1974 450SEL - D JET - Won't run, but will start under certain cond.

[chinny4290]

Hey guys.

I'm buying a friend's family inherited 1974 DJET 450SEL and I need help diagnosing the reasons as to why it won't run. I've spent the last few weeks trying to search Google and the countless Merc forums for my specific issue but I can't seem to find a similar thread.

The car sat for a year and before that year, it ran and drove. My friend noted that power was down but it still drove and ran.

Fast forward to today, and the car will turn over but die. With new fuel/filter and a flushed system, she'll start, run, then die.

The fuel pump only runs under these conditions: when I remove the fuel pump relay and jump the relay port accordingly, the fuel pump goes. Though, put a working relay in, and the fuel pump stops running.

Even with the fuel pump relay jumped and constantly running, the car won't run for any more than five seconds and will die. During the five seconds, we tried pressing the pedal, and it seemed it wanted to die quicker.

According to the various troubleshooting guides, the next step to ruling out problems if the fuel pump is found to be working is to replace the ECU. The problem is, ECUs are hard to find if not expensive when found. What should I do to diagnose the problem?

I tried slowly removing one of the fuel rail lines AFTER the fuel pressure regulator with a towel and even with the fuel pump NOT running, gas started squirting out under pressure. Another sign that tells me that the fuel pump is fine.

We put a small amount of fuel in the throttle body and when that happened, she would start up immediately and would run beautifully until all the fuel was burned. So that tells me it's still fuel delivery related...

What do you guys think?

Your help = awesome!

Thanks!

PS, if I need a new ECU, has anyone tried these?

http://www.***********************/sku/Mercedes_Benz/450SEL/Programa/Engine_Management_System/1974/Base/8_Cyl_4-dot-5L/W0133-1597140.html?tlc=Engine+%26+Drivetrain

[Tomguy]

This sounds like dirty trigger points or a bad connection to them. Your cold start valve is supplying fuel for a short burst and when it shuts off or is too lean for the car to run, it dies out. You may need to clean them. But before doing so, ensure all the injector grounds are tight. I believe they connect to the intake manifold itself on the W116 D-Jet engines.

[meltedpanda]

are you getting spark? Did you pull a plug , is it wet /dry?
have you checked for injector fuel spray,they may be clogged?
I assume you have set the points?
Have you pulled the trigger points to check them

First ensure that you are getting fuel , air and spark to the pistons , then let us know

ECU's rarely go bad, they do , but rarely You can test them for some of the functions at the pins, but do this first.

[chinny4290]

Hi Guys.

I thought I'd revive this once more...sorry it's been a while since I replied...I haven't had time to visit the car again (it's 3 hours away in Pittsburgh, PA).

But I will be returning to visit the car again to see if I can get it starting this up and coming weekend.

So I read some more and I also learned that my friend's caretaker replaced the trigger points on the 450 and measured them out by sight...I also read in regards to the trigger points, they need to be spot on, otherwise the car won't run well or at all.

So the plan is to pickup a Feeler gauge at the store and to measure the exact trigger point gap...can anyone link a guide as to how to do this and to check the trigger points?

I reread my OP and I've been able to deduct that it sounds like the injectors aren't pulsing either...Would fixing the trigger points heal this?

And there was mention of checking the injector grounds, can someone supply a picture as to where they are?

Also, any other advice for me as to what to prepare myself with before I see the car this weekend, would be greatly appreciated so I can order the parts or what not from my local shop.

TIA!

[meltedpanda]

you have to take the dizzy out to see if the trigger points are working properly , they cannot( well should not ) be adjusted. you can however gap the points and perhaps that is what you are talking about

Read here how to see if the TP's are close to specs, granted this is not a proven method, but will point you in the right direction.

http://www.peachparts.com/shopforum/vintage-mercedes/261032-trigger-points-old-d-jets.html

I have used this method and Graham and I have a LOT of jabber on trigger points on the SL forum

Tigger points "pulse the injectors"

As before , make sure you are getting fuel to the rails

[Frank Reiner]

chinny:

The advice from Tom and Ron on the subject of trigger points is a good starting point. Let me suggest that before you remove and disassemble the distributor, that you pull off the connector for the trigger points (multi-pin, located below the single wire lead for the ignition points) and thoroughly clean the pins and sockets, and reconnect. If that does not yield any results, then an investigation of the trigger points is in order. They are often contaminated with oil, and if the vehicle has many miles, the rubbing blocks on the trigger points may be quite worn.

You're fortunate if you can travel I-80; I do not miss the PA Turnpike one bit.

[meltedpanda]

Frank is right, and in fact make sure those wires are in tact and not broken ( in the connector), check for continuity.

If fuel was left in it you have a real chance of stuck open or closed injectors

Also make sure your fuel lines are not carcked and your vacuum lines are in tact

Good luck

[chinny4290]

Thanks guys. I'll definitely start with the distributor and trigger points.

PS, Fuel is in the rails since last time I tried disconnecting the fuel lines after the fuel pressure regulator, before the metal rails, fuel started squirting out, so there is pressure and the lines are pretty fresh and soft.

Either way. I'll keep you all updated.

What vacuum lines should I double check meltedpanda, any pics you could supply?

[meltedpanda]

Hmm, the ones to the throttle body, the one from the MPS,the one to the Aux Air valve, distributor ect. These were all on my 72, not sure if yours is the same. Basically any rubber /plastic line under that hood could affect performance, and starting

[chinny4290]

Hi guys. I'm with the car now but have no idea how to get to the trigger points. Sorry I'm really newb when it comes to looking into these things. I took off the distributor cap and rotor and things look ok under there. But the bottom half of the distributor is caked in oil and sludge so it may in fact be dirty trigger points.

I'll see if I can get some pic when I'm done with lunch.

But how do I get to the trigger points?

[Graham]

Originally Posted by chinny4290

Hi guys. I'm with the car now but have no idea how to get to the trigger points. Sorry I'm really newb when it comes to looking into these things. I took off the distributor cap and rotor and things look ok under there. But the bottom half of the distributor is caked in oil and sludge so it may in fact be dirty trigger points.

I'll see if I can get some pic when I'm done with lunch.

But how do I get to the trigger points?

Try here:

D-Jet Distributor Removal & InjectionTrigger Points Repair - Mercedes-Benz Forum

If you remove the distributor, take careful note of just exactly where the clamp is and where the rotor is pointing.

[Graham]

Originally Posted by chinny4290

PS, Fuel is in the rails since last time I tried disconnecting the fuel lines after the fuel pressure regulator, before the metal rails, fuel started squirting out,?

By the way, the fpr is downstream of the fuel rails. Fuel enters the rails at the front of the engine, then splits down each bank, then combines again at the fpr. After that, there is a damper and then fuel returns to the tank.

It does sound like the injectors may not be firing, and that would most likely be a trigger point problem. But you might check the fuel pressure and flow. You can measure pressure by inserting a tee - any cheap pressure gauge will work. Should be about 29psig. Fuel flow measured at line leaving fpr or damper should be 1 litre in 30 sec - easy enough to measure with relay jumpered. If both of those are good, then injectors must not be firing. There is a way to check - turn key on, but don't start. Then open throttle slowly and listen to injectors using stethoscope, piece of tube or whatever. You should hear 20 clicks. If injectors fire, then even more likely trigger point problem. You can check trigger points with meter - I forget terminals but it is in manual - available on line.