Hello everyone,

I have a 87 Trans-Am with a Edelbrock 1406 carb, and new distributor. Also has a new fuel filter. Mechanical fuel pump was replaced about a year ago by previous owner. The carb and Distributor were also replaced by previous owner.

Well let me explain the dilemma. On cold start fuel makes it to the fuel filter that is sitting next to the carb just fine and car runs like a champ. Now after the car reaches temperature, driven for about a mile or so, or just stuck at a light. The car starts to lose power, when i press the pedal is like no power is there. When i look under the hood, the fuel filter is empty. I did a fuel pressure test today and seems like the fuel pump is working fine. The tester had a clear hose attached to it im assuming for vacuum. When its buttom is pressed i get fuel with like air pockets and eventually followed by foam. When i let the car sit turned off for abut 15-30mins. The problem goes away but returns in a matter of minutes. I have attached a couple pics one of the engine bay and another showing the fuel pressure sand an empty fuel filter while the car is still running.

If anyone has any input on how to fix or diagnose this please let me know.
Thanks in advance.

P.S. Sorry for the size of the pics.

 

OK, so you have a fuel pressure gague with an "overflow" valve that lets you dump fuel or air bubbles out through a small plastic line. I think that's right based on what you posted. Yes?

If you hold that button in for an extended period of time, do you ever get pure fuel flow through the "dump" line with little or no air/foam?

You may not realize it, but your 87 came from the factory with a low-pressure in-tank electric fuel pump. If it's not operational any more, you're sucking fuel through a non-functional pump now. If there's a chance of sucking in air through an old, cracked flex line (perhaps near the fuel tank or even INSIDE it), it's going to play havoc on the block-mounted mechanical trying to pump fuel out of the tank and up to the engine.

Your fuel filter will NEVER be totally full of fuel (I know, I've used the same Fram G3 filter in similar setups many times). But that doesn't mean things aren't working right.

It's the TOTAL emptying of the fuel filter and the air pockets and "foamy" fuel that make me think there's more going on than the typical "trapped air bubble" phenomenon you're seeing through the case of the fuel filter.

 

Yes. It is the overflow valve. And no, holding it down for long period of time I get little fuel, alot of bubbles then nothing but foam. I didnt know there was another pump in the tank. Im baffled on what to do first.

 

next time its running bad/not getting fuel,....pop your gas cap loose. see if it runs better. for a carb, you need a vented gas cap. if it goes, "swoosh" when you crack it loose, thats a non-vented cap for fuel injection. imagine trying to suck water through a straw while your finger is on the other end.

anyway, i hope that works for ya.

 

Already tried and there was no swoosh sound. I can check again later today when I go to my part time. I did try
driving the car with the cap off and no luck it driving any better.

 

i might try the fuel filter next. the one under the car, behind the drivers seat area. pull it off and try to blow through it. could be pretty plugged up?

i put magnets under my tank, tranny, engine, rear, etc., to trap any ferous materials running around loose. (rust). i mean a good magnet, like break an old speaker apart that doesnt work. try and place it away from the pick-up area.

 

should look like this;
http://www.autozone.com/routine-main...618419_0_6138/


yea, if your still sucking through the electric pump, you might need to modify that?
i took my e-pump out and fabbed up a pick-up tube.
hopefully it doesnt come to that!
maybe the magnet will collect any rust in the tank or sock & fix your issues?

 

I was wondering where that other filter would be located. Gonna look into that one. And ima try that idea of using magnets to catch the rust and metal debris. I know the previous owner never dropped the tank. Ive only owned this car for a week and a 1/2. And dont know when ill ever have time to even attemp to drop it. Wish I knew good knowledgable people about this car in my area to seek a helping hand. Thanks again for the suggestions.

 

your welcome.

if you can jack the rear up, it's kinda in front of the rear tire area, sorta.
i forget the size wrenches,...maybe 15mm? or 2 adjustables, lol.
its easy. probably wouldnt take ya 20 minutes?

picking up a service manual like a haynes at the auto parts store, etc., is handy for things like this.

i had a camaro that sat for a few years. i had to put a new fuel filter on there, seems like every 2 weeks for about 2 months. stuck a magnet on the tank too. finally it cleared out and had no issues.

 

Sweet. Well my pt job is at auto zone so discount on anything I get. Prolly look into it this weekend. Been raining all day here last couple days. And no garage to go to.im going to look into the "how to" for remove the gas tank.

 

Well looked under the car theres no filter under the car, i followed the lines from the tank to the front. If the vent is bad would it cause this issue?

 

Update...vent valve removed and cleaned. Car still runs like crap and it doesnt even reach temperature before it starts. Now when I remove the gas cap now id does go swoosh and when I look at the cap it looks wet with fuel. Ran the car without it and it looked like it was throwing some heavy fumes and area looks damp with fuel. So im extremely confused and frustrated. Its my daily driver and cant even go the the grocery store without issues.

 

I still think you're drawing air into the line somewhere on the feed side of the mechanical fuel pump. Possibly the reason the PO changed the fuel pump, but then got frustrated and sold the car when that didn't fix it.

 

the places to check are the rubber lines near the tank and the short lines to the pump.

I will also throw out checking to ensure that the return line to the tank is not clogged or otherwise restricted.

There is no additional fuel filter under the car for an original carbed 87.

Ensure that the in-tank pump is working by jumping the relay and observing fuel flow through the lines. It should also run when the key in in 'run' and fuel should be observed to flow.

 

Which is the relay and how do I jump it...thats something ive never done before. The rubber lines by the pump look new and the ones by the tank I can double check. The other day I tapped with a screw driver the lines by the tank and tapped the tank. I was able to drive a good 10 miles before problems started. I might see if the carb is under warranty with autozone if it is im swapping it too. Thanks all with the info. I hope I get this resolved soon. So I can focus on other parts of the car.

 

Also. Would a can of the compressed air work? since I dont have a compressor handy to check the lines.

 

pump relay is near the brake booster, looks similar to the fan relay but jumping the wrong one will cause the fan to spin.

does your mechanical fuel pump have a return line connected to it?

you can blow compressed air through both the return and fuel supply lines and should be able to hear the pressure relief valve open (with gas cap tight).

 

Yep. It has a return line hooked up. I tried jumping the one closest to the booster. It started to click another relay by the battery..soooo idk.

 

Update. As of right now car is running good. Ended up removing the top half of the edelbrock carb and doing a good clean. Noticed that one of the bowls was not getting any fuel. After cleaning everything in there and out it back together for ts been running like a champ a little rich but running. The carb will need a rebuild at some point. Been running good since yesterday so fingers crossed for the rest of the week. Woot woot!

 

awesome!
glad to hear you got it figured out.