1989iroc-z

I just swapped a carbed 350 with a 350 tpi in my 89 iroc. I am able to start the car but it will only idle for about 15 seconds then it will die. Im thinking that it has to do with the fuel pump. When i turn the key the fuel pump turns on and primes the lines but if i dont stay on the throttle once it starts it just dies. I think that the fuel pump is turning off and when the engine is idleing it doesnt have enough vaccume to force fuel through but when im on the throttle it does. Does my reasoning make any sense? Has anyone else had this problem? Thanks

five7kid

iTrader: (14)

I assume you're using the in-tank electric fuel pump. What regulator did you use?

The way the TPI did it was to power the pump with a timed relay when the ignition was turned on. Then, oil pressure is required in order to keep power to the pump (via an oil pressure switch). Some versions used ECM input to operate the pump (I am now over my head).

Your reasoning doesn't make any sense, because vacuum has absolutely nothing to do with getting fuel to the carb. It does have something to do with getting the fuel from the fuel bowl to the venturi, but that's all.

Get a pressure gage in the fuel line (as close to the carb as possible would be best) to determine what's really going on.

1989iroc-z

Im using the mallory 4309 pressure reg. I have a gauge on the reg and it reads about 6 psi. I have the sending unit for oil pressure hooked up and it is working.

RB83L69

A good place to start would be to start it up, let it die, and then check the fuel bowl to see if there's gas in it.

Vacuum has nothing whatsoever to do with fuel system operation.

Ig the gauge reads 6 psi when it's dying, then odds are, there's fuel there, and your probelm isn't in the fuel system. Rather, it's tuning; and/or vacuum leak(s).

1989iroc-z

as the car dies so does the fuel pressure and I already checked for vaccume leaks and didnt find any

five7kid

iTrader: (14)

Are you talking about the oil pressure gage working, or the oil pressure fuel switch to the pump working?

five7kid

iTrader: (14)

We both posted at the same time.

If pressure is maintained all the while the engine is running (and not exceeding 6 psi), then it probably doesn't have anything to do with the fuel pump.

It is possible that the carb can't quite handle 6 psi. What carb are you using?

1989iroc-z

I just went out and played around with it for awhile and noticed when the fuel pump turns on to prime the lines i get about 6psi but after the car is started i am getting no pressure. Now I am really confused. The oil pressure gauge is hooked up. is that sending unit and the switch different?. The carb is an edelbrock 600 w/elec choke, It was just taken apart, checked out, cleaned and reassembled.

TN90RS

We've done the same thing at the same time. I get a good prime, then once the car is running, the pressure dies to less than a pound. I'm guessing that since the ECM doesn't control anything now, the oil pressure switch may also be bad. Hopefully someone will post soon to solve our problems. In the meantime, I'm going to attempt to direct wire the fuel pump relay and see if manual control of the pump makes any difference.

Stekman

Sounds like the problem lies in the oil pressure switch. The ECM powers the relay (and the pump) intitially to pressurize it, enough so that it can start. Once it starts, the oil pressure switch picks up pressure and kicks in, acting as the cut off switch. If that is bad, then there would be no reading from it and the FP relay would get no input, meaning the pump would not get power and the car would die out after the fuel suply from the initial priming has been exhausted.

Since it primes, the relay sounds like it's in good order. You're getting adequate pressure upon priming, so the pump seems to be ok. Sounds to me like you need a new oil pressure switch.

Hodge

I seem to be saying this all the time and it usually is the problem. maybe we could get it stickied somehow under a new post titled no fuel pressure after car is running ... or something along those lines. I can't take credit for this info either.. I obtained it here as well. but here it is. Copied from the post I replied to about 15 minutes ago


here is what I experienced with my TPI to carb conversion and it sounds like the same issue you have.


The ECM only runs the pump for the prime. after that the fuel pump is activated by an oil pressure switch. This oil pressure switch is located above the oil filter on the drivers side of the block. The oil pressure sensor on the back of the block by the distributor is the one that runs the gauge. The first one I mentioned above the oil filter is the one that actually runs the fuel pump. This is the only thing that tells the pump to turn on. Once this switch sees oil pressure it will activate the pump. Let me know if you need any more info about this switch.

Hodge

fbody85

I'm pretty sure your problem is your regulator, i had the same problem when i put my carbed 383 into a FI v6 car, since the stock pumps are made to put out much higher pressure (55psi?) for fuel injection then a carbureted engine would need, well when you you try and regulate that pressure down, the pump gets backed up with fuel, and it thinks an injector is stopped up or the fuel filter is stopped up and shuts itself off to prevent damage to the pump


now there is a fuel return line (next to the steering arm by your exhaust manifolds) that you may be able to put a T in the line before your regulator to flow that excess fuel bck to the tank

or you can get an aftermarket fuel pump that doesnt do this

Stekman

*EDIT* I'm too tired to pick this post apart.

fbody85

Not to tired to suck some **** though huh

Stekman

What does that have to do with anything?

ljnowell

Are you completely retarded? or are you just totally stupid?
I believe that the point he was going to make on your post, is that you are doing it the wrong way. You should be using a regulator with a return line in the first place. If you attempt to dead-head one of these stock fuel pumps they will burn up. But back to the point, This is a tech board, and if you cant post worthwhile, dont post garbage. If you dont like what someone says, or disagree, then handle it like an adult. My advice to you would be to create a new user name and try again, because you have already ruined this one.

Stekman

You are correct lj. That was the point i was going to make, but at that time at night (or in the morning, for that matter) I was too tired to type it all out. What I ended up typing was originally somewhat rude, so i edited it.

There is a right and a wrong way to use a EFI pump for carb applications. Either the Mallory or Barry Grant, as they are the only 2 return style regulators that i am aware of. You set the PSI and any excessive pressure gets bled back tot he tank via the return line. Several memebers are using this route, myself included. When done properly, you do no burn out the pump. Those Holley regulators that cost, what $20-$30? Those are intended pretty much for dual inlet carbs. Fuel comes in the bottom, and out the sides to the bowls.

As for the fuel pump shutting down because it thinks there is too much pressure, that is wrong. As both lj and myself have just pointed out, they do nut "shut down to prevent damage", they burn out from overheating from working to hard. You don't prevent damage, the damage has been done.

Couldl i have said it nicer in my above post, probably. Did that call for the blatant, rude, and completely idiodic reply? No. In lj's first question, I am leaning towards the later.

TN90RS

Evidently the oil pressure switch was faulty. I was able to run power straight to the relay and the problem went away. I didn't state it, but I already had a 4309 regulator plumbed in "with" a return line. The oil pressure switch has been replaced and all is well. Also bypassed the fuel pump relay related to the VATS, so now the whole car is computer free...... Thanks for the help and opinions. Couldn't have done it without you guys, well most of you....Really don't understand how we ventured to the queer side once, but anyhow...there are kids on every forum I suppose.

ljnowell

Glad to hear you got it worked out, and another thirdgen is on the streets.

We definately have our fair share here.

jbqualls

Just to be sure cause I couldnt seem to get a straight answer on this...if I get an inline pump, do I HAVE to take out the stock pump, or can I leave it in? What would be better doing that or getting a fuel pressure regulator. The only reason I ask is cause I'm not quite sure how to make the stock fuel pump work after the ecm is removed. Thanks

jbqualls

scratch that...I just found the answer to my own question...