1990 560SEL will start but not run after installing new injectors - PeachParts Mercedes-Benz Forum

bolomiester · #1 11-02-2018, 07:01 PM

I installed 4 new fuel injectors in my 1990 560SEL, including new holders and seals. I wanted to start it up so I could move the car over for better access to the other 4 but, while it will start it will only run about 15 seconds before the engine dies. The car ran perfectly before I installed the 4 new injectors. Could it be that the old pumps are ok with the old injectors but are too weak to fire the new ones?

pawoSD · #2 11-02-2018, 11:18 PM

Do the pumps do their initial short run when you turn the key to position two? When the car quits are the pumps still running then shut off a moment after? or are they already off?

Sounds like its firing up on the Cold start injector fuel then quitting when that shuts off....or possibly something is stuck in the air/fuel meter or there's air lock in the fuel lines...

bolomiester · #3 11-05-2018, 09:16 PM

I installed the rest of the new injectors. Now the car will start and run but it won't idle. It will only start if I hold the gas pedal down a little as I crank the engine. It then starts, revs and runs very smoothly but dies as soon as I take my foot off the gas.

I let it warm up to see if that would help but it didn't. I shut it off then discovered I had a fuel leak from one of the lines attached to the fuel distributor, probably the main supply line.

Would a fuel leak from the main supply line allow the engine to run and rev well but not idle?

Stretch · #4 11-05-2018, 11:20 PM

I assume you replaced the rubber bushings that fit on the injectors?

It sounds to me like the initial problem you had was due to not enough fuel reaching the injectors. After replacing injectors a bit of a life hack is to use a jumper cable on the fuel pump relay to get the fuel to circulate around the system before staring.

(Warning:- you should be careful with this because you might be filling the inlet manifold with fuel if run for too long - the other non jumper lead way is to flick the ignition switch several times to get the fuel pumps to prime)

The problem that you are now having sounds to me more like air leak related. Check - check - and double check all of the rubber pipe fittings near and around the injectors. If some of the connections seem loose a quick botch is to wrap self amalgamating tape around the rubber pipes to try and seal them. (This is a crappy long term fix - ideally you should replace rubber tubing with new if you know they leak - but it works well as a diagnostic "tool")

bolomiester · #5 11-08-2018, 05:05 PM

By using 1 foot on the brake and the other on the gas I was able to get the car out on the road, fortunately I live in a rural area so no traffic to contend with. The car runs great! The engine is very strong and smooth. Shifts great. Just won't idle. I've checked and rechecked every injector and they all seem well seated.

Something I did that I haven't talked about is that instead of installing the rubber tubes that fit over the nipple on each injector holder, I sealed them with rubber vacuum caps, then used a rubber cap over the fitting that goes to the air pump. Could this be the problem? The belt for air pump was taken off by the previous owner and an inspection of the pump revealed it is frozen. However, the car has always run well without a working pump. The plan has always been to replace it but there has been lots to do and the budget only stretches so far. Since the car car ran great without the pump I gave a low priority.

Was I wrong to seal these off, and could this be why it won't idle?

Frank Reiner · #6 11-08-2018, 10:12 PM

Quote:

Originally Posted by bolomiester

Something I did that I haven't talked about is that instead of installing the rubber tubes that fit over the nipple on each injector holder, I sealed them with rubber vacuum caps, then used a rubber cap over the fitting that goes to the air pump. Could this be the problem? The belt for air pump was taken off by the previous owner and an inspection of the pump revealed it is frozen.
Was I wrong to seal these off, and could this be why it won't idle?

The highlighted statement is the cause of no idle. You sealed off the idle air supply.

(The "smog" pump is not connected to the idle air system.)

bolomiester · #7 11-09-2018, 12:39 PM

It's amazing how well things work when put together correctly instead of taking a guess. I pulled the isolation plugs and replaced them with the correct distibution hoses and it starts right up and settles into a perfect idle.

I already had new distibution hose but no new plugs for the ends. I ordered them, 1169971286, this morning but bought some 1/2" rubber plugs from Ace Hardware so I could get it going today. They work very well.

Thanks to everyone for all the help, especially Frank Reiner, who hit the nail right on the head.