I have been restoring my 94 Jimmy for a while and I'm finally to the point that it just needs some tweaking. Here's what's happening

The truck shakes a little when it idles but the engine doesn't surge or stall. Acceleration feels sluggish, especially between 25 and 50 miles per hour. When I accelerate the exhaust sputters a little but doesn't backfire. And it seems like it doesn't want to shift. it stays at a high rpm for a while and then goes into the next gear.

The engine is new but the mechanic rebuilt it using parts from my old engine. I have dual exhaust but they didn't install headers like I asked. The only engine codes it has thrown are 13 and 18 according to my paper clip. I replaced the plugs, cap, coil, rotor, and MAP sensor. I plan to replace the EGR valve in the next few weeks. The plug wires actually look new. It no longer shows code 18 and always starts strong. The Service Engine light only comes on after driving for 15 - 20 minutes but then clears when I stop and restart. But other times I can drive for a couple of days and it doesn't turn on.

When I replaced the cap and rotor I did notice that the distributor seems loose. You can turn it left or right about a 1/4-1/2 inch and then it stops. When I reconnected the plug wires I did switch two by mistake. I corrected that but I wasn't sure how that would effect the timing.

The 02 sensor was repositioned when the exhaust was installed. It's now on the driver's side and I'm pretty sure it was on the passenger side before. I haven't gotten under there yet to check the voltage. I think it's supposed to be .5v on the harness but not sure. I saw that online so I want to confirm first. I do not have a cat. You can def smell the exhaust but it doesn't smell of Sulphur.

 

We need to get rid of that 13 code by identifying and fixing the problem. You have a 3 wire oxygen sensor, Pnk/Blk=heater +, Blk=heater -, ppl= sensor bias. This may improve performance, if not then we move on.

Unplug the sensor and get an incandescent test light on the two heater wires on the harness and then turn on the ignition. If no light start the truck. Report back. Grab a voltmeter and measure ppl to black on the harness with the ignition on and look for 0.450vdc. If nothing, start the truck and see what you get. Report back.

George

 

Thank you! I will be doing that this week and getting back with you

 

ugh.....When the dual exhaust was installed the O2 sensor was moved to the driver's side. They ran a pigtail over to the actual connector so now it is up above the transmission and it's difficult to get to. It might be awhile before I can get it done. I will probably need to at least get the truck up on some ramps so I have some wiggle room to get to it.

As far as I can see it only has one O2 sensor. I think the factory exhaust has one before and one after the cat. I don't have a cat so I'm wondering if they just didn't install a second sensor. Could the 13 code be due to only having 1 sensor? I found a couple of websites that say 13 would mean it was faulty or No Activity.

Oddly enough as I was trying to chase the wire to find the connector I did something and the truck wouldn't start, like it had no spark or gas. I popped the wire off the coil and snapped it back in place firmly. Then the truck started up with no issue. I did one test drive and it doesn't appear to be sputtering and the Service Engine light did not come back on. Maybe that ignition coil wire was loose and somehow was pulled all the way off then I was tugging on the O2 wire. I didn't pull it hard, not like i was trying to start a mower. Just enough to see it wiggling and try to see where it went. idk.

When I get a chance on a weekend to get the truck up and get my voltmeter on it I will still check to see what I'm getting. I appreciate the feedback to help clean it up.

 

Your truck only had one pre cat O2 sensor it looks like, in the exhaust Y. I see two potential issues. One, the wiring/voltages/ground/sensor which we have already discussed. The other is that they put the sensor into just one side then the truck will never run right if the banks get out of balance.

George

 

I have been trying to find a picture of what the stock O2 sensor position is on your '94 because I have not dealt with this myself, I got the "Y pipe" info from the wiring diagram. I found this one picture which suggests that even when its mounted in the Y pipe it may be off to one side and only measuring one bank, or since its so close to the Y maybe there is adequate mixing to measure the total exhaust output from both banks. Not sure on the layout part of this. I am more confident on what we need to do on the wiring and sensor. In any event, the original design may have only measured one bank.



George

 

Thank you for the help! I finally got it into the mechanic last week. They found the sensor the original mechanic used was a universal sensor and the wiring work was shoddy. They replaced it and rewired it and that seemed to clear the code.