Low power/no acceleration after warmed up
 

Hey guys,

I've had my blazer 99 for over 5 years now, over the past year it has been getting really low on power after warmed up and hard acceleration, the last couple of months it has got even worse.

Basically, if I push the accelerator down by an 'average' amount, there isn't any noticeable problem, it accelerates normally, however, if I push it to the floor (after warm) it is incredibly unresponsive, it's like it isn't sure what it should do.

If I'm doing about 50mph and the floor it, it hesitates, then changes down a gear, no acceleration, so it changes down another gear, and still no acceleration. The speed stays the same. It only does this after it's warm. When engine is cold it accelerates normally.

I should mention that a couple of times while warm, and in the summer, I would pull up to traffic lights and the engine would just cut out, it would restart immediately after turning the key and drive as if nothing happened. It hasn't done this for months, or ever in the winter.

I thought the issues could be the transmission or torque converter, but I had it serviced and trans oil changed and there weren't any issues.

So, over the last couple of weeks I have changed the air filter (which was in terrible condition, I wouldn't be surprised if any chunks of it found it's way past the wire mesh and into the intake :s), I have cleaned the MAF sensor, and this morning did the EGR.

I felt like it could be the EGR, but cleaning it hasn't seemed to make any difference.

You guys thoughts would be appreciated :)

Thanks,

Adam

I had the EXACT same problem with my 01, and it slowly got worse, to the point where it wouldn't go above 20MPH when warm. The catalytic converter was the culprit in my case. There are 2 different styles of exhaust on the 4.3 blazers, and I can't seem to find exactly where the cutoff is between the two, but most blazers have a bolt in cat that is replaceable on its own, bolted to a 1-piece Y-Pipe, whereas others have the cat as part of the 2 piece Y-pipe, with a smaller cat on the passengers side of the Y. The latter is not at all fun to deal with, and vastly more expensive.

I've been experiencing similar symptoms in my 2000 Blazer 4WD.

Once the truck has been driven a little while, I experience sluggish acceleration for a moment until the truck decides to shift into a higher gear. It sounds like a huge fan blowing under the hood. I notice the Temp gauge likes to toggle a little past the middle when this happens.

I replaced so many sensors already. Cant figure it out. My only thoughts is bad O2 sensors or clogged Cat Converter / Muffler.

Any advice on this symptom will be much appreciate...

Not the answer you need, but an unresponsive EGR would be bad ping at part throttle. EGR at all time would die at idle.

had the same issue, replace a ton of sensors and exhaust and a few other things and somewhere in there it got better, honestly cant remember what i replaced that made it better. but id start with exhaust and work from there, went from stock to duals on my 2001

Low power
 

EXACT same problem with my 01 Blazer. Took it to muffler shop this AM. The first (smaller) cat insides were shattered and blocked the second (larger) cat. I eliminated the smaller and had a new larger one installed. Works like a charm now. Hope this helps!!!! It did with mine.

Big dean/ Krafty,
Thanks for the response. Im going to look into ordering a new exhaust system this week. I'll leave the headers alone.

I'll post back the end results with the new repair.
*crosses fingers*

Take a look at Summit Racing. Just replaced the cat/pre-cat/y-pipe with one from them minus the pre-cat. $170 shipped to my door in very short order. Direct bolt in for a 2000 2dr 4wd. You will only need to get the gaskets.

AJ - thanks for the tip!

I just ordered a magnaflo cat direct fit ($607) and the gaskets you mentioned all from summit racing. Also used the online assistant to get the right part number for the gaskets. Pretty cool feature that summit racing offers.

Figured I'd go ahead and grab the O2 sensors from amazon.com. (ACDelco AFS105) as well. $25.00 ea x 3
Cant beat that!

As soon as it arrives, I'll install and update.

Update:

Installed new muffler, direct fit cat converter, & 3 new Oxygen sensors.

Drove around for a few miles and the truck was running fine. As i drove into around the 8th mile, the sluggish acceleration surfaced. (Along with the loud fan noise when accelerating)

Im completely lost and frustrated now...

when the truck is experiancing the issue open the hood and feel how hot the ign coil is. Maybe it's getting weak?

Sounds like something is messed up that isn't used in open loop but used in closed loop after warmed up. If i am thinking right there are 2 temp sensors on the vehicle, one for gauge and one for the ECU. I would suspect the one for the ECU, someone with a scan tool with data display could easily test it. It's also possible to ohm them out with a multimeter

I believe that year only has one sensor for the computer and gauge.
Has fuel pressure ever been checked? Fuel filter ever been changed?
Any check engine codes?

you are correct, 98-up had only one so if the temp gauge works then that isn't it

I replaced the "engine coolant temp sensor" and fuel filter about a month ago. And No Codes pop up. No Engine light or nothing.

Fuel pressure was at 60psi when started up. The needle shot way past, then settled. 60psi is where it set, then would drop to about 55psi after about 10min of idle.

I know there is a 65psi minimum. But if the problem is the fuel pump, "would this be the cause of my symptoms"?

My 99 is doing the same thing. Can u please post up if you figure out what it is?

Correction with the PSI readings. They are as follows;

1st switch, eng off - jumps to 64psi then falls to 54psi
2nd switch, eng off - jumps to 64psi then falls to 54psi
start car - sits at 53-54psi
slow rev to 2000 rpm - holds steady @ 53-54 psi
punch pedal down real quick - jumps to 64psi
idle for 5min - vehicle runs steady at 53-54psi
turn off engine - spikes up to 64psi then falls to 57psi
engine off for 10min - falls down to 45psi

engine off for 10min - falls down to 45psi

Problem, needs to stay above 55 for ten minuets with key on engine off.
May not be only problem but it is a problem.

After explaining my symptoms to several outlets, the fuel pump has came up as "the issue", once or twice.

the thing that throws me off though, is that my truck doesn't sputter/die after idling too long. And the sluggish acceleration is only consistent after it is warmed up but disappears when it has been turned off for a while.

I don't like messing with fuel, so I'll take it to a local mechanic and have them do a Fuel Pressure test and Fuel Pump test professionally by themselves.

I pray that they find something less expensive ! lol

I've had the luxury of replacing several sensors with zero results. :icon_doh: (sarcasm implied)

i'll definitely post my results.

I just replaced my fuel pump last week and mine is still doing what yours is doing

Anybody try just driving around with the MAF unplugged?

What's the MAF? How do I unplug it?

Out of curiosity,
1. Did you use a Delphi, Ac delco, or OEM pump?
2. Did your truck run great after the replacement, then after several miles the sluggish acceleration surfaced again?

Here this shows the MAF sensor.

I have a new one. Replaced about 2 months ago along with spark plugs/cap/ rotor/ wires. Replaced all at the same time.

Truck ran great for one night. Then sluggish acceleration surfaced again.

I can't sleep anymore, so I'll go unplug it and drive around after i test my pump relay w/volt meter.
Then im going to take fuel pressure readings while the truck is acting up. I'll post result in a few hrs

Update:
-Tested my relay, relay was fine.
-Drove truck until symptoms of sluggish acceleration (accompanied w/ loud fan noise under hood) and gave fuel pressure test.
(I can give readings, but they are irrelevant)
Drove truck around a little more until symptoms were very prominent, then pulled over and turned truck off, immediately unplugged MAF sensor, turned truck back on and drove off. Symptoms went away and truck drove fine to my house 3 miles away.

Does this mean i have a bad MAF Sensor? (Although i bought it 2 months ago?)

thats what it sounds like dude ive had to have my maf and air temp unplugged for about 1-1 1/2 years nows because i dont have the money to get them replaced but if i plug mine in it will barely move when warm unplug them running or not and it revs up to about 1500 then drops to 650 and runs perfect so yeah id say your maf or air temp is bad

btw mine is a 96 2wd

edit theres a way of testing both using a dmm just not sure what the readings are suposed to be or anything but they should be easy enough to find using google

Anybody running any special air filter?

If it work unplugged, then I'll unplug it for the time being. I have a DMM so I'll look into finding out how to test those two sensors before replacing again. I'd like to run the truck with all the sensors operating, if at all possible.

And "No special air filter" being used. just an ordinary K&N from autozone. no mod's done to the engine yet.

Im gonna go drive the truck around a little more to see if anything surfaces. I ran the truck with the MAF unplugged (about 1month ago) and it started running funny. but since then I have replaced the Cat/Muffler and 3 oxygen sensors. And now we have a different story... "so far"...

my experience with running without it is that your gas mileage wont be perfect and youll be lacking in performance but itll run just fine as a "get you there" until you can get it fixed

If its a K&N oiled filter throw it the F out. The oil screws with the MAF. Put in stock and clean the MAF. That's kind of what I meant by "special". K&N's are specially made to screw up MAF sensors. Bet you will be fine after.

No, it's stock. Not an oiled filter

But I do regret to inform the masses, i drove around just now after having the car sit for a few hrs (MAF still UNplugged) and the symptom came right back.

I'll still check the sensor with a DMM, but back to the drawing board nonetheless.

Get yourself a scanner and quit the guessing game. If you have a smartphone or tablet you can use a program called Torque along with a cheap Chinese scanner off of DX.com or Amazon.

have we ruled out clogged cat?

Yes. I installed new muffler/ direct fit cat/ 3 Oxygen sensors (ACDelco) just a few days ago.

And I just ordered an OBD2 dongle as "burned" had recently suggested.

Im researching Fuel Pressure Regulator and the Fuel injectors right now. I have a feeling it may be the faulty spider assembly.
(I hit 160,000 miles today)

fuel regulator is all about leakdown, your test results earlier dont show me any signs of immediate problems. Its clearly not 100% but driveability shouldn't suffer. But if a poppet is sticking it "could" cause a problem but you would surely get a misfire code with that. I would get a scan tool with data readouts form the sensor and monitor it when it's messing up to see what is out of whack

Yeah, I did just order a wireless OBD2 dongle last night and should be able to mess with it when it get here in a week or so. I also have a can of seafoam im gonna use and see how it runs.

I unplugged my MAF and it runs way better. But my check engine light came on. I plugged it back in and it's still on. Would the MAF have caused this? Or is it something else?

I think the check engine light 'is still on' because it was set and needs to be 'erased' from the PCM memory. Some are automatically erased after so many restarts without the DTC showing up.

my 95 blazer was doing the exact same things...sluggish/no power after warmed up loud fan noise. i replaced fuel filter sensor after sensor still wasnt fixed i got frustrated and sent it to a mechanic friend of mine to look at he adjusted the timing after that the truck runs great no issues no loud fan noise has great power and much better gas mileage im not much of a mechanic but whatever he did to the timing sure fixed my issues that are the same your having hope this helps