Knobguy

I am new to the Mercedes world. I recently purchased a1992 MB 310 otherwise known as a T1. It does not have the original motor in it. I’m told the engine in it is from a 1984 190E. It’s a carburated 2.3 L, M 102 motor with unknown milage. I can not get #3 and #4 cylinders to fire. I checked compression and all cylinders are consistently 148-150 PSI. I changed out the spark plugs, then the cap and rotor, then the plug wires, then the coil, then the distributor, all to no affect. Any advice on where I should go next would be greatly appreciated. Thanks

190Efan

I know that the carbureted versions exist but they were never sold in the U.S. It certainly sounds like you've done all of the right things. I wonder if it might be some sort of a fuel delivery issue?

dolucasi

With a single carbureted engine, the only fuel delivery issue would be the intake valves. We do not know the age of the engine so I would open the camshaft cover and inspect the lobes.
Pre-90 engines had weaker metallurgy for the rockers. It is a long shot but I would eliminate that.

I know you replaced all ignition components but I would still remove the spark plugs and check for presence of a healthy spark.

Does this engine even run? I would not think so with 2 missing cylinders.

Also check the timing with a timing strobe light. If you do not have one, buy one, they are dirt cheap.

- Cheers!

Knobguy

Thanks for your input. Yes it is amazing it runs on only two cylinders but it does. Even starts well. Would not an intake valve issue be reflected in a compression test? All cylinders have great, consistent compression.

190Efan

Sorry I forgot the part that the engine starts well. I guess that does end the possibility that it's a fuel delivery issue. That'll teach me to read posts more carefully. It's very strange that the compression for all of the cylinders is normal and yet #3 and #4 won't fire. Maybe recheck the compression tests a 2nd time to make sure that you get the same results again? I also like Dolucassi's suggestions as well.

dolucasi

Not sure if valves not opening completely would show up on an a compression test.
Compressions is good at catching leaks thru pistons rings and valves (how well they seal)

It does not even catch a blown gasket sometimes if you have some leak from one cylinder to the next.
I had that on my 2.6 and compression on all 6 cylinders were around 175psi. BTW you are at the lower end of the spec. assuming 4cyl spec is same as 6 cylinder.
Only a leakdown test will catch a blown gasket for example.

If you trust your ignition and timing, the only thing remaining is fuel, and it is possible two inlet valves as not opening all the way (unlikely but possible) or the carburetor is not spraying a nice mist.
Which 2 cylinders are not firing? The edge ones or the center ones?

Knobguy

Thanks for all of your input. I have finally found the problem. It is a leaky intake manifold gasket around those two cylinders.

dolucasi

That's great! Not your usual failure mechanism on M102/M103 engines. Must have been a serious leak. Maybe there was a botched installation by using the same gasket after a head removal.

- Cheers!

190Efan

Glad this got solved. It's possible that the shortcut and less expensive reuse of an old gasket caused the leak.