Fuel rail back pressure

[TNT4x4]

Fuel rail back pressure how much is too much? i have recently turbo'd my G16B single point injection and to get rid of the lean miss up high i have installed a pressure regulator on the return line to the tank, the reg is running the fuel px at 60 psi. I am only running 6 psi boost and it is still missing at around 4500 rpm. it is alot better however are there any after market injectors or what is the max back pressure i can run.
ps only new to asking for help on forums so be nice please

[11_evl]

back pressure can be as much as the fuel pump can handle. what your probably finding is your fuel pump cant keep up at 60psi.. its not the right wat to fix the problem by just uping psi but you can upgrade to a better pump to help out

[TNT4x4]

hi i have installed an overhauled VL pump so the amt of px should be fine just wondering what else i can do to fix the problem. is there any way i can change the duty cycle of the injector or are there larger injectors available. i know what i have done is not right but it is a bandaid fix to get the thing going

[zook4fun]

what else have you changed? is it a stumble or a big miss.

with forced induction you only need to up the psi buy 6 psi for the injector to work properly any way but are you maxing out the injector?

my bet is its got something to do with timing, heat range of plugs. have you put one way valves in the air lines?

[TNT4x4]

It is a definite cough (total loss of power). it only happens if i really stab it, gentle acceleration is fine. have changed the plugs not the timing and what air lines are you referring to as there is only a MAP connected and i figured it needed to be there. what timing should i be running? I believe that i have maxed the injector. is there a larger one available? is there a way to open it longer? there is a large resistor in the circuit for the injector and it will not run without it, i have tried to put a large pot in there to adjust the voltage and it did not work either. I personally grafted the motor and computer into an 88 1.3, including the wiring loom.(so i am not completely retarded) That is a job for the auto elec next time. i really do appreciate the advice as this is the first forced induction car i have played with. i just want to go wheelin soon

[zook4fun]

is the dizzy on it vac advance or the 4 pin elec one? it its a vac you need a one way valve in that.

i'd start about 8 btdc and go from there

[VooDoo]

From what i can tell you have 2 issues

Fuel volume and Fuel pressure.

A VL stock pump wont do either. You need a rising rate regulator and plumb it in to your vacume/boost line. That way when you run 3psi you get an extra 3psi of fuel pressure (and at 6psi obviously 6psi of fuel pressure)
You may also need a surge tank or at worst ensure you keep the tank over 1/2 full. Do you run a return line? Ive seen some issues with them being to large and flowing too well.


a Maxed injector means its open 100% of the time. IE you cant make it open longer. Having the resistor in the loom means the wrong ones are being used (but not uncommon) as there are high impedance and low impedance drivers for the PCM's. Its the cheats way around it and does open you up for some electrical weirdness from time to time.

[TNT4x4]

thanks for the help. the dizzy has two wires and the coil has four the timing is at 10 deg already with no pinking maybe more needed, there is no vac advance all electronic from the comp i am assuming. i have a rising rate reg and it is plummed into the return line to the tank and the upper deck px, this was supposed to increase the px on the injector and trick the injector ie. more px = more fuel for the same duty cycle (local mechanic) and it did work (almost) but i fear it should not be a permanent fix. the resistor came with the front clip i purchased, silver box, 2 wires, heat sink, suzuki part no, if not there no go. The VL pump that i have will do 80 psi easy....... but for how long? the pump scares me the most, so much so that i carried a spare in the breakdown box even before the turbo. this pound for pound fuel for air seems to be a myth from what i am experiencing ie. 3 psi fuel for 3psi boost. so far i am 60 psi fuel and 6 psi boost and still cough cough. agghhhhh

[VooDoo]

If you have 6psi pushing up against you injector then you need 6spi pushing down before any fuel comes out. Changing the timing of the injector to compensate for boost seems a VERY weird way of doing it. Of course there will be more fuel required and basic timing changes but without the RR Reg hooked up correctly your not getting the right amount of fuel to begin with and your mechanic is purely guessing. There needs to be a boost referance to the reg. It wont ping (its not called pinking) as you will be overfueling it rather than leaning it out. The VLT pump is only rated at 130L @ 3bar which is good for around 250hp. A decent 040 bosch is up around 235l and a much better replacement. Just because a pump can do 80psi doesnt mean it has the volume of fuel required. PSI is only a measurement of restriction not of flow or volume.

[TNT4x4]

i appreciate that the pump can "only " do 250 hp i am pretty sure i am nowhere near that. But i ask you this! if the pump can supply an rb30 (3000cc) at 7psi at 6000 rpm why can it not supply a 1598cc at 6psi at 4500 rpm? one more thing and i hate to correct you but the correct term is "PINKING" it is just that most laymen call it pinging therefore it has become folklore, as the "k" has been lost due to slang. i do not wish to insult any ones intelligence. i have 20+ years as an aeronautical engineer and this is the first "CAR" i have force fed, aircraft are like boats in the respect that they are set at a power setting and it does not change ie MAP and RPM remain constant no acceleration it is a "static" setting. Cars are a dynamic setting ie the rpm changes so does the fuel. once again i do not wish to be rude i am just curious how a pump can power an engine that is essentially twice the size happily and not mine

[VooDoo]

A smaller engine can require more fuel than a larger one. As ive said, psi is a measurement of restriction not of volume. You can have 60psi of fuel pressure but with very small fuel lines and have the pump keep up. Compare that with 60spi with larger fuel lines and the pump struggles. One of the very first mods recommended for VLT's is to replace the fuel pumps. If your using the original stock ones then no it wont keep up. Even on a stock car it struggles. The 040 is a direct replacement with a much better flow rate. Dont just look at the pressure, look at the volume required. You may also find that your injectors are actually to big. Does it idle ok? OH and Pinking is the UK term for pinging (used in the rest of the world) both are correct but in Australia we use pinging.

(you never mentioned the engine combo so ive tried to keep things as generic as possible)

[TNT4x4]

sorry by the engine combo i think you mean G16B tbi and the turbo is a single from a nissan GTR twin setup. before i restricted the fuel return i was not able to get it over around 2500 before detonation (lean miss) the timing and plugs helped but the regulator on the fuel return got me to 4500 rpm under full nose but 60 psi was starting to raise alarm bells so i checked the pump and it is definitely VLT(it came out of a mates vl running 18 psi boost) i am pretty sure that volume is not the issue. it may still be that i need more advance or different plugs. this is my first time asking for help on forums

[11_evl]

To me the TBI is the problem. I just assumed it was MPI. I think tbi is single or double injector which means you could jam 100 psi up it's bum and still not help.

Out of curiosity, with the return line in a cup (after reg) how much fuel is returned??

[VooDoo]

sorry by the engine combo i think you mean G16B tbi and the turbo is a single from a nissan GTR twin setup. before i restricted the fuel return i was not able to get it over around 2500 before detonation (lean miss) the timing and plugs helped but the regulator on the fuel return got me to 4500 rpm under full nose but 60 psi was starting to raise alarm bells so i checked the pump and it is definitely VLT(it came out of a mates vl running 18 psi boost) i am pretty sure that volume is not the issue. it may still be that i need more advance or different plugs. this is my first time asking for help on forums

My appologies if my posts come across as harsh or critical. I am genuinely trying to understand your issue and attempting to help. I run a 408ci supercharged LS1 at over 800hp so fuel systems are critical. In your case its even more so as you can kill the engine in seconds with a lean out. How are you measuring fuel pressure? Have you checked each injector? It could be a simple timing issue and tune. More advance will just lean it further. Has it been tuned correctly or just by eye? What does the dyno show? Have you measured the AFR's accross the rev range? Have you logged the fuel pressure? It does sound like a pretty serious fuel issue but without knowing the exact setup its had for anyone to diagnose the issue.

[zook4fun]

its not the pump, i had a turbo sierra with a vl pump and no problems ever!

going around in circles but have you had a guage on it and it tell you its got 60 psi at the tbi? if yes its not the problem you have plenty of fuel next qusetion is if the injector big enough to get the fuel into the engine? need to know what size injector it is

is your mechanical advance working right?

whats your plug gaps/ heat range where is the timing burn mark on the plug? this might help

http://www.4secondsflat.com/Spark_plug_reading.html" onclick="window.open(this.href);return false;

also when is it coming on boost? is it holding boost even or spiking?

[TNT4x4]

hi guys sorry for the no reply i really do appreciate all this time and knowledge being shared. firstly there us buckets of fuel being returned to the tank so volume/flow is not the issue. yes i have a rising rate regulator with a gauge attached which i took to work today and checked for calibration it is pretty close. the advance is controlled by the MAP sensor i believe now here is where the fun begins, i am unsure if the MAP sensor can measure above 30" or 15 psi (standard atmosphere) i am also unsure if the computer can accept values for the timing, A/F ratio above Standard atmosphere in its mapping. the base timing will be changed on saturday as i have access to an O2 sniffer and data logger from then. the plugs are just NGK R plugs which a mate uses in his R33 at around 650 hp maybe the gap is wrong? i will find out. as for the size of the injector it is the standard injector there is only one maybe another is required in the plenum on a map switch. lastly i am not running the O2 sensor in the exhaust( i was told it only does fine adjustments. maybe time to get the thing connected.) also there is no air temp probe in the plenum it is attached to it but not inside maybe it is time to drill a hole and install this too

[VooDoo]

ok, with that info we can get somewhere.

Firstly the O2 sensors are basicly a narrow band sensor that reads your AFR's. This helps the ECU control fuel as does the air temp sensor in the intake. I wouldnt think that the car would fail to rev without them but the tune will be a lot better and smoother with them.

You definately need a 2bar MAP sensor for boost (or even a 3bar for safety)

You can tune the car in open loop where it will ignore the O2's but unless you have logged some decent dyno time im guessing that hasnt happened. Some good info on the types of tuning can be found here http://www.enginebasics.com/EFI%20Tunin ... %20o2.html" onclick="window.open(this.href);return false;

[tazmanier]

Quick question. Does the engine have a MAF sensor with a vane inside it that moves as air flow increases, or a MAP sensor that can be somewhat smaller and just measures pressure? Some might argue that the difference between the two are semantics but I thought the older G16B’s had a mechanical MAF sensor.

You have probably figured it out by now but your injectors are modulated so no resistor in line with them will change their duty cycle. The main influence on their duty cycle (how much fuel is released) is the MAF sensor input (how much air is coming in) therefore giving a correct mixture.

From reading these forums for a while I believe the O2 sensor has very little effect on the air/fuel mixture and when disconnected or not working correctly the computer defaults to the safest setting which is a rich mixture (what you want)

I’m also GUESSING that the air temp sensor doesn’t matter much either, perhaps a way to test this is to disconnect it and see if the engine runs. If it does then I can’t see it changing the mapping that much. My logic is that if a sensor can dramatically change engine performance then as an engineer I wouldn’t let the engine run without it. My logic also says the engine will default to the safest setting, a rich mixture.

Also wondering are you in the Air Force?

Ah one more thing now I read the title, you could pinch the return line somewhere where its rubber during pinging, raising the line pressure and see if it helps?

Cheers.
-Sean

[Drew]

most single point injection systems run low fuel pressure 15psi odd ,they have been known not to open with excessive pressure.

sorry but i think you best bet is multipoint & programable ecu

cheers Drew

[TNT4x4]

you are correct MPI is the way to go however i am on a strict budget. no offence but this is my first ZOOK and you guys are mad, which i suppose makes me even more insane. i came from an 80 series running 37 and hilux running 35's to a Zook on 33's having said that the thing is TOO TOO much fun. (i digress) so on sat morning i will be putting an external O2 sensor on and doing some tuning plugging and unplugging sensors pulling plugs and dicking around with the timing

There is a TPS and a MAP no MAF the engine is out of a 89 swift i believe.

And sorry no i am not in the airforce i run a small workshop of 8 on in sydney

[zook4fun]

another qusetion is the maf before or after the the turbo? if its after try moving it to before it so its not getting boost but still reading how much air is going into the engine.

[TNT4x4]

Hi guys sorry for the slackness i am sure you are hanging on every post (LOL) i have been busy with work but have finally had a chance to do some. ok so here is what i know at the moment after putting a wideband O2 sensor on i have discovered that the fuel mixture at idle is 10.3 : 1 which is rich but doable. at 5500 rpm with 6 psi boost the fuel is 13.6 : 1 with a rising rate regulator set to 25 psi at idle so the mixture is great. therefore the injector can handle the excess airflow (ie not maxed). I stupidly purchased a 1 bar map sensor thinking it would be 1 bar above atmosphere however 1 bar means 1 bar total as in for naturally aspirated cars only, despite the dude telling me otherwise. lesson learned. am waiting for a 2 bar map sensor now as the pop i thought was a lean mix is the computer cutting out as the excessive map is telling it to. the base timing has been as far as 10 degrees retarded and still it cut. monday the new map sensor arrives so hopefully tuesday will be a very happy one

[TNT4x4]

hi guys it has been a while. i had given up until rego was due so here is the solution to the problem for the next bloke

1 rising rate fuel regulator set to 30 psi base pressure
2 standard map sensor with 40 ohms of resistance in the +5 volt wire to confuse the computer
into thinking that the 7 psi is max standard atmospheric now 4.6 volts = 7psi
3 timing set to 1.5 degrees advanced with the computer test wire (purple on my install) grounded

i hope that this helps someone. thanks for the correspondence

Cheers Brett

[redzook]

hi guys it has been a while. i had given up until rego was due so here is the solution to the problem for the next bloke

1 rising rate fuel regulator set to 30 psi base pressure
2 standard map sensor with 40 ohms of resistance in the +5 volt wire to confuse the computer
into thinking that the 7 psi is max standard atmospheric now 4.6 volts = 7psi
3 timing set to 1.5 degrees advanced with the computer test wire (purple on my install) grounded

i hope that this helps someone. thanks for the correspondence

Cheers Brett

so did you end up getting it to run nice?
i am also running the single point injected swift motor so i am keen to hear how you like the turbo and if you would do it again

[TNT4x4]

on the road it is awesome however with the vitara centres and the rock hopper transfer it screams through the gears really quick. i have played a little on some boulders and i can feel the difference but have not really had a good wheel yet. it runs sweet, all really clean, smooth through the range on and off boost. it boosts really quick as the turbo is probably a little small ( off a nissan gtr twin RB25 but i am only running one) maybe an intercooler will fix it but it! which is stage two of the plan. it does not spike in boost and no noticeable lag. would i do it again? yep i would. i enjoy engineering things, i also grafted the engine/computer into it myself. i will see if i can get some pics uploaded on the weekend.