skullyyy

Hello I have a 92 300sl and just did the head gasket myself and started the car and was bummed to see it misfiring but my biggest issue is I believe it’s related to the timing bc I have new rotor and plugs and injectors and etc and plugs are dry but when I set the crank pulley to tdc and also have my crankshaft set with the 4mm drill bit the car still wants to misfire and I’m wondering if I’m doing something wrong with the timing? I have no leaks or white smoke or lights on the dash or any metal noises or anything alarming just a misfire and if someone could show me how to diagnose which cylinders are missing any info will help as I pretty much know little on the m104 thank you

dolucasi

Do you mean it is rough or does it not run at all? Or is it backfiring from the intake, etc.
I did not do this on my M104 engine, but even on my M103 aligning the crankshaft with camshaft got tricky at the end even though I was super careful to mark and fix the sprocket to the chain.
They went misaligned by a couple of teeth but I noticed that before I finished the job.

But in the end my car still did not want to start and had nothing to do with the camshaft alignment. Turns out I knocked off the HV pin in the distributor cap and it was not making good contact.

Long story short, I would start with checking timing with a strobe light. I noticed my problem when I did this and sure enough the timing was all over the place during cranking.

I know different engine and ignition but make make sure your ignition is not the problem as you have replaced a lot of part during your job.

My 2 cents worth.

skullyyy

Thank you very much for the help and sorry for late response been at work but yes the car is running rough takes a long crank then runs roughly and stutters when given gas now the timing light is an amazing idea and I actually have one to borrow but when using the timing light on a m104 is there a vacuum I need to unplug for accurate reading? And to begin do I set the car at tdc then hook up the timing light then point for results and adjust the crank pulley from there?

dolucasi

On M103 the strobe light will only tell you when the ignition is firing in relation to crankshaft position. So if your timing chain/sprocket was misaligned strobe light can not help you there.
That is mechanical alignment.

But since this is an interference motor if misaligned it can not be that much as otherwise the valves would hit the pistons.

I would do the strobe light just to make sure you are getting consistent strobes at idle. I do not know your engine with the 24 valves. So I can not comment further.
M103 spec is 10 degree BTDC. Not sure about the M104. You should look it up.

But, how did you makes sure the camshaft is ligned up with the crankshaft as you were mounting the cylinder head? I am just curious.

dolucasi

One last thing, if you run out of ideas, and are convinced that the injectors and spark plugs are firing at the right time and consistently, you will have to open up the head cover an make sure your camshaft and crankshaft are aligned.

However, like I say my knowledge of M104 diagnosis is limited as I sold my car after 25 years of ownership and never had engine issues when I sold it at 145K miles.

Is your emissions HFM or CIS-E? Seems it may be the transition CIS-E with M104. Much easier to diagnose (at least for me)
And does it have the dreaded bio-degradable harness issue?

skullyyy

Hey man thank you very very much for all of your input as it’s super helpful! I wanted to ask you another question regarding the timing light so thankfully today I was able to get my hands on and check the timing step 1 involved me setting the crank pulley to tdc to check marks which went well with the 4mm holes lining with the head and the OT lined up with its mark step 2 I hooked up my timing light which was a funky challenge due to the battery in the trunk haha but after that step 3 was just using the timing light to get my results and afterwords this is what I found.

(Picture was taken while using timing light)

in this picture the green line represents the TDC MARKER and the red line is the degrees so judging from this picture of the timing light would I say I’m 10 maybe 11 degrees BTDC??? And if so what’s the next step from here?

dolucasi

If you are getting a consistent and nice strobe and you already verified you are mechanically aligned. You are good on ignition.

Can you answer my questions
(1) HFM or KE-Jetronic emissions system
(2) and biodegradable versus old stile harnesses for your engine?

skullyyy

Sorry to answer your questions I have KE and fortunately no biodegradable but today i started with the timing light and found out what I sent earlier. After that I re checked my cams and saw my exhaust sprocket was slightly off so after triple checking and aligning I had the cams aligned perfectly with the head and at tdc and everything chain wise was good and how it’s supposed to be but still when I went to crank the engine today it was still rough and seemed to be slightly rougher then when I first cranked it when using the timing light is there something I’m doing completely wrong or not looking for or just not doing at all bc I’m scratching my head as to what is causing rough idle as I just really want to get back on the road thanks

dolucasi

OK. So at least you should be good on the KE front or at least I can help you there if you run into trouble. Good to know you do not have biodegradable harnesses.

So you have you checked that your TDC mark is perfectly aligned with the cam lobes to make sure? This is more complicated on a 24V engine an I'm not familiar with those.
But on a 12V, TDC means the 2 valve lobes (one for intake and one for exhaust will form a perfect V shape and pointing up for the #1cylinder when your timing TDC mask on the front pully is at 0 degrees.

Yours has multiples of these lobes but still, they need to be pointing up at TDC with the #1 cylinder. Also since you have easy access with the spark plugs removed the pistons of #1 an #6 cylinders should be at their peak.
Double check that by rotating the engine (clockwise) and seeing something like a long screwdriver in the spar plug hole.

I'm going on memory here so do not quote me on this.

But at the end of the day do not be surprised if something else completely unrelated is your problem.

Does this early 24V engine have any variable cam/valve timing? Meaning something akin to VANOS? Or is it straight up no cam advance/retard at all since it is gen1.