I just recently put a new intake runners and 22bls injectors on my 89 Formula 350. I finally got it to run but it has a HARD time running under 900 RPMS. And when i shut the car off I can here the fuel pump run for 15 secs and I hear fuel going all through the fuel rails and diaphram while the pump is going and then it gets quieter then boom it stops like it should after 2 secs but it takes 15 secs? Any idea y? Is this causeing my bad idle or is the timing off a tooth? If so How can i perfectly time my car. No codes or anything. Thanks

 

I think you have two seperate problems here! Your idle problem could very well be the IAC! Check it out!!

The fuel pump running tho' is a totally different thing! The fuel pump and the oil pressure switch communicate with each other! (If the oil pressure switch isn't working, neither will the fuel pump!) When you shut the engine off, the fuel pump shuts off when the oil pressure goes down to a certain level!! In cold weather especially, oil is thicker so it takes longer for the oil pressure to drop once you shut the engine off!! So once you shut off the engine, the fuel pump will stay running until the oil pressure drops to the proper level....then the fuel pump clicks off!!

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1986 Trans AM
305 TPI
4 Wheel Discs
9 bolt Borg Warner Rear
Completely Stock
Soon to upgrade to a 383 stroker w/TPI, Hedman Shorty Headers, 64cc Pocket Ported Worlds Product Sportsman-II heads, ported intake, comp cam, TPIS air foil, Adjustable Fuel Pressure Regulator, and 24 lb/hr SVO injectors!
Current project: Keeping my car running until I get the money for the above mentioned project! :-)

 

I partialy argree with the above statement. The oil pressure switch is wired directly to the battery, so as long as there is 4 psi in the oil galleries in the block, the fuel pump will run. If the switch ever gets stuck closed, the pump will run untill the battery dies. I guess you could try a new oil pressure switch, but theres no garuntee that its actually bad.

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ASE Master Tech + L1
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'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

could it be a relay getting stuck?

 

My fuel pump ran all night a few weeks ago. I replaced the fuel pump relay and everything is fine now. Occasionally, the fuel pump runs for a few seconds after I shut the car off. I have assumed that it was the oil pressure that was doing it.

Check this thread:
https://www.thirdgen.org/messgboard/...ML/004290.html

 

Mine does the same thing but only on extremely cold days. (5 - 20* F). Glad i read this post, otherwise i woulda thought yet another problem with my car has arised. At least i hope not another problem has tried to speak up..

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Problems every other day with the car (probably not a mod, but to me it sure makes a difference)

 

The fuel pump staying on for a few seconds (maybe up to 15) after you shut the car off is totally normal. I have found its inconsistent too, varies alot.
You need a timing light to set the timing, I would put it at 8 with the brown/black stripe wire over on the passenger side disconnected. It may fix your idle problem.