92 Yoda

Hi guys,

I've been having some trouble with my runner starting recently. It cranks over for 5+ second before gurgling to a start. Once running, it has no noticeable issue other than a very infrequent misfire (might have been there before). I pulled a line from the pump and it's working, checked for leaks along the line and changed the fuel filter (Pain in the ass ). The truck started easily this morning but now the truck is just cranking over.

I plan on pulling the pump and checking it visually, testing actual pressure and checking for spark. The reason I thought it was fuel related was because I've been running her near empty a lot recently and have been getting it stuttering around corners or fast stops (low fuel).

Anyone have possible ideas?

Also is the the pump supposed to only come on when cranking or running?

92 Yoda

Anyone?

scope103

The pump only comes on when cranking or running (when you let go of the key, airflow through the VAF activates a switch, which keeps the COR closed, which powers the fuel pump.)

First things first. Is the COR VAF circuit working? Easy to test. Jumper FP to B+ (the location of the connector is different in older 4Runners: http://www.4crawler.com/4x4/CheapTri...shtml#FuelPump). With key-on, this forces the fuel pump to run. If this clears up your problem, you have a VAF-COR issue (don't drive around with the jumper in; the VAF-COR is there to save your life in a collision that breaks a fuel line).

Next, check for flow. DON'T "pull a line from the pump." The crush washers are one-time-use, so you need to replace them EACH TIME. Instead, pull the fuel return line (low pressure, just hose clamps). With the fuel pump forced to run with the jumper, you should get about 1/2 liter/minute through the return line.

92 Yoda

Jumped the pump and still no start, pulled the low pressure line and jumped it again but not getting any fuel. I hear the pump but there's no flow, can I assume it needs a fuel pump?

92 Yoda

Also just pulled the pump and it seems like the tank was under vacuum... Is that normal?

Terrys87

iTrader: (1)

How is your fuel filter? I see the Return Lines get clogged on these all the time. On my build threads in my signature below, I show usually on the first couple of pages of them being clogged and the "J" line on the fuel pump assembly gets clogged as well. I will try and see which build it is on and post a link.

You really need to check the line all the way from the fire wall back to the tank. I fill my line up with Marvel Mystery Oil and let it soak for a few days and then clear with an air hose.


This is from my 85 and I think the Return and Vent lines are located a little different they your truck. I use a gear oil bottle cap as a funnel to start soaking the crud in the lines to loosen it up and so far I have always gotten the lines cleared that way.

Since I am talking about clearing the junk out of the lines, I do the same thing for brake and clutch lines. You should see all the rust that come out of them.

Copied from my 85 truck build.
Here I am checking to see if one of the fuel return lines is clear. I pop the gas cap off and you will hear air or bubbles in the tank. I have seen these return lines clogged.


Checking the other line.

scope103

No. The fuel cap is vented to let air in, but does NOT allow fumes out. The fumes go to the evap canister (where they are later simply sucked into the throttle body.)

If the fuel cap wasn't vented, the vacuum created by the fuel pump would simply crush the tank.

Your tank wasn't crushed (was it?) but if the fuel cap was bad the vacuum could inhibit fuel flow. Easy to check; use the jumper with the fuel cap off. Or just spring for a few bucks and replace it; it's a standard item.

But I suspect your problem is much simpler. if the fuel pump runs but pushes no fuel, it is either a completely clogged fuel line, a disconnection at the pump, or a bad pump.

92 Yoda

I've got the pump out now, figured I'd check the screen on it but it seems to be fine. I tried jumping it to a old battery I have but it doesn't go at all.
Is there any special way to jump it or does it have to be submerged?
Also I'm going to check all the lines while I'm at it to make sure there's no plug there.
I also tried running it without the cap on but still nada, is there a vent tube that could be blocked or is it only the gas cap that does the venting?

92 Yoda

I don't have a compressor at home, think some canned air would be sufficient to check for blockages?

Terrys87

iTrader: (1)

What I do is with the jumper in the test block, is remove the fuel line off of the back of the fuel rail and run it into a container. With the key on, it should fill a quart jar in 1-1 1/2 minutes as a general rule of thumb. It should be enough to get a general idea if the fuel pump is pumping like it should.

Canned air would not have enough pressure or volume to clear a line in my opinion. Might would work for a light clog but I would bet if it is clogged, it will be a bad clog. The fuel, years of build up, moisture and other things is what you probably are going to be dealing with.

Fp +B Fuel Pump Test for 87 and newer. Use a paper clip for better results.

scope103

It's just an electric motor; if you properly connect 12v to it and nothing happens, then the motor is bad (it has to be submerged in operation as gasoline cools the motor, but not having it submerged won't keep it from starting).

The evap line goes both ways, the cap vents "in" only. If you think you have vacuum in the tank (it's surprisingly hard to distinguish from pressure in the tank, which is normal), just replace the cap.

Checking for a clogged line is probably a good idea, but since you know the reason you're not getting any fuel is a bad pump, I doubt you have a blocked line. While you'd need a compressor to actually "blow" it out, I think all you need to do is check it, and lung power would be enough for that.

92 Yoda

I let the pump soak in a 50/50 injector cleaner fuel mix over night and now it spins like a top and moves fuel well. I think I'm going to try putting it back in and see how she goes.

92 Yoda

Update: Changed the pump, not getting power any more. Test port no longer works and I've gone through most of the fuses with no luck. Killed the battery cranking it, going to charge it and start trouble shooting it again tomorrow.