300SEL 3.5, engine started after 2 years

[Tomguy]

The EFI trigger points in the distributor. Depending on your car, you'll either have a plug that goes into the distributor, or a "Pigtail" plug that goes from the distributor to a block. Most likely the former on a 108. Just unplug it. And yes, unplugging the CSV will keep it from opening. Doing these prevents all gas from entering the engine.

[werminghausen]

Originally Posted by GGR

Yes, it is preferable so that you don't fool the engine. You can do that by disconnecting the fuel pump or by pulling out the fuel pump relay.



Yes




That's very good. Scale is in psi.

GGR: I thought if the gauge drops from 45 to 20 ...this might be a bad sign. If you say these readings are good I am happy..at least I don't need to change this oil pump.

[werminghausen]

Originally Posted by Tomguy

The EFI trigger points in the distributor. Depending on your car, you'll either have a plug that goes into the distributor, or a "Pigtail" plug that goes from the distributor to a block. Most likely the former on a 108. Just unplug it. And yes, unplugging the CSV will keep it from opening. Doing these prevents all gas from entering the engine.

Tomguy: I have a line from a cylindrical box (a Bosch thingy) on the left fender side to the distributor.
This cable connected to the distributor just plugs in there. This box might 'produce' the high voltage for the sparks? I'll disconnect this one, correct?
Along with the cold start valve plug.

Then the injectors are non functional. I guess distributor and CSV are giving input for the injector relay...meaning if the input is not there then no signal to injectors and they don't spray?

[werminghausen]

Originally Posted by GGR

That's the problem. On your car it is burried somewhere under the ECU and access is not that easy. It may be easier to just undo one of the wires at the pump.

Good to know, I'll do what Tomguy says: unplug distributor and CSV.
I'll dig up the compression tester and do the job tomorrow.

[GGR]

Originally Posted by werminghausen

Tomguy: I have a line from a cylindrical box (a Bosch thingy) on the left fender side to the distributor.
This cable connected to the distributor just plugs in there. This box might 'produce' the high voltage for the sparks?

What you're describing looks like the HT coil. Does it plug on the center top of the distributor cap, among the other spark plug wires? If yes that does not have anything to do with the injectors. The plug Tomguy is talking about is down on the left side of the dizzy body when you face the engine. It should be covered by a rubber protection cap. Manipulate it gently as wires are often cooked by years of heat. Frankly, I would disconnect one of the wires at the fuel pump. Thas just one nut and you can't go wrong.

[werminghausen]

Originally Posted by GGR

What you're describing looks like the HT coil. Does it plug on the center top of the distributor cap, among the other spark plug wires? If yes that does not have anything to do with the injectors. The plug Tomguy is talking about is down on the left side of the dizzy body when you face the engine. It should be covered by a rubber protection cap. Manipulate it gently as wires are often cooked by years of heat. Frankly, I would disconnect one of the wires at the fuel pump. Thas just one nut and you can't go wrong.

Where do I find the fuel pump?

[werminghausen]

I was taking off the airfilter housing tonight and adjusting the trottle linkage again, as I still had not the 1mm gap at the butterfly end stop when accelerator is touching the kick down...then going to end stop when pressing the kick down switch. It is fine now. I adjusted the last rod to butterfly again.

Then I wanted to adjust fuel pressure as the pressure regulator was open.
I started the engine ...didn't run well at all without the air filter. The I remembered that I should connect the el. plug that is in the airfilter intake pipe...don't know what it does.... so I unscrewed the plug from the airfilter and connected to the wires but idle was still poor, engine stalled.
I don't know what happened and why it didn't run.
In the time the engine run poorly I saw that the fuel pressure was at 28PSI (well I had seen 32 PSI the other day which is a 4PSI difference- how can this be?) and I increased pressure to 30 PSI.
I then installed the airfilter again and connected the CSV with the fuel line and started the engine hoping the engine will run smoothly as it did the days before.
But no...engine ran poorly and was stalling several times. Was pretty frustrating.
Any idea what happened?

[mercmad6.3]

Fuel pump is under the rear of the car.left side behind the rear axle. You will have the pump ,Filter and sound damper bolted in a pack to the floor.
As you have never seen this before,inspect the rubber fuel lines. They probably all need replacing by now.

28PIS is about the max. Try and keep it at that level.
The poor running could be fouled spark plugs cuased by short running. These older engine designs need to run until the engine temp is at 80C or 175 F minimum .
Also,Do Not try to tune and adjust the engine until it has run at these temps for at least 5 minutes.

[werminghausen]

Originally Posted by mercmad6.3

Fuel pump is under the rear of the car.left side behind the rear axle. You will have the pump ,Filter and sound damper bolted in a pack to the floor.
As you have never seen this before,inspect the rubber fuel lines. They probably all need replacing by now.

28PIS is about the max. Try and keep it at that level.
The poor running could be fouled spark plugs cuased by short running. These older engine designs need to run until the engine temp is at 80C or 175 F minimum .
Also,Do Not try to tune and adjust the engine until it has run at these temps for at least 5 minutes.

Thanks, I'll find the pump and inspect the rubber hoses.
poor running engine: The engine is not starting any more and I run out of battery.

Is it possible that I screwed something up 1) with the fuel pressure? or 2) the throttle adjustment?

I adjusted fuel pressure when engine was relatively cold...I was thinking an electrical pump doesn't care if engine is cold or hot. It would produce same fuel pressure no matter what the engine is doing...but maybe I am wrong.
I was just amazed that pressure reading was different to my reading the day before (32/33PSI versus 28 yesterday) which was with warm engine

Can it be that did something wrong with throttle linkage?

I hoped to get the engine going and do the compression test for the cylinders... and then inspect the spark plugs. But this is done with engine warm. I need to get this engine going somehow.

[werminghausen]

I was charging the battery and was able to start the engine again.
Engine was running poorly the first 10 minutes and watched what was going on.
Once in a while the engine speed dropped, then came back.
Vacuum was very poor, below 10" when engine was cold. It started at about 7", then climbed.
I waited until engine temperature went up to 200. Vacuum climbed slowly up to 14/15". It took about 15-20 minutes at idle.
Does anyone know why vacuum is not present right away?
In general I was happy that the engine was running (after the scene yesterday). When the engine is warmed up it seems to run more stable.
Especially the cold engine is very unstable and makes weird noises after start up. When engine is warm it sound better.
I decided to do the compression test, removed the plugs and disconnected the fuel pump. Most of the cylinders were fine. Pressure readings were
#1:160PSI (90PSI at first stroke)
#2:160PSI (90PSI at first stroke)
#3:165PSI (90PSI at first stroke)
#4:150PSI (90PSI at first stroke)
#5:135PSI (90PSI at first stroke)
#6:138PSI (90PSI at first stroke)
#7:162PSI (90PSI at first stroke)
#8:120PSI (70PSI at first stroke)

I guess #5, #6 and especially #8 are not great.
What do you think of these readings?
Is the condition of the engine the reason for the poor engine vacuum? What is the next step.

[mercmad6.3]

The compressions are good and not too bad for an engine that has sat for a long time . Low vacuum at idle is normal because the cold air bypass is wide open . This allows the engine to run faster (1200 RPM) until it reaches operating temp.
Have you checked the cold start valve to make sure it isn't leaking?
The next step is to either replace the injectors ($$$) or get them cleaned and replace the injector seals to eliminate any vacuum leaks .

[GGR]

Compressions on the cyl you mentioned are not that great (you shouldn't have more than 15% difference among cylinders) but as Ron said it's not that bad for an engine that sat for a long time. Things may get better after you drove the car around for a bit. They are certainly good enough to have the engine run reasonably well and enjoy the car anyway.

You said you played with the richness at idle adjustment on the ECU. Engine warm, did you set it where idle is fastest?

Also make sure you didn't intervert some plug wires at some point. Firing order is marked on the right cam cover.

[werminghausen]

Originally Posted by mercmad6.3

The compressions are good and not too bad for an engine that has sat for a long time . Low vacuum at idle is normal because the cold air bypass is wide open . This allows the engine to run faster (1200 RPM) until it reaches operating temp.
Have you checked the cold start valve to make sure it isn't leaking?
The next step is to either replace the injectors ($$$) or get them cleaned and replace the injector seals to eliminate any vacuum leaks .

Thanks. I am very glad to hear the compression readings are not a disaster.
Do you think that the engine condition is not the reason for poor vacuum readings at idle?

For the vacuum leaks
1) I have not checked the cold start valve for leaks. How do I do this? Do you have a manual?
2) injectors: well, I don't have the money to replace them... I guess.
How can I test/ clean them? Is it a major job and doable to change the seals (even if I leave the injectors themselves)?
The bottom seals:Are these the ones I can see at the bottom of the injectors connecting to the head?
3) Modulator/Vacuum line to transmission: I guess there is a vacuum line going to the transmission modulator (for shift firmness) starting at rear of engine where the door lock vacuum hose is starting? I saw that this line is metal? I didn't check or touch this line but why should it leak?
4) I took off the vacuum line at the booster and plugged it. No difference in readings
5) donuts or manifold halves: where are these donuts? These might leak too?
I'll test these ones with crab cleaner and see if idle is going up.

Well maybe I am overly concerned with the vacuum reading of 7" for cold engine and 14/15 with engine warm but I am not thrilled will how the engine is idling when cold.

[werminghausen]

Originally Posted by GGR

Compressions on the cyl you mentioned are not that great (you shouldn't have more than 15% difference among cylinders) but as Ron said it's not that bad for an engine that sat for a long time. Things may get better after you drove the car around for a bit. They are certainly good enough to have the engine run reasonably well and enjoy the car anyway.

You said you played with the richness at idle adjustment on the ECU. Engine warm, did you set it where idle is fastest?

Also make sure you didn't intervert some plug wires at some point. Firing order is marked on the right cam cover.

Hi GGR, thanks so much for your patience. Glad that my engine is kind of ok, not great but drivable. I was caught up finding vacuum leaks (and I am still trying to find them...unless someone tells me it is fine- just stop worrying)
I was fiddling with the fuel pressure (28 - 30 PSI) and I was confused why I had 2 different readings. First reading was 32/33 PSI at the CSV with engine warm, then 2 days later iI tested again in order to adjust without the air filter obviously- or how can you do it with airfilter in place? This time without the filter idle was very poor and engine stalling, got it run and reading was 28 PSI (with engine cold) and I turned pressure up to 30 PSI.

So I am not clear now and will test fuel pressure again with the air filter in place and warm engine.

Yes I fiddled with ECU and set i when idles was fastest.

I still need to check ignition timing at 1500 (+/- 1
deg at TDC) and at 3000 rpm (34 degrees BTDC).
I need to get another method of reading engine speed. with my laser tach it is difficult to quickly read speed at crank. Is there ant pulley running same speed as crank? Then I could easily take this reading - would be much easier.

[GGR]

You could clean the injectors and part of the fuel system by poring ATF in the gas tank, up to 4%. I do that regularly when I go on a long trip, one or two full tanks with 4% ATF and usually the engine runs smoother after that.

If your idle improved when you put fuel pressure back to 30 psi this means your idle mixture is too lean. You have to choose which pressure you want to run 28 as Ron suggests, 30 as my engine likes (Graham runs even more presure to combat vapor lock but fiddled with the pressure sensor to compensate). And then play with idle richness. On my car the bolt on top of the fuel regulator pressure is accessible from behind the air filter, that may not be the case on yours.

You say you set the idle richness where idle is fastest: Where is the potentiometer? somewhere in the middle or at one of the ends? Fastest idle means this is where your mixture burns best. But some engines prefer a slightly richer mixture at idle, so you can try adding 2 to 3 clicks clockwise to get a more stable idle.

For vacuum leaks, try the carb cleaner trick. The donuts are between the intake manifold runners (the pipes you see on top) and the air plenum (the box on which the TB bolts on). They are not really accessible.

But if you can stall your engine by tightening the idle air screw, and if the fastest idle is not when the potentiometer on the ECU is completely turned clockwise, I wouldn't bother too much about vacuum leaks at this point as this means you are still able to get the correct amount of air in at idle, whatever the path it takes.