1996 Jimmy code P0301

[jimmyMonroe]

Hi:

My 96 Jimmy has 162,000 miles and has been running fine until recently. I am experiencing an intermittent code 301 which suggests misfiring in Cylinder 1. I noticed that it has a rough idle and accelerates smooth unless I am going up a hill. Some days it runs fine and others the light comes on and flashes a series of times. A year ago I replaced the wires, plugs, distributor cap and rotor. Since the problem started I've replaced the #1 spark plug, the fuel filter and have run 2 cans of Chemtool B-12 cleaner through it. Does anyone have any other suggestions so I can get this problem fixed?

[GMCTECHKY]

You May Need To Check Your Spider Under The Throttlebody For A Cracked Or Dry-rotted Rubber/plastic Hose

[jimmyMonroe]

My code P0301 has turned into a P0300. I kept smelling fuel after it started up. After several cans of injector cleaner I removed the plenum and found a washed out area on the side of the 1, 3, 5, injector poppets. I ordered the MFI fuel System kit and replaced the CSFI injector. I installed it and the fuel smell went away but when I measure fuel pressure it is 52-54 PSI with key on (not started). It runs about 52-54 while idling.It still idles rough too. This seems too low for what the Chilton Manual says. Can the fuel pump be the cause of this problem. I replaced the filter 3 months ago. The current fuel pump was replaced by a mechanic 4-5 years ago.

[jimmyMonroe]

After replacing the CSFI system with the AC/DELCO MFI kit it solved the leaky fuel problem but I still have low fuel pressure. I tried some troubleshooting this weekend. I tested the fuel pressure. First I changed the fuel filter. Then I tested the fuel pressure. I turned the key on and the pressure went up to 52 PSI. Then I turned the key on and off several times and the pressure built up to 60 PSI but as soon as the pump shut off it dropped off immediately to 52 PSI. I replaced the fuel filter and tested again and the same results. I swapped the fuel pump relay with another one and still no change. I tested the battery voltage 12.58 with ignition off and 14.1 with engine on. When the engine is running I get 52 PSI steady. I am getting a flashing service engine light and a codde P0300. I think I know what the problem is, the fuel pump needs to be replaced but I would like the opinion of others before I get into this nightmare of a job.

[600cuin]

Jimmy did you ever resolve this issue-did you replace the fuel pump and have it work?

[jimmyMonroe]

It turned out that I had 2 problems. One was to replace the fuel pump and the other was to replace the distributor cap. The new fuel pump restored the pressure and the distributor cap (which was fairly new but NOT OEM) had a burn between cylinders 1 and 2 on the underside and was causing it to misfire because cylinder 1 was receiving spark from 2. I would recommend replacing parts with AC-Delco especially the distributor cap. I still have the Jimmy and that problem has been resolved ever since. The fuel pump replacement wasn't too bad I had found a how-to on this forum and it guided me through the whole process.

[600cuin]

Thanks, I have the new fuel pump coming today, and will order the distributer from GMC. I have bought 2 new distributers but not GMC factory, got them from other auto stores.

This isn't one of those that it is easier to lift the body to get to the fuel tank is it?

Thanks for your quick response. Will let you know how it goes...

[jimmyMonroe]

My 96 Jimmy is the 4 door model. I drove the rear wheels onto some ramps and removed the spare tire from underneath and that gave me plenty of room to work. You have probably read that there is a small plastic vent valve on the upper front of the fuel tank. I had snapped my off because I didn't know about it. Just lower the tank partially and remove the rubber hose to it and you should be fine. Its a dealer item if you do break it off. Good Luck.

Originally Posted by 600cuin

Thanks, I have the new fuel pump coming today, and will order the distributer from GMC. I have bought 2 new distributers but not GMC factory, got them from other auto stores.

This isn't one of those that it is easier to lift the body to get to the fuel tank is it?

Thanks for your quick response. Will let you know how it goes...

[600cuin]

I have changed the distributer cap with an actual GM Cap, and I changed the fuel pump with an actual GM fuel pump. Still getting the multiple misfires from the computer readings. I guess the next thing other mechanics have told me to do is change the spider. I also have been told it could be the computer modual. Anyone else have any information on this? This is a 96 Jimmy 4 door V6 vortec engine... Engine has been rebuilt and it ran good for about 6 months and then started running rough and I haven't been able to rectify the problem.

Originally Posted by jimmyMonroe

My 96 Jimmy is the 4 door model. I drove the rear wheels onto some ramps and removed the spare tire from underneath and that gave me plenty of room to work. You have probably read that there is a small plastic vent valve on the upper front of the fuel tank. I had snapped my off because I didn't know about it. Just lower the tank partially and remove the rubber hose to it and you should be fine. Its a dealer item if you do break it off. Good Luck.

[ZL1power69]

Originally Posted by 600cuin

Jimmy did you ever resolve this issue-did you replace the fuel pump and have it work?

600, this thread is over 2 years old. Feel free to make a new thread the problem diagnosis section if need be.