Stumbling Start-Up (Page 1/2)
labbe001 FEB 27, 03:50 PM
Hi All
I purchased an 87GT 5 speed recently and am having issue where it turns over for a long period of time (Maybe 5-7 seconds) before starting up. When it starts, it slowly stumbles around for a bit before coming up to normal (or slightly high) RPMs. The engine runs good otherwise....it just doesn't hit and fire right up like 87GTs I've owned in the past.

A couple of things to note. The previous owner did some re-wiring that I've not really investigated yet. However, both the radiator fan as well as the blower fan in the trunk run constantly with the key in the own position. Additionally, the fuel pump will run constantly with the key in the on position as well. Could this have something to do with it stumbling around before starting up?
Thanks
Patrick FEB 27, 05:23 PM

quote
Originally posted by labbe001:

Additionally, the fuel pump will run constantly with the key in the on position as well.



With the engine not running? That could potentially be a very dangerous issue. The last thing you'd want, is to be in an accident, knocked unconscious, the engine catches fire... and the fuel pump continues to supply an accelerant.
labbe001 FEB 27, 06:12 PM

quote
Originally posted by Patrick:

With the engine not running? That could potentially be a very dangerous issue. The last thing you'd want, is to be in an accident, knocked unconscious, the engine catches fire... and the fuel pump continues to supply an accelerant.




Yes….if the key is in the on position, it’s running. I would like for it to function as intended. Any where I could start for diagnosing why it runs continuously? Could this be why it takes so long to start up and why it stumbles on start up? Not sure if flooding is even a possibility on a V6 Fiero but that’s almost how it acts when starting up.
Patrick FEB 27, 06:51 PM

quote
Originally posted by labbe001:

Any where I could start for diagnosing why it runs continuously?



I've had no experience with this myself, but I believe a faulty oil pressure sender can lead to this problem. Maybe someone more familiar with this issue can chime in.

Stingray92 FEB 27, 06:54 PM
Get your hands on a schematic and start trying to figure out what the PO may have done with the fuel pump circuit. Pretty darn sure the oil pressure switch should be in the circuit to open up on low pressure/not starting. As to taking 5-7 seconds cranking before starting sounds like the fuel pressure regulator isn't working the way it should. You could also have air trapped in the fuel rail.
labbe001 FEB 27, 08:45 PM
So the best I can tell, it seems this modification has been made to the fuel pump wiring. It looks like the oil pressure sending unit has been taken out of the loop. Would they make the fuel pump run with the key in the on position?

http://www.gmtuners.com/fiero/hot_wire.htm
Here is a pic of the connector that goes down to the fuel tank:

[This message has been edited by labbe001 (edited 02-27-2024).]

Additivewalnut FEB 28, 11:46 AM
My best guess for the pump being on at all times is that somewhere, either wiring or a sensor went bad and the previous owner didn't want to or couldn't diagnose it, so they just made it work. I've done that before, admittedly. As far as your stumbling and slightly high RPM at idle, smoke test the engine. Could be a really small vac leak that the IAC can figure out after a while.
Stingray92 FEB 28, 07:44 PM
I don't have the schematic for your engine/year readily available but from what you described and what is on the gm tuners site, yes it looks like the oil pressure switch has been taken out of the circuit. I don't know about you but having a fuel pump that stays on continuously without the engine running is not something I would be comfortable with. The switch is pretty simple in function the contacts close when it's got good pressure. If I recall correctly it's pretty low maybe 5-10 psi.
labbe001 FEB 28, 08:49 PM

quote
Originally posted by Stingray92:

I don't have the schematic for your engine/year readily available but from what you described and what is on the gm tuners site, yes it looks like the oil pressure switch has been taken out of the circuit. I don't know about you but having a fuel pump that stays on continuously without the engine running is not something I would be comfortable with. The switch is pretty simple in function the contacts close when it's got good pressure. If I recall correctly it's pretty low maybe 5-10 psi.




Yeah I’m not comfortable with the fuel pump running constantly hence why I’m trying to get this issue diagnosed and fixed to work as designed.
A couple of developments….I have confirmed that the oil pressure switch has been removed from the circuit. With that being said, will this alone cause the fuel pump to run with the key in the on position?
Another item is my fuel gauge reading as always empty. I unhooked the C502 connector at the firewall and the gauge we’ll all the way to full. I ohmed out the power and ground wires for the sending unit going to the tank and they are grounded together. So it seems there is an issue bt the connector and the sending unit in the fuel tank. So I’m going to drop the tank and take a look at the wiring to the fuel pump and sending unit and verify/fix any wiring issues.
TM_Fiero FEB 29, 07:40 PM
I had a very similar problem. I eventually found out the engine was flooding itself when starting. Ran normal once started and warmed up. Turned out to be the cold start injector system not working properly. Unplugged the temp sensor for the cold start system. Now starts without any problems. Would be an easy thing to check, just pull one plug and give it a try.