Formularacing831

I have a 1994 Pontiac Firebird Formula, Back in October of 07 my car stopped running it would crank but would not start. Towed vehicle to dealer, they told me it was the coil and opti spark they wanted to charge $2,000 to complete the job. So i towed the vehicle back to my house and did the repairs my self. I installed an MSD Optispark, Coil, and wires. Then it still would not start, bought a new ignition control module and the vehicle fired right up. The car ran for 1 month no problems. After that month the same problem came back but now it will fire up sometimes and then shut right off. I checked fuel PSI and it was lower than the min. Replaced fuel pump and filter, got the psi up to 44psi (still will not start). I put my scanner on to check for codes (none present), I got the vehicle to start but it ran really rough, my scanner reset itself and when it came back on the idle smoothed out, so I figured must be the computer. Just installed new computer and still the same problems exist. I've run out of ideas, if somebody has any input please let me know.

joelster

Check the fuel pressure again with the car running, not just a test before cranking it over. It should stay high ALL THE TIME. Buy one of those guages and duct tape it to your hood so you can see it while you drive it. Take it around the block if you can and stare at the guage, it should never move. If you have a new pump, a new filter, and the pressure fluctuates, time to check the regulator on the fuel rail.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

Formularacing831

It does have a new fuel reg., I did the psi check and the psi stay steady and does not fluctuate. When cranking when it does not start the fuel psi is steady and I have spark. (checked Coil, #2,4,3,and5 cylenders for spark). Could it be the ignition lock cylender, switch, or maybe the chip in the key is bad, because once I get it running it will run fine, its just when I shut the car off 9 times out of ten it will not start back up.

joelster

If the fuel pressure is steady, the motor is turning over,AND you have spark, then something is telling the injectors NOT to open. Let me dig around, i'll post back.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

joelster

Could be TPS sensor. Basically if you put your foot to the floor the PCM will tell the injectors to stop firing so you won't flood the motor. Unplug the TPS sensor after you try cranking the motor over and it wont fire.

Unplug the MAF sensor too. A bad MAF can cause all sorts of weird stuff to happen. It will force the motor into speed density mode, yes it will run fine.

Check the grounds for your ignition, add an additional ground for giggles.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

Formularacing831

Awsome thanks I'll give it a try, I'll post back with the results.

Formularacing831

Okay I unplugged both sensors and no change, I'm going to put some gas into a squirt bottle and spray into the intake to see if it will start.

Formularacing831

Okay I sprayed gas into the intake the car ran for about two seconds and shut off, so now the queastion is what is causing the injectors not to fire? I did an injector test a month ago on it with the injector test tool and all the injectors passed.

joelster

As far as injectors not pulsing check your tach carefully when cranking the engine it should register 100-200 RPM if not suspect the low res Opti signal not getting to the PCM. When you checked the hi & low Opti resolution you saw +5 volts, those lines are pulses not DC voltage the low res should be 8 pulses per camshaft revolution and the high is 360 pulses per cam rev. Try the AC multimeter settings if still at +5 something is weird. Also .. See shbox's web site for checking out the opti... and fuel regulator http://shbox.com/1/4th_gen_tech2.html#opti_test http://shbox.com/1/4th_gen_tech2.htm...essure_testing
Good luck....

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

Formularacing831

Thanks a lot I appreciate your help.