Backfires pop off valve in blower manifold

[dp_rcp]

Ver 2.02 Board, MS-II Card, 2.920 Code
'57 Corvette, 355 cu in GMC blower, Enderle 3 port hat, B-W 4 speed

These problems have been tormenting me since I built this car in '08. I thought the MS-II, which I installed during this past winter, would help because of the 12X12 tables, but no dice!

When I try to accelerate, the engine will backfire or stumble depending on how hard I step on the pedal and it is not predictable that I can tell. I also cannot get a stable idle. Once I can get past the trouble spots and I can get the rev's up a little, it pulls like a freight train but it goes to around 10 and richer AFR. When cruising at a steady throttle, the AFR is around 12.3ish to 17ish and with a little more (careful) pedal pressure it might bang or gag or go pretty good. It is scary fast the few times I've had the nerve to half way try it!
I have been reading everything again and again and probably missed something.
Thanx,
Dennis
Here are some data logs and .MSQ.

CurrentTune.msq

2015-06-10_18.21.08.msl

2015-06-11_16.51.19.msl

There are more logs but they won't go.

[Bernard Fife]

Dennis,

Backfires and stumbles sound like accel. enrichment issues to me. Have you tried tuning the AE? There is some advice here: http://www.useasydocs.com/details/us3tune.htm#accel Don't try to tune accel enrichments with the EGO sensor, it doesn't work well. Instead, tune for maximum engine responsiveness at various rates of opening the throttle.

Resets can cause all sorts of drivability issues so it's good that you are on top of that.

Lance.

[dp_rcp]

Wide band AEM O2

Lance,

Since I installed the MS_II card I can set the tpsdot & mapdot threshold to 255 and any combo of 0% to 100% in the AE Wizzard and still get the (green) accel LED on the MS controller to light. any # lower than 255 and any % will cause the green LED to blink while idling and stay on if I tap the accel pedal and will flood the engine if I let it. If the engine stalls the Green LED will stay lit until I turn the key off. There is a lot of action on the graph at all settings. Gad this is hard to explain!

Before I up graded to the MS_II card I could turn off the AE with a tpsdot threshold of 5 to 49. 2.3 would allow AE without uninvited accel So I had some AE control with the 69hc908 and have no control with the daughter card.

Is there a reason for suggesting the microsquirt tuning page? If so what do I look for that is different than the MS-II ver 2.2 board and how will it work?

I was hoping the timing feature would help make this car run better on accel but it didn't.

I am not so sure those are resets now because I don't see the "reset x" counter displayed at the lower right corner of TS so if they are not resets, what could those tach counts going to '0' be? I really don't notice the engine hick-up while running steady state.

This car has an ammeter and the alternator wire (10 gage) and battery wire (12 gage) from the starter runs along with the MS wire harness thru a grommet above the bell housing in floor to the ammeter.the area between the grommet and ammeter is where the MS controller is located. I am in the process of moving those wires over to the right side of the car and through the floor and maybe use a voltmeter instead.

Dennis

[Bernard Fife]

Dennis,

I don't see an instance in either log where the accel enrichment is being triggered inappropriately. Every time the AE is invoked the TP (throttle position) is moving substantially. I don't see any incidents where the AE is triggered but the TPS is not moving.

In the first log, the fuel spikes from 3.381 msec to 14.873msec when the throttle is stabbed from -1.3% to 100% in 1/8 of a second, which seems like a lot to me. (BTW, you should calibrate the TPS).

In the second (non-alternator) log, the fuel pulse width is only going from about 10 to about 12 in your log, and that may not be enough (backfiring in the intake is a classic sign of a lean condition under accel). So you might want to raise the accel enrichments to get the best response.

But it's not clear from the logs where the problem is occurring. I would expect a backfire to produce a large positive spike in the MAP reading, but that happens only once that I can see.

You MAP doesn't appear to change at all in the non-alternator log. Was the MAP sensor hooked up then? In that log, it only varies from 97.2 to 97.3, and I don't think that is correct. The rpm doesn't change at all either (1912 to 1913), for dozens of seconds, is that right?

RPM and MAP do change in the alternator log, where the MAP spikes to 113.7 at 638.282 seconds. That's not a huge value to spike to, but it does seem to indicate a cough in the intake (and not boost building). However, I suspect the cough is the result of the immediate decel event reducing the fuel to 20% of the normal value while the MAP is still high. 20% is probably much too low for the decel enrichment (actually an 'enleanment').

If this was mine I would set the decel fuel amount to 100% until this is sorted (you can lower it later once you have it running properly). The I would start from scratch tuning the accel enrichments.

It looks like you have XTau turned off, but check it to make sure.

There is more here: http://www.megamanual.com/mt29.htm#tl and here: http://www.megamanual.com/mt29.htm#u

Lance.

[dp_rcp]

Lance,

I set the decel fuel to 100% and tried to play with AE with no good luck at all. Still seems like not enough fuel (backfiring hard against the pop off valve) or too much fuel (activating acc LED with attempted tip in or just idling at around 900 to 1300 RPM). Then I re-routed the battery and alternator wires away from the MS wire harness to the right side of the car and continue to the ammeter. I also moved the MS-II card to my other 2.2 board thinking something may be wrong there. Didn't change anything. I have decided to try to fix these RPM drop outs but am unable to grasp what I see on the logs so I am hoping to get some insight. I think this is a good one. I am standing next to the car at the left rear wheel while the engine idles.

Those other data logs were done with the stimulator. My apologies. The pop off valve is relieving the pressure before it gets very high so you may not see a big number but I've seen 196 kPa on one of these logs. Found it.

CurrentTune.msq

2015-06-19_13.51.40.msl

2015-06-11_18.42.44.msl

[drholl]

I spotted the tach going to "0" in one of your posts. A long time ago I had that happen with an old (many years of use) HEI distributor that had a reluctor that was losing its magnetism. I didn't know that magnets could lose their power. The "back EMF" from the little coil in the distributor caused this weakening in the magnet over many years. The "0" RPM caused many issues with the idle also. Like the 4 seconds of startup "high idle" etc. My problem was most noticeable at lower RPMs, particularly stopped at a red light, just as it turned green. Bummer.
I bought a rebuilt HEI, problem solved. The old HEI spun freely. The new HEI was sticky, it sort of "clicked" as it was spun and wanted to stop at one of the 8 posts on the reluctor.

I hope this helps.
Holl