Hesitation, staggering on acceleration and poor gas mileage.

[JoshBarber]

I did a search, but wanted to see if anyone currently on the board had any suggestions with this.

98 Chevy Blazer LT w/ 4whl Drive
Approx 120k miles

Last "tune up" (wires/plugs/cap/rotor) was less than a year ago.
Last fuel filter replacement was less then 4k miles ago

Ran a injector cleaner a week ago...with some, yet little improvement.
Vehicle still seems sluggish.

I had a feeling it was more of a sensor issue...something with MAS or MAP, but I have no warning lights, and the computer shows no error codes. I dont want to replace either for $100 + and find out its neither.

Any common issues that people have found and fixed?

[JoshBarber]

Noone at all has any advice here?

[MT-2500]

Well I will get you started.
What engine?
What kind of spark plugs? Air filter? Any missing?
How is that fuel pressure?
Hard to start cold.
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.

Pull plugs and have a look at them.
And double check that fuel filter.
Check for good hot blue spark to aall plugs.
Also if good fuel pressure and good ignition.
You may need to check that back pressure on the exhust system.
MT

[JoshBarber]

I do have trouble cold starting. Usually takes the second time around.
I dont want to sound too stupid, but once I get a fuel pressure gauge, how do I connect it to check?
thanks
J

[swalt]

Is it constant or intermittent? You mentioned all the basics that you replaced, but wires have been known to fail. If you say intermittent, are the outside conditions damp, or cold and the problem presents itself (staggering) after a few minutes of driving. Do you have problems after rain or a carwash?

[JoshBarber]

intermittant......and I havent found any consistent conditions that contribute to or lessen the effect.

[BlazerLT]

MAF sensor needs cleaning.

[JoshBarber]

MAF is clean

[MT-2500]

Originally Posted by JoshBarber

I do have trouble cold starting. Usually takes the second time around.
I dont want to sound too stupid, but once I get a fuel pressure gauge, how do I connect it to check?
thanks
J

There is a test port/adpter on your fuel rail.
A good type fuel pressure gauge will have the fittings to hook it up.
Even if no cold start problems you need to run a the full fuel pressure test.
It is the only way to seperated from a fuel problem or other.
Tape the fuel gauge to windshield or mirrow and have it on there when it does it.
MT

[blazee]

Regardless of personal feelings and past behavior, personal attacks can not and will not be tolerated. I have removed all the inappropriate material from this thread. If this continues, I'll be forced to lock this thread.

[BlazerLT]

I would still point the finger at a malfunctioning MAF sensor.

Most hesitation on tuned up engines is caused by it.

[JoshBarber]

if both sides of the connection are clean, what more can you do other than replace it? I was trying to get a more definate answer before I dropped $100+ and realized it was still happening

[MT-2500]

Originally Posted by JoshBarber

if both sides of the connection are clean, what more can you do other than replace it? I was trying to get a more definate answer before I dropped $100+ and realized it was still happening

A lot of times a good cleaning can help a MAF sensor.
Get some good quick dry electrical cleaner or the special MAT sensor cleaner and just spary the sensor wires inside it good. Do it at least twice spray and let dry and spray it again. No scrubbing or rubbing. Carb cleaner is it next best cleaner.
If you are running a K & N air filter go easy on the oil in it. The oil from them will get in MAF and air tempt sensors and throw them off. Or even road dust from a regular air filter will get dirt in a MAF sensor.
Clean it and see if it helps. Check fuel filter and fuel pressure to post back readings.
How is the spark plugs? How old and what kind? AC-delco?
MT

[JoshBarber]

thanks MT.
Will spray it anyway just as an attempt. I would think it wouldve set off a check engine light if there was a problem with it though. will check the plugs also. replaced them not even a year ago with properly gapped AC Delco plugs.

[swalt]

Josh, You mentioned you did an injector flush, but was this a fuel additive or did you have a professional flush done?

In the past, my mechanic has always done the fuel flush with the single can (IV setup) to the Shrader valve, got the truck running on the cleaner and then pulled the fuel pump relay to run the truck simply on the cleaner. His shop recently switched over to a 3 bottle system. Two bottles hang on the IV rack, one to the Shrader, one hose into the throttle body and a can in the tank afterwards. It does a full cleaning and takes about 30 minutes for the truck to go through the can. The throttle body attachment is like a small injector that sprays into the barrel as the truck idles. My throttle body and butterfly valve had quite a bit of carbon. After the cleaning, a nice bright aluminum/gold colour. Just a thought. I never realized how sluggish my truck felt until after having the system cleaned in this manner. Throttle response is like night and day.