tony soprano
11-04-2007, 08:07 PM
Finding time to wrap up the install has been increasingly difficult these last couple of months. I've been thrown a couple of curveballs that have largely kept me away from working on the car. The frustrating thing for me was that I had actually been done with the install for weeks but hadn't been able to finish up the little loose ends that were left to do, nor chase down a terrible stumble and miss that the car had. The car was pretty much undriveable...until today!
My first inclination was something was wrong with the PC PROs until I took off the supercharger belt and disconnected the PC PROs entirely. The horrendous stumble persisted. I was getting error codes that corresponded to problems with the MAF, TPS, and IAC. Because there was a terrible throttle tip-in stumble, Tom suggested I look at my TPS setting. I had been suspicious of the TPS setting too and had reset it probably a dozen times so by this point, so I was confident that I had it set correctly.
At one point during my troubleshooting, in desperation, I had loosened a common ground connector to sand it clean and make sure I was getting a good ground. Tom shared in an email with me that undoing that ground may have tripped the error codes. I cleared the codes and started the car. Sure enough, that cleared the TPS and IAC codes, but the MAF code persisted.
I started to focus on the MAF harness extension I had made. I had used a 5 circuit Molex connector. Was one of my crimps bad? Had I crossed a wire? I used a DVM to check continuity of the harness extension I had made and it was fine. Now what?!!? :ack2: I reset the MAF code several times but it would reappear immediately at startup. I shared with Tom in another email that instead of splicing into the MAF harness near the MAF connector, I had done it way back towards where the main engine harness enters the engine compartment near the master cylinder. I mentioned to him that two of the five wires changed from the MAF connector back to where I had made my splice.
On a '94, at the MAF connector there is a black wire with a green strip. However, if you trace that single wire back into the harness, it becomes two black/green stripe wires that are spliced together. Also, at the MAF connector there is a single red wire. If you trace that single red wire back into the harness, it becomes a larger gauge grey wire. If you're still hanging in there with me, this is where the puzzle is solved. It turns out, that larger grey wire is simply shielding for the single red wire at the MAF. When I made my splice into that grey wire, under the grey insulation was a fine wire mesh (shielding) under that wire mesh was the red wire you see at the MAF connector. It just so happens that red wire carries the MAF signal.
What happens if I didn't trim back all that wire shielding when I made my wire crimp? What if an errant wire from the shielding was crimped with the MAF signal wire? I mentioned the possibility to Tom in an email and he said that shielding goes to ground. If I had missed just one of those fine wires when I was trimming it back and making my crimp, I was effectively shorting out the MAF signal!! Checking continuity wouldn't discover this problem!
Today, I redid that crimp making sure that every wire that made up that shielding mesh was trimmed far back from my crimped connection. I fired up the car, let it warm up, and slowly rolled into the throttle. Before, that would have resulted in a horrendous stumble and/or stall. However, this time the car responded exactly as it should. Throttle response was perfect. I was able to take the car for a drive today for the first time without it stumbling, bucking, or surging! FINALLY!!
I still have a few issues to work on. It pulls clean up to 5K RPM and then runs out of steam. I'll continue with my normal progression of troubleshooting. I may have fouled the plugs when I was experiencing the MAF issue. I may have a bad cat. It may be as simple as I'm not getting true WOT with my foot to the floor. So, I have a few things to take a look at. However, the car starts up with ease, idles like a stocker, and is driveable!! :cheers2:
My first inclination was something was wrong with the PC PROs until I took off the supercharger belt and disconnected the PC PROs entirely. The horrendous stumble persisted. I was getting error codes that corresponded to problems with the MAF, TPS, and IAC. Because there was a terrible throttle tip-in stumble, Tom suggested I look at my TPS setting. I had been suspicious of the TPS setting too and had reset it probably a dozen times so by this point, so I was confident that I had it set correctly.
At one point during my troubleshooting, in desperation, I had loosened a common ground connector to sand it clean and make sure I was getting a good ground. Tom shared in an email with me that undoing that ground may have tripped the error codes. I cleared the codes and started the car. Sure enough, that cleared the TPS and IAC codes, but the MAF code persisted.
I started to focus on the MAF harness extension I had made. I had used a 5 circuit Molex connector. Was one of my crimps bad? Had I crossed a wire? I used a DVM to check continuity of the harness extension I had made and it was fine. Now what?!!? :ack2: I reset the MAF code several times but it would reappear immediately at startup. I shared with Tom in another email that instead of splicing into the MAF harness near the MAF connector, I had done it way back towards where the main engine harness enters the engine compartment near the master cylinder. I mentioned to him that two of the five wires changed from the MAF connector back to where I had made my splice.
On a '94, at the MAF connector there is a black wire with a green strip. However, if you trace that single wire back into the harness, it becomes two black/green stripe wires that are spliced together. Also, at the MAF connector there is a single red wire. If you trace that single red wire back into the harness, it becomes a larger gauge grey wire. If you're still hanging in there with me, this is where the puzzle is solved. It turns out, that larger grey wire is simply shielding for the single red wire at the MAF. When I made my splice into that grey wire, under the grey insulation was a fine wire mesh (shielding) under that wire mesh was the red wire you see at the MAF connector. It just so happens that red wire carries the MAF signal.
What happens if I didn't trim back all that wire shielding when I made my wire crimp? What if an errant wire from the shielding was crimped with the MAF signal wire? I mentioned the possibility to Tom in an email and he said that shielding goes to ground. If I had missed just one of those fine wires when I was trimming it back and making my crimp, I was effectively shorting out the MAF signal!! Checking continuity wouldn't discover this problem!
Today, I redid that crimp making sure that every wire that made up that shielding mesh was trimmed far back from my crimped connection. I fired up the car, let it warm up, and slowly rolled into the throttle. Before, that would have resulted in a horrendous stumble and/or stall. However, this time the car responded exactly as it should. Throttle response was perfect. I was able to take the car for a drive today for the first time without it stumbling, bucking, or surging! FINALLY!!
I still have a few issues to work on. It pulls clean up to 5K RPM and then runs out of steam. I'll continue with my normal progression of troubleshooting. I may have fouled the plugs when I was experiencing the MAF issue. I may have a bad cat. It may be as simple as I'm not getting true WOT with my foot to the floor. So, I have a few things to take a look at. However, the car starts up with ease, idles like a stocker, and is driveable!! :cheers2: