Car shakes violently and boost limited @ 9 (RESOLVED: SHORT)

[free5ty1e]

I seriously can't wait to get off work and go get spark plugs and a fuel filter (yeah, might as well tune it up) and see how those affect my remaining issue.

This morning, on the way to work, I can tell now the worst of the stumbling at or under atmospheric pressures was simply caused by the intermittent short that kept wreaking havoc with my electrical system. Now, since that issue has been fixed, all I have remaining is the stumbling on boost. Car drives quite normally everywhere except >5psi. It's not nearly as rough of a stumble as before, either, but I can def. tell something ain't right - as before, A/F gauge reads all over the place at WOT - although it does spool to 9psi as expected, but I expect the A/F gauge to read pretty much full rich under boost (as it has for the rest of my Subaru driving career thus far). This hopefully is just my spark plugs being in such bad shape that they can't keep up with even a little boost.

I also need to run a nice fresh remote turn on wire down to my bass amp in the back but - for once - that's not my top priority.


Also - since fixing the intermittent short, my car once again starts up EVERY TIME on the first or second crank / revolution. No more of this 4-5 cranks to start up crap.

[free5ty1e]

Well, got a late start yesterday, had to stay at work a bit longer than I thought and the NAPA trip took a while as I needed some other tools... I didn't get very far before I had to eat and clean up;

I had removed the EGI/TC fuse from under the dash as Josh suggested, since I figured the 30 min reset could happen while I was doing the work. Gapped the new plugs, they were pretty much right on .041. The new wires look as though they will reach just fine.

I didn't dig into it because I knew I was starting late and had to get to work in the morning. However, as a result of the false start, the EGI/TC fuse was indeed out for at least 30 mins before I put it back in.

This morning, I didn't think anything of it. I started it up and drove to work as normal. At one point, I had to get on the boost a little bit and flinched as I expected the stumble to say "NO you can't have more than 5 lbs of boost"... and it pulled normally! I tried a WOT run and it ran nice and rich at 9psi and didn't stumble. I wonder if the short I fixed hadn't tricked the ECU into pulling just about all the timing advance from the spark or what -- after the ECU lost it's memory it's driving great! Maybe it was just too much to learn back around in a reasonable amount of time without a reset. Must have been severe timing retard!

I still plan to replace the spark plugs and wires and fuel filter and run some seafoam this weekend -- but it's really awesome to know that the main issue has been resolved!


Edit: Even lower throttle and boost levels felt faster today than before. I'm really thinking the issue I was seeing was the ECU pulling / retarding timing as far back as it could and it was stuck there, possibly attempting to learn its way back to normal but unable to get good readings from the severely retarded timing.

[Legacy777]

Yup, it's always a good idea to clear the ECU's memory after addressing a problem.

[free5ty1e]

Whats wierd is I started the car at one point while this egi/tc fuse was removed and I had the car started and idling before I remembered I needed to put that fuse back in. I guess it doesn't prevent the ecu from seeing power but maybe just the memory circuitry. ..?

Sent from my SAMSUNG-SGH-I337 using Tapatalk 4 Beta

[Legacy777]

Yeah, the EGI/TCU fuse just provides backup power to the ECU's memory. It won't prevent the ECu from powering up.

[free5ty1e]

Aha! Athank you once more, Josh!

[free5ty1e]

Just in case anyone is interested in the state of my old spark plugs.. they ended up with gaps of:

Driver's side:
rear:.054
front:.051
Passenger side:
rear:.055 (needed cheater pipe!!)
front:.051

Originally they were gapped at .040. I suppose this is expected as the electrode gets burned away over time...? Anyway they were due. Car feels even better with fresh plugs.

Here are images of the old spark plugs side by side with the fresh plugs. All are NGK BKR6E-11 (I thought I got photos of all 4 but one is missing; oh well):