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Miss when hot, and fan running. Microsquirt

HiSPL

HiSPL

Fanking Champion 1993
Joined
Jan 8, 2015
Location
College Station, TX
I have a persistant miss that happens every now and then which I believe only happens when the engine is hot and the E-fan is running. I have the OG 80 amp Bosch alternator, but when watching my voltage in TS it never goes below 12.7. The voltage, however never fully goes to 14.4 while driving (measured by the ECU) but is in the 13's.

What could I look at to start chasing this down? Is it an interference issue with the fan running? I'm not showing any sync loss.
Is it just low voltage/too heavy a draw to run the fan?
Old Coil/low voltage situation? It's the OG bosch/distributor setup my car always had (1988, LH2.2, Chrysler-ectomy).


Where should I start poking this bear?

Car is an 88 244. Microquirt conversion. Original coil and distributor. Using the Original hall sensor in the the Distributor. No crank/cam sensor.
 
Charging voltage between 12.7 and mid 13s is fine. You may need to use a scope to catch any low-voltage spikes when the e-fan kicks on and off. You could try disabling the voltage filtering in the MS and see if it shows more variation - in General Settings, set .../Battery/... lag factor to 100 for no filtering.

You'll need to figure out how to get it to misbehave and run a Tooth Logger log, plus a normal log, while misbehaving. It may not be possible for MS to detect a sync loss with the stock LH2.2 distributor due to the low tooth count (only 2 teeth per rev).
 
bobxyz said:
Charging voltage between 12.7 and mid 13s is fine. You may need to use a scope to catch any low-voltage spikes when the e-fan kicks on and off. You could try disabling the voltage filtering in the MS and see if it shows more variation - in General Settings, set .../Battery/... lag factor to 100 for no filtering.
Click to expand...
Great idea!

You'll need to figure out how to get it to misbehave and run a Tooth Logger log, plus a normal log, while misbehaving. It may not be possible for MS to detect a sync loss with the stock LH2.2 distributor due to the low tooth count (only 2 teeth per rev).
Click to expand...
Yeah I was unsure of how well that would work and exactly how to read it since it's a trailing edge setup.
 
Is this like a continuoual miss whenever the fan is on or just when the fan kicks on
 
I might have figured it out. Happened to be watching the dash in TS at a stop light when it had a "miss".

It is activating accel enrich when I'm sitting still with my foot off the gas. The miss could just be a rich bog.

Put my TPS dot up on the screen and sure enough its jumping around at closed throttle. Not sure if its the sensor or noise, but its rock steady everywhere else. Only at full closed throttle does the tps dot jump around.
 
HiSPL said:
I might have figured it out. Happened to be watching the dash in TS at a stop light when it had a "miss".

It is activating accel enrich when I'm sitting still with my foot off the gas. The miss could just be a rich bog.

Put my TPS dot up on the screen and sure enough its jumping around at closed throttle. Not sure if its the sensor or noise, but its rock steady everywhere else. Only at full closed throttle does the tps dot jump around.
Click to expand...

Do you have an idle valve?
 
HiSPL said:
I might have figured it out. Happened to be watching the dash in TS at a stop light when it had a "miss".

It is activating accel enrich when I'm sitting still with my foot off the gas. The miss could just be a rich bog.

Put my TPS dot up on the screen and sure enough its jumping around at closed throttle. Not sure if its the sensor or noise, but its rock steady everywhere else. Only at full closed throttle does the tps dot jump around.
Click to expand...
Yeah looks like that's it. Your tpsdot threshold is set to 20% but the added enrichment thing starts at 125% tpsdot. So whenever the TPS noise hits 20% it's adding that minimum 2.5pw enrichment.

JQVqdTw.png


Try changing the highlighted things to something like this

The TPS in my car has wayyy more noise than yours by the way. I just tuned around it because I gave up on fixing it for real.
 
@Cwazywazy - great catch finding the minimum point on the TPS AE enrinchment curve of 2.5ms / 125% versus the 20% threshold. MS doesn't interpolate off the end of the curve, so it uses the 2.5ms fuel adder for TPSdot between 20% and 125%, which is way too much at idle.

@HiSPL you might also want to disable TPSdot uses %WOT mode - it effectively multiplies any TPS noise at idle by ~5x based on your curve:
TPS WOT curve.png

You can see when the fan turns on and off by plotting the On/Off Outputs Status Bits value.
 
bobxyz said:
@Cwazywazy - great catch finding the minimum point on the TPS AE enrinchment curve of 2.5ms / 125% versus the 20% threshold. MS doesn't interpolate off the end of the curve, so it uses the 2.5ms fuel adder for TPSdot between 20% and 125%, which is way too much at idle.

@HiSPL you might also want to disable TPSdot uses %WOT mode - it effectively multiplies any TPS noise at idle by ~5x based on your curve:
View attachment 35045

You can see when the fan turns on and off by plotting the On/Off Outputs Status Bits value.
Click to expand...
I will then.

AE has been the hardest thing to wrap my head around so far.
 
bobxyz said:
you might also want to disable TPSdot uses %WOT mode - it effectively multiplies any TPS noise at idle by ~5x based on your curve:
View attachment 35045

.
Click to expand...
I didn't know it worked like that. I assumed it just ignored tps above whatever % it's set to. How are you supposed to stop it from going really rich if you hammer down at low rpm?

HiSPL said:
I will then.

AE has been the hardest thing to wrap my head around so far.
Click to expand...
After you figure it out, turn on EAE for a new and exciting challenge/headache.
 
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