ovhd

Need some help, my 91 starts up, idle is good with no codes or lights. When accelerating and opening secondaries starts to stumble. It almost feels like a coil pack is going bad. If the valet key is turned off the car runs perfect. I tried plugs no help. Thought is was the vaccum pump but just made sure it cycles the way it should. I put injectors in it last year and put maybe 500 miles on it since then. After injectors car was perfect and now this. Gas is fresh, Anyone have any ideas??

FASTAZU

may be a bad Secondary fuel pump

ovhd

any quick ways to check it?

dallas916

Well, you can pull the fuse for the primary and see if the secondary pump turns on at "key on". If it turns on you know the power is there and the pump is activated. To go further you need a pressure guage attached to the fuel rail to see if it pumps full pressure. There are many threads on this problem.

Just for kicks, check your computer connections at the ECM. Those pins can become loose or gunked up. Just becareful with them.

VetteMed

Check intake duct, to be sure it's not collapsing? Might only do it when secondaries are enabled...

ovhd

ok so far i checked the intake for collapsing seems good. Read up on the forum found a thread says to pull ENG 2 fuse ( INJ 2 ) and then pull fp1 fuse. Never made it that far, as soon as inj 2 fuse pulled car dies. Can hear a clicking in the back but doesnt sound like a pump running. How can i confirm it needs a secondary fuel pump?? Guys thanks for the help your a bunch of life savers.

dallas916

Offhand I don't think you need to pull the inj fuse unless you are going to be testing an open fuel port. The circuit for the secondary pump will excite the #2 pump when the key is turned on. What you want is to kill the #1 pump by pulling its fuse so you can hear if the #2 pump turns on. If it's a dual circuit you might need to pull another, but what you want to kow is if the #2 pump turns on without the #1 pump having any power. Normally, it will come on without running the engine...and you will be able to hear it (and have pressure at the rail).

ovhd

With a set of guages hooked up to the fuel rail, what fuel pressures should i be looking for and how can i tell if secondary pump is running?

Aurora40

Just FYI to the OP, I believe this is only with a cold engine. So don't try this after driving around.
Fuel pressure ranges are in the FSM, but basically in the 45-55psi ballpark. When there is no vacuum in the intake (engine not running, or at WOT), the pressure should be towards the higher side of that. When there is vacuum, it should drop to the lower end of that range.

Also if you have a gauge, tape it to the windshield and go for a drive. See if the pressure holds when you get on the gas.

Coil packs shouldn't be affected by the key on/off position, I wouldn't think.

ovhd

ok, today hooked up set of guages idle around 42 psi. Took it for a ride when activating secondarys goes up to about 53-55 psi. With the valet key off press does about the same. I am assuming secondary pump working as it should. Any other suggestions.

ShawnZR-1

Do you have any stored codes? Does the SES light come on when you start the car (for a bulb check)?

When exactly does it stumble? What gear, what RPM, what throttle position?
I'm wondering if the butterflies are opening. If one of the actuators has failed or the linkage is jammed, I would think it would cause problems such as this...