i'm running a SD TPI on a 350 TBI engine

sometimes (mostly when the engine is cold) it starts promptly in the moment i turn the key

but sometimes (happens oftener when the engine is warm) it cranks 1 or 2 revs before it starts to fire the injectors.


i was just wondering what makes the ECM to start with injector firing - i guess it's the reference signal from the distributor, right? but since i have spark on all 8 cyls from the first moment on, i think, the culprit cannot be the PickUp-Coil, but the EST module - anyway, it's a remanufactured distributor from S&P with new coil and module

BTW: even all other TPI related parts are new, all the sensors, injectors, pressure regulator, fuel pump, wiring (painless)... so i thought maybe it's not a hardware fault, but a problem in the software - is there anything i can look for in the bin? i'm using the S_AUJP as base file, but with modified VE and spark tables for the TBI block with very mild cam and heads that don't allow as much spark advance as the TPI heads.

 

Are you sure it's the injectors not firing right away? Usually this symptom is attributed to too much or too little fuel for the warmer engine on the restart, IAC settings and park positions, etc.

 

Sounds like a fuel relay symptom. The relays when they are going bad usually work when cold. When they get warm they fail. If you are running a oil pressure switch the fuel pump turns on after turning the car over and the elect for the pump goes through the switch. This is real easy if you can hear the 2 second pump prime when you turn the key on run the car and try it again when it is warm. If you don't hear the 2 sec pump prime then it is the relay or the ECM. Most usually the relay.

 

thats what i supposed, but shouldnt the S_AUJP settings work ok even on my engine?


yes i know, the relays are new - but i'll give it a try to give the fuel pump 12V on it's test connector

 

After you've confirmed everything else is NOT the problem,
There are a few bin changes that may help starting.
Startup Enrichment Vs Temp table at 8431-440
Startup Enrichment Vs MAP table at 846F-47F

If you have changed your injectors to a different size than stock 22#,
You may want to change the "Crank PW Vs Coolant Temp" table scalar value.
It is located at 83AD-83AE (16 bit value)
Change the value by the percentage diffeence of the injectors.

The table this effects is the "Crank PW Vs Coolant Temp" at 83AF-83BC.

Some have changed the table directly with results but RBob suggested to change the scalar for all the values to make the startup work with any size injectors.

There is also a "crank PW multiplier Vs ref pulses" at 83C7-83ED.
I've heard that can add more fuel during cranking but have not heard any results from it.
These are from $8D and will apply to the S_AUJP you are running.
HTH

 

thank you Sir

yep, i always take care not to try to solve hardware problems by software changes

but in case of my TPI, i guess i can say, theres everything ok with the hardware - but i will double check everything before i look into the bin

 

If you are running the old style relays they are notorous for going bad even new. Your question pertains more to a hard starting issue when the car is warm. The biggest factor is you have to have pressure in the rail to get the gas in the first place. I would highly recommend checking the line pressure before changing your bin in this case.

 

 

Does it start quicker if you cycle the fuel pump a few times, before you start it? Might have a bad check valve or leaking regulator or heat soaked fuel rails kinda vaporlocking.

Heard of a few guys advancing the timing. Might try that, get the engine hot and set the timing 4degree or so more advanced than your running now, see if that helps, if it does, change your base timing in your prom to reflect where you set it at. This seams to help because the only advance your engine gets during cranking is what your distributor is set at, once it gets past 400rpm IIRC the ecm takes over.

HTH