280SE 4.5 - Need Timing Specs

[JoeyTheB]

71 280SE 4.5 - Trying to bring back to daily driver status.
I know I need the manual, but I'm on thin ice on spending at the
moment.

I installed the Crane XR3000 w/PS60 coil to hopefully solve
my running hot, point eating problem. The kit installed ok,
and ran pretty well, but things went south when I
kept tweaking with a bad/cracked dist cap.
Fouled a set of Champions pretty quickly.

I now have new dist cap/rotor/vacuum advance,
and changed vac lines. Cleaned up the fouled plugs,
and she's running, but a little rough.

Currently running with vacuum/emissions/ac/switch bypassed.
Vacuum is stronger, but with no gauge, it's hard to say.

Back to the subject line:
Trying to set the timing and see varying remarks on posts.

Have a timing light and dwell meter that reads up to 2k rpm.
Have a white dot on zero (?) from last reputable shop tuneup.
Have not messed with fuel mix or cold start (the BIG screw
at front of manifold).

7 BTDC w/o vac, cranking speed
(That would be where the white dot is to the left/before
the pointy marker - right ?)

5 ATDC w/vac @ idle
White dot on right/after pointy marker

Tonite, with the VAC on (switch bypassed),
semi-clean fouled plugs still in,
the car will run at BTDC or ZERO, but not ATDC.
It sputters and dies.

Have not changed any fuel settings, such as mix or cold start valve. I realize they may need adjusting now the vacuum
system is coming back into the picture.

[Rackne]

Don't forget to do a test light check of the impulses from the injector points to the injectors. Each set of points controls two injectors. Also I've heard that playing w/ the mixture adjustment is disastrous if done with the car running.

[JoeyTheB]

Thanks for reply - this is a GREAT forum !

Re: test light -
Could you give a little more detail (like connect what to what),
and do you use a little test lite from the parts house ?
I Realize we're trying to ensure injectors are getting
the signal to turn on/off, but just not sure where to test.

Re: Fuel mix - yeah, I made that mistake myself.
Heard it's best to leave that to the shop....

[wbain5280]

You might want to chack to make sure the chain is not stretched or the guides worn too much.

[psfred]

Here goes:

Factory spec is 5 ATDC with vac applied. If you have it off, or disconnected, 7 BTDC. I suspect you have the following "goodies" going on.

1). Someone "hotwired" the points to run direct rather than through the transistor unit, probably because the transistor unit croaked and THEY croaked when the got the price estimate for a new one. The other two possibilities are a shorted resistor (unlikely) or no grease on the points rubbing block, in which case the timing retards pretty fast in service as the rubbing block gets eaten off.

Both fixed by the Crane unit. Should eliminate all point/timing problems forever.

2). Champion plugs aren't a real good match for this engine. Get Bosch Supers (non resistor) if you have stock wires (1500 ohm plug connectors). If you want to keep the Champoins, they will need to be run a while to burn all the carbon off in place, but you can clean them pronto with a propane torch -- hold the plug with a pair of pliers and hold the electrodes just above the tip of the inner blue cone on the flame until the carbon burns off and the insulator gets dull red. Scraping or brushing won't work, it leaves carbon tracks.

3). If you have poor condition wires, it ain't gonna run, ditto for dead gas. Make SURE you get spark to all the plugs and that the wires are connecting properly -- if you have the stock cable set, the little wire spring can get bent so that it prevents the connector fitting down, leaving the boot floating around. Don't forget that the coil can be bad, too. If you didn't replace it, check for carbon tracking on the secondary side connector. Also check resistance -- if high, or there is carbon tracking, replace.

4). Crank with the coil wire grounded and listen for all the injectors clicking. Check the big nest of brown ground wires on the firewall behind the battery -- all the injectors and the control unit ground here, so a bad connection will result in erratic fuel delivery. Clean trigger points if all the injectors don't work, with the proviso that if only one isn't working, it's either sick or has a bad ground, they operate in pairs. Trigger points almost never burn, but they do get oil on them and fail to trigger injection. you must pull the distributor to get the trigger points out.

5). Rotate the engine by hand so you can see the marks on the balancer with the engine off. Verify that the correct ones are marked (TDC is 0|0) and that you have #1 spark plug wire (front cylinder, right side) lined up right and all wires in correct order -- #1 is NOT the front left piston...... 5 ATDC is marked at the factory, and usually the other mark will be 7 BTDC marked by someone later, but CHECK -- it may be 0 instead. Verify that the cam lobes for #1 are correctly positioned at TDC -- that is , both valves closed, cam lobes at equal angles. You can see them well enough with the oil filler cap off, but you may also want to check the chain stretch, too -- line the slot in teh trust washer of the right side cam up with the mark on the front cam tower, the read the degree mark on the balancer. 8 degrees or more, you need a new chain.

Also, be aware that the balancer can come adrift on the hub -- it is bonded rubber and, very amusingly, can slip. This makes setting timing a challange....

You cannot set the timing correctly if the spark isn't good, for obvious reasons.

6). This probably should be first -- you must check for vac leaks. This system is very sensitive to vac leaks. I've seen a big ball bearing stuck in the blowby line to reduce the idle speed!. The system only measures pressure, not flow, so will happily add fuel when the pressure goes up, making the engine race. If you fixed some vac leaks, you need to raise the idle speed by screwing the big screw out.

The big screw is the idle speed screw, can be adjusted at will.

More info if you need it.

Peter

[JoeyTheB]

Thks for all the help, got it working again.

Problem was a combination of weak spark from
fouled plugs and crossed wires on the drivers side.

Put in some new bosch supers and we're back in business.

I'll double check the timing, set idle and check out injectors today.

FYI, the wires were OEM, 1.5 yrs old.
Learned my lesson about putting non-OEM ignition components in.

Thanks again ya'll....

[psfred]

Joey:

Champion plugs are the best thing going for Chrysler engines. Considerably less sucessful in a Benz -- you want to stick to Bosch Supers, Bosch Platinums (you must use non-resistor wires with these, not the OEM ones), or NGKs.

Crossed wires do indeed make it run strangely!

Glad you go it going -- I certainly love driving my 280 SE!

Peter