Misfire under boost

[MattStrike]

'93 SE L67 again. Intermittent.

Typical drive:
Startup cold, warms up a bit, then leave. Step on the gas for a brisk acceleration and it goes fine normally. Everything gets warmed up, and I go for a WOT pull and maybe 50% of the time it will start to miss. If it starts to miss and I don't let up it just gets more severe until it backfires. With the SC on the top I can't tell if it's fuel in the intake igniting or if it's in the exhaust. After the backfire, it will continue to misfire if I maintain a cruise speed but will slowly return back to normal. Immediatly after it recovers I can hit it WOT again and about 50% of the time it pulls hard without a misfire. Sometimes I just can't get into boost without it starting to misfire, and other times it just goes on like nothing was wrong.

I can't see this as a mechanical failure, maybe fuel related, but the intermittent thing is throwing me off.

[J Wikoff]

My guesses are coils or fuel pump.

[Kajidono]

Same thing is happening on mine but it's not throwing any related codes.

[2000Silverbullet]

Fuel Pump.
Just did one on my 94. Similar symptoms.

[Kajidono]

Ah, I saw your thread on the silver goose. I was hoping that wasn't it, but at 227,000 miles I guess it's had a good run.

[2000Silverbullet]

The fuel pump on a SC L67 is specific and a higher volume than the standard NA SE pump.

[Bob Dillon]

Sounds like fuel delivery to me. I'd watch maintaining WOT with a supercharged engine and a mixture lean enough to misfire, too. If that's what it is, it's not helping the piston tops any.

Changed the fuel filter lately? I'd check both the filter and fuel pressure first.

[MattStrike]

Is this going to be a situation where the correct SC fuel pump isn't available anymore? Maybe I can kill two birds here by using my SSEi pump here and upgrading the SSEi pump.

What model is the Walbro pump everyone is using? http://walbrofuelpumps.com/1992-1993-po ... -3-8l.html

[J Wikoff]

Check willwren's posts to see which one he used on his 93. It might be in his signature.

[Kajidono]

Rockauto has the fuel pumps.

[2000Silverbullet]

I bought the complete unit from RockAuto including the level float. It comes complete with ring and rubber gasket all wired plug and play for $130.

[MattStrike]

*reviving from the dead for closure*

Guess what it was? A bad ignition coil. It would spark good at idle, but could drop out under boost. It wasn't until the last few weeks that it got bad enough that it was always dropping out that I was able to find it. With good weather on the horizon, we had taken the car to the carwash and I sprayed down the engine bay. Of course the weak coil stopped firing on one cylinder due to the water, which is how I found it. Swapped out the coil and now it screams like a banshee again.

It's odd, because I've swapped out the entire ICM and all 3 coils already without finding this, so it means I've got another bad coil on the shelf to root out.

[Kajidono]

Mine turned out to be the intake manifold, so ¯\(ツ)/¯

[J Wikoff]

What did we learn here?

If I make two guesses and everyone goes with the second, it was guaranteed to be the first. Lol!