Often overlooked! Cause of a lot of problems!

The fuses. all of the other electriclal connections have seals and connectors. the fuses are open to the elements. And just because there is a cover over them, there is no cover on the bottom. Has anyone ever taken out a fuse and looked at the blades? Are they silver or brown? most of your trouble could be coming from something as simple as this. Pull your fuses and take a look at them!! If they are not making a good electrical connection CLEAN THEM! Be it with a pencil erasure or emery cloth. Just check them. And remember, just because they are not blown has nothing to do with the connection.

i wanted to add something to this thead of overlooked items:
The MAF sensor


I had the typical sluggish performance, hesitation, gasping for air, hard to go up hills. I replaced the Plugs, wires, cap, rotor, PCV, fuel filter. i should have stopped right there and confirmed a bad MAF, but the voltage was right on. So i kept going replacing the Cat, the muffler, the O2 sensro, trying different fuels.....on and on. Until my buddy who drives a Blazer by chance mentioned plugging his MAF into my truck, i said what the hell, and it drove like a million bucks. I can only assume that it was intermittently failing. One way to tell if this is the problem is the burnout. If you cant even hold the brake and burn out without it sputtering you probably have a bad MAF. Well i hope this finds some desperate person well.

I agree, check the simplist things first , don't replace anything until you rule out things like vacuum hoses, inline fuses (Battery), battery posts corosion (poor a coke on it and then wash it off), Security light on (read owners manual) this is why a lot of late model Blazers turn over and will not start (cuts power to the fuel injectors), Bad sparkplug wires (missing), After a rain or in the early morning truck does not start (water vapor in the cap), after going through a puddle and truck dies (air filter wet), In wet weather no power (loose engine or transmision ground), wipers do not work (unclip elec connection at the wiper motor and push pins toward the front and reconnect, push on the conector while wiper switch is engaged and see if they operate), and so on. Check the simplist thing first, and with the money and agrevation that you don't have to go through, take a night out.

A lot of the time you don't have to replace the MAF. They are fairly easy to clean... JUST BE CAREFUL OF THE WIRES!!!
Run a search on the forum for MAF and you will find a clear and concise description and step by step procedure for cleaning the MAF. After I cleaned mine it ran 1000 times better -- okay maybe only 100 times, but you know....

The fuses. all of the other electriclal connections have seals and connectors. the fuses are open to the elements. And just because there is a cover over them, there is no cover on the bottom. Has anyone ever taken out a fuse and looked at the blades? Are they silver or brown? most of your trouble could be coming from something as simple as this. Pull your fuses and take a look at them!! If they are not making a good electrical connection CLEAN THEM! Be it with a pencil erasure or emery cloth. Just check them. And remember, just because they are not blown has nothing to do with the connection.

Lets start before that
Try this method
Strategy Based Diagnosis
The goal of Strategy Based Diagnostics is to provide guidance when you create a plan of action for each specific diagnostic situation. Following a similar plan for each diagnostic situation, you will achieve maximum efficiency when you diagnose and repair vehicles.
(1) Verify the Customer Concern: The first part of this step is to obtain as much information as possible from the customer. Are there aftermarket accessories on the vehicle? When does the condition occur? Where does the condition occur? How long does the condition last? How often does the condition occur? In order to verify the concern, the technician should be familiar with the normal operation of the system and refer to the owner or service manual for any information needed.
(2) Preliminary Checks: Conduct a thorough visual inspection. Detect unusual sounds or odors. Gather diagnostic trouble code (DTC) information in order to achieve an effective repair.
(3) Perform Published Diagnostic System Checks: One or more DTCs may not support a system. System checks verify the proper operation of the system. This will lead the technician in an organized approach to diagnostics.
(4) Check Bulletins, Recalls and Preliminary Information (PI)s.
(5.1) Stored DTCs: Follow the designated DTC table exactly in order to make an effective repair.
(5.2) Symptom No DTC: Select the symptom from the symptom tables. Follow the diagnostic steps or suggestions in order to complete the repair, or refer to the applicable component/system check.
(5.3) No Published Diagnostics: Analyze the Concern. Develop a plan for the diagnostics. The service manual schematics will help you to see system power, ground, input and output circuits. You can also identify splices and other areas where multiple circuits are tied together. Look at component locations to see if components, connectors or harnesses may be exposed to extreme temperature, moisture, road salt or other corrosives battery acid, oil or other fluids. Utilize the wiring diagrams, system description and operation, and system circuit description.
(5.4) Intermittents: An intermittent condition is one that does not occur continuously and will occur when certain conditions are met. Generally, intermittents are caused by faulty electrical connections and wiring, malfunctioning components, electromagnetic/radio frequency interference, and aftermarket equipment. Combine technician knowledge with efficient use of the available service information. Evaluate the symptoms and conditions described by the customer. Use a check sheet or other method in order to identify the component. Follow the suggestions for intermittent diagnosis found in the service manual. The Tech 1 and Tech 2 scan tools, and the J 39200 (Fluke 87) have data capturing capabilities that can assist in detection of intermittents.
(5.5) Vehicle Operates as Designed: This condition exists when the vehicle is found to operate normally. The condition described by the customer may be normal. Verify against another like vehicle that is operating normally under the same conditions described by the customer. Explain your findings and the operation of that system to the customer.
(6) Re-examine the Concern: If a technician cannot successfully find or isolate the concern, a re-evaluation is necessary. Re-verify the concern. The concern could be an intermittent or normal.
(7) Repair and Verify Fix: After isolating the cause, make the repairs and validate for proper operation. Verify that the symptom has been corrected, which may involve road testing the vehicle.

A lot of the time you don't have to replace the MAF. They are fairly easy to clean... JUST BE CAREFUL OF THE WIRES!!!
Run a search on the forum for MAF and you will find a clear and concise description and step by step procedure for cleaning the MAF. After I cleaned mine it ran 1000 times better -- okay maybe only 100 times, but you know....




That is true, i cleaned mine and it seemed to help, enough for me to convince myself it wasnt the culprit. But it was beyond fixable as it was.

Also a second or third opinion is allowed, HAVE SOMEONE ELSE drive it , Pay a dealer if all else fails for a diagnostic, just play stupid, and pay for not more than for 1 hour of testing. After they tell you what it is, CHANGE IT YOURSELF!! remember you don't need a scanner to get a trouble code, you can do it with a paper clip and watch and count the times that the check engine light flashes get a chilton or haynes manual,it will give you a step by step procedure, and i'm sure if asked someone on this forum will provide you with the directions. Do not change the item that the code provides , check the system that the item belongs to it could be a bad connection. Or something else, remember a code only provides you a guide!

1996 and newer vehicles REQUIRE that a scanner be used to retrieve DTC's. These vehicles have OBDII and even the highest quality paperclips WILL NOT WORK! Moral of the story: Don't buy your automotive test equipment at Office Depot.

My mistake. thanks for the correction. I keep thinking of the 86 that I had. I now have a 98 . I also have a hypertec that also shows DTC's. Another tip if you suspect that you have a clogged muffler or cat, Pull a few of your oxygen sensors above the cat. After removal plug them back in and let them hang. Start your truck, if it runs a lot better you have a clog. If not, its not in the exhaust. Now is a good time to take a look at your sensors and see what color the probes are. If covered in oil or ash or just plain clogged check upstream. now check your trans ground. then your trans elec connection. And so on, I mean your down there anyway why not look?

Please check your connections!! As I look at most of the questions a lot of them can be fixed just by checking your connections. If you have a aftermarket remote starter you have a passlock adapter installed . If any of the wire's are loose you will get a security override, and your Blazer will not start.

your 4L60e transmision is computor controled you have 3 connections on it. The most important one is on the passenger side next to the dipstick, this connection has a tendency to rise up about a quarter of an inch, causing bad shifting and destroying your Blazers gas mileage! Push this back down into the socket. Next check all of the connections on the transfer case especially the vacumn cluster on the top.

Bad speakers in the doors, with the factory radio sometimes the speakers are not bad at all, the culprit is the radio connector, pull your radio and make sure that the harness and the wires in it are fully inserted into the radio, The symptoms are a lot of static (from one or more speakers) Intermitent output (works sometimes) or speaker works or stops working after traveling over rough terain. While you have your dash cover off check to see that all wire connectors that you have access to are fully seated!

Please ,Please do not replace anything until you check the obvious first!! DTC's are a guide having to do with that system shown, or indicated , it's not always just the item itself. ie; ABS malfunction, Do you ? Check the Brake fluid leval? See if the harness is connected at the wheel or at the abs module itself? Clean around the hub sensor? Or do you replace all 4 tires? Replace all of your brake pads and rotors and calipers? Not to mention both front hubs, real fun especialy if you have a 4x4. First things first. Keep your money in your pocket