What shorted out?!?!

[94Reborn]

My truck is running rough at idle and under acceleration. It seems like a misfire, a timing issue, or maybe even a cylinder not firing. After checking and double checking everything I noticed my blinkers wouldn't blink either but were only lighting up solid. I found a loose ground, I believe its called G101. The ground on the radiator support drivers side by the edis module. After tightening, the lights now work like normal but engine condition is unchanged. What components are affected by this ground?

It is on the same part of the harness as the MAF, EDIS module, and PCM but I don't know if this ground has anything to do with them. I switched the edis as I have a spare and that did nothing. I unplugged the maf and it runs the same, and I opened up the pcm and it doesn't have noticeable internal damage. HELP?!

 

[wr250rdr]

What all did you check when you said checked and double checked everything? Are you sure your getting spark on all cylinders? Did you pull the plugs and check to see their condition? Are you sure you don't have an internal break in your plug wires( checked with a multimeter)? No codes?

 

[94Reborn]

I pulled each wire at the coil and all have good blue spark, I checked the secondary coil resistance values and all were good (between 13 and 15k ohms). Pulled the plugs, still clean as they are only a few weeks old, as are the wires. I checked for codes a few times and its 11 system pass, so the computer is clueless.

Not sure that it's pertinent or not, but the truck ran fine before I left town for 4 days. Came back and it ran like this. But my assumption is the ground was already loose and didn't short anything until I started it when I got back.

 

[94Reborn]

I had a failed pcm in the truck after I first swapped this motor in a few weeks ago. But that pcm gave a failure code for itself, as did the bad maf that I swapped before I left last week.

 

[wr250rdr]

I'm 99% sure that ground has nothing to do with your issues it is most likely just the ground for that portion of the lighting harness. Are you sure your still in time?

 

[94Reborn]

Well I know that is the closest ground to the maf and edis so I'm not sure if they use it or not. But as for the timing I'm not sure if its still right, but the timing isn't adjustable anyway. If the timing is off it would still be my edis, pcm, or it could also be the crank sensor I suppose. But I would think the timing being off would throw a misfire code right? I don't think it has jumped timing, as it ran well at idle, then I shut it off, I didn't drive it or run up in the rpms, then on the next crank a few days later it runs bad.

I did try to start it with the spout plug out and it ran worse, so at least I know that the pcm and edis are advancing the timing.

 

[94Reborn]

I tried switching the maf out yesterday night. I switched it with my old one, which was bad but still made the truck idle fine, and it made no change but popped the maf code up. So I don't suspect the maf as its getting signal to the pcm...I think? But I still think the pcm could be the culprit. I'm going to try cleaning the iac and the throttle body out real good and see if that makes a difference.

 

[XLTbeater]

Check your vacuum lines running from all vacuum sources to the intake. If you didn't replace the lines during the engine swap, they may have been severed or have dry-rotted.



XLTbeater

 

[94Reborn]

I already checked them over and sprayed everywhere with starting fluid, the only leak was from the upper intake manifold so I replaced it, with little to no change. Does anybody know where g101 supplies ground to other than the blinkers? I was thinking of disconnecting that ground completely and attempting to start the truck to track down what it feeds, but could that cause more issues?

 

[94Reborn]

I was told that g101 supplies ground to the pcm, maf, and pcm relay. But I replaced the pcm and maf already, and switched the fuel pump and pcm relays around and there was no change. My thoughts are the oil pump is going and caused head damage, or I have a bad injector. I dropped the truck off at my mechanic today, so now I have to wait and see what he thinks.

 

[94Reborn]

If anyone is still following this, that ground does affect those components, but as mentioned above, it was probably a coincidence. I've got no compression on cylinder 5. I'm going to pull of the valve cover and investigate when I get it back on Tuesday. I could have saved 50 bucks doing my own compression test, but I figure a gauge would have cost close to that. If its a bad lifter and not just a pushrod or rocker arm, I'll have a 4.0 that needs a lifter going up for sale...haha

Thanks for all the troubleshooting guys.