Starting problems '87- 420 SEL
 

I bougt this car one year ago and it has been running perfectly.
About two weeks ago, on the advise of a friend, I added one bottle of "Wynn Fuel Injector Cleaner" when I filled up the tank.
Since then the car has been hard to start and now won't start at all. When it did start, it would idle for about 10 to 20 seconds and stall,unless I kept my foot on the gas to increase the idle speed.
When it ran well enough to shift into gear he car would run without exibiting any problems. Starting the engine when warm was also no problem.
I would appreciate any advise anyone may have.

This has all the markings of a possible blown overvoltage protection relay fuse, or a bad overvoltage protection relay. Near the battery, this relay has a clear plastic flip-open lid on top, under the lid is a red 10 amp fuse. Check that fue, see if it's blown.
Gilly

Thank you, I have already replaced that fuse but no luck.

Dieter

Replace OVP
 

Do you think I should replace the whole relay, or are there other things to check for first?

Dieter:
It just seems strange that before adding this product that now it is doing this. Any chance that the fuel itself is bad? it seems unlikely that a container of injector cleaner would cause a problem like this. Wynns is a well respected name, been around a long time. I prefer Chevron Techron, but wouldn't hesitate to use Wynns products. Since one would be led to believe the problem is somehow fuel related, I would start by having someone attempt to start the car while you listen at the rear to see if the fuel pump/pumps run or not. The pumps are located roughly in the area of the right rear wheel under the car. You could also check a spark plug to see if it seems wet and smells of fuel, or dry as though no fuel is being delivered, you could also check for spark at the same time. You could also remove the fuel supply line at the fuel distributor and obtain a glass jar, put the supply hose into the jar and have someone turn the key to on. You can then check that the pump seems to be working adequately and also check the fuel for appearance (cloudyness or if it seems dirty, make sure it isn't Diesel fuel or mostly water).
Gilly

I wonder if the additive is safe for the Oxygen sensor?

Ed: I believe the engine will at least run with a bad oxygen sensor, he's saying it doesn't run now.
Gilly

Maybe the cleaner loosened a lot of junk in the fuel system and clogged the filter or some other fuel delivery related component such as the duel distributor?

Justa thought.

Fuel Filter
 

Thank you Gilly and all, I will persue these avenues next. As for the fuel filter, I had a new one installed but now wonderif it was the right one. I checked the Fastlane catalouge and see there are different filters for cars with dual fuel pumps as opposed to sngle pumps. If it is the wrong filter could it cause the car notstart?
Thanks again,

I had the same exact scenario on 86 420 sel. I added fuel cleaner and few days later problems starting the car. I would add gas through the air intake and it would start, run all day then the next day gave same problem. After few weeks adding the gas did not work either. changed fuel filter no avail. finally changed fuel pump and relay . worked and now 18 months later not starting again. check the fuel pump

I had a simular problem with an 87 420 SEL that I cleaned the Air/fuel mixture intake (the unit under the air filter with the vacuum operated door) and it appears that my cleaning it threw the air fuel mixture way off. I used dewl meter and adjusted the On/off ratio back to 50% and it started right up and has been running OK. Might be worth a try.


Jorge.

I concur with Jorge. My 300TE would be a bear to start until I adjusted the air fuel mixture about 1/2 turn ccw. Before I did that, I had to turn the switch on/off 6 times or so (without cranking) to get the cold start to shoot a bit of fuel to the engine each time, then it would start easily but run rough until it warmed up. Now, with the adjustment, it is running perfectly.