ignition/injection mystery

[Mr Basil]

Hi,
I bought the '68 280 SE one week ago as an anniversary present for my wife. It is really a pleasure to drive, yet sometimes, particularly in it's first half hour of operation after sitting all night, dies after a feeble attempt to rev during acceleration after stopping at a stop sign or light. It's a dangerous condition for two intersections we travel through frequently. It seems to handle the rest of the RPM range fine and idles OK, but it has trouble getting from idle to slightly higher RPM's after which there is no trouble. About half the days we have owned it it hasn't happened and if the engine has been operating for an hour or two or more there hasn't been a problem. The POs have moved to India so all we know about the vehicle is that it has a new fuel pump. Perhaps it means nothing but the worst days were the days after I bought gas for it at the same local station. Anybody have a solution?
Thanks
Basil

[Arthur Dalton]

Do a fuel flow test.
Tank filter and pump filter are common faults on MFI.
You are looking for 1 ltr/15 secs flow.

[NoSpark]

I'm probably stating the obvious, but before attacking something like this, give it a full tuneup and don't forget to set/replace the points. Over the years this has fixed 95% of my problems, even when I had convinced myself that it was a fueling problem.

[Arthur Dalton]

Originally Posted by NoSpark

I'm probably stating the obvious, but before attacking something like this, give it a full tuneup and don't forget to set/replace the points. Over the years this has fixed 95% of my problems, even when I had convinced myself that it was a fueling problem.

I agreee that ignition is a possible and should be to spec BEFORE fuel pump adjustments , BUT, a fuel flow test takes one minute to verify and is a very COMMON fail spec on these MFI chassis. [ and should be checked w/tune up anyway]

[barry123400]

It sounds a little like the points may have an extremely low dwell angle. They are too close together. Easy, easy, check. Just look and see if there is a reasonable gap. Part of your problem makes me think it could be. Another part of the description makes me think perhaps not.

[300SDog]

Best diagnostic tool might be the spark plugs..... wet fouled from running rich?

And if its running rich i'd suspect the injector tips are worn beyond spec, no longer vaporizing fuel. Calculate the fuel mileage too. It should get more then 16mpg, better yet 18 if driven gently. Running rich fits the scenario of performing best when completely warmed up.

(edit: Another item that can help is trying the next hotter range of spark plug, gapped to normal specs (.24mm?). Hotter plugs made all the difference in the world to one of my 220Sb's.

[Jengasan]

Hi, I assume you have a 280se/8 model (6 cylinder, mechanical fuel injection). First off I'd have to agree with the other guys that you should fully check the function of the ignition system (including the advance) and things like the fuel flow and filters first before interfering with the actual MFI.

Interesting point about your gas station, as a matter of interest what is the RON rating of the fuel you are using? I have to say that the fact that your problems seems to 'go away' when warm bugs me.

Anyway I just wanted to say that I have the factory manual (MBNA) as do a lot of guys on here, so if you get stuck for tech data (ignition settings etc) just give me a shout.

Cheers

[Arthur Dalton]

<>

Low dwell is larger point gap, high is smaller gap.

[Mr Basil]

Hi and thanks to everybody replying

Seems like a pretty great forum.

Fuel injection is brand new to me (in the hands-on sense). I'm used to setting the points with a feeler guage and the timing and carburation (idle) by "ear" on my old International trucks. They'll run pretty well even if you are off quite a bit from the optimum.
Still, I look forward to learning. I have a E-bay service manual on the way, but I just bought it minutes ago so it won't be here for awhile....

Jengasan, if you don't mind sharing some info, it will fall on welcome ears!
Yes, it's a six, mfi. I guess I need to know the favored plug #, plug gap, points gap, timing procedure ( I have TL, tach/dwell meter... sounds like I need a fuel flow meter...), fuel flow metering procedure, dwell angle, idle rpm, and anything else?

Thanks again!

I think it may be a tad rich by the way it sounds going down steep hills with the foot off the gas-like an occasional well muffled backfire- but... my ears are virginal. I can't really check mph until I figure where to vent the gas tank, PO had two lines (from the side of the fill tube) opening in the trunk, I'm not filling it past 3/4 (after my first stinky fill up). I was going to wait until I got the manual to figure out where to run the lines (currently short cut-off rubber) but I can hardly wait to find where they are supposed to go, so I don't mind if someone can tell me.

Basil

[wbain5280]

Those lines go to a small plastic cup on the left side of the tail area, at least on my 220S they do. Yours should be similar.

You may have to overhaul the fuel line system Be aware, Bosch mechanical fuel injection is similar to a diesel pump. The fuel must be clean and the filters in place. There is a large filter in a canister attached to the left, drivers side, of the engine mount. The fuel pump also has a small filter in it.

Here's a link to the SL forum. The car's systems and mechanicals are similar.

http://www.sl113.org/articles/default.asp

You must not adjust any of the linkage stops. They do not adjust the idle speed. Idle speed is adjsted by the air bypass screw on the intake manifold and the fuel governot adjusting knob on the back of the FI pump. NEVER move the knurled knob when the engine is running.

Make sure the FI pump has enough oil. Earlier models need oil added and changed, later models use engine oil.

The front suspension, driveshaft and rear axle need to be greased. get a grease gun with a flexible hose and make sure they can be greased. Jiffy Lube will hate you.

There are various switches on the FI pump for fuel cutoff on decelration. It may need some adjustment.

More later.

[wbain5280]

when starting a HOT engine, turn the key on for 5 seconds then start. Fresh fuel needs to replace the vaporized fuel in the FI pump.

Here's another link to the Russian parts catalog.

http://www.detali.ru/cat/oem_mb0.asp?TP=1

and your car:

http://www.detali.ru/cat/oem_mb1.asp?TP=1&F=108018&VIN=

for example:

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=108018&M=130%2E980&CT=M&cat=230&SID=07&SGR=001&SGN=01

and the fuel tank you had questions about:

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=108018&M=130%2E980&CT=F&cat=232&SID=47&SGR=001&SGN=01

The front axle including the grease zerk fittings:

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=108018&M=130%2E980&CT=F&cat=232&SID=33&SGR=001&SGN=01

[Arthur Dalton]

<>

Yes , you do.
It consist of a clear plastic hose and a container.

Take the fuel feed line off at the CSV and put the hose on the line. Drop the other end in a measure container and turn the key on for 15 seconds... measure the amout of fuel in the container..should be 1 litre.
The reason for the CLEAR hose is so you can also monitor the flow for air bubbles ..there should br none.
It is recommended to do flow test with a 1/2 tank gas.
If this test fails , try same test using the feed line at the fuel filter. If this passes , the filter is plugged...if that test fails, one of the screens may be plugged ..there is one in the tank [ hex plug at bottom of tank]and one in the fuel pump inlet port. These are common problem areas on MFI, mainly due to crap in the old tank.

[Jengasan]

Hi

Ok acccording to what I have here you need:

1968 280SE/8

Engine - M130 (130.980 high octane or 130.984 low octane)

Firing order 1 - 5 - 3 - 6 - 2 - 4

DWELL (with standard coil) adjusting value 40° ± 1° for NEW points
DWELL (with standard coil) inspection value 34°-41° for USED (in service) points
DWELL change between idle and 3000rpm max. ± 3°
Min. Gap of points in mm = 0.3

DWELL (with Transistorised coil - should be blue with finned switch unit and two series resistors) Inspection and Adjusting value at idle 30°-36°
DWELL change between idle and 3000rpm max. ± 3°
Min. Gap of points in mm = 0.4

Timing (assuming US Emission Control model year '68/69)
Adjusting value of dsitributer WITHOUT vacuum at 4500rpm - 30°

Using strobe, with vacuum 3° ± 1° ATDC at idle speed and
12°-19° at 1500rpm.

Forgive me I'm still trying to find the spark plug table ! being Mercedes Benz, there are of course about 3 pages of explanitory notes and exceptions for the above but I think that lot should do you. I reckon your engine is a 130.984 high octane but you can check on the plate, if it is give it the good stuff and it will definately run better ! (I'm remembering your comments about a certain gas station). I've also assumed you have the USA emission control system. I'll get back to you when/if I find the plug data - good luck !

Jengasan

[Mr Basil]

Hi,
I should be able to check some things tomorrow. I am not sure if the engine is high or low octane. Jamb plate is missing. Engine casting reads: 3-9.5E 130 016 0001
(???)
I've been using octane 87 from the PO's advice (he didn't strike me as an expert, however). Problem seems about the same even though I've changed gas stations.
What does CSV stand for?
I'll check the dwell in an idle moment (what is idle speed anyway?).
When using the strobe, do I clamp to #1 plug wire? (It's #8 on my old IHC trucks).
Thanks again for all the help, it's fun to have minor problems to work on instead of serious ones!
Basil

[Jengasan]

Hello again

Sorry I'm at work again so it'll have to wait a few hours before I can give you good answers however, using a strobe you should clamp number 1 HT lead. I believe Arthur is refereing to the Cold Start Valve but I'm not sure where that is on a six with MFI. Give me till later (Scottish time) and I'll look up the stuff. I'm tempted to say idle is 700-750 like mine but I've got a V8 so that's probably a bit low for a six, leave it with me. I have a niggle about that engine number too, it doesn't sound like a US emission control version (which is probably a good thing for power...don't tell Mr Schwarzenegger I said that!) but it was late last night so I may have missread something.

Cheers