codes but they want to charge me $95 to hook the computer up and take it for a ride to see what she is doing and why she is running funny. Does that sound right????

If they do a good job and test everything right yes.
Good work is priceless and worth it weight in gold.

But hear is what I would ask for.
Tip on going to the dealer
Ask that only a factory certified gasoline engine performance specialist work on your car.
Not all dealerships are concerned with how repairs are dispatched, and not all dealership techs bother to take advantage of the training offered by factory (the vast majority of which is paid training). If the dealer is uncooperative, ask for your money back and call around for a dealer that will accommodate you.

Good luck and let us know whatt they find.
MT

I will see what I can do, I can't have them do it today as I am so broke from buying a house and getting married soon but I will have it done soon. Thanks guys

I will see what I can do, I can't have them do it today as I am so broke from buying a house and getting married soon but I will have it done soon. Thanks guys

We already know what the problem is.

You said you unplugged the MAF and it smoothed out.

Why you are paying them the US$95 when you could be putting that towards your new MAF is confusing me. Hell, a MAF isn't much more than that.

True, I will take one more test run with the MAF unplugged and see what happens when i start up and run hard on the highway

I have not had a chance to unplug the MAF yet but what could possibly cause the lower rpm's to feel like a misfire and once you pass 2200rpm's or so to be fine? If I ease the throttle very gently I don't feel anything funny, but if I jump on it it stumbles and almost feels like a stick shift car when you let the clutch out to fast.... any ideas???

Unplugged the MAF and issue got worse or stayed same. Can't figure it out!!!

Unplugged the MAF and issue got worse or stayed same. Can't figure it out!!!

Could be a bum TPS or the fuel pressure could not be up to par.

How old is the fuel filter again?

Unplugged the MAF and issue got worse or stayed same. Can't figure it out!!!

Here is how to test the MAF sensor.
You also need to match your Baro readings to you altitude.

BAROMETRIC PRESSURE REFERENCE CHART
Barometric Barometric BARO/MAP Altitude Above
Pressure Pressure PID Sea Level
(in. Hg.) (kPa) (Hz) (ft)
3.5 - 11.8 -89.3
5 - 16.9 -92.8
10 - 33.8 -104.6
15 - 50.7 -117.0 -14,000
20 - 67.5 - 129.6 -10,000
21 - 70.9 - 132.5 -9,000
22 - 74.3 - 135.4 -8,000
23 - 77.7 - 138.3 -7,000
24 - 81.1 - 141.1 -6,000
25 - 84.4 - 144.0 -5,000
26 - 87.8 - 146.9 -4,000
27 - 91.2 - 149.8 -3,000
28 - 94.6 - 152.8 -2,000
29 - 97.9 - 155.8 -1,000
30 - 101.3 158.9 -0 -(sea level

On a fully warmed up engine, look at Long Term Fuel Trim at idle, in Neutral, A/C off, (LONGFT1 and/or LONGFT2 PIDs). If it is more negative than -12%, the fuel system has learned lean corrections which may be due to the MAF sensor over-estimating air flow at idle. Note that both Banks 1 and 2 will exhibit negative corrections for 2-bank system. If only one bank of a 2-bank system has negative corrections, the MAP sensor is probably not contaminated.

3. On a fully warmed up engine, look at MAF voltage at idle, in
Neutral, A/C off (MAF V PID). If it's 30% greater than the nominal MAF V voltage listed in the Powertrain Control/Emissions Diagnosis (PC/ED) Diagnostic Value Reference Charts for your vehicle, or greater than 1.1 volts as a rough guide, the MAF sensor is
over-estimating air flow at idle.

4

If at least two of the previous three steps are true, proceed to disconnect the MAF sensor connector. This puts the vehicle in to Failure Mode and Effects Management (FMEM). In FMEM mode, air flow is inferred by using rpm and throttle position instead of reading the MAF sensor. (!n addition, the BARO value is reset to a base/unlearned value.) If the lean driveability symptoms go away, Replace the MAF sensor. If not go back to the repair manual

MT

MT, thank you. I will attempt to do what you stated and follow your steps.

LT, fuel filter is less then two years old.

Problem seems to be intermittent, sometimes just sitting in park it will only stumble a little when given some throttle, sometimes stumble a lot. And well sometimes not at all. Seriously just feels like it is going to do then all of a sudden takes off, like I said early, as if you were driving a stick and you let the clutch out too fast. :(

MT, thank you. I will attempt to do what you stated and follow your steps.

LT, fuel filter is less then two years old.

Problem seems to be intermittent, sometimes just sitting in park it will only stumble a little when given some throttle, sometimes stumble a lot. And well sometimes not at all. Seriously just feels like it is going to do then all of a sudden takes off, like I said early, as if you were driving a stick and you let the clutch out too fast. :(

Replace the MAF bud, it is more than likely your problem, it controls the fuel curves on acceleration.

I know it does LT but what about when I unplug it, it throws a SES right away, as it should, but the problem does not get any better. Shouldn't it stop the problem at first then the truck will run in limp home mode after?

I know it does LT but what about when I unplug it, it throws a SES right away, as it should, but the problem does not get any better. Shouldn't it stop the problem at first then the truck will run in limp home mode after?

I helped a guy over the phone that had the same problem as you had, he did EVERYTHING and it came down to the MAF was the only thing that he hadn't changed.

He picked one up at Autozone to test it out and it never came back off.

The MAF measures the airflow going into the engine and if it can't do it properly, it will throw everything out of whack.

Test it out, grab one and plug it in and take it for a test drive. If it doesn't solve it, take it back.

Great idea. Question, I think I know the answer but to just make sure. My mother has a 2000 Blazer, same exact MAF I assume correct? I am going to pull hers and put it on mine, that shoud prove if it is the MAF right? Thanks for the help. Funny thing is, no symptoms this morning. Got to love Chevy's!

Yes, it will work.

Will quickly clear out the driveability problems if that is the cause.

I hope so. Funny thing is I jumped in my truck to grab lunch and no problem at all. I can tell I will have issues when I start the truck up and get a bad gas smell when I first start up. Weird