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roger 02-20-2001 03:36 AM

95 SL Head Replacement
I just got through putting a rebuilt head on my 95 SL. Suffered from the oil in the coolant problem. It has 120K on it, so I don't qualify for the free replacement. After I got it all back together, I couldn't get the car to start. It cranks fine. I've got good spark to all four cylinders. I think I'm getting gas to the cylinders. After about 10 seconds cranking, I check the plugs and they are wet. Smells like gas.

I've browsed through the Tech Talk Board (all 51 pages, some great info.). I hoping some of the experts here can point me in the right direction. I'm wondering if I've fouled up the injector timing somehow.

Any help would be greatly appreciated.

Heartbeat - '95 SL2 02-20-2001 12:32 PM

Welcome aboard Roger! If you're replacing heads, I would've thought you'd be answering questions here rather than asking 'em ;o)

Sorry you're problem's waaaaay over my head, but everybody here <i>really</i> knows their stuff, so hold tight and good luck!

Doug_E_95_SL2 02-20-2001 02:05 PM

Might be the timing. If the Crank and the Cams are out of sync. the car won't start.

When you put the new head on were the cams in exactly the same position as the old cams?

sattech 02-20-2001 10:00 PM

Check your timing first just in case, but sometimes the lifters stay pumped after reinstalling in the new head. With foot to floor keep trying with 10 min. breaks in between. When engine finally does start let off gas slowly until it will run by itself. Within a couple minutes after start it should be hitting on all 4. If there is still some tapping after a couple minutes., holding the RPM at a steady 2k for 30 sec increments seems to help clear everything out.

roger 02-20-2001 11:30 PM

Thanks for the responses so far. I'll try several times to clear the lifters as suggested.

The thing I'm really puzzled about is how does the injector timing work? Since the plugs fire in pairs, the crank to cam timing can be 180 deg out and the ignition timing will still work. The injectors, OTOH, have to know when each cylinder is on the intake stroke. If I understand right, injector timing is based on the crankshaft position sensor. How does it determine the cam/crank relationship?

I actually pulled the valve cover and timing cover. Removed the timing chain, rotated the crank on revolution, and put it back together. Still won't start. I did have to rotate the cam 90 deg and then back to keep pistons and valves from fighting. I think I'll put it back as it was, because I followed the Haynes sequence closely when I first did the work. Since I have the valve cover off, is there an easy way to check the lifters before I put it back?

Thanks again for your help. Hopefully, I'll be able to return the favor in the future.

sattech 02-21-2001 12:22 AM

the ign and the injectors rely on the crank sensor for info as to when to fire. Like the coils, the injectors fire twice per cycle. At around power stroke then at intake stroke. That way half of the fuel charge is waiting aqt the intake valve an dthe other half is delivered when the intake opens. This is not as fuel efficient as sequential injection, when all the fuel charge is delivered as the valve opens. But this way there is no need to know when the valves open , just when the piston is going down. If the mechanical timing was correct and you are getting fuel and spark, try replacing the plugs and try again. Sometimes this process has taken .5 hrs of on and off extended cranking.

roger 02-22-2001 01:54 AM

Thanks for the response. That's pretty amazing, this car gets 35 to 40 mpg with the "less efficient" fuel injection. I'm impressed. I'm also impressed by how much the ignition/fuel timing is simplified by the efficiency sacrifice. Actually, even though I'm bummed about the cracked head, this has been a really good car. We bought it new. Have done nothing except gas, oil, tires and brakes for 120K miles. I'm hoping to get another 80 to 100K out of it with the head replacement.

I am also a real convert on regular oil changes. We have been pretty religious about them. When I pulled the head and inspected the cylinders, I could still see the crosshatch pattern from the original honing. There is no ridge. You can tell where the pison travel stops because theres a little shine in the ring travel area.

Thanks again for the response. I'm taking tommorrow afternoon off to put it back together. Weather man says snow/rain on Friday and Saturday. Since my garage is full of tools, I'm working in the driveway.

Boog 02-25-2001 03:16 AM

while your at it check the coolant temp sensor it will also cause the injectors to flood the car if its reading -30 or so when bad.common when replacing a head.cracked head = got hot = cracked temp sensor.

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