car idle drop

[98gsxNJ]

I have a 95 gsx a few upgrades done to the car redid the head cams front mount injectors, the car idels at 1g rpm but when i hit the clutch it drops and the car wants to shut off anyone have advice ??

 

[the_mork]

What did you do with the injectors? If they are bigger then what are you tuning them with? Have you done a boost leak test?

 

[Smurf2gGSX]

could be because of a vented BOV?

 

[fedj18]

I have a 95 gsx a few upgrades done to the car redid the head cams front mount injectors, the car idels at 1g rpm but when i hit the clutch it drops and the car wants to shut off anyone have advice ??

Yea depending on how big you went with the injectors you may be seeing the results of the car runng excessively rich at idle. I'd say if you went 100cc's or more larger you should get a way to remap the fuel injectors.

Also to compound on top of this if you went overly aggrerssive with the cams the combination of a rich mixture and changing the valve overlap can have serious affects on how the car runs at idle.

 

[the_mork]

I completely missed that you added cams. Changing your cams will have a hug effect on your idle and many people end up having to adjust it by using the BISS. Don't just start adjusting it though. There is a proper procedure outlined here. Visual Frequently Answered Questions - Home Page

For the record fedj18, any change in injectors should be compensated for. There is absolutely no point in placing different injectors in your car whatsoever if you don't tune them.

 

[98gsxNJ]

thanks guys i went back to the stock injectors alot better im waiting to get a dsm link to tune the car just money is a bit tight right now thanks for your help

 

[the_mork]

Have you considered other tuning options? Link is a great product but when money is tight there are other ways to go. Seeing as you have a 98 you can get a tactrix 2.0 cable and use ecuflash to tune your car for a total investment of about $220 including a very good logger (Evoscan). If you want more options like NLTS, electronic boost control, SD, knockCEL, etc. Then an evo8 ecu might be right for you with a total investment around $260 if you choose the 1.3 cable.

Tuning should be your next mod though. The FMIC, cams, and injectors you bought will give you almost no advantage until you have the ability to tune your car and make real use of them.

By the way please fill in your profile, if your cams are just re-done stock cams then you can ignore everything I've said about them.

 

[fedj18]

Well if you increase the amount of fuel that an injector sprays then the car will run rich due to the fact that the ecm is running the base fuel map assuming an injector of a certain size. that means that when the injector opens for 4 milliseconds on a 450cc injector you will get X amount of fuel, however if you have a larger flow rate injector (such as a 650cc) when the ecm runs the base fuel mapping and opens the injector for 4 milliseconds you will get approximately 50% more fuel than X.

The flow rate is based upon how much fuel is dispensed in a certain amount of time when the injector is held open. I'm not sure what the time and pressure standard are but I know that they should be measured off the same standards.

So assuming the injectors supply 50% more fuel for the same injector pulse width you would have to shorten the injector pulse width to meter the fuel to the correct amount, which all makes sense except that the ecm has a built in threshold for the pulse width limiting how far the ecm can adjust fuel delivery.

 

[the_mork]

You can assume 42.5psi for fuel pressure at all times because of the rising rate FPR (on a 2g, on a 1g with a manual transmissionI think it is 38.5 but you would have to double check and higher for the automatics), I'm not sure of actual IPW limits but I don't think there are any besides 0. A flashed ecu can handle 1000cc injectors and larger while maintaining a decent idle and well above that on e85. Basically there are no limits on injector size so long as the injectors can handle a small enough pulse width (short deadtime) to get the car to idle.

Generally in a DSM you don't need to talk about a base fuel map. We have injector scaling to handle different injector sizes and the fuel map translates to a desired AF map.

 

[fedj18]

but you still have a base that would be factory, as the engineers designed, mapping and from there you will get the long term fuel adjustments to adjust for conditons. but if you look at the fuel mapping the ecm will generally freak out if it's expecting the IPW to be beween say 2ms and 3.5ms at idle and you are running an injector that only requires 1-2ms. That is where things such as DSM link and other ecm tuning products come into play because they "override" the ecm's normal operation and allow the injectors to shorten the PW below the expected. Especially in a car that is OBDII and heavily reliant on the on board readiness tests used for emissions purposes.

 

[the_mork]

I think we may be on different pages here. If you are talking about using larger injectors in closed loop then I absolutely agree with you there are limits but the ecu will compensate to some degree. The problem with that though is that the car comes out of closed loop at WOT and high loads which means that putting larger injectors into the car can never be anything but detrimental unless they are adjusted for.

A flashable ecu can be adjusted so that it compensates for these injectors quite easily and has the same basic abilities as a system like dsmlink because on a basic level they operate the same way.

 

[fedj18]

Yes!!! and at idle and warmed up it would be in closed loop.

 

[the_mork]

I guess I don't know what you're getting at then since in closed loop the fuel map is ignored anyway.

 

[fedj18]

The fuel map is ignored in open loop because the car will run a cold start program keeping it extra rich until the car warms up and the o2 sensors are reading properly. once it is in closed loop it uses the long term fuel trim mapping as the base settings and the short trim as the current adjusted mapping. but the long term fuel mapping is simply calculated over many trips and is the learned mapping value.

for example, say you start off with your fuel mapping at the factory 0 setting and we'll call this 100% mixture because it is the optimum desired fuel map. The first time you drive the car the short term fuel adjusts to 110%, meaning that the vehicle is demanding 10% more fuel than the factory settings which would be 100%. Over time the Ecm will adjust the LONG term feul trim to 110%. From that point on the car will be adjusting the short term based upon the long term being at 110%. However if the short term starts adding 10% more fuel again the long term will then increase again to 115% or more. There fore there will still be the threshold where the long term adjustment will adjust to the max, however high that is, and no longer be able to compensate for running conditions.

 

[the_mork]

I understand how closed loop and open loop work quite well as well as cold start enrichment and a number of other routines to compensate for driving conditions and user inputs. What I don't understand is why you're telling me about open loop and closed loop when they don't particularly fit with the OPs question. We know that the car is capable of handling a small change in injector size at cruise and partial throttle but there there is no situation where larger injectors are beneficial if they aren't compensated for.

For the record open loop always references the fuel map even when it is in a cold start condition. There is a fuel table for cold start enrichment which is an "adder" and enriches each cell by a certain amount (the value of the enrichment cell). There are also enlean tables that pull fuel under certain conditions.

So what exactly are you getting at? Your posts seem somewhat unclear to me.

 

[fedj18]

I'm simply stating that larger injectors cannot be properly metered with a stock ecu. No matter what brand of car, you always have to have a fuel controller when you are modifying the fuel delivery of the injectors. That is the reason there are products like SAFC II, etc.

 

[the_mork]

I see, and I agree with you. Just for the sake of disseminating information though you should be aware that in general at this point 2g cars no longer need fuel controllers or external devices of any kind. 95 ecus have an eprom chip which can be changed to be set up for anything and also have the option of ecmlink. 98/99 ecus can be flashed to change literally any of the stock code. Evo8 ecus can be swapped into any DSM and are nearly as capable of adjustments as most full blown standalone EMS packages.

 

[fedj18]

Yes I'm aware of the EPROM etc. I have one in my 1g. But since he neglected to mention that he had the ECU reflashed or anything of the sort, I was assuming it was still OEM programming. BTW I used the SAFC II just as reference to the MANY options. I'm finally glad to see an actual discussion on here debating a subject and everyone can be mature about it.