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Old 06-04-2010, 10:00 PM   #1
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Surging, Stalling & Running rich

I have a 1994 Firebird Formula that has been having issues. I can't drive for more than 5-10 minutes before it starts to surge and then eventually stall out.
This started a few weeks ago and was doing it every few days at first. Now it does it all the time. When it stalls, it is very hard to start and if it does start, it runs very rough. If I wait a while its starts and runs fine. It also smells like gas when running. When I first drive the car it runs great and has all its power. It never feels slow or boogy, but it feels like it randomly cuts out and then comes back. Sometimes it will backfire, and sometimes it will die when this happens.

I pulled my plugs and all were black and sooty, so I replaced them.
About 6 months ago I replaced spark plug wires, coil + harness, ICM + harness, opti + harness, MAF, O2 sensors, Cat converter, and EGR solenoid. After that it ran great and passed smog with flying colors.

I checked my opti for moisture and it looks perfect. I tried swapping my ICM again but no change. I don't think it's spark related mostly because all my ignition parts are fairly new AC delco.
Anyone have any idea what this could be?
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Old 06-04-2010, 10:22 PM   #2
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Have you checked to see if it starts running bad when it goes into closed loop? Meaning it runs fine when cold in open loop and once it goes into closed loop it begins to act up. Is your car an a4 or m6?
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Old 06-04-2010, 10:43 PM   #3
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When the problem first started, it would happen after driving for about 20-30 miles and the temp would be about 180-210. It would be running fine at 180-210 temp for a while before it would happen. Now it happens within a mile or two, temp is anywhere between 120 -160. Each time it happened it progressively got worse. I could drive for 30 miles before it started happening, then 20, then 5, then 3.
I have let it idle in my drive way for about 15 minutes, then tested it. Temp about 185 and it still went a few miles and was running great before it started happening. It does not seem to matter if the car is cold or hot.
My car is a M6 also.
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Old 06-04-2010, 10:48 PM   #4
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Man take a lesson from me, don't do anything untill you scan it. What brand 02 sensors? I know you smell gas, but your fuel pump could be going out what's fuel pressure?
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Old 06-04-2010, 11:11 PM   #5
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The o2 sensors were Delphi. The fuel pressure with key on engine off was 43.5, I didn't get to test it anymore than that because the gauge was leaking a tiny bit and when it tried to tighten it, the gauge crushed itself. Cheap Harbor Freight Tool
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Old 06-05-2010, 07:33 AM   #6
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When did you put the hotcam kit in and did you have the PCM reprogrammed?
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Old 06-05-2010, 09:54 PM   #7
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I have the stock cam and heads with stock tune.
I took off the fuel pressure regulator hose while running, plugged it and installed a vacuum pump in its place. I pumped the regulator to 15 psi, and the car died. The car does not want to start after I did this also, it seems like I flooded it.
Does this sound normal?
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Old 06-05-2010, 10:26 PM   #8
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Are you saying you pulled a 15psi vacuum on the fuel pressure regulator diaphragm? Are you in Death Valley? Maximum possible vacuum at sea level is 14.7psi, and most pumps can not pull a full vacuum. What were you trying to accomplish by pulling the vacuum? All that would do, assuming the fuel pressure regulator is working, is reduce the rail pressure 15psi below the regulator set pressure, and reduce the fuel flow significantly.
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Old 06-05-2010, 11:19 PM   #9
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Yeah that's what I did. I was trying to see if the fuel pressure regulator diaphragm was leaking by applying vacuum to it while running, and then check the vacuum line for fuel.

As for the psi on the vacuum pump it was pretty close to 15 (maybe 14.5) with the engine running, I tried to pump it one more time and it died right away.
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Old 06-05-2010, 11:28 PM   #10
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You would have dropped the fuel pressure to ~29psi, reducing fuel flow through the injectors by almost 20%. Lean it out that much and its going to stall.

Is it possible you damaged the diaphragm with that last pump?
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94 Formula A3+1: 381ci all-forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / Comp Cams custom solid roller / TH400+GearVendors OD/4.11's / Strange 12-bolt / 300-shot N2O / Spohn Suspension / 6-pt roll bar with integrated SFC's / full AutoMeter instrumentation / MoTeC M48 Pro engine management system / a few other odds 'n ends. 800HP/800LB-FT at the flywheel.
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Old 06-09-2010, 01:10 PM   #11
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Ok, I finally figured it out. The black/gray coil connector was weak and losing spark after a few minutes. I replaced the connector and it has been running fine.
I was a little worried that I might have damaged the fuel regulator diaphragm, so I pumped it up to 14 psi with the engine off this time and left it for about 10 minutes to see if it stills holds vacuum. It held so I guess it's fine.
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Old 06-09-2010, 01:10 PM
 
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