Terrible Bog in 93 Chevy Silverado

[tweeknuts]

• The truck is bogging something fierce.
  
  Seems that the bog is at it's worse when the RPMs are between 1200 - 2200. Sometimes when the traffic lights turn green when sitting there, I will give it gas and seems that there was a blip of power then gone and comes back which results in me slamming my head into my steering wheel haha. When I'm in overdrive, I can hardly make it up a small hill, sometimes same case scenario in 3rd gear. Not sure if it's coincidence but when it's really cold out and I left it outside for the night, the bogging is at it worse. Leaving it a warm garage seems to work for a little bit then gets worse.
  
  There are times where it works perfect for a while though. So ofcourse when I bring it into a shop, they can't always figure it out because the issue doesn't reoccur for them.
  
  I also noticed wayyyyy to much gas in the air cleaner. Pretty bad when the gas makes my air filter stick where I almost have to pry it out.
  
  Here is the list of stuff I have already changed or replaced:
  
  NEW PARTS
• Have the truck scanner. Nothing showed up.
• Put in a new Throttle Positioning Sensor.
• Fuel Pump Relay
• Fuel Filter
• EGR Valve
• A Couple of New Hoses
• Spark Plugs
• Spark Plug Wires
• Cap
• Rotor
• Full Distributor
• Fuel Pressure Regulator (probably wrong name for it)
• New Computer PLUS new Prom for it.
• New Map Sensor
• Coolant Sensor

TESTED GOOD AND CLEANED

• O2 Sensor Read Fine
• Tested Backpresser which was fine
• Tested Fuel Pressure
• Test Injectors which checked out good.
• Adjusted Timing so that's correct
• Soaked the plug wires and no changes.
• 
  I know the Catalytic converter is getting decently bad but pretty sure that's not the issue. Otherwise that would always bog it I would think. Fuel Pump seemed fine too.
  
  I'm pretty sure I missed a couple of things but if anybody else has some other ideas, that would be awesomeeeee. I dropped like 2 grand or more only because of this issue. Most of which was due to hours at the mechanics. Even brought this straight the GM thinkin they have this issue on record. Guess not. I seen a lot of the same types of issues on other forums with this truck in general but ofcourse if someone fixed theirs, they never came back to the forum to tell you what fixed it. Haha.
  
  Oh yeah, My vehicle specs
  93' Chevy Silverado
  k1500 4.3L Throttle Body
  4X4
  
  Sorry for the long post, haha. Thank you!

[maxwedge]

Welcome to AF, this of course is not a classic, I am moving this to the Silv. forum below.

[tweeknuts]

Oh sorry about that.

[autotech234]

I would have to say you have a fuel pump problem or resticked exh. To check fuel pressure you will need to tape a fuel guage to the windoow and drive it. check pressure when problem is happening. if it gos down that is your problem. here is the fuel test

PROCEDURE

A fuel system pressure test is part of several of the Diagnostic Charts and Symptom Checks. To perform this test, follow this procedure:

Note : To perform residual pressure check refer to: Fuel Pump, Testing and Inspection.

1. Turn engine OFF to relieve system pressure.

• • Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start the engine.
  • Loosen fuel filler cap to relieve tank vapor pressure.
  • The constant bleed feature relieves fuel pump system pressure when the engine is turned "OFF".

1. Uncouple fuel supply flexible hose in engine compartment. Install fuel pressure gauge between steel line and flexible hose.
2. Tighten gauge in line to insure no leaks occur during testing.
3. Connect negative battery terminal and START engine and observe fuel pressure reading. It should be 62-90 kPa (9-13 psi). If not, refer to DIAGNOSTIC CHARTS/FUEL SYSTEM PRESSURE TEST (CHART A-6).
4. Turn engine OFF to relieve system pressure.

• • Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start the engine.
  • Loosen fuel filler cap to relieve tank vapor pressure.

1. Remove fuel pressure gauge.
2. Install new O-ring on fuel feed line. Reinstall fuel line.
3. Connect negative battery terminal and START engine and check for fuel leaks.
4. Install air cleaner assembly.

If that is not your problem I would suspect resticked exh. If the cat is melted the bogging will get worse when motor is hot. If it just has loose stuff inside it could be causeing a intermmtent problem.

Hope this helps.

[tweeknuts]

Well for my understanding... a fuel pumper works or it doesn't. Don't think I'm getting a lack of pressure considering my air cleaner is caked with fuel. So seems like my truck is getting too much gas. I thought I might have fixed that issue with the new fuel pressure regulator ans map sensor but no go. Is there some ground wire near the fuel pump maybe that isn't getting good connection maybe? I checked the ground under my thermostat but nothin wrong there

[autotech234]

There is a ground for the fuel pump located on top of the frame rail right at the rear of the gas tank. Its held down by a 13mm bolt.

Also are you getting any smoke coming out the tail pipe and what color. This can help tell you if its running rich or not.

[tweeknuts]

I get smoke out of the tailpipe but it's only because i live in Minnesota...... haha. It's freakin cold here atm. I will pull it into my garage where I have it heated and see if there is anything.

[tweeknuts]

K sorry for the belated post here. I didn't see any smoke. I just added more thinks to this truck that didnt fix it. MAP sensor and whole new exhaust system (headerpipe to tail pipe). Still didn't fix it. So i'm going to look for vacuum leaks when the problem occurs. I had vacuum leak tests already but doesnt seem to run bad when it's been sittin in a warm garage. So I'm goin to see what I can do outside in the cold! haha.

[tweeknuts]

Here I will update everything I have changed.

NEW PARTS
Had the truck scanned. Nothing showed up.
Put in a new Throttle Positioning Sensor.
Fuel Pump Relay
Fuel Filter
EGR Valve
A Couple of New Hoses
Spark Plugs
Spark Plug Wires
Cap
Rotor
Coil
MAP Sensor
Full Distributor
Fuel Pressure Regulator (probably wrong name for it)
New Computer PLUS new Prom for it.
Complete Exhaust System (Header pipe to tail pipe)
Fuel Injectors
Thermostat
Coolant Sensor
Throttle Body
Idle Sensor
New gerbils on a wheel to charge my battery....

TESTED GOOD AND CLEANED
O2 Sensor Read Fine
Tested Backpresser which was fine
Tested Fuel Pressure
Test Injectors which checked out good. (new injectors now listed above..)
Adjusted Timing so that's correct
Soaked the plug wires and no changes.
Sprayed carb cleaner around the manifold. No jump in idle. (Unless I'm spraying int he wrong spots...)
Checked all possible grounds.

[mwid73]

Hey tweeknuts, did you ever get this figured out??? I am starting to have the same problem with my '93 Silvy ( 201,000 miles ). I'm thinking it might be a plugged cat. but I have yet to tear into it...

[tweeknuts]

Nope. Still haven't figured this thing out. I might be hooking up a vacuum gauge and taping it to my windshield so when the issue happens, i can see if it's really a vacuum leak or not.

[tweeknuts]

What is you're issue. Is it like mine? I'm pretty sure I'm flooding nonstop.. not enough air or something. Who kows.. haha

[2000CAYukon]

Factory Manual for 1990 under "Hesitation, Sag, Stumble"

Check:
- Fuel Pressure
- Ignition Timing (How is the timing chain?)
- TPS for binding or sticking
- Alternator output voltage (Should not be > 16 volts)
- For open HEI ground
- Canister Purge system for proper operation
- EGR Valve Operation

I would also check EGR valve solenoid (I did not see it the parts list).

On my 90, I found that the vacuum hose the MAP was bad and would not hold a vacuum. Also make sure MAP vacuum port on the TBI is clean.

How is the compression?

//2000CAYukon

[mharmond77]

Hey man, i also have a 93 chevy with a 4.3 and have the exact same problem. Mine was a combination of three things. The coolant temp sensor, Knock sensor, and the grounds on the thermostat housing. I moved the grounds directly to the intake. I noticed a hole where a bolt should be next to the thermostat housing. ( the previous owner had had the engine out of the truck) i grounded the wires there. Still ran like crap. I had a friend of mine read the codes from the computer. It read coolant temp sensor ( which you said you already replaced) , and the Knock sensor. These worked for me.
If i am correct the bad coolant temp was making it pump more fuel to the engine, the knock sensor which will retard the timing if i tick or ping is detected , resulting in my overloading problem. I hope this can help you man.

[cramer_77]

not sure if its too late, but i had kinda the same problem with a truck at work. it would run fine every now and then, but when it would run bad it would run bad. Come to find out, it was the ditributor. It was on its second distributor already. You might look at having the distributor warrantied if it ain't too late.