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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 09-26-2009, 01:46 PM   #1
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How does one check in-tank fuel pump without a press gauge?

I have a victim of attempted car theft, and I have a multitude of problems after the workshop "repaired" the electrics so it atleast starts and can be driven.

However, the car struggles alot when you hit the gas, seems to run way lean, caughs through the air filter etc. It has the same symptoms as another time the carb was adjusted wrongly to a way too low float level, hence it ran out of gas.

So, it seems it's running out of gas, the mechanical pump I changed for a brand new one 3 weeks ago. Carb was overhauled and adjusted perfectly 2 years ago or so.

Now, I need to be able to check if this is actually the case that the in tank pump dont run, so I can ask the garage to fix it, since it's covered on the insurance to begin with. They did alot of electrical work after the damage to the wires the thiefs made.

Question is, how do I check the operational status of the in-tank electric pump when I dont have a pressure gauge?

Yeah, It's a -87 canadian/export LG4.
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Old 09-26-2009, 03:18 PM   #2
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re: How does one check in-tank fuel pump without a press gauge?

There is no in tank pump on a carbed car. The mechanical pump on the pass side of the block is more than sufficient to provide enough fuel for your carb.
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Old 09-26-2009, 03:48 PM   #3
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re: How does one check in-tank fuel pump without a press gauge?

Well, the GM factory repair manual disagrees with you, so does 57kid in some post I read once. It might be an -87 only though.
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Old 09-26-2009, 05:08 PM   #4
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re: How does one check in-tank fuel pump without a press gauge?

That's pretty wierd. I guess you learn something new every day. If you do need to check it and don't have a gauge you will have to take off your feed line to the mech pump, put the end in a bucket and turn the key.
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Old 09-28-2009, 07:21 AM   #5
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re: How does one check in-tank fuel pump without a press gauge?

The Canadian model may, or may not, have had an in-tank pump. The US versions used the ECM harness to control the pump and the export model may not have the ECM.

If so equipped you'll find a two-wire oil pressure switch behind the distributor tee'd off the brass fitting screwed into the china wall. It should be connected along with the oil pressure sending unit (one-wire) for the dash guage.

You can test the fuel pump by disconnecting the rubber supply line and jumping the fuel pump relay pigtail. The fuel pump relay will look like the fan relay but you should be able to trace the wires to tell which is which (the fan relay should be on the left side, I can't remember on the fuel pump). If not just jump either and if the fan turns on you'll know you've got the wrong one. Use a jumper wire between the two larger gage wires into the pigtail.

You won't need a fuel pressure guage, just ensure that fuel flows while the pump is running.
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Old 10-07-2009, 04:56 PM   #6
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re: How does one check in-tank fuel pump without a press gauge?

OK, thanks, that was a good tip. I'm going to try that aswell.

However, I now have the fuel gauge, but I'm unsure which is the feed line. Thing is, I'm doing this alone, and when I cranked the engine, there did come some fuel out, but the gauge didnt move. I could not see from where it came. I am unsure if the fitting isnt tight enough, or that the fuel came out from the carburetur return line possibly.

Annyways, Do you know which is the feed line from the tank on the pump?

No.3 is obviously the line to the carb. But is it No.1 or No.2 that is the feed line/return line to/from tank?
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Old 10-07-2009, 06:05 PM   #7
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re: How does one check in-tank fuel pump without a press gauge?

Well, I simply took off both hoses where they connected to the metal fuel lines going rearwards, and ran the engine. Absolutely NOTHING came out of those two lines whatsoever. I did hear alot of sucking from the mechanical pump though.

Guess I have established there is no fuel supply from the tank. Question is, is there supposed to be any? This being an export model and all...


I took a few pics of the engine compartment, could anyone possibly recognise the fuel pump relay, if present?

Is this it, in this first picture? THe two other pictures I added in case anyone could tell if it had that thing behind the distributor or not naf talked about.
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Old 10-07-2009, 06:31 PM   #8
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#1 is the supply line, #2 is the return line, and #3 is the output to the carb.

Your first picture does show a relay, but that may be the radiator fan relay. We can't see the oil pressure sender/switch from the angle of your photos.

Weird for an '87 to have a large cap coil-in-cap distributor. Being vacuum/mechanical advance (non-computer), that may be what they used. Center bolt valve covers are consistent with '87, though.

I'd guess you don't have an in-tank electric pump. You might want to crawl underneath and look for the wires going to the tank - if just two, you don't have an in-tank electric pump.

Last edited by five7kid; 10-07-2009 at 06:34 PM.
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Old 10-07-2009, 06:45 PM   #9
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Re: How does one check in-tank fuel pump without a press gauge?

Don't see a fuel pump relay. The relay in #1 should be the fan relay. Best way to check is to look for the oil pressure switch (2-wire) located adjacent to the oil pressure sender (1-wire), behind the dist. The pic don't show the area, but you should see a round canister (maybe 1" in diameter and 1-1/2" long) back there that is the sender unit for the guage. Both are attached to a bronze (or brass) tube that comes up from the china wall about 1-1-1/2 inches, driver's side of the dist.

Pretty sure it's not there though. Would be consistent with the wiring harness, that controls the oil pressure switch through the ECM harness.
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Old 10-07-2009, 06:45 PM
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