92formulaRI

I got a 92 formula with the 305 and one day I was driving around and it randomly started bucking and stalled out. I had to get a tow home and ever since then it will start right up but then stalls out about 30 seconds later. I have replaced the fuel pump, fuel filter, distributor cap/rotor, plugs and wires, ignition coil, and IAC valve. Even after I replaced all that it still starts right back up and bogs down and stalls soon after. If I give it some gas after starting it stalls out right away than if I just let it idle. I’m starting to get at a loss here of what it could be. There is no check engine light on either. Any ideas?

Thank you

vinny R

Check your fuel pressure with a gauge. Bucking and stalling after start could be a lack of fuel. I see you replaced the pump and filter but you may have a pressure regulator issue.
When you key on your pump should prime to low 30's on the gague. It should hold steady when starting. hopefully it runs long enough to remove the vacuum line from the fuel pressure regulator. The pressure should go up to 42-45 psi on the gauge.

92formulaRI

I will check the pressure sometime this week and see what it shows, not sure it will run long enough for me to disconnect the vacuum line but will try.

alan91z28

you should also verify the injectors. if you disconnect the the plugs to each injector you can measure them with an ohm meter... typically should measure around 16 ohms.

92formulaRI

I tested the pressure and it was 42psi when it started and then stalled before I could disconnect the vacuum line. This would mean it’s getting too much fuel?

KyleF

No, 42PSI is fine for the test you ran.

"Ideal" setting is 43.5lbs with the vacuum line disconnected, but it has an acceptable range. Doesn't have to be spot on. When you are testing the fuel pressure before starting, there is no vacuum so it will be where the regulator is providing max pressure, but your pump is only receiving a momentary pulse of power.

After it didn't start, did you monitor the pressure decay?

I had a similar issue caused by a MAF (you can read my thread - currently near the top of the page). Your car is newer and a MAP, but you may want to disconnect the MAP and see if it will run in limp mode. I didn't get any MAF codes either.

Here was my fuel pressure readings:

Checked Fuel Pressure:
KOEO: 42PSI
Idle (W/Vacuum): 38PSI
Idle (W/O Vacuum): 46PSI

Leak Down
0 min: 42PSI
5min: 34PSI
10min: 25PSI
15min: 22PSI
20min: 19PSI
25min: 18PSI
30min: 16PSI

92formulaRI

I finally got around to working on it this weekend as it has been a busy summer. So I replaced the fuel pressure regulator and fuel injectors and it now runs and does not stall. It is idling around 700rpms. Now I just have to replace the brakes and should be good to drive. Thanks everyone for the insight.

Tuned Performance

iTrader: (92)

We’re the injectors the original multecs ?

92formulaRI

Yes they were original

Tuned Performance

iTrader: (92)

Anything over the stock is a great upgrade. Glad you got it figured out.