MoGas
Central Scrutinizer
September 2017 - June 2020...
The Jeep was running pretty good, but I had 2 issues with it.
The first, and probably most dangerous was that every once in a while, it would just die. Just like turning the key off. I never had this issue before I installed the TBI setup, so naturally, I automatically focused on that as the culprit.
The scenario was this: It would randomly die. no difference in engine operating time, outside temperature or weather, vehicle speed, or anything. Purely random. I bought a logger to hopefully capture the issue. I had logged about 20 different instances of this happening. I sent the data to Norm at AFI, and he couldn't see anything other than it just shut off. I sent the data to another guy that is a GM TBI dude, and he also saw nothing that was causal.
If you just tried to restart it, it would crank, but not start. You had to turn the key all the way off and then crank it, and it would run just fine.
I started to really dig into the wiring schematics of the Jeep and the TBI to see if I could figure it out.
I had a long weekend with my then fiancé out of town, so I was able to really get after it. I got to a point where I jumped the power to the TBI system straight from the battery. I drove about 3 hours like that and it never shut off. OK, now I'm on to something. I reattached the system to the Jeep harness, and it came right back.
What I ended up finding was that the ignition switch had a little corrosion on the power contact that fed the TBI computer relay, so every once in a while, that would cause the relay hold circuit to drop power for a tiny bit of time, but enough time that the relay would shut off. That's why it would crank but not start unless I shut it off and reset the relay. I I replaced the ignition switch and there was no more shut off issue.
The second issue was a random tailpipe backfire. I really was getting crazy with this one. My distributor is a computer controlled unit, so there is no mechanical or vacuum advance. it was also a problem that I could not induce. I chased this for a while.
My lady and I got married 12/31/19 in Sedona, and I was also pretty busy with my job. I was a Subsea Engineer for a company, and I worked on the Blowout Preventer and associated systems on rigs all over the world.
Until... I had come home from a rig early April 2020. It had been a 6 week job recertifying the BOP out in the Mexican waters of the Gulf of Mexico near Ciudad del Carmen. There was this thing called "Covid" that was really getting attention and changing the world. I was on a rig where I don't speak Spanish, the TV is all in Spanish, and I had very limited communication with the outside world. I finished my job and started my travel back, headed to a world I didn't recognize anymore. I had to get medical clearance to travel. I had to get special permission to travel internationally. There were so many checkpoints where I had to get my temperature taken and answer various medical questions. The Mexico City arport is normally pretty packed. It was like a Zombie movie. There were few people, almost all the businesses were shut down. There were only a couple restaraunts open It was surreal. I got home, and was sequestered to our guest room for 2 weeks. My wife would make food for me or bring things to my door and that's how I lived for that time. During this time, oil prices crashed to negative 13 dollars a barrel at one point. It was nuts. On May 9th, I was laid off as they were shutting down the field service group since there were no jobs scheduled for the next several months.
Now I had tons of time available, so after I got all my honey do's handled, I started working on my Jeep, trying to figure out the backfire issue.
I figured I'd check for slack in the timing chain. I set the engine to TDC, pulled the cap, marked the rotor position, and turned the crank the opposite direction. I found that the crank would move about 13 degrees before the distributor rotor would move. The drive gear on the distributor was in good shape, so I figured I might as well pull the timing cover and inspect the timing chain.
This is what I found...
youtube.com
The Jeep was running pretty good, but I had 2 issues with it.
The first, and probably most dangerous was that every once in a while, it would just die. Just like turning the key off. I never had this issue before I installed the TBI setup, so naturally, I automatically focused on that as the culprit.
The scenario was this: It would randomly die. no difference in engine operating time, outside temperature or weather, vehicle speed, or anything. Purely random. I bought a logger to hopefully capture the issue. I had logged about 20 different instances of this happening. I sent the data to Norm at AFI, and he couldn't see anything other than it just shut off. I sent the data to another guy that is a GM TBI dude, and he also saw nothing that was causal.
If you just tried to restart it, it would crank, but not start. You had to turn the key all the way off and then crank it, and it would run just fine.
I started to really dig into the wiring schematics of the Jeep and the TBI to see if I could figure it out.
I had a long weekend with my then fiancé out of town, so I was able to really get after it. I got to a point where I jumped the power to the TBI system straight from the battery. I drove about 3 hours like that and it never shut off. OK, now I'm on to something. I reattached the system to the Jeep harness, and it came right back.
What I ended up finding was that the ignition switch had a little corrosion on the power contact that fed the TBI computer relay, so every once in a while, that would cause the relay hold circuit to drop power for a tiny bit of time, but enough time that the relay would shut off. That's why it would crank but not start unless I shut it off and reset the relay. I I replaced the ignition switch and there was no more shut off issue.
The second issue was a random tailpipe backfire. I really was getting crazy with this one. My distributor is a computer controlled unit, so there is no mechanical or vacuum advance. it was also a problem that I could not induce. I chased this for a while.
My lady and I got married 12/31/19 in Sedona, and I was also pretty busy with my job. I was a Subsea Engineer for a company, and I worked on the Blowout Preventer and associated systems on rigs all over the world.
Until... I had come home from a rig early April 2020. It had been a 6 week job recertifying the BOP out in the Mexican waters of the Gulf of Mexico near Ciudad del Carmen. There was this thing called "Covid" that was really getting attention and changing the world. I was on a rig where I don't speak Spanish, the TV is all in Spanish, and I had very limited communication with the outside world. I finished my job and started my travel back, headed to a world I didn't recognize anymore. I had to get medical clearance to travel. I had to get special permission to travel internationally. There were so many checkpoints where I had to get my temperature taken and answer various medical questions. The Mexico City arport is normally pretty packed. It was like a Zombie movie. There were few people, almost all the businesses were shut down. There were only a couple restaraunts open It was surreal. I got home, and was sequestered to our guest room for 2 weeks. My wife would make food for me or bring things to my door and that's how I lived for that time. During this time, oil prices crashed to negative 13 dollars a barrel at one point. It was nuts. On May 9th, I was laid off as they were shutting down the field service group since there were no jobs scheduled for the next several months.
Now I had tons of time available, so after I got all my honey do's handled, I started working on my Jeep, trying to figure out the backfire issue.
I figured I'd check for slack in the timing chain. I set the engine to TDC, pulled the cap, marked the rotor position, and turned the crank the opposite direction. I found that the crank would move about 13 degrees before the distributor rotor would move. The drive gear on the distributor was in good shape, so I figured I might as well pull the timing cover and inspect the timing chain.
This is what I found...
Loose Timing Chain
I was having some random backfire issue. Found that the timing wouldn't hold because of the strech in the timing chain. There was 13 degrees of slack betwe...
youtube.com