Hi everyone, I'm the new owner of a 1991 Firebird 3.1 MPFI that's been sitting for a long time.

Once we got home, we discovered the fuel pump wasn't working. After replacing it (a painstaking job), the Firebird starts right away, but only lasts for 10-15 seconds, then stalls.
Accelerating also doesn't work; it doesn't respond to the accelerator pedal at all and stalls immediately when you try to accelerate.

• Where should I start? I assume the fuel pump and injection are working normally... and the ignition and spark plugs are also working... where should I start looking? Sorry, I've tried reading numerous posts, but I'm not getting any wiser, and that's because I'm a novice in this field. My
  apologies again.

 

Start with actuality checking fuel pressure even if pump is new. If it’s sat for a long time you might have possibly varnished fuel injectors. You are trying to start with fresh fuel?

 

Yes, fresh and premium one...
You mean to check the fuel pressure from the top of the "fuelblock"?

 

One thing, I see the fuel system has been modified, partly because this car also ran on LPG (no LPG tank now, so only gasoline). So they installed a switch to turn the fuel pump on and off. And disabled the relays, as shown in the photo?

 

It has also no maf sensor? And the tps sensor located wrong? Chatgpt making me crazy 😅

 

It is speed density, I’m not seeing the tps issue

 

A little update after some checks and tests:

1. Fuel System:

Fuel pump operational, audible humming confirmed.

Fuel pressure measured at 3.1–3.2 bar (within spec).

Injector Resistance: All injectors measured individually between approximately 12.8 and 13.4 ohms, which is within typical specification.

Injector Voltage Signal: Voltage at injector connectors during cranking pulses up to ~1.0 V DC, indicating pulse signals are present but on the low side.


2. Throttle Position Sensor (TPS):

Voltage at closed throttle: ~0.78 V

Voltage at open throttle: ~4.3 V

Sensor functioning normally.


3. Ignition System:

Ignition module power supply (pink wire): 12.53 V with ignition ON.

Ignition module ground (green wire): 0 Ω resistance to chassis (good ground).

Trigger signal (yellow wire): fluctuates very low, ~0.005 V AC during cranking (expected to be higher).

Coil power supply (red/white wire): 12.5 V with ignition ON.

Coil trigger wire (red/black): ~0.025–0.032 V DC during cranking (very low, expected to pulse between 0 and 12 V)


4. Spark Test:

Motor runs briefly on starting fluid but no sustained start.

Spark presence uncertain; trigger signal low, suggesting ignition signal issues.


5. Additional Observations:

Battery voltage: 12.53 V

 

My 1986 2.8L MPI sat for about 30 years as well before I got her back into running condition.
1. When you replaced the fuel pump did the inside of the tank look rusty? Mine sure was so I had the tank repaired and a plastic liner put in to stop future rust.





2. Did you replace the fuel filter under the car?


3. On my car because of the rust in the tank the fuel injectors were plugged on the intake side. You may have to pull yours and inspect them. I changed mine out..

 

Being quiet desperate 😞

Fuel pump new= ok
Injectors are spraying and working cleaned and tested with direct battery = ok
Fuel is coming and has 3.2bar pressure= ok
Fuel is new and premium one = ok
Battery is full , ignition and sparking doing well = ok
New or refurb ecu/ECM replaced and also put my prom in the new one = ok
There is oil pressure fuel gauge and others are working = ok

But the injectors are not getting pulsed or controlled to spray 🤯🤯🤯🤯🤯


Where do I need to search and doing tests...

 

If no injector pulse do you have a volt ohm better with hz setting ? Sounds like a vats issue or could still be a icm issue if ecm isn’t seeing a reference pulse .

 

🤯 Blown fuse at inj1 fuse- slot


After the injector relay lost 12 volt power, I checked the fuses. The Inj1 fuse was blown... so that was the problem?
Replaced it, and the Firebird starts and runs like a charm!

• After checking the inj2 fuse, I noticed that (without the fuse) there was 12V on both sides. Is this intentional, or is it still a cause for concern?

But for now I can sleep well tonight. 😅

 

Inj 1 and inj 2 don’t run through a relay. But who knows what was done with the cng conversion.