Bought an 86 z28 a few months back. Original computer controlled Q-Jet, poorly converted to an Edelbrock carb. LOTS of splices, missing wire and vacuum lines, etc. etc. I was after the dark blue, Non Iroc Z28 with T tops. Knew before I bought it that the 305 was coming out. I've got a Carbed vortec 350 ready to go in, with a 2 port in/out mechanical fuel pump. I've heard some of these cars got an electric in tank pump to help with vapor lock etc. etc., but never really learned too much about this. Started the removal process last weekend and found I've got a return fuel line, and of course the obligatory 3 port mechanical pump. I have questions.

First, does the return line mean I've got the in tank pump, or do all the cc/qjet cars have this? Haven't looked for wiring at the tank yet, but I'm sure that'll tell the tale.
Second, if I do NOT have the in tank pump, I can just cap the return line and use my old school two port pump, right?
If I DO have the in-tank, is it worth using? - and then I assume I should get a 3 port mechanical pump......Or the in tank pump not worth the bother, and should I just remove it all together?

From what I've found, it looks like the in-tank pump bumps the pressure too high to be used without a return line, and if I have it, I just assume use it. -but they do go bad, and they ARE in the tank, lol, sooooo, I dunno. Thoughts???

I've got many many years playing with EFI, and even installed and learned to tune my Holley EFI, but carbs are completely new to me, so I'm learning!!!!

 

After some further reading, seems a lot of older cars did in fact have a return line, though I can't directly speak for the thirdgens. Wouldn't surprise me though. Guess I 'll have to get under there and see if I've got and power going back to the car for a pump.

 

No. That arrangement was stock on pretty much all cars from the mid 70s onward.

No. Before that time, not all cars had returns, and some that did, handled it differently. For example 69 Chevelle 396 cars had the bypass coming off of the fuel filter.

Sure. And then be in the same Hell you see all manner of people in, whose cars have "vapor lock" (they don't, butt that's what they like to call it anyway), flooding on hot starts, and so on. Just because you "can" hack something doesn't automatically make it A Good Idea.

Carbed cars in general worked fine for A REALLY LONG TIME with mech fuel pumps and no "helper" in the tank. Personally I question the efficacy of adding that extra bit of gadgetry; while I'm a long way from outright declaring it's unnecessary, I am STRONGLY skeptical of it. I think if I had a car with that, I'd get rid of it, if the occasion ever arose. My 83 L69 car for example doesn't have it. It has and has ALWAYS had the STOCK 3-port mech pump for 305, which ran a 400 with a big solid cam, headers, Holley 800, etc. for MANY years without difficulty. I'd add incidentally, the STOCK single-fan cooling system with the STOCK fan switch ALSO worked fine in that situation.

First thing I'd do in your situation is GET RID OF the 2-port mech pump and put just yerbasic STOCK REPLACEMENT one back on it, with a lightweight fuel pump drive rod and a phenolic blockoff plater instead of the stock steel one. Then I'd look it over real good and see if it has an in-tank one, and probably just leave it alone if it does, as long as it works. Shouldn't be any trouble to tell: it would need a relay to turn it on, and an extra wire going into the tank in addition to the gas gauge one which IIRC is pink. You should be able to spot that instantly under the back seat where the tank harness goes through the floor. Then I'd drive it and see how it does, and not mess with it any further unless it needs it somehow.

 

87 was the only year that the LG4 got the helper pump. I just replaced the original fuel pump on my 86 LG4 with a NOS one and both have the return.

 

Thanks for the replies guys. -Sofa, your response makes total sense. -I'm a little ways from having it ready to crank and run, BUT......if it does NOT have the pump (according to Gearhead), which is likely the case, I'll get a 3 port like you mentioned, use the return line, and call it a day.

Thanks

 

I seem to remember a post where someone mentioned that if an LG4 prior to 1987 has an in tank pump, it was likely done by the dealer back in the day to help with vapor lock. Not sure if that was an official GM fix for that issue.

 

In fact it was. Never seen one myself though. There was also a little blower fan that they had the stealerships put on beside the carb that just blew air at it. *smh*

 

Yeah, I've seen that post too. I wasn't gonna question your statement, as I am certainly not sure, and didn't know the difference year to year between from GM, from the dealer, blah blah blah and all that. Only really need to figure out if I have one. Doubt I do, but I'll letcha know later tonight after I get home!

 

2 wires at the tank harness connector, not the 3 I'm used to. Even has the weatherproof plug in the third hole. No pump.