'88 300TE SSS ideas? - PeachParts Mercedes-Benz Forum

Merkey · #1 05-23-2006, 10:53 AM

I have searched and read all I can see.

1988 300TE with 64,000 miles.
A/C not working.

Starts fine, runs fine until 85deg is showing, and then begins irratic misfire that shakes the whole car. Not constant, sometimes 3 secs betweeen misses and sometimes 10 secs.
The car is also alway very sluggish at low rpm.
Normal idle speed is showing 750/800rpm. When the miss happens, that idle drops by 100/200 rpm. Economy gauge normally reads halfway between the stop and the start of the red section.
It has stalled once in this condition but started again instantly.

Yesterday it did something different.
First thing was that the battery was dead. I think it was the alarm. I charged it for a while, disconnected the alarm under the carpet and it started instantly.

When I drove it, I noticed the miss was a little harsher, I was sitting waiting for my son, and I watched as over a few mins the idle speed crept up to 1000rpm...I noticed that the economy gauge was pinned to the left stop... ie max vac..... then "boom" the engine just quit.
No miss and stall, it was lights out, like I had turned off the key!
I restarted it and it fired instantly.
The idle resumed at 1000rpm and after a min or so it repeated the same thing.
It restarted instantly again.
Just after the 3 time it did this my son arrived and we drove away.
The miss and stumble was all the way up the rev range and continued all the way home.

I knew that the car had an issue like this, but am pretty handy, so was not put off.
I do know that I may have a vac leak as there appears to be a pipe missing from the valve cover to air filter housing pipe.
The OVR has not been replaced according to the bills I have, but the fuel injectors have, as has the potentiometer, ignition leads, cap and rotor.
The car sat for 12 years or so from 1990 to 2002, and failed its first smog badly.
Its most recent smog it only just passed.... HC was on the max at 105 and 81PPM. The PO said it was missing when it was tested.
I listened to the fuel pump/pumps and they sound a little odd to my ear. Kinda "gritty", not like I know Bosch pumps normally sound, but if there are two, maybe its me.

So, I know this is common, but with so much info, where should I start?
OVR?
Idle control?
Ignition system?
Vac system?
Fuel filters/pumps/relay?
Mixture?

I guess I need some help with the priorities to figure this out?

mbdoc · #2 05-23-2006, 12:03 PM

You need to see if the O2 sensor is working & if the Lamda (duty cycle) is adjusted properly...

OF course the engine should have a GOOD secondary ignition tune-up OR scopped to make sure that it is in good order...coil output is very important on a HOT CIS engine.

GVB · #3 05-23-2006, 12:11 PM

Replace the cap, rotor, wires with good brand, not Bosh, and most important, replace the distributor cap o-ring seal. Sound like you have bad ignition to me.

Merkey · #4 05-23-2006, 04:00 PM

Thanks for the responses.
The secondary ignition system looks like it was done, but I will look at the bills tonight and see what make they were.
The O2 senser was replaced recently... I assume cos I see a bill for the part!

I agree that it sounds like an ignition issue because of the suddeness of the stall.
I am new to MB, but have a quite a lot of mechanical experience, so what tools will I need to check the duty cycle? I have a good analog multimeter, but love tools, and always prefer to buy and invest in stuff that pays back over time!
Or would it be better/cost effective to just take it to my local Indie?
It seems from a lot of the posts that this issue is difficult, expensive and hit and miss even using the Indie!

Should I order a new OVP?

Merkey · #5 05-25-2006, 11:14 AM

I took off the airfilter and looked all around, could not see any loose connectors or vac cables. Looked at all the vac lines and the vac tube to the IAC, all looked ok.
Here is a pic.

I pulled the cable from the IAC and the revs went up from 750ish to 1000...
When I pushed the connector back on the engine stalled straight away... is that normal?

GVB · #6 05-25-2006, 11:41 AM

Yes. Thats a good sighn. You need to visably look at the ignition system. Even if the cap was replaced, No one, for some reason, never changes the o=ring that seals the cap from moisture, and then it ruins the new cap.

BENZ-LGB · #7 05-25-2006, 01:31 PM

Merkey:

This weekend I will take pictures of my 300TE engine, from the same perspective so that you can do a comparo.

I will also take a picture form the other side, so you can see whether there are any plumbing differences between the two engines.

In your picture I can't see the thin hose leading up to the big, fat breather hose.

BTW, while you have the air cleaner assembly off, you may want to clean and lube the throtle linkage.

Your engine looks very clean, reflecting its low mileage