Hesitation on acceleration?

This blazer has hesitation runs rough it had alternator replaced previously, though not due to studdering. It went to shop and mechanic replaced fuel pump which I didn't think it needed. It's my ex husband's truck (he has a bad bad heart in hospital as we speak) mechanic replaced fuel pump, maf sensor(or map sensor) so he says but then truck wouldn't even start. Mechanic said no codes. Cost him 400.00 + 60.00. Got it to my place and the maff/map sensor looked used. My mechanic friend came over and replaced the fuel pressure regulator, then truck started. Drove good cold then started to stumble hesitate again. We took it to advance auto and it read code p0340 and mmisfire either cylinder 4 or 5. He replaced camshaft sensor as tests showed an 11/.8 volts, not 12 volts andd zero. Still hesitation so we replaced coil. Car ran worse. Like a bad erg problem. Please advise

As far as misfire, I can list the possibilities if you want, the list is probably as long as your arm. If you want it, I'll be glad to post list.

Go to this link for more information on hesitation: https://www.2carpros.com/articles/engine-hesitates

I dont have a way to perform the cylinder balance test

This is for misfire isolation. I don't usually unplug any sensor with engine running. This info is from our database. Start engine. Disconnect iac motor. Using insulated pliers, remove one spark plug wire from a spark plug, and ground it against engine. Note engine rpm as wire is grounded, reconnect spark plug wire. Repeat procedure for all cylinders. Stop engine and reconnect iac motor. If engine speed drops equally, within 50 rpms on all cylinders, refer to " rough, unstable or incorrect idle" symptom. If there is no engine rpm drop or no excessive variation on one or more cylinders, check spark or compression on respective cylinder/s.

Some possible causes. Check for restricted exhaust. Bent push rods--broken valve springs--worn cam lobes. Problem with ignition wires. CCheck distributor cap for dust--cracks-- moisture. Check ignition system for faulty grounds. Check spark plug tips for wetness-- heavy deposits, anything that doesn't look right. Check poor fuel quality and fuel pressure. Check egr valve. Check ecm for proper grounds. Check tps. I'm sure I probably left something out.

My blazer has a bad "hesitation" problem when I 1st start it up in the morning and after a period of being turned off. I just had a tune up and a new fuel pump put in but it still acts the same as it did before! Any Ideas?

Have the injector poppets, scfi fuel system, been cleaned?

Are there any misfire codes? If there is a misfire code, it should point you at the problem cylinder. Some of the national brand auto stores will check codes for free.

There are bulletins about this fuel system.

When accelerating gently the truck does a jerky hesitation, but not when pushing the pedal about half way. I did a complete tune up about 20,000 miles ago - plugs, wires, cap and rotor, air and fuel filters, PCV valve.

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

Dear Professional Mechanics,

I am facing problems with my Blazer for the last months. The problem started with a speed variatiion
when the car is idle. After that it hesitates driving and accelerating.
No error message was found I stared to replace the following:
1- throttle position sensor;
2 - changed all the spark plugs;
3- fuel injector cleaned
4 - speed sensor
5- Gas Pump and filter;
6- idle air control
7 - coil tested ok

One issue was detected related to the temperature
it seems the engine is running cold. (75 centigrates)

Is it possible to loose power when the engine is running under low temperature?

Thank in advance for any help.

Regards,
Gaspar - Brazil

Here is something to try, disconnect the MAF sensor located on the air cleaner hose and drive it, and see if you have power then.

Hi, I have a 1998 Chevy S-10 Blazer that has a problem when I try to accelerate. When I push on the gas pedal 1/2 way to full throttle, it would hesitate and loose power and it would sound like it has no gas going into the engine until I let off the pedal and then it would work fine. I noticed this a few months ago and it was a problem to me but no trouble codes showed up. Now it has a hard time starting and idling and it keeps dying after 30 seconds or so. After 4 to 5 restarts, it will stay idling but I cant go more than 1/2 way down on the gas pedal otherwise it will feel like it wants to stall. I replaced the fuel pump, fuel filter, throttle posititioning Sensor, and air filter. I cleaned the trottle assembly and MAF sensor and a small sensor that is located next to the MAF sensor. I think it may be the Fuel pressure regulator, but I could be wrong. Any ideas or input on this fuel related problem? Let me know what you think. Thanks.

Possibilities: Inspect and test all the following listed below:

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard

While my truck is cold it runs like a dream but as soon as it gets to normal running temp it begins to hesitate like it wants to stall, and if I don't quickly rev the engine it will. I have to pull over and rev the engine a few times and it eventually clears, you smell a burn off and then it acts fine. It happens the same time everyday and on a bad day it can happen up to 5 times. Any ideas on why this happens?

Lack of acceleration, chugging, hesitating, jerking, bogging, misfiring etc. Could be caused by one of the following below:

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard it.

I have a 1992 chevy s-10 blazer. When I push on the gas pedal to accelarate it hesitates like it is out of gas but I have a full tank of gas in it. I can accelerate to the speed limit but while I am driving it still hesitates, almost like it is bucking or slowing down or losing power some how. What would be the things I need to look at?

Inspect and test all the following listed below:

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard

Fine driving in the dry. Just after or during rain fall it is as if I am running out of gas (on a 1/2 or full tank of gas). Thinking electrical sprkwhr. Dist. Coil. Something?

With the engine running on a dry warm night or in a dark garage take a spray bottle of salt water and water and spray them slowly on each part of the ignition system. You should see the electricity arc through the mixture when you find hte bad part or the vehicle will start to idle or run roughly.