Low Voltage to Fuel Pump on 71 280SL

[71Blue280SL]

I just got around to messing with my 71 280SL after about eight years of having it in storage.  In the process of swapping all the fluids and filters, I try to pump the fuel out of the fuel pump, and it does not turn.  Car ran great when I parked it eight years ago.

Checking the voltage to the pump, I am only getting 10.7V.  The battery is brand new, and cranks the engine just fine.

Any ideas where to start looking?  The wires running through the trunk and down to the pump look fine.

I looked in the service manual to see if I could find a pump relay, but could not find any pictures.

Thanks.

[ctaylor738]

No relay.

The current path is something like:

battery
starter lug
alternator
light switch
ignition switch
fuse 4
fuel pump

But 10.7 volts should run the pump.  It may be stuck from sitting, and you might try giving it a smack to see if that gets it going.

[w113dude]

Like Chuck said, most likely the pump is gelled up, if smacking doesn't do it take the bottom cover off the pump and clean it with some solvent, in most case that is the area that stops from spinning.

[71Blue280SL]

A couple of taps would not loosen it up, so I put 12V from a battery charger on it, and it spun right up.

Now it is pumping like it should, but the car still will not start.

Gas is flowing strong from the return line, and I pulled a plug to validate that it is getting spark, but it appears that gas is not making it to the cylinders (plug was dry).

Any ideas on what I should hit next with a hammer?

Thanks.

[George Des]

Check the fuel filter and if you are getting fuel to the FI pump. Whatever you do, don't hit the FI pump with that hammer!

[71Blue280SL]

I pulled the fuel return line from the FI pump, turned on the ignition (fuel pump), and fuel came gushing out.  So I assume it is not a filter issue?

The car ran when I parked it years ago, but is it possible that the FI pump wouldn't turn even if the engine is turning?

Maybe the fuel flow is good, but the pressure is too low?  Seems like the engine would just run poorly under those circumstances.

Thanks.

[ctaylor738]

You did put some fresh fuel in the tank?

The cold start valve should supply enough fuel to at least get the engine to fire.  You can try disconnecting the wire to it and run a lead from the positive terminal of the batteryl.  Have someone crank the starter while you touch the lead to the screw on the CSV.  That should provide a shot of gas, get the engine started, and provide some fuel to the injectors.

[w113dude]

to make sure you are actually getting fuel where you should crack open one of the fuel injector lines just to make sure you have gas there. you do this while cranking the engine.

[71Blue280SL]

Thank you for the advice.  Yes, drained the tank to get rid of all the old gas, and put in five gallons on fresh gas.

Where is the cold start valve?

I tried to unscrew one of the injectors, to test that very thing, but they are hard to get a wrench on, and I was worried I might mess it up.  I assume you are talking about unscrewing the injector end?

Thanks.

[ja17]

Don't forget to check to see if you are getting spark!

[kampala]

Firstly, good to hear that you are getting another pagoda back on the road ... I am sure many here would like to read the "story" behind the 8 year storage and your ownership prior to that ... maybe once you get it going. Welcome ... I am new as well.

Maybe I am being to simplistic about this ... but ...

Seems to me, you need to just try the basics ... since your engine is already turning strong:

1. get a spray can of starting fluid.
2. check you have spark going to the distributor.
3. check your points are gapping ... after 8 years, you should run some emery cloth/file between the contacts in the points so you have good spark.
3. check you have spark getting to the plugs.
4. check that your plugs are good enough to provide a spark (or just put new ones).
5. spray starting fluid into air intake while cranking.
6. if it starts and then stops when you have stopped spraying -- you have a fuel delivery issue.
7. if it does not start with starting fluid AND confirmed spark, you have other problems besides fuel delivery.

I know these are not pagoda specific suggestions ... but given where you are at ... this would be my approach.

best of luck ...

[w113dude]

Thank you for the advice.  Yes, drained the tank to get rid of all the old gas, and put in five gallons on fresh gas.

Where is the cold start valve?

I tried to unscrew one of the injectors, to test that very thing, but they are hard to get a wrench on, and I was worried I might mess it up.  I assume you are talking about unscrewing the injector end?

Thanks.

Yes, at the injector end, if you see any sign of fuel then you are good with fuel and the problem is electric.
The cold starter valve is on the side of the intake manifold, it has one wire going to it kind of battery shape looking.

[71Blue280SL]

Thanks to everyone for the advice.

The problem is definitely with gas not getting to the cylinders.  I pulled the number 6 cylinder injector line, and it is dry.  Turning the engine over does not cause any gas to come out.

Other items I have done:

1) Car runs great if I keep spraying starting fluid into the intake.
2) Pulled the fuel line to the CSV, turned the engine over and gas went all over the place.
3) Actuated the CSV with a 12V line to the battery, but the car still would not run.
4) Pulled the check valve on the CSV to validate that the check ball was free, and it was.
5) Checked to see if the Start Solenoid on the Injection Pump was getting 12V at start-up, but it was not.
6) Ran 12V from the battery to the Start Solenoid on the Injection Pump, but still did not start.
7) Ran 12V from the battery straight to the fuel pump, and still no engine start.

Is there a by-pass or something in the Injection Pump that is keeping gas out of the cylinders?

As to my history with the car, it is the standard story, though maybe a little more drawn out:

I bought the car in 1989.  It ran OK at the time, but needed a lot of body work.  Also leaked a lot of oil.  Over the next 10 years I had the mechanicals and body redone, with only the interior currently needing attention (assuming I get the current mechanicals running).  I drove it regularly for a few years, but kids, work, other projects eventually led me to store it. 

I now have the time and space to enjoy the car, so back on the road it will hopefully go.

[Bonnyboy]

Where is the fuel and how far upstream does it get?

Without getting to the cold start valve etc. I am wondering about basics.  Is there gas leaving the fuel pump? If yes, is there fuel getting to the injection pump?  If yes, is there fuel leaving Injection pump?  If yes is there fuel returning to the tank?

If you have any NO's then you have something to look at.   

I had a plugged fuel tank, plugged and stuck fuel pump, crimped fuel return line and a plugged fuel line back into the tank.  Once I got everything cleaned up I realized that the pump wasn't giving me the pressure that I needed so I rebuilt the pump.   The pump gives a high volume to cool down the injection pump so only a portion of the fuel pumped is used, the rest goes back home so there is lots of pressure alll along the way.  My pump wasn't putting out enough pressure to get the correct volume through the check valve into the injection pump.

[71Blue280SL]

The pressure and the check valve are what I am wondering about.  Flow is strong, but I do not have a gauge to check pressure. 

Fuel gushes out of the return line on the injection pump.  I have not checked for back into the tank, but a plug there would only help my pressure concern.

I appreciate all the logical approaches.

Thanks

[w113dude]

this is a long shot but clogged injectors maybe?

[George Des]

I think you need to crack open the lines at the injectors to seemit the FI is putting out fuel. If it is the next stop are the injectors themselves.

[71Blue280SL]

I pulled the fuel line to the number six cylinder, where it connects to the injector, but nothing comes out, so the injectors are not a problem yet.

Pulling the injector pump side of that line is a good idea.  I'll let you know how that turns out.

Thanks.

[George Des]

Yeah to me it sounds like there is an issue with the FI pump itself. The lines may be clogged up but if the FI pump were putting out enough pressure you would see at least some fuel coming out the nozzle end. The delivery pumps near the fuel tank are relatively low pressure pumps. The atomizing pressure is from the FI pump so as long as enough fuel is making it from the tank to the FI pump I don't think you would see the issue you have

[71Blue280SL]

Just pulled the other end of the number six line (closest to the front on the FI pump), turned the engine over and nothing comes out of the FI pump.

Blew air through the line from the cylinder back to the pump and it is all clear.

So why is fuel going in and out the return line of the FI pump, but not into the pumping cylinders?

[w113dude]

I had a similar situation once, I had to crank the engine for a while before fuel got to the injectors.

[George Des]

You may want to do a search on the Forum. I recall many discussions in the past on how to free up the rack and some other FI internals.  I believe Joe A had some sage advice on how to best do this. Sounds like this is what you may need to do.

[Benz Dr.]

You have a number f problems but lets start with the simple stuff. Do you have any compression? How much? Squirt some oil into the cylinders before you start. I would leave the spark plugs out while trying to get fuel flowing to the injectors.

 Good fuel flow means you have good fuel pressure. These engines need at least 12 PSI and run a lot better at 16 PSI. I liter in 15 seconds is the majic number.

 I believe your CSV is plugged up. You won't be able to clean it yourself. If you do let us know how you did that. You can check this by using a flash light and a mirror to look inside the intake plenum. No fuel means no start.

Good chance that some of the injection elements inside your pump could be stuck. Or maybe it's just number 6 and it's not working. Never assume anything or count something out. In the end, it's almost always something simple. Over thinking the problem is often the problem. Basic trouble shooting is your friend here.

A note of caution:

Always hold the jumper cable on the terminal of the CSV first and then have someone touch it to the positive battery terminal. If you have any sort of a fuel leak at the CSV you could be up in flames by hitting it with voltage because your hand will get burned. Always check that you have no fuel leaks anywhere before you do this test.

[71Blue280SL]

All good tips.

The car runs fine on starting fluid, so I am confident it is a gas delivery issue.

From reading other threads, I believe that the IP rack is froze up, and maybe some/all of the IP pistons.  My IP has the rubber cover over the rack access in the front, and I still have not found a thread that explains the best way to take it off and push on the rack?  I did see a thread where that rubber cover was $107, so I want some solid instructions.

The shop manual says in the event of a stuck rack to pull the return line and fill the area with fresh gas.  Based on how many times I have run the fuel pump, it should be nothing but fresh gas in there anyway.

[kampala]

I remember reading this the thread below ... I have not done this myself ... and you may have read this thread ... but just in case

http://www.sl113.org/forums/index.php?topic=9677.msg63790#msg63790