my car has been idling very low when i turn it on then it just shut off after changing the iac valve and fuel filter i think my problem is the fuel pump it turns on I checked it by giving power to diognostics plug but i believe is not giving enough pressure what other possible things might be wrong? and also if it is the fuel pump which fuel pump do you guys recomend i have a vortec supercharger wit about 3-6 psi and the rest is stock what would be the best fit for my car thanks

 

Get ahold of a fuel pressure gauge. Why do you think it's not getting enough pressure? Buying a fuel presure gauge is cheaper then replacing a fuel pump that's didn't need replacing.

 

do you know which is the fuel pressuere gauge that will fit because i went to autozone and the ones that they have there dont say that they will fit a tpi 5.7 it only says 5.0 tbi engines will these gauge still work for my engine? so if its not getting enough pressure what could be the possible problems? the car turms on but then after a few seconds it turns off then if u put in gear it also turns off u have to be giving gas so it could stay on but it feels like if its not responding properly

 

Yes it will fit

 

yeah you should hook up a mech gauge and actually see what the fuel pressure is at.. what kind of fuel pressure gauge was it that said it was for tbi? Thats kind of strange.. You need a fuel pressure gauge that will screw onto the schrader valve, its next to the fuel pressure regulator on the pass side fuel rail if you have tpi.. AFAIK 3rd gens with tbi didn't even have a schrader valve.. only reason I can think that they would say its for tbi is that perhaps it can only handle low pressure?

 

I'm having the same problem, my PSI with key on is 36-38 and it is not starting. Check your FPR vac hose to see if there is fuel in the line, I think that also could cause a drop in fuel pressure, is that correct?

 

Fuel pressure is inversely proportional to vacuum e.g. high vacuum lowers fuel pressure and low vacuum increases it. A hole in the diaphram will allow fuel to filll the vacuum side of the diaphram which reduces vacuum and increasing fuel pressure.

 

my car is actting the same way have hooked a fuel press up to it yet let me know if you fixed the prob my car is a daily driver need fix asap

 

my fuel pressure is at 38 psi and the resistance on the injectors resitance is around 16 all around so i dont know what else to check what other things could be wrong thanks

 

Well your Fuel pressure would not be at the top of my priority list. Right now it's enough to keep the engine idling.

Have you done the minimum air rate setting procedure and TPS adjustment?

 

what is a minimum air rate setting procedure havent adjusted tps either i guess ill do that next have no other ideas can you let me know how to do the other thing thanks

 

ok i adjusted tps to specification than i was trying to do the minum air rate but the car doesnt stay on enough time so i could do it as soon as i let go of the gas it turns off does it matter if im adjustin while somebody hold the gas thnaks

 

Now that you've set the pressure I'd suggest checking flow volume first; 1pt in 30 sec, or 1gal in 4 minutes.

MPFI throttle bodies are dry (carbs are wet) and will get dirtier sooner because there's no fuel to help wash the carbon build up. So, clean it and the IAC before attempting to set minimum air.

It's minimum air rate first then TPS.

If you have a scanner that can log real time then use it to display the idle while someone holds the pedal at the required rpm because the cars tach is not a precise instrument and can some times be off up to 100 rpm, (remember the ECM gets it's rpm reference signal from the distributor not the Tach.) Then adjust the idle screw to hold the throttle open at that angle. Finally, with the scanner still connected adjust the TPS, if it still won't idle there's a couple of things you can do that might help.
1. add .09 volts to the TPS minimum, but do not exceed .69 volts
2. replace PCV with a non variable type (if it rattles it a variable type.)

FYI: To idle properly the engine needs steady 16-22Hg

 

i did clean the iac and all the carbon build up in throttle body i dont have a scanner is there any other way to do it. could my problem be coming from my maf is there a way to check that

 

Performance Tach should be very precise.

With a scanner you'll be able to see much more than just the engine RPM, and log it as well.
The ALDL ALDU1 converter and Cable1 from Moates.net is $80.
The TunerPro RT is a freedown load, but should be registered for $30.
Well worth the expense.

 

this is the program that you connect to the computer or is it a scanner like the ones they sell in autozone and places like that

 

THe ALDU1/Cable1 allows a Computer to Scan the ECM for Codes & clear them. You can monitor and log any/all signals of the data stream.
You can edit the file, say for larger injectors and save it then use it to reprogram you ECM with a chip burner, or have someone burn it for you.
I use a chip emulator so I just make the change and upload it on the fly.

I've reprogrammed my injector size, base timing, and fan control.

I plan on keeping my Z for the rest of my life so these tools are necessary for diagnostics and tuning.

 

defnitly goin to consider it because i dont plan on selling my iroc either this will definatly come in handy thanks