300SE W126 Will not start
 

Hello All,

This is my first posting and I need some advice on how to diagnose 89 300SE not starting. When I start the car it cranks and I can hear the fuel pump in the back whirlling. Sometimes it starts a second then dies. Since the fuel pump runs, does this mean that the Fuel Pump Relay works. I've seen in another forum advicing to bridge the port 87 and 30 of the Fuel pump relay which will continually run the fuel pump. I didn't do this because the pump runs, so I presume the fuel pump relay is good (and fuel pump). Is my novice oppinion correct?

There is a spark in the plug so I assume that eliminates the problem (also confirms when it fires for a second).

I also checked the throttle Microswitch and there is continuity when I press the swith on/off.

I pulled the OVP relay and checked the fuse continuitiy and it checked out OK. How can I be certain that the OVP relay is good or bad? Is there anything else I should be checkin?

I would appreciate any advice. Thank You

Max

Check your fuel pressure. I would also suggest removing the distributor cap and performing a thorough visual inspection. Did it all of a sudden just quit or were there any indications that it was running poorly?

The car had no prior indication of runnin poorly, it just quit. In fact, I just pulled it in the garage and then 2 hours later it won't start.

I will check the distributor cap. How do I test the fuel pressure?

Thanks for your advice.

Max

all the time or??
 

so the car just won't start at all!!It is not dependent on whether it is a hot start or cold start right??

Thanks for your reply. Hot or cold it won't start. I went to the dealer and bought a new OVP relay and Fuel Filter Relay. That didn't solve the problem but the dealer was kind enough to give me a full refund if it didn't work.

I visually checked the distributor cap and removed one of the spark plug and had my wife start the car and it showed sparks. The Spark plug is very dry which probably means there is no fuel coming in.

At one time I removed the gas cap and it had a hissing sound which probably indicate there is pressure in the tank.

I tapped the filter and fuel pump several times and the car started while the gas pedal is pressed into full throttle. However, when I released the gas pedal it died again and won't start anymore; even after several attemps to tapped the filter and fuel pump. Once gain when I removed the gas cap, there is no more hissing sound after I several attempts to start it.

Do you have any advice?

Max

Pull the aircleaner and have someone crank the car as you push against the airflow meter plate. It should be distinctly harder to push when the car is starting and is getting full fuel pressure. The fuel pump running does not mean there is sufficient fuel pressure. What if there were no fuel in the tank!

If when cranking and pushing on the airflow plate the car starts and runs fast if the plate is held look for a large air leak.

listen
 

if there is anyone you are going to listen to on this forum!!! You better listen to stevebfl!!!! Man I wish his shop was close to where I lived!!!!

Barely Starts but only at High RPM
 

Thank you Steve.

I removed the AIrCleaner and pushed the Air Flow plate while my wife cranked the car. It barely started and the gas pedal had to be pushed all the way down. But as soon as she released the pedal, it dies.

By the way, the car has 3/4 full of gas. We repeated the above procedure several times and in one case, I didn't push the air flow plate which also started. We had the car running at high RPM for 10 minutes but as soon as the gas pedal is released it died.

After 10 minutes of reveing the engine and after it died, I removed the gas cap and I didn't hear the usual hissing sound.
Perhaps I don't have enough fuel pressure and what would cause it to go low. Do I need to replace the fuel pump? If I do, what else needs to be replaced while I'm down there?

I sincerely thank this forum for their advice. It been great and it's a great website.

Maxwell

I doubt you need a fuel pump if it ran for 10 minutes. Good chance for a big air leak.

Steve is correct the fuel pump is working. I removed the wires connecting to the fuel pump and connected the battery directly to the pump and I can hear the fuel circulating into the fuel line and into the engine. The noise is very prominent towards the engine specially when I push the air flow check plate.

Since this (not starting) happened 5 years ago and I dug into my mainteance record from the dealer, and their diagnosis is STUCK THROTTLE. How do you get into unstucking a throttle? Or does anyone have any other ideas? Thank for all your help.

Maxwell

Loosen one of the injection lines at the fuel distributer. Run the fuel pump with your jumper and see if fuel flows out of the fuel distributer. IT SHOULD NOT. If you then depress the airflow plate it should!.

Throttle being stuck means nothing to me unless they were really meaning the fuel distributer piston was stuck. If it is stuck there will be play in the airflow plate before touching the piston and the fuel will flow even with no airflow.

Steve You are A Genious
 

When you said there is a major leak you are absolutely correct. I found two rubber hoses that are very brittle connected to a round part (with electrical connection to it) and the hose conection to the injector was disconnected. It was very hard to see because of all the wires and fuel line blocking the view.

Anyway, I pushed the rubber back which comes off very easily and it took a while to start but once it started it stayed on.

I am very sure this is the problem. I will buy the two hoses tomorrow and replace them.


THANK YOU AGAIN FOR THIS FORUM ... and specially to Steve.

Maxwell Oligane,
New Cumberland, PA

88 300SE won't quite start after sitting for months
 

HI, I have a similar problem. I let my 1988 300SE sit for about 18 months. I moved it every couple of months, but recently it started running rough right after starting and dieing after 30 seconds or so, then it got so that it would not fire at all when cranked. By reading this and other posts, I jumped the fuel pump relay terminals and determined that the fuel pump was dead. I installed a new filter and fuel pump, and drained the old smelly gas. I added fresh gas and cycled the ignition switch several times to prime the pump (I can hear it run now). The car started and ran pretty rough for about 20 seconds then died. Now I can only get it to fire some when cranked
After reading the comments from Stevebfl, I looked for airleaks but didn't see anything. I loosened an injection line at the fuel distributor and turned the key so the fuel pump started. No fuel came out. I then pushed the airflow plate down and fuel came out. I then tried to start the car while pushing on the airflow plate. The plate was harder to push, but the car would only fire occasionally. When cranking the car normally the plate opens about 1/8th inch so it seems like there is not a large air leak. I took out a spark plug and it sparked brightly when cranking the engine. The car ran so well when I parked it, and it started several times since. I'm wondering if the old gas somehow clogged the injectors. It ran for a little bit after replacing the filter/pump. Any ideas about what might be causing it not to start?
Thanks!

Help
 

I really need some feedback on this problem. Any help will be greatly appriciated!

Remember that pushing the airflow plate only adds fuel. If the problem is that you are too rich adding fuel doesn't help starting. To lean it out one must pull the plate up (kinda hard) or turn the allen. The problem with doing that is that if the issue is ignition or timing then you have created a second problem. Experience makes these issue a snap but you can easily get yourself ina knot if you add problems.

Sometimes a better plan is to pull the fuel pump relay and crank it a bit to clear it out and then give it a shot of starter fluid. If that doesn't geta reaction, one should look elsewhere.