Cranking Pulse-width/cold Start Valve Questions

[Paulusc44]

Recently fired up my S1 R25DE+T, engine has received alot of work over the last 6 months including larger turbo, injectors, fresh gaskets throughout etc..

First time starting with new setup and eprom tune.

Runs pretty good, still have a few little things to sort but its all there.

The engine now runs 550cc RX-7 injectors with walbro 255 LPH pump and adj pressure reg.

Its sometimes hesitant to start, I believe its putting too much fuel into the engine whilst cranking, I deleted the cold start valve when I did the new setup but am now thinking of putting in back in, I have done a resistance test on it and its perfect according to my R32 workshop manual, will this aid in supplying less fuel to the engine on start up? Or put the engine in open loop and put even more fuel in? basically, Will this help the engine start?

Any info/help is great as start up is really the only issue, it currently has no O2 sensor but I will be putting a new NTK item in over the next few weeks with new downpipe, vehicle has only idled/lightly revved so far.

Cheers

[GTSBoy]

The cold start valve lets air into the system. So it has absolutely no effect on how much fuel is injected. If you actually do have too much fuel at cranking time, then letting more air in won't be a bad thing.

The best thing you can do is do a Nistune ECu at least (or some other programmable jobbie) and deal with the starting mixture issue directly.

[Ben C34]

And the next best thing to do would be get some at least half decent injectors rather than those old heaps of shit in there now

[Paulusc44]

And the next best thing to do would be get some at least half decent injectors rather than those old heaps of shit in there now

The build was done on a planned budget so I only had x amount to spend on each item, 6 x 666cc or 1000cc bosh injectors go for $660 & $780 respectively here, IDs are no cheaper.. I picked these up for $280 shipped, have you actually thrown a pair of 20 year old JECS into a injector bench tester before? Hardly "old heaps of shit"..

[Paulusc44]

The cold start valve lets air into the system. So it has absolutely no effect on how much fuel is injected. If you actually do have too much fuel at cranking time, then letting more air in won't be a bad thing.

The best thing you can do is do a Nistune ECu at least (or some other programmable jobbie) and deal with the starting mixture issue directly.

Cheers GTSBoy.. Was originally going with a Nistune board as I can get them for a really sharp price here in NZ.. But due to study Im forced to sell the 32 and clear up funds.. Most people would sell the car as is but im one of those anal pricks and want top dollar haha

[GTSBoy]

Hardly "old heaps of shit"..

Actually, they are. It's not the quality of the spray pattern at high flow that has improved....it is how well they work at low pulse widths that is better with the newer injectors.

[Paulusc44]

Actually, they are. It's not the quality of the spray pattern at high flow that has improved....it is how well they work at low pulse widths that is better with the newer injectors.

I know the modern fuel-injector has a far improved idle (low pulse width and duty cycle) Im just not willing to write them off as "old heaps of shit"?? Tuned correctly, Idle isnt bad with older injectors, (remember were talking late 80s/early 90s JECS here) and as previously discussed, spray-pattern/atomizing of fuel at high duty cycle and pulse width is fine. My point is, this is a S1 RB25+T running a factory-like setup to achieve a simple 200-220 KW on low boost, not a built RB26 aiming for 400KW for example, spending $800-$1000 on injectors is foolish when one can get a set of S5 RX7 550cc injectors and dyno tuned Nistune board for $1200?

Edited May 28, 2016 by Paulusc44

[GTSBoy]

Well, to still keep refuting your point....once you buy some old dinosaur injectors, then get them cleaned and tested, you are most of the way to a set of brand new modern injectors. Using 2nd hand injectors without a clean and test is a lottery I'm not willing to play with an engine I care enough about to modify.