Engine: '74 Djet 2.0
Weather: sunny mid 60s

Drove my daughter to work today at 11:30am
Car was driving great - feeling strong, no major hiccups
Drove about 25 miles (35 min or so) and stopped at the mall so she could run in and get some supplies. I let the car idle while waiting but after about 10 minutes, it slowly died
I tried to restart and no luck. Seemed like a fuel issue to me so I turned the key on and off a few times to verify the pump was running. It was.
Got out and took a closer look. Lucky for me the PO had had the fuel pump hot wired to the coil. I have been running without this wire connected but never bothered removing it altogether. I turned the key to the ON position and connected the wire to the coil. The pump ran and I could see air moving through the fuel lines. I ran it for a few moments and then tried starting the car. Fired right up - with wire to coil.
So I then drove my daughter to her workplace and on to home. Car was not as strong feeling as before and would not rev over 4000 rpm.
Got home, disconnected the hot wire, and tried to start it. Fired right up. Shut it off and went inside to get some work done.
At 3:45 this afternoon, went to pick up my youngest daughter from school. Hot wire disconnected and the car started right up. Drove to her school - about a 10 min drive - and it felt strong. On the way back home, started feeling sluggish again. Difficult to reach 4k rpm.

Any ideas on what may be going on?
Seems odd that it works for a while just fine and then starts to deteriorate.
Suggestions on what to check are very welcome!

thanks.

On D-Jet, the fuel pump needs to be controlled by the FI brain!!!

Might be trash in the fuel tank that blocks the pick up tube. I've seen this alot when the screen is missing or the lines are reversed at the tank. Once the car dies, the suction against the pick up drops and the offending piece of junk floats off the pick up till the next time.

Does it seem like a warm issue Steve? The pump wired to the hot side of the coil is just a power source. With it hooked up as well as the power source controled by the FI, that would just give you 2 seperate power sources. Kinda like a redundant system. Could it be an indication of a failing wire/connection at the 14 pin connector?

Try loosening the gas cap next time.

Yes, it sounds as if you have a blockage in the tank or fuel lines. As the fuel pump gets under load from the blockage, it runs slower ( meaning you have a voltage drop somewhere). Hooking the jumper up to the coil gives you twice the power path and the pump runs fast again. Something at a connection is dirty or you may have a relay failing ( dirty contacts). It sounds if you have it operating correctly thru the ECU most of the time? Just a jumper for the emergency's? The relay is on the relay board, third one from front. Try changing it out with the fourth one back ( heater fan).
How did you see air moving thru the fuel lines? I would think if air is getting in, fuel would be getting out, not good!
Tom

The more I think about it, the more I believe 914Mels may have it right.
I can see debris being pulled to the filter sock and inhibiting the flow of fuel and then, once the car is off and pressure relieved, the debris starts floating around again. Running the fuel pump off the coil simply helped in pulling the fuel through the line to get it back to the engine.
I have an extra fuel tank that I will have cleaned and installed. Need to do that anyway since my current one has pinholes and leaks slowly if I fill above 2/3 full

Thanks for the feedback, guys.

PS: Jeff - I will try your gas cap trick next time it happens

Could cavitation on the pump end (blocked supply) or high temps produce some bubbles.

Common tank issue after 35 years.

Going to start happening more often as they age. The gas we get nowadays is never the same, even at the same gas stop, as many station owners are shopping around for better prices. You can add injector or STP type treatment for a while, but that's just a temp fix.

New filter is cheap, swap those lines in the tunnel to stainless when the opportunity arises as well. Pull your FIs and soak in injector cleaner overnight, reinstalling with new seals. Replace the gas tank sock mentioned above. Check all grounds while you are at it as a little surface corrosion can go a long way to driving you absolutely nuts.

Oh, refresh/boil your tank and recoat it when the opportunity arises. Or, buy one of my rebuilt/refreshed units, ready to drop in - that's my shameless plug of the day:--)

I have an extra tank that I plan on having cleaned and treated. How much are yours?
Also, my engine will be coming out in the next couple months and I plan on cleaning up grounds, wiring, sheet metal, and other engine bay issues at that time.

Tom - I will try the relay swap and see what happens. And, yes, it is running off the ECU and the hot wire is there but disconnected. I think once I got the pump primed again, I could have disconnected the wire and it would have worked fine.

How long have you had the car?

Is this the first time this has happened to you?

Is the fuel pump in the stock location?

Is your heating system completely hooked up (correctly)?

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One possibility is as some of the others have suggested, trash in your fuel tank and or fuel filter.

Another possibility exists:


There are some heater valves out there that can dump HOT air right in the vicinity of the fuel pump when everything is in the stock configuration especially if sitting still idling. The engine fan still moves air through the heat exchangers and the heater valve dumps this hot air right next to the fuel pump.

This is one of the reasons that way back when, it was suggested to move the fuel pump from the original location. One of the "other" fixes of the day was to hotwire the fuel pump either from jumpers in the engine compartment relay panel or from the "hot" side of the coil.

Since when you hooked up the jumper wire at the coil and you reported seeing air bubbles move through the line, I suspect that you had a classic case of vapor lock in your fuel ring.

More than likely it was caused by excessive heat in the are of the fuel pump.

Let the FI control the pump and make sure your pressure regulator is set for the right running pressure.

Check your fuel filter and your passenger side heater valve to see if the heat is being dumped right on your fuel pump. If it is, you may also find that the fuel pump rubber mounts are hard as a brick or already broken.


just my free advice.

Refer to my response in this post...

http://www.914world.com/bbs2/index.php?sho...amp;hl=gas+tank

When I first saw that, I thought but after reading your explanation, this could be at least part of the problem since my heater system is not hooked up on the passenger side. I will look into this. Thanks!

John is correct in that.

Even with everything in place, when the heater lever is in the down(off) position all the hot air is dumped to atmosphere. Guess where it points? I really doubt this is a vapor lock problem due to the ambient air temps this time of year. I'll be very surprised if I'm wrong on this one.

I am thinking it could be a combination of debris in the fuel and vapor lock. I will deal with both to rule them out.

Thanks for all the input, everybody.

How many feet above sea level?

It's also been extremely hot/humid/strange for a Jan/Feb in the SouthEast, so don't bet your eye teeth yet...

He did report letting the car sit still idling for a while.... I have seen this "modern" fuel we use today boil at fairly low temperatures.


If you do find evidence of brittle fuel pump mount rubber, please also take a look at the plastic fuel lines and rubber fuel lines in this same area. They may be hard and ready to crack as well. I would really hate to hear another story of one bursting into flames and burning to the ground.

Hope you find the cure.

John - Thanks for that reminder.



---> PLEASE MAKE SURE YOU ARE NOT IN YOUR CAR OR UNDER HOODS WITHOUT POWER DISCONNECTED WHEN T-SHOOTING <---

John is dead on here, no pun intended - too many fires the last 18 months.

Be Carefull

Fuel lines look OK. And, yeah, I always disconnect the battery when messing with the fuel system.