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1973 450 with some kind of fuel problem

2K views 20 replies 6 participants last post by  Rbeguelin 
#1 ·
Hi all,

I haven't posted a lot since I finished my rebuild of my 1973 450 SL a few years back but I now have a problem with which I could use some advice. The car starts and runs fine. It accelerates and idles just fine and then...it is like it runs out of gas. BY constantly working the gas pedal I can keep the engine running; barely, but no power. Eventually, I give up and let it stall. I try to restart and it wants to start but dies instantly. After waiting awhile, say 5 minutes It will start and run. It may run for the rest of the trip or it may stall again. Varies. There is no gas smell like a flooded engine or leak.
My thinking is that something is wrong with the fuel system. During the rebuild all fuel lines were replaced and the clamps have been checked. I have not checked to see if I hear the fuel pump go on during one of these episodes as I am normally to frustrated (seems to happen in intersections or along busy highways) and I am not sure if I could hear it anyway. The pump is probably original. I have not checked the pressure regulator either though I am not sure how it could cut out and then come back on. :confused:
Does anyone have any experience like this? If the consensus is the fuel pump does anyone know where I can get one???

Thanks,
Rob
 
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#2 ·
Start with the fuel pump relay. Top left of the relays. Try swapping one from the right side of the panel. They are all the same. It could be the pump is drawing too many amps due to a clogged filter or tank stainer. That could possibly cause the relay to over heat and fail.
 
#3 ·
I had a loose battery connection on my 74 and the car would stall seemingly out of nowhere, maybe going around a turn. Sounds somewhat similar. I wouldn't expect a running car to need power from the battery, but that's just what mine did. Not sure why. I could replicate the problem by disconnecting the battery in my driveway.


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#4 ·
You can check the pump flow and pressure quite easily. Better to do this before looking for new pump. You should have at least 28psig measured anywhere in the fuel rail. If you disconnect the return line after the fpr and damper, then jumper relay or apply 12v to pump from another battery, you should get a flow of 2L/sec or 1L in 30 sec. This with engine off.

Bosch do have a replacement Djet pump. Not sold anywhere I know in USA, but available in Uk and Europe for something like $400. If you do a search, you should find my previous posts as to why you should use a proper djet pump as well as the model numbers. You can use a pump off a Nissan 280z, from about 1978. Again, I dont have exact details on my tablet, but a search should bring up the info.
 
#9 ·
A number of the pumps suggested in the above posts are simply wrong and unsafe to use. Please don't suggest these pumps without first doing research.

The only pumps with the required internal relief valve are made by Bosch. And these do not include the Bosch K-jet pumps.
 
#11 ·
Thanks for the insights. :thumbsup: I will check the relays however I am not hopeful...the relay would overheat at approx. the same time everytime if the pump was being forced to draw more amps than rated. This symptom is the maddenly "intermittent" problem, ie it does this "running out of gas" symptom at very different lengths of driving time.:rolleyes: I could check the pressure on the fuel rail but I need to do this when the event is happening... which is not normally near my garage. I may try to idle her until it happens (if t it happens) and then check to hear the pump, and then check the relay and then check the rail pressure.
How could I bench test the pump without adversely effecting it. Can I take it out, hook it up to a 12v supply and let it run for awhile to see if it stops. Should I put a load on it - if so how???
Thanks for the links to a $300 Bosch pump...should I buy it as a back up? :eek:

Rob
 
#12 · (Edited)
Thanks for the links to a $300 Bosch pump...should I buy it as a back up? :eek:

Rob

The used 005 Bosch Pump or the Nissan pump will both work. Stay away from the Airtex pumps because they don't have the internal safety relief valve.

If your current pump is the original, I doubt it is the problem, but a spare is always nice to have. I have the original 005 pump in my 72 car and I have a Nissan/Bosch pump as a spare. The Nissan pump is actually a Bosch Djet pump that was made in Japan by an associated company.

Suggestions:
- Check what type of pump you currently have.
- Do the pressure and flow test even if car is running OK. This will confirm that the pump is good.
- Get under the back of the car and clean the wiring connections to the pump.
- Do as Rowdie suggested and switch the upper left relay (Fuel pump) for one of the others. Clean the pins and sockets while you are about it.
- Pull all your fuses or at least the fuel pump fuse, clean the sockets and install new fuses with copper/brass bases.

Your problem sounds like fuel starvation. Even if the pump is running, it may be that there is resistance at connections causing it to get a low voltage. Low voltage on a DC pump equals low flow.

Once you know your pump is putting out the proper pressure and flow, you can look at other things:

- Does this happen with full tank? Could be a problem with blocked screen or return line venturi.
- Trigger points. If mileage is over say 120k miles and trigger points are original, the rubbing blocks could be worn down. But this is unlikely to give an intermittent problem.
- Ground connections for injectors. (clean them (located under air cleaner a rear of engine)

Nothing is easy :)
 
#13 ·
I have thought about this problem for a few days. I am thinking I will order a new fuel pump relay from German Star approx. $46. Even if it is not the problem it would be good to have an extra relay around. I pulled out my Startek CD and did some research there...what happened to the website???I remember it being a lot better than it's current form! Anyway, I think I will follow the "checking delivery pressure" section 07.4-130. It will tell me if the pump delivers the correct amount of fuel and that the regulator and dampener are working correctly. It seems pretty straight forward...anything I should watch out for?
First though I am going to check the wires and connections to the fuel pump apparently I should read 11.5 volts minimum with the pump on. I have not checked to exactly verify which pump I have but I recall it to be an original pump and it looks like the one offered on flea bay for $300. I may have to bite the bullet there.
:thumbsup:
 
#19 ·
That's a good price! Even the eBay unit from nissanofchesapeake at $249 is good. Does Tasca have on line link for the pump?

I don't think these old style djet pumps are being made anymore, so at these prices great buy. My spare cost me double those prices.
 
#21 ·
MB,
I have ordered the relay and I added two plastic nipples to the T that came with my gauge. I will add some fuel hose to that and attach it to the rail and clamp it all together. I will not get to this until next weekend...family plans :rolleyes:
For two hundred buying the Nissan pump seems like cheap insurance?
Rowdie
Thanks for the pictures - makes life a lot easier...Can you identify the other relays?
BTW thanks for the mention of EPC...I had forgotten about it...I used it extensively 6 years ago! :thumbsup:

Rob
 
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