348 Thank you Brotherhood: Misfire Solved

I just wanted to say thank you to everyone who is enthusiastic about these cars. Between online tutorials, the entire workshop manual, wealth of online resources, and bugging plugzit with noob questions, my car is running better than ever. Keep stooging. Story below in case this can help someone in the future:

A few months ago, I pulled my car out to meet a few friends for a drive. About 3 blocks from my house (thankfully), my car develops a horrible misfire. By the time I coast to the bottom of a hill, the car is already dead. I was able to start it back up and limp her home. Every time I hit neutral, the car died. I probably had to restart it 5 times in the few blocks home. It also threw a SDL on the the 5-8 bank. The exhaust smelled like gas, and the left side felt really hot so that SDL made since. I knew I was getting fuel. I parked it in my garage, and then life happened. I wasn't able to touch it for a few weeks.

Based on the failure mode (fuel + sudden failure after warm), I assumed it was the coil. No worries. I looked at the x-ref part list and realized I could order a new coil pack for $50. I bought one for both sides. They were 30 years old so it couldn't hurt. I eventually get around to swapping them. All in, a 30 min job. No change. Lots of un-burnt fuel, and a terrible miss.

Well, it still seems like the car isn't getting spark. The igniters are next in line, and also pretty cheap. I order a set based on a (gasp) 993 911 part number. I also bought the dow thermal paste the directions specified. I like to follow rules, apparently. Shocking to nobody, that didn't fix the problem either.

It looked like I needed to actually be a mechanic instead just throw parts at the problem. This is typically fine, except I mostly have experience wrenching on diesels. This ignition witchcraft? Get the hell out of here.

I pull the plugs. It is very obvious cylinder 6 and 7 were not getting spark. The plugs were black and dripping in gas. Thinking back to when the car broke-down, it really really felt like a coil went. I throw on new plugs, just in case with no effect.

Finally, I test spark on each plug. Not shocking (pun intended), I have no spark on 6/7. A few things cross my mind, but I recall the coil only having 3 wires. One has to be for 5/8, 6/7, and a ground, right? I dig into the wiring diagram in the shop manual (thank you whoever shared the google docs link a long time ago!!!). After looking and extensive use of the zoom function in PDF, I realize there is a pin on the ecu (pin #1) that eventually controls spark plug 6&7. I "borrow" a super nice multimeter from work and start checking continuity. The wiring harness checks out. The ecu on the other hand, looks like this:

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Well, that might be an issue. I use a combination of contact cleaner, a wire brush, fine sand paper, compressed air, and swearing to clean the pins. I hook everything back up, say a lengthy prayer, and fire up the car. FIXED

The car is absolutely purring (minus the normal warmup procedure hunting)

I change the oil due to fear of gas contamination based on the instructions on my348.com and the oil I bought at Walmart.

I met some friends in Malibu this morning, put 125 miles on the car, 70 of them really hard, and the car ran abso****inglutely perfect. Knock on wood, but I think this issue is solved, for now. I want to do the Ernie re-pin, but that might need to wait until me next major.

Long story short, thank you guys for going through all of this and posting how to fix issues as they come up. Without all of you and the online resources, I might not have even looked at a 348. This site was a huge part of my consideration on this car. A competent mechanic probably could have figured this out in an hour, it took me a few weeks. But if someone as incompetent and ham-fisted as me can own these cars, so can you. Get wrenching!

Happy Stooging

 

Thank you for the diagram, I book marked that! I plan to do the other pins in short order as well as get some corrosion inhibitor on them asap. Also, I'm going to look into investing in a nice multimeter. Borrowing one from work is not ideal haha