W124 260E powerless after headgasket replacement

[H1lmar]

I just bought myself my first Mercedes, been wanting to own a w124 for some time now and got myself a cheap 1990 260E auto driven 330.000km with running problems. I've been trying to sort it out but I'm at a dead end right now. I'm trying to get the engine running before I try to find a replacement engine. The car starts and idles at first like a champ. After being running and warming up a little bit it loses almost all power and I can't even rev it. Does not choke, just no power to even rev the engine alone. And it is like it is idling to low, shaking and might be losing some cylinders, not sure. Has some power at first, not enough to pass 10-15mph, but that only last for like 20secs.

Bear with me please, english is not my primary language.

So, this is the story. This guy buys the car with a supposed failed headgasket. He replaces the headgasket and probably all the gaskets that are in the headgasket set. Intake and exhaust gaskets and so on. He gets the head checked and valves reseated. And assembles the engine. He has according to him been trying to fix this on and off for about three weeks before I buy the car. Replacing spark plugs and leads, bought a replacement fuel distributor but did not install and some basic checks.

He takes it to some shop to get the car checked after giving up, they say that the piston rings are the problem. They say did compression tests and got low compression, but similar compression on all six cylinders.

And that is where I buy it.

I've got some experience with repairs so I check the basic stuff. Did not see smoke from exhaust, the exhaust is broken in half somewhere under the front seats though. Rest of exhaust system not under. Don't notice air blowing from oilcap or dipstick. Recheck the compression. I did dry tests on cold and hot engine, getting from 170 to 180psi cold and 160 to 170 hot. So I thought it should compress enough to not cause this huge powerloss. Checked timing, spot on and valves seem to move freely. Checked spark plugs after reading about the resistor spark plugs problems, the car had resistor ones in it, replaced those with NGK non resistor ones that should be used with the M103. That changed nothing. I noticed that the middle springpin in the distributor cap was broken so I replaced the cap, still the same.



That is where I'm at now. Note that the alternator and fan belt is not installed doing those tests but I have a good battery so I guess it's not a problem, I think he had it installed while doing his own troubleshooting. Alternator is in the trunk so I can reinstall it.

So, in short, supposed headgasket problems, don't know the symptoms.
Headgasket replaced
Got some head work professionally
No power after assembly
Timing correct
Seems to compress
Ignition system seems to work and correct spark plugs
Problem seems to get worse as the engine warms up.

So, this leaves me with a bit of a headache, I suspect electrical problems or he screwed up the assembly of the engine.

What should I try next?

Compression testing again, hot/cold and wet/dry? Leak down?
What sensors or electrical stuff should I check?
Could this be a vacuum related problem?

Please help me so I can enjoy my first Mercedes

[filon102]

Did you check your lambda sensor? (o2) Since, as you said it works fine when cold, but when the engine is warmed up it runs like crap. Obviously when the engine reaches certain temperature, the computer goes off of the lambda sensor for air/fuel mixture

Good luck

[H1lmar]

Originally Posted by filon102

Did you check your lambda sensor? (o2) Since, as you said it works fine when cold, but when the engine is warmed up it runs like crap. Obviously when the engine reaches certain temperature, the computer goes off of the lambda sensor for air/fuel mixture

Good luck

It runs when cold, but does not rev freely, but everything gets worse as it gets warmer. Just did the fuel filter as I found a new one laying in the trunk, no change. Ignition timing check next when I get my hand on a timing light, O2 sensor would be the next step. Found a used injector with an electric plug on it, I guess some cold start injector of some sort. Is between the fuel distributor and the valve cover.
also some air pump located in front of the fuel distributor under the plastic cover for the loom. Don't know if i need those.

Still no power. Was going to bolt in the alternator but the wiring is hiding somewhere. Got to find it to hook the alternator up.

[97 SL320]

Why was the head gasket replaced by the previous owner?

Since compression is low on all cylinders, valve timing may be incorrect ( check camshaft and timing chain ) Also check valve lash , it may be too tight. This still matters on a engine with hydraulic lifters / hydraulic lash adjusters. Hydraulic adjusters still need to be operated in their proper range otherwise the valves can be heald open.

Does the car have a catalytic converter? It may be restricted.

A oxygen sensor ( lambda sensor , o2 ) generally does not have enough control to make the car run that badly. O2 sensors are more to trim fuel mixture.

[H1lmar]

Originally Posted by 97 SL320

Why was the head gasket replaced by the previous owner?

Since compression is low on all cylinders, valve timing may be incorrect ( check camshaft and timing chain ) Also check valve lash , it may be too tight. This still matters on a engine with hydraulic lifters / hydraulic lash adjusters. Hydraulic adjusters still need to be operated in their proper range otherwise the valves can be heald open.

Does the car have a catalytic converter? It may be restricted.

A oxygen sensor ( lambda sensor , o2 ) generally does not have enough control to make the car run that badly. O2 sensors are more to trim fuel mixture.

This guy I buy the car from bought it with a supposed head gasket failure so he replaced it. Im starting to lean towards blocked cats or fuel starvation. Going to try tomorrow to use start spray as extra fuel to check if it gives more power. If not I'm going to disconnect the exhaust from the headers to rule out the cats. Then I'm going to put some 40 litres of fresh gas as the gas that is in the tank may be some months old and the fuel light just went on. Doublechecking compression and valve clearance will be next after that. There is not going to be much left to test soon.. But I will post my solution when I find it. I'm not giving up, it's 2am now and I've been working on it for a few hours now.

[sasquatchgeoff]

I am also leaning towards the potential of incorrect timing brought by timing chain mis-position. Was head gasket replacement done by a competent mechanic with knowledge of MB head re-installation procedures? IMHO, checking the timing should be the next step.

[H1lmar]

Originally Posted by sasquatchgeoff

I am also leaning towards the potential of incorrect timing brought by timing chain mis-position. Was head gasket replacement done by a competent mechanic with knowledge of MB head re-installation procedures? IMHO, checking the timing should be the next step.

Timing has been checked and doublechecked, is spot on. It was done by an amateur but has done head gasket replacements and other maintenance on some cars before, I don't know his exact experience. Just a kid trying to fix it, sell it and make money. He might have screwed this up.

@97 SL320 Well, I'm only the second owner to try to fix this problem, the last owner tried and failed after his head gasket replacement.

It has CIS, correct. I will be checking vacuum and air hoses and that stuff sometime tomorrow. Spark plugs are new since yesterday, have maybe run like 3 minutes max and never warmed up fully, will check them for oil when I recheck compression.

Thanks for any advice you guys, I appreciate them all, no matter how big or small they are.

[H1lmar]

Bumping for solution, disconnected both headers from the engine and the car is running perfect. Most likely solution is one or both cats are blocked. Car started up and revved for the first seconds and then became heavy and unresponsive. Disconnected headers, no problem, full throttle response.

Started tonight again working on the car, replaced the fuel filter, disconnected the injector lines at the distributor and bridged the fuel pump and checked the flow, even and nice flow but the gas did not smell good enough, smelled old. I disconnected the fuel line from the pump to the distributor at the distributor and ran the pump to empty the tank. Poured in 5 litres and ran that throug, poured in 20 litres and ran the pump for a few secs to get the air out. Started the car and no change.

Did another compression test, now wet and dry on a warm motor, not cold and not at operating temperature. 150-165psi steady in all cylenders, 4 cylenders at 160, one at 150 and one at 165. No change when oiled.

Checked the sparkplugs, 1,2,3 were heavily sooted, while 4,5,6 were somewhat good looking.

The spark plugs, were bought new during this repair process. Have not been driven on. In correct order, cyl 1 on left, cyl 6 on right.


So, being that the headers are two 3 cylender headers I figured it must have something to do with it. Disconnected those and the car runs great, full power and no problems. Just have to empty out the cats or make a new exhaust system, the old one is fubar.

[97 SL320]

It sounds like the car has been making the rounds with each owner trying to fix it. I'm guessing the previous owner was trying to fix the poor power problem also.

The gas has to be very old to cause the problem you have.

I just bought a E320 that had been sitting since 2008. Put a battery in it, cranked 2 times, and it ran on 3 year old gas. Oh the wonders of fuel injection and sealed fuel tanks. ( restarts after that took a bit of cranking but car ran fine on the road. )


It sounds like you have CIS injection correct? All of the intake plumbing and vacuum lines must be installed properly, if unmetered air enters the engine but not the air flow meter / fuel distributor the engine will run very lean.

Pull a spark plugs and see if they are chalky white ( very lean ) or black ( rich ). The chalky white from lean won't show up unless the car is driven under a load. Also look at the ground strap, if very lean it will sometimes turn blue and be bubbly.