Double stoich, halve IFR = engine starts for a second then dies?

Hey guys,

2008 Silverado 1500 4.8L (non-flex fuel) w/ trick racing turbo stage III + AEM WBO2, everything else pretty stock.

I recently installed 95 lb injectors from Fuel Injector Connection (because my stock injectors were running 110% duty cycle at 3 psi!). I used the old double stoich, halve the IFR trick and wrote that. When I try to start the truck, it turns over, seems to start for a second, then dies. When I stomp on the throttle this keeps it alive for half a second longer but still dies (I wish I had a cable throttle rather than an electronic throttle, I feel it might stay alive longer).

I reverted back to stock stoich settings, maxed out the IFR table at 63.5 lb and now my truck at least runs, just really rich.

I haven't yet tried scaling the long way (especially because my VE values are expressed as coefficients, and haven't yet converted to values to use the custom 2 bar OS available), and wanted to know if someone could suggest why the double stoich/halve IFR didn't work?

Any help would be great, thanks!

Did you halve the IFR data that was there ? I believe you have to half the values for the new injectors, not the old ones.

I halved the IFR data for my new injectors. So the news values in the IFR tables were bigger than the stock values, though not nearly as big as the actual data would have been.

Is that the only change you made ? No clue then. I used that trick when changing injectors with no issue. I think you need to post up the tune. Is the injector data you have right ?

put stock values in with stock injectors, it should run fine. then cut the ifr and double stoich. it should run the same. then put in the new injectors with the half ifr and data

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Originally Posted by realcanuk

Is that the only change you made ? No clue then. I used that trick when changing injectors with no issue. I think you need to post up the tune. Is the injector data you have right ?

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Glad to hear the trick usually works! I will post up the tune tonight when I get home from work.

I'm not sure the injector data is right. Fuel Injector Connection has yet to send me the data. All I know is that they are supposed to flow 95 lb @ 43.5 psi, so from that, I calculated what they should be flowing at all the other pressures using the formula: new flow = old flow * sqrt(new pressure/old pressure).

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Originally Posted by carlrx7

put stock values in with stock injectors, it should run fine. then cut the ifr and double stoich. it should run the same. then put in the new injectors with the half ifr and data

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That's a good idea, it would be a good test. It would just take me a bit of time to swap the injectors now that the new ones are installed. I'm thinking it might be quicker to gradually increase the stoich and decrease the IFRs and see if there comes a point when the truck dies. Thanks for the suggestion though.

Thanks for the reply Carlx7,
by data you mean flow rate vs kpa, short pulse limit, adder, injector offset vs volts etc?

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Originally Posted by ttbestas

Thanks for the reply Carlx7,
by data you mean flow rate vs kpa, short pulse limit, adder, injector offset vs volts etc?

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The only data I changed was the flow rate vs kpa ... do the others changes with different injectors as well?

yes, Injector data includes a lot more than just IFR vs KPA. I think we just found your problem.

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Originally Posted by carlrx7

yes, Injector data includes a lot more than just IFR vs KPA. I think we just found your problem.

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so when doing the stoich trick, your saying that we also need to halve the offset, short pulse adders and limits,and min inj pulse ?

im also having problems on scaled injectors on cold start but have only doubled stoich and halved the IFR - the other injector tables i have left as the ID application data has given

bump ...

I've mostly fixed this problem. At first when I had problems, I just reverted to stock stoich and put max IFR (63.5) across the board which for my 100# injectors resulted in a really rich mix, but I had no problems starting, so I figure it was a low fuel issue.

Then I doubled the stoich and used all the injector data (rather than just IFR vs KPA) which made a big difference, but still isn't perfect. I increased the cranking fuel by 20% which seems to help some, but now it sometimes stalls as soon as I try to put it in gear cold. I'm thinking of maybe upping the idle for low ECTs.

IFR multiplied by .5 and AFR multiplied by 2 works wonders. The first time I did this I doubled my AFR so it was like 7.3 and had the issue you did .

Without your offsets Im not surprised your having issues though.

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Originally Posted by rob-ecc

so when doing the stoich trick, your saying that we also need to halve the offset, short pulse adders and limits,and min inj pulse ?

im also having problems on scaled injectors on cold start but have only doubled stoich and halved the IFR - the other injector tables i have left as the ID application data has given

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Can someone please answer if these additional tables need halved as well??

...I've been chasing my tail now for awhile, would be a nice breakthrough...

Take the injector flow rate of your new injectors and plug them in as half of what they are.

Then, double the stoich AFR table.

Do not screw with the short pulse or offsets.

Thank you Dsteck.

I was actually just coming back to say I think I found my answer (..answered by you in another thread..)

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Originally Posted by alexl226

Thank you Dsteck.

I was actually just coming back to say I think I found my answer (..answered by you in another thread..)

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You still need proper data for those tables.. he isn't saying leave it stock. He's saying leave it as supplied from the injector manufacturer (assuming you have data from them). Just wanted to make sure that was clear.

And I'm using the double stoich/half IFR technique right now on mine and it works perfectly fine

Yes. That is clear. I have id725's and the appropriate data entered. Running MAF only for about a year and it works...good. I feel there is still an underlying issues however with transients, as throttle response is lacking and I cannot for the life of me get above 9 or 10 mpg..