87 420 SEL no start - Mercedes-Benz Forum
 
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post #1 of 6 Old 03-04-2011, 03:07 PM Thread Starter
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87 420 SEL no start

Have an 87 420 SEL in the shop with a no start condition. It stalled dead on the road, no stumble or warning. will not start on starting fluid. it has fuel pressure at the fuel distributor (cant check the psi, dont have the right fitting, but its alot) and plenty of spark. have checked spark with an inline tester and a clip on. checked timing, around 8 degrees. both fuel pumps are running and putting out plenty of pressure. fuel is coming out of the ports on top of the distributor when disconnected and i crank it with the sensor plate pressed down a little, but none comes out when cranking if i dont press on the gas or push down the sensor plate. have replaced the coolant temp sensor and the fuel pump relay already. once in a while, it will try to start, but never quite make it. most of the time, it will catch momentarily on the first turn after sitting for a while, but then not even catch or try to after that. have pulled the plugs and they are not wet, so it isnt flooding. took the fuel distributor apart and it is fine. no binding. any ideas? have checked just about everything we can think of.
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post #2 of 6 Old 03-05-2011, 12:16 AM
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after a lot of cranking I would expect to see some wetness on the plugs..

Trying jumpering the fuel pump relay (pins 7 & 8) that will have the pumps running all the time.. depress the air flow plate slightly, you should hear the injectors "sing".. give her a crank, see if she'll fire.

If not and you are Sure you have spark and good compression it must be a case of bad Timing of said spark...in which case I would lean towards the EZL unit having given up.

Any friends w/ a 420 or 560 series mercedes around??

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post #3 of 6 Old 03-07-2011, 12:39 PM Thread Starter
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jumped the fuel pump and checked flow at the injectors, nothing. pulled the line off the top of the fuel dist unit, when pressing the plate there is no flow (thought there was originally, but ive been working on this thing so much im getting delirious) no matter what i do. so it has fuel pressure at the dist (i can hear it when i put my ear close to the unit) and can physically see its flow when i crack the line going in but no amount of pressure on the airflow plate allows flow through the top of the distributor, so its not even making it to the injector. could this be a case of too low fuel pressure? how much is needed to push the poppet valve in the injector? like i said, cant check the pressure due to no adapter for our gauge so although it seems high, i have no idea the number. both fuel pumps are operating, but who knows at what pressure...
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post #4 of 6 Old 03-07-2011, 12:58 PM
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these systems use about 90psi of pressure.

Could be your fuel distro is ALL gummed up from sitting.. I think you can get CISE pressure gauges for about 100$ or so online.

Try cracking the return line and depressing the plate.

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post #5 of 6 Old 03-07-2011, 01:13 PM Thread Starter
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took the dist apart on friday and cleaned it and checked it over. no problems at all, moving freely, no gum, no nothing. am currently checking the pumps again, the filter isnt clogged, can blow through it with little resistance. going to try to find some way to test the pressure, dont have the time to wait on a gauge online unfortunately. will check the return line pressure like suggested as soon as i put it back on the floor. what should i expect there? and what will it tell me if i have some or have none. trying to understand this system better...
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post #6 of 6 Old 03-07-2011, 02:27 PM Thread Starter
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was able to get a fuel pressure gauge on it, max's out the 100psi gauge at the dist unit. fuel still will not come out of the spider arms (dont know what you guys call them, thats what we call them on a GM) when the plate it depressed even though we have 100psi going in. took the dist unit apart the other day and it looked fine, but its complicated in there and wasnt 100% sure on everything i was looking at. it seems that there is a mechanical disconnect somewhere in the unit as it has the pressure to it, but does not push it out the individual injector arms when signalled to by the plate. ideas?
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