what is [1st & 2nd prime pulse width vs coolant temp] used for, is it for bank 1 and bank 2. also what is [added prime pulse width vs coolant temp] used for. Hey I got to ask, that's the only way that I will learn this tuning.
thanks

 

I'd like to know the official answer too, I interpret these as one of the cranking fuel calculations for the various coolant temps, Im thinking it's the initial injector fuel spray amount that the pcm fires when you turn the key to crank, but I dont know for sure... it would make sense since these types of settings are required for electronics to mimick the physics of which a carb does by design automatically (airflow drawn past fuel sitting behind an oriface gets pulled in via physics, fuel in an injector does not).

When my motor is cold it fires up strong in under 1/2 a crank revolution (seems faster than it should be for real) and when it's fully warmed up cranking usually takes longer, sometimes up to 4ish seconds until it fires up, if you tap the gas during cranking it will fire up right away.

This all happened on one of my injector scalings (im using 2bar sensor on a stock pcm). Anyway there is something temp realted about it so I assume it's these type of settings that need adjustment.

 

OK, I have found three answers and not sure which one is correct.
1 - the 1st and 2nd prime pulse width is used for bank 1 and bank 2, but there is a big difference in the numbers.
2 - the 1st and 2nd prime pulse width is used only for start up, bank 1 and bank 2, but there again a big difference in the numbers.
3 - 1st prime is used according the RPMs, when a higher RPM is reached the 2nd prime comes in, then at higher RPM the Added Prime Pulse Width comes in.

The last answer makes more sense to me being there is a EXt spark table to rasie or lower spark, so I think you would need to increase/decrease fuel the same way, if the computer doesn't put in enough fuel or take out enough fuel to get the proper afr according to load on the car.
Anyone have a better answer, I would love to hear it.

 

Official Answer:


Hi Dan,

1. 1st Prime Pulse Width Vs. Coolant Temp. table controls the injector pulse width of the first prime fuel pulse during cranking as a function of engine coolant temperature. Similarly the 2nd Prime Pulse Width Vs. Coolant Temp. table controls the injector pulse width of the second prime fuel pulse during cranking as a function of engine coolant temperature. These tables were in the '96/97 LT1 calibrations. In the '94/95 LT1 calibrations these two tables are combined into a single table (Prime Pulse Width Vs. Coolant Temp.).

2. The 'Crank AFR Vs. Distrib. Refer. Pulse Vs. Cool. Temp.' table sets the target AFR during cranking as a function of coolant temperature and the number of distributor reference pulses.

3. If the engine is still cranking after the time specified by the 'Added Prime Pulse Enable Crank Time Vs. Cool. Temp.' table then another prime pulse is output and the pulse width of this added pulse is specified by the 'Added Prime Pulse Width Vs. Coolant Temp.' table.

4. As soon as the PCM declares that the engine is running the fuel is temporarily enriched as specified by the 'Initial Startup AFR Enrichment Vs. Coolant Temp.' table. This enrichment is then gradually removed.


Best regards,

TC

 

dookie, thanks for following up on this.. printed it out and saved it in my tuning log book.... IMO looks like these tables should not be messed with unless your seeing long cranking required to start it up. Apparently these 3-4 tables are designed to replace you foot pumping the pedal on the old carburetor engines.. I did notice my "Added Prime Pulse Enable Crank Time Vs. Cool. Temp." table stock settings are out around 32-10 seconds depending on temp. Seems like a long time to keep it cranking before it shoots additional fuel. However I've never had any problems going past 1/2 sec to kick over, so the other settings must be working OK..

 

I have found that my car practically explodes to life on the first cold start, and it also starts differently on a warm restart. If I crank it immediately when warm, it will crank for a while, then start; however if I turn the ignition on and wait a second, then crank, it fires right up. In my car, it is probably a function of the fuel system I have built and the regulator I am using. I have considered trying to adjust the prime pulswidths to get a faster warm restart more like the cold start, but it isn't really an issue of I pause for a moment after turning the igniton on but before cranking it.

 

That describeds it perfectly, it really does explode to life when cold, ha

Do you wait to start it when cold? I would think a fuel system would cause lowest fuel pressure during cold start compared to warm start.

Either way increasing the pulse when warm should help.

 

yea I agree with you, most people dont have to mess with it, I think only the few that put huge injectors in AND scaled the injector consant drastically to run a 2 bar MAP, the stock numbers just dont do it at this point, makes sense since every other fuel and timing parameter's been adjusted aside from this.

 

kevin, looking at the stock ODB1 settings the settings, 1st/2nd prime pulse widths in msec below 70*F (20*C) are 39.1/39.1 . At 175*F (80*C) they are 6.3/3.1. Assuming your FP is OK it looks like you could try increasing the >175*F pulses duration to see if it effects hot start time. If you try it please post the results.. Bob D.

 

Kevin,
My warm start delay annoyance problem is all fixed!! Starts right up warm like it did when stock FINALLY! I also normalized the "exploding to life" cold starts as well.

All you have to do is LEAN out WARM CRANK FUEL in a couple tables:
1) Prime Pulse Width Vs. Coolant Temp
2) Crank AFR Vs. Distrib. Refer. Pulse Vs. Cool. Temp

Initially I thought it was too lean so I was adding fuel and this only made warm start worse, so I went back to stock then removed about 1/2 the values and sure enough when warm it starts right up quick and clean everytime! No more tapping the throttle to get it to start. Bout time