Top 10 1994 GMC Jimmy Questions & Answers

How do you know that it is the regulator?
these 4.3 motors had a lot of trouble from 93 to 98, I know I had 2 of them.
What happened to mine was that the intake kept getting very carboned up. After I would clean it, the truck would run fine for about 5 or 6 months, then same thing.
Theres actually a class action lawsuit about this that I believe has been settled, you may have recourse if you bought it through a dealer. Good luck.You'll need it.

check the temperature sensor for the computer. it may be telling the computer that the engine is still cold and causing the engine to run too rich at warmer temps

this engine takes about 5 quarts with filter after a hot drain, add 4 quarts and then run and top off, remember to fill the oil filter up before installing to prevent "dry" start up, u can use 5W-30 or 10W-30, either will work, in summer or hot climates use 10W-30, never use a heavier oil.

Below is the diagram you requested. It's for a 94 Jimmy with a 4.3L engine. Best of luck.
Greg

These trucks are plagued with weak fuel pumps and need a high amount of pressure to start...especially in coder weather.

Remove the air intake on front of engine, it is the rubber tube that is around 5 inches in diameter, be careful as there is a sensor attached on the underside. Squirt some starting fluid into the intake and try starting it right away. If it starts or even acts like it is going to start, you are having a fuel problem.

If you did see a difference by doing the above, then you need to test the fuel pressure with a gauge. The fuel pressure test gauge can be bought for very cheap (around $20) from your local auto parts store. It hooks up to the fuel rail test port on the drivers side of the engine. The test port looks like an overgrown air inlet that you would use to put air in a tire. It should have a plastic cover that you unscrew.

Once the gauge is hooked up, turn the key to prime your fuel pump...do not crank the engine. Look at the gauge to see if you are at least to 56psi, closer to 60 is more desirable. Also take notice if the fuel pressure is dropping, it should stay steady. If it is slowly dropping, then you need to take a look at your hoses from the fuel pump to this point.

If it is steady and within the required psi, then you are looking at a problem within the plenum. The plenum is the aluminum colored cover that is on top of the engine, under your black plastic Vortec label. inside the plenum you will find what is referred to as the "spider assembly". The spider assembly houses the fuel pressure regulator, injector and propet nozzle hoses (6 hoses). A common failure of this unit is the hoses leading to it that supply fuel, they are known to leak. You can easily see if it is leaking by looking for "wash marks". Wash marks are where fuel has leaked and cleaned the inside of the plenum in spots. If this is your case, buy a rebuild kit for the hoses. There is also the possibility of your fuel pressure regulator acting up. This part can be bought separatly from the whole spider assembly, even though you will be told otherwise. I have had to buy it online.

If your psi was not within par, you more than likely have a weak or bad fuel pump. But before going through the fun of replacing it, I would first check to see if the ground for the pump is making a good connection. The ground comes right out of the top of the fuel tank and connects to the rear bumper, it is a tight fit and may not be the easiest to access it. Unbolt it fromt he bumper and take soem sand paper to remove any rust on both the bumper and the wire connection. Put it back together and test your fuel pressure again.

If no change, then you are looking at replacing the fuel pump. You will need a basic socket set, screw drivers, jack, tire iron, hammer and basic wrench set. If you have access to air tools, it really helps with removing the gas tank. Use the jack to not let the tank fall and to lower it down so you can disconnect the hoses going into the fuel tank. Once tank is removed, use the screw driver and hammer to spin the retaining plate around. CAREFULLY remove the fuel pump, DO NOT bend the float arm, if you do, your gas gauge will not display correctly. Pull the fuel pimp out of the assembly and put your new one into it. Do not forget to install the filter that goes on the bottom of it. Once you have that done, put it all back together. Make sure that the hoses to pump are snug, you do not want an air leak. Also make sure that the ground is clean and snug.

Once it is all back together, your psi should be within an acceptable range.

Almost forgot, change your fuel filter while under the truck. Also, when you buy a replacement fuel pump, make sure it is the high output (there are 2 different fuel pumps for this truck) and do not skimp on price. I have seen cheap pumps burn out in under a year. If you can, buy an OEM pump. Copy down your VIN number and take it with you when buying the pump, you will be asked if you have a W or Z vin.

Buying a repair manual for this truck is worth it. Nice truck overall, the egine has the same horse power as the 305 did for that year. You can beat it, abuse it, neglect it and it still runs fine for a long time.

you need to have the codes checked to know what direction to start repairs,Autozone does this for free

The "spider" injector is the problem. You're right that one of the injectors is stuck open, unfortunately it has to be replaced as an assembly. This a common problem on the Vortec V-6's. When you were checking the fuel pressure, the fuel was passing through the open injector, giving you a low reading. After replacing the injector assembly, be sure to change your oil before you start the engine. I'd be willing to be you have a pint or two of gasoline that has gotten into the crankcase. That injector unit will cost you around $350. It's not too hard to put in, just be careful.

I am sorry but i know this symptom on this exact transmission and u are going to need an overhaul.

If it's a metal line, Your local auto parts store should be able to order it for you or worst case you'll have to make your own from straight tubbing and a bender. I don't recall ever seeing diagrams for metal lines, usually there pre made to replace the factory one or you can splice a replacement piece in place of a damaged section. AS far as the line goes to the module, try following it up to it with a good flahlight and a sharppe from the rear forward.

This should give you everything you need...