Strange operation (vaccum), misfiring at peak torque - 93 TW

[macipusy]

I want to see what you guys think about the strange vacuum readings on my 93 TW.

It is run by a Haltech standalone ECU and is running a speed density setup.

I've been having issues with the car lately. I thought the skipped timing belt was the cause of all of the issues, but apparently not.

I have noticed that my boost gauge basically moves to 0 atmosphere from 18 inHg directly proportional to the throttle movement. If I move the gas pedal, it is immediately at 0 atm. Does not matter if in park or cruising under load. There is zero delay between moving the pedal and the movement of needle on the boost gauge.

On the RSTi it takes a bit of RPMs to get to atmosphere, maybe a second or 2 delay.


This seems strange to me, and could be related to the misfires I am seeing in boost.

What do you guys think of this?

[robertpaige]

Is this a mechanical or electrical boost gauge?

[macipusy]

Mechanical.

I will verify this with my standalone, just to eliminate the boost gauge.

[macipusy]

I verified with the vacuum behavior with the standalone....blip the throttle. Immediately goes form 19 inHg to 3 inHg....a little strange, but maybe its normal for that car???

I did some logging and was able to catch the misfires. Break up happens at or right before peak torque, and sometimes after 5K rpm...more rare and mild.

I am running 8 psi, with 15 degrees of advance at peak torque tapering to 22 degrees at redline. On 91 octane. AFR is 11.5:1 tapering to 10.8:1 in boost.

When I pulled out 7 degrees, it was breaking up all over the place.

I'll try to pull out 4 degrees and see what it does.
I'll verify base timing to make sure 10 is really 10...
I'll do a vacuum leak test as well.

Ideas what else to look at.

I might swap back the coil pack and ignitor....I was swapping stuff when troubleshooting the skipped timing belt.

[Legacy777]

Where on the manifold are you teeing into for the vaccum/boost reading for the ECU & boost gauge?

I agree to verify base timing and do a vacuum leak test. Other than those things, equipment failure is what would come to mind for the misfire, but not sure how that would correlate to the vacuum reading.

[Legacy777]

Out of curiosity, have you done a compression or leak down test on the engine to see if there may be a sticking/leaking valve?

[macipusy]

I have not done a compression test yet.

Vacuum seems good while idling. It's just the quick ramp up which is strange to me, but might be normal.

The misfire and vacuum are probably not related. It's just strange how I notice all these things all of a sudden. Maybe the failing transmission was masking some issues and maybe the timing was always skipped a tooth or two on this motor since the junkyard.

I ended up pulling out 18 degrees from the trigger angle setting on the ECU, and it runs ok. Feels retarded, but no misfire.
When I used the timing light and locked timing at 10, it was showing -10. Pulled out the 18 from trigger angle setting to get it to move to 10....and then tested it by locking 0, it moved there.

My concern is that the notch on the crank pulley might not be correct, for TDC #1. That is what I'm using as a reference.

I need to take off the crank pulley and t-belt cover and line up #1 TDC, then mark the pulley at the 0 degree mark off the t-belt cover. Then I can verify base timing. I've been running the same settings as my 91SS, which was calibrated by a friend...I did not verify it, since we were tag teaming the standalone install back in 2007.

When I review the Subaru base maps for the ECU, they have the trigger angle 8 degrees more then my original setting, 26 more degrees then I have it currently. Something is fishy.

[Legacy777]

Let us know what you find out with the base timing. I used the timing mark on the stock pulley to set the base timing in my Link. I haven't gone back and verified it, but I'd be curious to hear what you find out.

[macipusy]

I will update this once I verify. I'm going to be gone for a couple weeks and won't have time until I get back.

For now I'm just running it on the safe side of things. But it sure is pointing in the direction of incorrect base timing.

[macipusy]

I have not had a chance to verify the bast timing yet. I will update the thread with the data, once I pull off the timing belt cover and verify TDC location to the mark on the pulley.

The misfiring started to happen again, even at the newly set conservative trigger angle.

I filled up the other day with new fuel....and all gone.

I am wondering if it was bad gas causing the misfiring under load.

[macipusy]

The misfiring came back soon after the new tank of gas, back in mid January.

I did a full inspection of the motor and found the FPR vacuum line was popped off. That did not solve the misfiring.

I double checked the base timing and it was set correctly.

Finally I removed the coil pack to test that and I found that the contacts on the spark plug wires coming into the coil pack were loose. The boots on the plug wire made it seem like they were tight, but close inspection verified that the contacts needed expansion. I used pliers to open up the contacts and the misfiring immediately went away.

Super happy with the find, since it's been 4 months of sub-par performance.

[Legacy777]

Yeah, that's a really good find!

The contacts going to the coil pack don't seem to be as robust since if metal is crimped tighter it loses connection. I guess that's one of the reasons they may have gone with the different style on the newer cars.

[Alphius]

Oh man, if I had seen this back than that would've been my first suggestion. A misfire at peak torque is almost always spark blowout caused by too much gap or weak spark. Bad contact on a plug wire definitely gives you weak spark. You can sometimes hide it by retarding timing which is exactly what you did. All that does is lower peak cylinder pressure and preserve the spark.

Also, I'm sure you're not worried about it now but your boost gauge/vacuum reading behavior sounds exactly right to me.

Good fix!