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Old 03-20-2009, 04:46 PM
Registered User
Join Date: Dec 2008
Location: california
Posts: 26

Hi All,
I have a 1986 420 SEL with a starting problem. It has been 8 or 9 months since I have started it, I keep it as a spare car.
Tried to start it the other day and it would not go. I shot starting fluid down the intake and it immediately started but for only a few seconds. I repeated the same thing 3 or 4 times with same result.

Since it tried to start but would not continue running I am feeling fairly confident that it is a fuel issue and probably NOT and electrical problem. Knowing that the gas is old I added about 3 gallons of new gas

I have learned from reading Arthur Dalton's and others posts to try to give some kind of sequence, or order, of what has and has not been done by us rookie's.
I just changed my fuel filter yesterday ( that was plugged) checked that both pumps were working (they seemed to be) but no fuel up to the distributor. I read that if return line was plugged there would be problems so I blew out the return line to tank with a compressor.

I did not blow out the line leading from gas tank to pumps b/c when changing filter there seemed to be plenty of fuel spilling out of everything I loosened or disassembled, also, after the job was done I discovered a leak from one of the pump connections which led me to believe fuel was getting to the pumps.

The only things that are different from before I changed the filter and now are. (1) Before filter change I could get a small amount of fuel from fuel line by cracking line at injector but now I get nothing. (2) I notice some clicking noises that sound as though they are coming from fuel distributor or left front drivers fender not heard before.

I have found the fuel pump relay and the ovp. Fuse looks good on ovp and I have learned how to jump the fuel pump relay pin #30 and #87 (thanks to the forum).

I am using a 12 gauge solid copper wire as a jumper. Is there any certain size I should use or is that one ok? Can I blow or burn anything up if I leave that jumper in the relay for an extended period of time? Would I have time to check if the fuel pumps are getting 12 volts at the pump as Arthur Dalton suggested. Probably to many questions for one post!!!! HUH!!!

Don't exactly know where to go next so any suggestions will be muchly appreciated.


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Old 03-21-2009, 11:28 AM
Registered User
Join Date: Jan 2004
Location: Jacksonville, FL
Posts: 474
When you turn the key to the "on" position can you hear the fuel pumps buzz for a second or two? If not, either no power to the pumps or the pumps are gummed up from sitting. Old or E10 gas cause problems very quickly. Do not leave the jumper wire connected for too long if the pumps aren't running---my bet is it will overheat the gas in the pump chambers and ultimately BOOM! Mark
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Old 03-21-2009, 02:45 PM
Registered User
Join Date: Dec 2008
Location: california
Posts: 26
Hi Mark, Thank You!
I am certainly not interested in the "ultimate boom"!
Yes the pumps do run when turning the key on and when I jumper the relay. Is it possible that the pumps will run but do not pump the gas? Today I am going to take off the in fuel line to the distributor and see if I can get fuel up to the distributor.
Would you know if the fuel distributor would make a clicking noise if air was being pumped into it from the fuel line?

Thanks again
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Old 03-21-2009, 04:40 PM
Registered User
Join Date: Jan 2004
Location: Jacksonville, FL
Posts: 474
Are you sure there is gas in the gas tank and if so how long has it been in there. After some time (a year or two) the gas turns to gum and clogs the fuel tank screen thus preventing fuel flow. Mark
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Old 03-21-2009, 09:02 PM
Registered User
Join Date: Dec 2008
Location: california
Posts: 26
The only thing I haven't tried or checked is the fuel flow from tank to pumps.
The old fuel has been a big concern from the start but it's a job I really wanted to avoid if possible. However it is probably going on at least a year and a half since fueling and you are probably right on the money.
Today I took off the pressure side of the gas line hopefully to relieve any resistance for the pumps but still didn't get any gas. It is getting narrowed down to no flow from tank or faulty fuel pump(s)
Before draining the tank I think I will test those pumps individually to make sure that both are working. If I use a battery charger (10 amp) and put the leads on the pump posts would that be too much amperage for those pumps or would I damage something. Also could a check valve in the fuel pump be stuck shut with gum or crap?

Hope this is not too many questions! Thanks for responding!! Dale
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Old 03-21-2009, 11:25 PM
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Join Date: May 2008
Location: Spokane WA
Posts: 312
Put a pan under the tank and unhook the line coming from the tank to the pump. If fuel poors out its not the tank screen. If it doesn't poor out put a hose on the pump and run it into the can. If the car starts you know your pump is good and the tank is plugged.
81 300SD daily driver/project
86 420SEL (sold)
85 380SE(in the graveyard)
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Old 03-29-2009, 01:34 PM
Registered User
Join Date: Dec 2008
Location: california
Posts: 26
Hi Guys.
Thanks for your input. Her is an update.
After reading your posts I decided to start all over. I siphoned out all of the old gas and removed alll of the fuel delivery components. I thought that both fuel pumps were working but discovered after bench testing that one pump was seized and in fact was not working. I then blew out the line from pumps to the gas tank poured new gas in tank to verify screen was not clogged.

I then started shopping for parts. I found an entire unit of two pumps, new filter, accumulator and all the hardware for $160.00. Yesterday I installed everything back in the car and now have good fuel delivery to the fuel distributor. I have tried to start car and still does not start so I guess it is time to learn about the fuel distributor and if it could be gummed up from sitting or if something else is broken. I have read that the plunger in the FD could be gummed up and not moving freely.

Any suggestions as to where I should go from here. I know nothing about FD's

Thanks Dale
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