Real1shepherd

'92 w124 300TE4matic wagon, M103 engine. I just installed the rebuilt head, new cylinder head gasket etc. Head was set by machinist (after rebuild), to TDC on #1 cylinder, flywheel was set @OT (and a visual check of #1 piston). Everything went by the book, except I broke the head free at the intake manifold seals (instead of taking the manifold and FI system off as a unit which the book says to do).

I can crank and crank and no start. The plugs spark fine against a ground. It sounds like the fuel system is pressuring up when I turn the key...but the plugs aren't wet at all after long cranking and no gas spurts out of the top of any injector if I take their individual supply line off.

The only thing that was touched in the FI system was a fuel line from the top of the fuel distributor to an electric sensor, that positions on a vacuum hose to the head. It seems to me, the system isn't pressuring up. If after long cranking, shouldn't I get significant pressure if I crack any fitting on top of any injector?

I'll check compression tomorrow, because I did replace the timing chain. Other than the OVP, what other things can I check out? I think I have a gauge somewhere, so I can tie into the fuel distributor for a pressure check. What are some symptoms for CPS failure? MAS is working if I hear the system attempt to pressurize when I turn the key?

Kevin

ps2cho

If you are getting no fuel I'd check the fuel pump relay first. I believe you can jump it via certain pins, but I forget exactly which ones. A good search here or at mercedesshop/peachparts should find you something.

Real1shepherd

Well, there's some gas up to the fuel distributor and I hear the fuel pumps when I turn the key....just not building pressure it seems. Thanks for the suggestion, I'll check it out.

Kevin

ps2cho

Seeing as the fuel distributor, as far as I understand, is physically linked the the throttle plate opening as well, you may want to check it is actually opening enough to let the fuel flow through. Make sure its not jammed or anything.

Real1shepherd

Yeah, throttle works fine and I lubed everything in there that day with ATF, as the German's suggest. I'm going to see if I have fuel being pushed fwd to the fuel distributor with the key on. Also, going to make sure I have good compression. Thanks.

Kevin

Real1shepherd

ps2cho, I think I might be on to something. At the rear of the head on top, is a temp sensor screwed into a coolant gallery. This is one of the few electrical components that came off during the rebuild. I'm starving for accurate nomenclature, but my guess is that it sends a message to the cold start injector to work. On reassembling this sensor, it has four marked, male pins:1,2,3,4. However, there is no corresponding marks on the female pin holder. It will push-in in a number of different way....obviously there is only one correct way.

Do you remember this part on your head reassembly? Boy, if it could only be that simple! I still can't get back to the car until Friday night or Sat morning.

Kevin

124-Fan

I presume you installed a new ( and correct ) inlet manifold gasket and cleaned the surfaces? - Just wondering about false air, since there are two or three types of inlet manifold gaskets, if I remember correctly.

-Cheers,

ps2cho

That coolant temperature sensor at the back of the head on mine is a simple plug, yours is different?

That sensor is purely for the CIS when in closed-loop. As far as I understand, it does not relay any information until the engine has warmed up. The cold-start valve "really" only works in very low temperature climates. You shouldn't really need it to start after some cranking.

Did the compression test come up okay?

Real1shepherd

It came from autohaus and looked like the original in pattern, but a little different in material.

Kevin

Real1shepherd

I'm learning at another forum that the senor (ECT), is very important on start up. Here is what was said:

That component at the back of the head is the engine coolant temp (ECT) sensor. It is the single most important sensor for determining how much fuel is delivered when the engine is cold and the control system is in open loop operation. Once the O2 sensor heats up *it* becomes the most important sensor.
The ECT design varies over the years. The earlier cars have a 2-pin connector where one of the pins provides data to the Jetronic brain while the other provides data to the spark control module (EZL). To test the ECT you measure resistance between each of the pins and ground -- resistance values should be very nearly the same at a given temp.
Like most manufacturers, Benz stopped using chassis ground for a sensor current path. That's why later 124s have a 4-pin ECT. IIRC you measure sensor resistance across opposite poles (1 & 3, 2 & 4) one side being + and the other -. Again, the measured values should be about the same across each pole. At 32F expect about 6k ohms, at 68F 2500 ohms, and at operating temp a little under 200 ohms.
(These same resistance values apply for the intake air temp (IAT) sensor which is located at the air cleaner inlet duct.)
I'll have to double check this but I'm pretty sure that the ECT data to the Jetronic module is processed and passed on to the fuel pump relay. That relay then operates the cold start injector.

No, haven't had time to do anything with the car yet.

Kevin

ps2cho

Interesting, I had it backward. Thanks for posting it.

Let us know what the compression test yields.

Real1shepherd

We're over 100 degrees here today....if it cools down some in a few hrs, I'll do some compression checks. My leak down tester was stolen with the rest of my mechanic tools, but I bought a simple compression tester today on the way home from work.

Kevin

Real1shepherd

*Update:Propped the intake open and did a compression check on all cylinders, while backing up the battery with a big NAPA charger.

33lbs exactly across the board in all my cylinders. And...it's now shooting gas mix out of the spark plug orifices. What a bummer...I was so careful putting this motor back together. Out of the thirty something odd engines I've rebuilt, I never had anything like this problem. I should have been suspect originally, because the starter was turning over the engine way too easily. The gas of course, isn't going to ignite if the compression isn't there. The head gasket goes in one way only, if I remember correctly. The intake manifold gasket was of different material than the original, but was punched out the same.

I have to have some reasonable course of action here, short of taking the head off again....any ideas? It was suggested on another forum that the machinist might have over torqued and stripped my rocker arm cap bolts. If he was consistent in the damage or more likely, he didn't torque high enough to spec, that would explain 33lbs across all the cylinders. This would be a nightmare for me because this is the most respected shop in town. I'd be better off buying a factory reconditioned head somewhere, than doing battle with this shop. If he did over-torque, the threaded holes would be ruined and inserts etc needed. What a nightmare.

I'm thinking about buying a leakdown tester similar to the one I had stolen and putting some compressed air into #1 and seeing where it goes. If the rocker arms cap bolts are stripped, then air would go rushing out of the intake or exhaust valve (or both). That's the only thing I have come up with so far. Or....pick the rocker arm cap bolts on #1 and using a torque wrench, see if they feel mushy after loosening, then re-torquing.


Kevin

ps2cho

Ah man....I was hoping it was not the problem, but I had the feeling it was because you didn't touch anything on the CIS... You followed the correct torque sequence for the head bolts right? X(forgot exact #) lbs/ft then 90 degree's each, followed by another 90 degrees, right?

Definitely start with the leakdown though. Maybe you will be lucky and have the wrong intake gasket or something as you said it was a different material...

Real1shepherd

Yeah, went exactly by the book on the head bolt sequence. I wouldn't touch an aluminum head otherwise. I'm betting on the rocker arm cap bolts....that would explain exactly 33lbs on each cylinder. If I'm lucky, he just didn't tighten them to spec. Putting #1 in TDC and listening for air with the leakdown test, is my best solution so far. I'm going to see today if the rocker arm cap bolts might be the culprit.

Kevin

124-Fan

Kevin wrote: "33lbs exactly across the board in all my cylinders. And...it's now shooting gas mix out of the spark plug orifices."

-Are you sure the timing is correct? Sounds like you might timed it incorrectly when assembling.. ?
When at 0 degrees at crankshaft pulley, (TDC) there is a notch in the camshaft aligning with a notch in the no. 1 cam holder. ??

Cheers,

Real1shepherd

Yeah I know, everyone on another forum thinks it's timing. I was very careful; checked the OT balancer mark against the piston in TDC on #1 while the head was off. Used the line up notch on the camshaft as pictured in the MB literature and then put my sprocket & chain back on.

Just to rule out error, I'm waiting on a graduated spring plunger TDC tool to find exact TDC...then compare again with the OT notch on the balancer and the camshaft notch. I'll be very surprised if there is a mistake, but I'm desperate to try anything at this point. I'm pulling the head as a last ditch effort....probably after I use a leakdown tester to see where the air is going.

Kevin

Real1shepherd

Just as an update.....that picture in all the CD manuals that shows the overhead view of the camshaft/sprocket/ chain all lined up is not the camshaft in #1 TDC position. The picture shows #517 and #22 lined up together. According to a certified MB mechanic in another forum, that picture is 180 degrees off. I haven't had the time to check all this out yet, but would explain everything! It's also the same picture used by my machinist to put the camshaft in #1 TDC for me.

To quote the mechanic:
There is a dimple in the cam flange itself that lines up
with #517. #22 is not a timing mark, just a locating pin
for the sprocket.

The misleading picture is here:
http://www.ps2cho.net/downloads/MB%2...03/01-4150.pdf

They didn't make a mistake exactly...they assume that you used/marked your chain and sprocket for final reassembly. I replaced my chain so that wasn't possible, along with rotating the engine to clean up the top of the cylinders and block face. I was using that picture for #1 TDC alignment of the camshaft (as was my machinist).

Kevin