BajaBrad

Hello, picked up a 97' 272 with a 502 mag a couple of weeks ago and had problems ever since. It wouldn't idle after about 15min on the first outing, but ran great at mid range and full throttle. I replaced the air idle control the next week. It idled great for about 30min, then started dying again, still ran strong above idle. I then put a fuel pressure guage on it and found it fluctuates between 5psi-30psi.erraticly. When it is at 20-30 it idles fine just doesn;t stay there very long. I relaced the fuel filter, checked for blockage in the fuel line from the tank to the filter, it was clear. I figure fuel pressure is too blame, but how is it running good wide open at that low psi? Which pump would be responsible? The mechanical or electrical?
I'm very aggravated with this thing so any help is appreciated!

sonicss42

Get the ECM scanned for codes and save yourself a ton of headaches and guesswork. BTDT. You will be glad you did.

AllDodge

iTrader: (1)

Being a 97 you might have a VST or cool fuel Gen II, and maybe MEFI 1. You could make up a code reader by going to radio shack and getting a 12V resister LED and a paper clip If you have a MEFI 1 ECM your probably not going to find much, but is always worth checking.

You should be running 37 psi. The low and fluctuating pressure could be caused by the high or low pressure pump, fuel pressure regulator or restriction in the fuel system (tank, anti-siphon valve, line, fitting or filter). The motor won't idle because its not getting enough fuel and the IAC is having trouble compensating. At higher rpms the IAC is not used and your probably runnin lean so if you continue your going to be buying another motor

BajaBrad

Alright, we replaced the electric pump at the vst, ran fine, then died putting it on the trailer. We also replaced the mechanical pump, started and ran it, sounds good but only has 29psi of fuel pressure at idle or revved up. We unhooked the vaccum line to the regulator and it has 34psi all the time, which still ran well but obviously not right? Any more ideas appreciated!
Also in all this I have replaced the fuel filter, cleaned out the vst, removed the check ball in the fitting coming out of the tank.

AllDodge

iTrader: (1)

Your pressure is getting better and leads me to suspect the regulator (item 15). It can be tested on the bench, but the issue is removing it. To remove the plenum needs to be lifted slightly. It may be able to remove without lifting the plenum but so far I have found no one which can do it. Removing/lifting is easy enough but then the gaskets need replaced.

To bench test, need a air regulator and apply pressure to the input side and increase air pressure until the regulator opens

Tractionless

What was the solution, (if any) Brad?

fst72vette

any chance it could be the risers leaking into the cylinders? Any trouble at startup?