I'm getting pretty close to having all the hardware in place. I'll still need to have my chip burned to disable VATS and EGR. I also still have to make the under-dash wiring modifications.

Regarding the fuel pump, I've done some searches and come up with lots of info. Unfortunately, I could not find answers to these questions:

1) is the factory in-tank pump strong enough to use with TPI? I've already removed/blocked off the mechanical fuel pump.

2) I've bought an external in-line pump. If I use this, will I need to remove the in-tank pump? Will the in-tank pump cause an obstruction to fuel flow?

3) What is the best method of wiring the pump? I am removing the oil pressure switch on the block, so the wiring for the in-tank fuel pump probably will not be getting any power.


Thanks guys!

 

No, the intank pump is only 40#

I would connect it so it feeds the external pump.

If you connect the wires on the oil switch it will run the intank pump.
HTH

 

Sounds good. My only concern would be if the in-tank pump is still there, is there a possiblity (under hard driving conditions) that the internal pump could not keep up with the external - and thus cause an 'obstruction'?

Thanks, you've been a big help!

 

Personally, if my LG4 had the intank pump, I'd have removed it and put an internal Walbro 255lph pump inside.
since my LG4 didn't have an intank pump, I just used an external holley 230lph universal pump.

Disadvantages to in external pump are noise and pump life.
Pros are that it takes no time to change.

 

If I were building the car for a high-performance application - I would. However, this will just be my daily driver as I build up my '71. I went to TPI strictly for the reliability/fuel efficiency. I could go with a stocker fuel pump for about $60 (autozone) if this is truly the best approach.

 

Another issue I have is that the harness is from an '89 MAF TPI...and it does not appear the harness has a provision for oil pressure fuel pump switch.

I have a FSM from the '87, and both the TPI and LG4 had what appear to be the same connector in the same location. Did it move in '89 or was it eliminated?

*scratches head*

[edit]

I found this...and I found the 3-wire plug in question...now to decide how best to proceed since my car is not equipped with the necessary switch and I failed to get it from the donor...

 

You don't need the switch.
I just used the stock oil pressure sender and on my 86 Trans Am the wire for the sender was not part of the engine harness, it was part of the harness that goes into the firewall down and to the left of the brake booster if you are standing at the front of the car.

I did have to use the 2 piece brass fittings with the old style oil pressure switch and sender since the stock one piece brass fitting was too tall for the TPI. the pressure switch was there but it's only use on my car was to plug up the hole on the brass fitting.

 

Well, since I've found the connector, and removed the plug from the hole for the oil pressure sender just above the oil filter, I think I'm going to wire it up just like it would have been as an '89 (the year of the wiring harness). The sender is only $25 or so...unless I can find a good one used. Once I get an in-tank fuel pump and install it (not looking forward to that) then the fuel system will be wired just like from the factory.

I'll just use my external fuel pump on my '71 project car.

 

Ah, yes...the ongoing saga.

After doing all the above (including replacing the in-tank pump), I find that the power lines for the in-tank pump on the '87 go through the IP connector at the pass front near the ECM. The '89 harness had no provision for these connections to get them to the fuel pump relay/oil pressure switch.

Any way to fix this the 'right' way? I could connect two of the wires effectively supplying the FP the power needed and bypassing the relay and switch - but should I?

Any feedback is appreciated.

 

As a temporary step to make sure all was working well, I jumped the power wire from the fuel pump to a wire that is hot when the ignition is keyed on.

I can hear the pump run, I put a fuel pressure gauge on and it gets to 50psi before it stops rising. I can hear a "hissing" noise (possibly air in the lines). I'm not positive if the fuel is returning to the tank through the fuel pressure regulator or leaking out the injectors. This intake was off a car that was parted out, so I was hoping I wouldn't have a whole host of issues to deal with.

Right now, there is no power to the injectors. Do they stay open when not powered, or closed.

Also, when I turn the key off, the fuel pressure will drop back nearly to zero. At no point does the fuel pump stop running. There was a little gas at the valve (small leak) but no other visible signs of leakage.

HELP ME! LOL!

 

injectors are closed when no pulse is sent to them.
Pressure dropping to 0 means you have a leak, could be the pump, injector(s), cold start injector, or regulator.

I had my pump wired to the relay and was controlled by ignition power.

 

I'm thinking it may be the regulator since fuel pressure drops to near-0 pretty darn quick (less than a min). Unless ALL the injectors are stuck open. Fuel pump is new (0 miles). All fuel lines appear to be leak-free.

When the fuel pump charges the system when you turn the ignition to "run" - what makes it cut out after 2-5 seconds?

Sorry, I'm just getting a bit frustrated since I just put this "supposedly good" intake together.

- also, no cold start injector being used....

 

The ECM primes the fuel pump for 2 seconds. I didn't have it hooked up like that since I had it wired a little different before I got the harness modified and just left it the way I had it.

If I all the injectors were stuck open you would have 0 pressure instantly when the pump turned off.
We had 2 leaky injectors, leaking cold start injector, bad regulator and a bad check ball on a new fuel pump on my friends 86 Z28. We put all new parts on the car and and crimped the line for the CSI and all was fine.

 

OK, so I guess I'm not going to find an easy way around yanking the intake to get to the fuel lines, eh?

I was surprised that the FP will get to (and hold) 50psi if the regulator and/or injectors are letting go.

I've got some checking to do. I'll post up my results...

Thanks alot Zepher!

 

OK. I yanked the upper plenum and got enough clearance so I could get the injectors up out of their holes a bit...they all seem fine.

I can audibly hear a humming from the intake area - so it must be the regulator...

I read that you can check to see if the pressure holds by pinching off the flexible section of the return line (smaller flexible fuel line). I *gently* did this and the flow appeared to stop. I could still hear a hum from the fuel pump as it was trying to push fuel...but it was noticibly quieter. I guess I have a faulty regulator then, huh?

Might as well go adjustable while I'm in there I guess...

 

sounds like it.
Squeeze the rubber line on the return and turn the pump off to see if it really holds.

 

Just tried it. When it's pinched off, it shoots up to 75psi. After cutting the ignition, its slooooowly creeping down over the course of a min or two to 60psi.

Seems kinda high - even for a new pump. Unless my gauge is defective (almost new actron)

 

If I remember correctly, the shut off pressure for a TPI pump is 75-90psi... So that makes sense that it would go up that high if you have the return blocked off..

 

Whew! OK then...so a stock FPR is *always* bypassing some of the pressure to keep the system at 40psi or thereabouts? I think I understand now.

I charged it up again (return blocked) and it went down to about 65-70 after a min or two...then I removed the return block and it went down to 40 almost immediately...and it inched its wa down over a 10min span to 20psi

I think a new regulator will be the answer.