Hello all, I've got a 93 gmc c1500 4.3 tbi. I'll make this as short as possible. I recently purchase this truck and 3 days later, the fuel pump went out. So, tilted the bed and replaced fuel pump. Truck started right up, went for a 20min drive and all was well. Got home and noticed the intake manifold leaking coolant at the front right side. Removed manifold, replaced gaskets and put everything back together. Now the truck seems down on power. Idle is low, if I put my foot to the floor it just wants to sputter and die. If I turn the ac on it sputters and dies as well. Any ideas?

 

Check O2 sensor make sure its plugged in. Fuel filter not clogged. i had that issue.. Timing set right after pulling manifold and replaced gaskets? Check all air vacum hoses and make sure it is not haveing a leak. I just replaced my Manifold gaskets and valve and had a airleak issue on the vacum side. was sluggish.. then fixed and runs a lot better.

 

Did you stuff any paper towels into the intake ports that you may have forgotten to remove? I’ve made this mistake several times.

How much RTV did you apply to the ends of the valley? A smaller bead isn’t usually enough to adequately seal it, and if you got a Fel Pro gasket set, that tiny tube they gave you definitely isn’t enough. It takes about a 1/2” thick bead between the heads.

If you did apply an adequate bead, how long did you allow it to cure? The heavier the bead the more time it needs so if it didn’t sit (minimum) overnight, it’s possible it wasn’t cured enough to stay in place.

Check vacuum at idle - normal readings are 15-22 in-Hg - anything lower than that indicates a breathing problem with the engine due to restriction or vacuum leak.

You can also monitor the MAP signal at idle - back probe the center wire at the sensor and check the voltage - it should be about 1.5 VDC at idle and increase up to 4.5 VDC as engine speed increases. If it’s reading above 1.5 volts at idle a vacuum leak is indicated.

Otherwise you can check for codes (see below) and double check that you installed all vacuum hoses and controls correctly. In 1993, many of the sensor connectors were identical except for the location of a slot in the connector barrels. It’s not difficult to swap them between components if you’re not paying attention (or if they’ve been damaged).

To check for codes, jump pins A & B together at the OBD 1 connector with the key off. Then turn the key to on/run without starting the engine and watch the service engine soon light on the dash. It will blink to read out codes.

Each code will repeat 3 times before it begins blinking out the next code; and keep in mind that the first code you get will be 12 - System Pass - even if other codes are stored.

Here’s an example of what code 12 looks like once the key is on. Each hyphen represents a pause, and 2 hyphens means long pause.

BLINK - BLINK BLINK - - BLINK - BLINK BLINK - - BLINK - BLINK BLINK

Following the 3rd set, any other codes will begin blinking out.



OBD 1 Connector