W111 3.5 engine not firing up at all

[sjefke]

OK, I have a problem (again): my 280SE 3.5 coupe will not fire up anymore.

It happened after I fixed my slave cylinder just after Christmas.

I started the car (on stands) to check everything, and it ran fine. While checking (still on stands in garage), I felt the engine suddenly loose power like several cylinders where not firing. I pulled front driver side spark plug and engine speed went down. Same with rear driver side plug, although less chance. Several days went by and when trying again, car would not fire up at all. It does not even have a partial fire or any kind of misfire at all.

It suggest that it does not get any spark at all, or no fuel at all.

Here is what I have done so far:
1 - Gas was low, so I added gas. Plenty of gas in tank now.
2 - I checked fuel supply and fuel is quirting out under pressure at the injector rail
3 - I noticed a tear in vacuum hose to air pressure sensor and replaced it - no effect (what a pain to get that hose clamp off - broke plastic fuel pressure line in process )
4 - Checked spark from coil to distributor. Was good, but I decided to install Petronix system to be sure coil was not the problem. Now I have Petronix ignitor and flamethrower coil. Tested spark from coil lead wire and it is massive (can hold wire 1 inch from ground and it still sparks)
5 - Cleaned distributor cap contacts on inside
6 - Checked several wires to spark plugs and they also spark (albeit less so). Have not (yet) replaced rotor or spark plugs.
7 - Took out trigger points from distributor and checked visually. They look very clean. Did not clean them yet.
8 - Tested trottle valve and when opening, I do get the brrrrrrt sound of injector firing.
9 - Took connector of ECU and put 12V on each injector pair contact. I heard each pair firing. Checked ECU main power and it gets 12V.
10 - Tested connectivity for each wire from trigger point plug to ecu connector. Each has almost zero resistance, so no wire break
11 - Cranked the engine while listening for injectors firing. I am pretty sure I heard injectors firing, so trigger points seem to be trigger injector events.

Given that the engine does not even stutter when cranked, it must be a complete no spark or no fuel situation. Or is it a massive vacuum leak somewhere that could cause this, and if so, where?

Any suggestions?

I did not change timing and even when it is off, it should still (mis)fire, right?

Thanks,

Bert

[GaryF]

Does it stink of Gas? It's either flooded at this point or none at all getting through?
Can't imagine a vacuum leak could stop the car starting or at least spluttering.

[Tony H]

Hi Bert,
If you are sure the ignition is OK maybe you can try this. Pull the fuse to the ECU, crank the car a bit with throttle WO to clear out any unburnt fuel and spray some starting fluid in (don't over do it) and see if it runs. Just a crude test of ignition system. If you think your ECU is NG I can loan you a 4.5 ECU to test.
Tony

[ABDow]

I feel your pain. Try a new set of plugs, rotor button and use some "Start ya bastard" or some other similar product. Before doing so remove the fuel pump fuse and turn the engine over for 30 seconds or so to clear any unburned fuel. If it does not work at least you have a spare set of plugs that you can rotate.
If it does not start check the plugs for wetness - this will at least tell you whether your injectors are working.
Also - a stray thought, have you checked to see that your distributor is firmly clamped. If that has rotated it could be a timing issue.

[GGR]

Hi Bert,

sorry to hear about your problems. I second all what has been said avove.

As always, first check that ignition is all in order. Check your timing at cranking speed, it should be around 4° after TDC.

If thats's fine, as other suggested, spray some "start pilot" through the opened Throttle body into the air plenum and try to start the engine. If it's sputters and then dies, then you have to look in the injection side. If nothing happens and your plugs are flooded, come back on the ignition side.

If it's the injection, make sure your fuel pressure is around 28 to 30 PSI by measuring it at the cold start valve. Also, for this exercice, try to bypass the 3 seconds timing set-up by supplying power to the pump directly from the battery. You can do that just by running a wire in between two plots of the fuel pump relay. You then have to make sure you hear your pump running continuously.

Good luck, and keep us posted!

[ABDow]

You can do that just by running a wire in between two plots of the fuel pump relay

Can you describe how to do that in more detail - for a 280 SE 3.5?
I've attempted to do that
D jet fuel pressure question
but without success.

[thebenzbar]

Yes, check the Fuel Pump... you know how notorious and temperamental they can be.
If FP is ok, check flow rate as well from tank to FP (your pressure is a good indicator) since the dreaded 'flower pot' in the tank can get clogged or gunked-up over time... fuel lines to/from included.

[Tomguy]

Does it sound different when cranking? Hate to think you jumped a tooth but that "Sudden loss of power" thing seems to sound like what happens when a tooth is jumped and cam timing is thrown off.

Otherwise, take a few plugs out before you go any further and see if you're flooded. If you are, pull the pigtail for the trigger points, plugs for the injectors, or the ECU fuse, as Tony suggests. Then crank with the throttle wide open. I wouldn't add any ether yet. But these engines get flooded easily when a no-spark or bad timing condition exists, from my experience, and do not "unflood" easily without turning all fuel off, as D-Jet LOVES to dump in gas to a cold engine.

[sjefke]

Fuel pump works fine and I can control it. There is a whole thread from me on that issue...

Engine does not sound different when cranking. Very smooth, no clatter anywhere (I also worried about broken timing chains...). Just as normal, except no firing on any cylinder.

I suspect the sudden loss of power may have come from the rupture in the vacuum hose for the pressure sensor. I had the car on axle stands under the chassis and had accidentally lowered the jack under the motor mounts so the engine dropped a bit, straining the very old hose. It did fire a couple of times up with that, but as I said, at one point after a couple of days sitting, it did not want to fire up at all anymore.

My suspicion is ignition because when I pulled plugs the other day, one seemed wet. I may have had a bad coil and now that I have installed petronix, the timing may be off. Nevertheless, I am surprised I don't even get a sputter. I had my MG V8 once off by 180 degrees after an engine pull, and it still barked (talk about backfire...). My next step is to check timing but my strobe light is kaput. I may just have my son try to start it while I rotate the distributor a bit to see whether it makes a difference.

Which is the fuse for the ECU? I thought it was controlled by the master relay which gets power directly from battery? Or are you talking about fuse 2?

Thanks,

Bert

[GGR]

You could take both your cam covers off and check if both your camshafts are on the mark when your crank pulley is on "0", just to make sure. While you are there you could check that your rotor inside the dizzy is in front of the plot for cylinder 1 of the cover. That will be good enough a timing to allow you starting the engine.

[sjefke]

I am starting on a timing check this weekend.

Question: What size and type is the crankshaft bolt?

I want to rotate the engine/crankshaft by hand but could not find a good clear answer in MB books as to whether it is a hex or allen key bolt, and what size it is.

Or is it such a big pain that I should just rig a remote starting switch together to rotate the engine (I have been doing that so far with a wire touching battery + with starter terminal on engine, but it does not help me see the timing marks under the car)

Bert

[ctaylor738]

Should be a 27mm socket.

[sjefke]

Update and a question:

I was able to set the timing statically to about 3 degree before TDC. By chance, the starter put the white dot I had put on TDC just about 3 degree before the mark on the block. Rotor was correctly pointing to cylinder 1 mark in distributor and a peek in oil filler hole indicated that camshaft was up and valves of No 1 were closed. So I hooked everything up and turned the distributor until I heard a light "crack" indicating spark had jumped in distributor. Tightened everything up and tried starting car. It had a small fire hickup (hope at last!), but that was about it. Tried it several times. On all occasions, engine smelled like gasoline after a while so it seems to be flooding indicating plenty of fuel going in.

So my thoughts were going back to weak spark/ignition.

I measured resistance from main lead in distributor cap to carbon tip and it showed good continuity, so no broken carbon tip or connection.

Wondering whether I had a broken solid core coil lead, I put an Ohm meter on the main lead from coil to distributor and it showed an unexpectedly high resistance. It does show continuity, but Ohms are high. I also measured the spark plug cable from distributor to cylinder 1 and it had less than half the resistance of the coil lead, and I had to push a wire in to get a contact at the back, so it probably was not a great contact either.

Question: The coil distributor cable is a Bosch 7mm silicon cable. Is it supposed to have a high resistance?

One theory I have is that the coil cable may have an internal break causing a weak spark. It was the only cable I pulled off during my slave cylinder repair because I wanted to check that the clutch and transmission internals were fine by cranking the engine without ignition. It was sticky, so I am suspicious whether I accidentally caused a crack/break in the silicone near the distributor end. I did see a long spark earlier, but perhaps that was a fluke spark due to break being accidentally closed when I held is tight together in a plier.

Do you think it is the coil lead?

Thanks,

Bert

[Tony H]

I think my car has correct wires-my coil wire shows 2.26K ohms. Did you pull the distributor when you installed the Pertronix? Did it ever run with the Pertronix?

[sjefke]

Tony,

On a 20K Ohm scale, I read 16.27 on my digital multi meter yesterday. On a 2K ohm scale, my meter indicated "1" - meaning no continuity. Sounds to me like my wire has 8 times more resistance than yours. What type of wires do you have?

Car never ran with Petronix, but did not run anymore before I installed it either.

I did pull distributor, but was VERY careful not to twist it to loose timing. I verified yesterday that distributor is indeed in correct position. I heared the petronix firing (sounds like "tack" in the distributor) when I turned the distributor around yesterday during the static ignition timing with ignition on.

Any more thoughts on coil wire resitance? Or recommendations for replacement? Should I stay with solid core (silicone) or go with copper strand?

Thanks,

Bert