masterprice33

I own a 1985 and have been trying to figure out this stalling problem. I had another post with lots of replies, but I'm thinking I should start a new one based on this. The fuel pump, having been replaced already, will NOT prime when the ignition is in the ON position. So the engine will not start, only crank and crank. The mechanic I've been working with installed some kind of manual switch so that the fuel pump would power on manually so that the car can start. Anyone know of a list of possible culprits for this? Also, when the car is started, it stalls randomly, like sometimes in idle, sometimes while coasting. And most of the time will start right back up, sometimes will not and have to wait awhile. Replaced ignition module because it was bad, but still same problems. I will place my other thread inside this one in case you want to know anymore specifics, would REALLY appreciate some help, well more help I guess .

http://forums.corvetteforum.com/show....php?t=1411327

VtVette

Have you confirmed that the pump is indeed working at all? I assume you are using a pressure gauge at the rail to determine fuel pressure? Can you hear the pump come on when you turn the car on (or flick the switch on)?

masterprice33

yes the pump itself is working, when we flip on the manual switch we CAN hear it, and that's when it works fine. But we CANNOT hear the pump run when the key is turned to the ON position without switch turned on. Fuel pressure is normal at 42 psi and holds after shutdown.

Bruce Witherspoon

Find the fuel pump relay and see if it clicks when you turn the key to the on position.

rick lambert

If the fuel pump relay isn't working and cranking doesn't start it, that means the oil pressure switch and relay are not getting power, both get their power from a fusible link, the link comes off the power terminal behind the battery, at a point it branches off, one branch going to the fuel pump relay, the other branch going to the oil pressure switch.

My guess, the fusible link has blown.

RRT vette

The fusible link could be the issue here. You can use a test light and touch the fuel pump fuse and turn the ignition on and it should light up for two seconds... you can do the same for the connector harness at the pump on the tan wire (I think), and same result. If neither light up go to the fuel pump relay harness and use a jumper wire on the first and last wires in the connector. If the relay is bad, doing this should prime the pump when the key is turned. The jumper wire will bypass what the relay does, and send power from one point to the other. You can also use a test light on the relay connector(orange or red wire) should light up when the key is turned on...if not the fusible link would be it. Make sure the fuel pump fuse is good.

Neither the fuel pump relay or the oil pressure switch getting power would be a result of what Rick said.

RRT vette

Oh, you can run a wire from the + side of the battery to terminal G of the ALDL. This will run the pump until the wire is removed, assuming the circuit is good.

masterprice33

thanks very much, I had a feeling it might be that fusible link that will be where we go from here. We replaced the fuel pump relay thinking it may be bad so the fuel pump relay in the car is brand new. The fuel pump fuse WAS blown before, but even after we put a brand new fuse in it still acts the same, is it possible that fusible link problems can lead to the fuel pump fuse blowing? thank you RRT for the detailed description of the steps I should take, I will report back as soon as I can or if I have any other concerns that may need to be addressed concerning this issue.

rick lambert

Quite possible whatever caused the fusible link to blow (if it's blown) could have also blown the fuse.

masterprice33

what kinds of things could cause a fusible link to blow? This problem did pretty much start after I took it into to shop for a diagnostic test for a check engine light (which doesn't concern this problem since it was the speed sensor). Could the mechanics at the shop have done something while either changing my oil or messing with the diagnostic port to cause this?

masterprice33

does anyone know what type of fusible link I need for this issue? I'm seeing various ones on Ebay and I'm not sure which one I need, like the size and whatnot.

masterprice33

Had another question concerning this issue. With the fusible link problem aside, the fact remains that the car will STILL stall randomly even when the manual switch is turned on so the fuel pump will run. Having said that, what possibilities could make this happen?

RRT vette

A grounded wire can cause the fusible link to short, also shorting fuses in the fuse panel. Is the Service Engine Soon light on? If so, does it flash a code 12 when the ALDL terminal A and B is grounded? You never know what a mechanic shop will do unless you standing there watching them do it. This is the main reason I do my own work, so I know it's done right and if any problems, I know where to look. It is possible that they cut into a circuit/wire, causing all these problems.

I'm not sure of the size of the links. I haven't had to purchase any but I would take a guess and say 10ga or 12ga. But not reliable advise.

Well besides doing anymore guessing I will say to get the fuel pressure guage on the fuel rail and watch it as you drive...what the pressure did when you turn the pump on, start the engine, go WOT, and come off throttle to brake. The best advise I can give is to connect a scanner to the ALDL and see what happens when it stalls. Your losing either fuel or spark and after replacing the IM, if it's not some bad wires/connection somewhere, the manual switch on the fuel pump needs to be taken off and the fuel pump circuit check out. The manual switch would be called a bandaid solution.

rick lambert

Go to NAPPA, tell them you need a .5 orange fusible link, that's what the FSM calls out...don't be surprised if it's black, I had to wrap mine with orange tape. Its been along time, but someone posted about the connections to the fuel pump being a culprit for them. I'm gonna try to find Ray Quayle or Agent86 and ask if one would post the schematics for you, both nice guys, and I don't know how or I would.

Ray Quayle

This is really Agent86's job, but here ya go:
Fuel Delivery

rick lambert

That's it Ray, thanks. Now just print this off and take it to your mechanic.

Ray Quayle

Here ya go in color jpg. Sorry if they are a bit blurry, I was in a rush. This os for 1986 BTW, but is largely the same as '85.

rick lambert

Ray...you are the man

RRT vette

Very nice Ray, this should give a good starting point to figure out why the fuel system isn't functioning correctly.

masterprice33

wow that is very nice! I'm very happy you guys could help out in this matter. I swear when it gets fixed I'll put a picture of the car on here so you all know what I'm driving, or am WANTING TO BE ABLE to drive this summer, my black beauty . I'll try to get a hold of the mechanic and get some **** done! thanks again everyone, this site is THE best.