TPI cold start injector ?

[iroc343]

I have a 1987 IROC that I have installed a fast burn 383 utilizing the TPI system. It seems to be very rich upon initial start. It runs fine once it's got some heat in it. That leads me to believe its something to do with the cold start injector. The TPI is the same as it was on the 350 that was in there prior and it ran fine then. Can anyone tell me what triggers the cold start enrichment mode?

[89IROC&RS]

this sounds like a morley question........ (one of the more technically knowledgeable members here)

but if i had to guess, id say the increased displacement and larger cam are drawing a helluva lot more air thorugh the MAF than the 350 did, and the increased air flow is triggering the computer to enrich the mix, but why its only doing it durring warm up... im not really sure of. It probly did the same thing with the 350, but its reacting more with the increased displacement.

to get rid of it youll probly have to reflash the EPROM or something along those lines.

[Genopsyde]

agreed, a chip program is definately needed to run that engine properly.

[Morley]

The cold start injector is a totally independant system (no ECM function). It uses the thermotime switch located in the front of the intake manifold next to the coolant temp sensor. The switch activates when coolant temp is below 95* F and runs for up to 8 seconds (depending on actual temp), which triggers the coldstart injector.
What I did was disable the cold start system and reprogram my chip with a modified version of the ARAP .bin file (1989 Corvette program) and did further scans and reprograms to fine tune it. The ARAP .bin doesn't use the cold start injector, enrichment is handled by the ECM using the engine's injectors.

With the bigger cam and displacement your O2 sensor is probably reading quite lean, so the ECM is dumping fuel in to try to compensate. You need to get a scanner on it and see what the BLM's are reading. A BLM of 128 is optimal, higher than that is lean, and lower is rich. The leanest it can read/indicate is 160 and the richest is 108. All of this is done in closed loop mode.

A question...what injectors are you using?

[wrightz28]

Originally Posted by Morley

It uses the thermotime switch located in the front of the intake manifold next to the coolant temp sensor. The switch activates when coolant temp is below 95* F and runs for up to 8 seconds (depending on actual temp), which triggers the coldstart injector.

So that's what the hell that "sensor" was Never really dug into the injection system, but when I replaced the CTS I couldn't fathom what the heck it was.

[iroc343]

I am using accell 24 lb/hr injectors. Funny thing is, as long as I keep it running and cleaned out for 30 seconds it's fine.

[Morley]

Originally Posted by iroc343

I am using accell 24 lb/hr injectors. Funny thing is, as long as I keep it running and cleaned out for 30 seconds it's fine.

It only "seems" fine. Your rich condition in open loop tells you that something isn't quite right. You are running a MAF TPI system. Because the MAF sensor knows exactly how much air is entering the engine it can compensate for a multitude of "sins" (mods). If you were to run a scanner while your engine is in closed loop I would bet that your BLM's were nearly firewalled at 160.
The Accel 24# injectors aren't 24#. I used to have them in my car after switching from a 305 to a 350 with heavy mods and I had to "lie" to the ECM and tell it they were 20# injectors (makes the injector pulse them longer) to get my BLM's down to the low 130's. I finally replaced them when I got the Accel TPI base and put in LS1 injectors (25#) and only had to fib a little to the ECM to get the BLM's to read 126-130 (the "happy" range).