Hi again!

In my quest to get a neglected '89 300E running properly again, I replaced injectors 2 and 5 last night. Those plugs had powdery black deposits on them while the rest were fine. I had replaced those plugs prior to replacing the injectors, and while the idle did improve over what it was with the fouled plugs, it still wasn't right. The PO said those two plugs would keep fouling on him after driving it for a bit. Injectors were suspect though not definitely the cause - however, they're relatively cheap and easy to replace, so I figured I'd give them a try.

Anyways, that's my preamble...

I replaced the injectors last night and when I started it up, it purred beautifully - much better than I've ever had it running. I did notice, however, some exhaust gases escaping in the engine bay that I'd not seen before. Couldn't identify the exact source. Left the engine idling as I put my tools away, moved my wife's car, etc. As it was starting to warm up I noticed the exhaust leak was no longer visible, and the idle was slightly beginning to suffer. Vacuum gauge was slowly heading towards the red.

Went for a brief drive, and the car was bogging and chugging and lacking power - getting worse and worse the further I went. Barely got it back to the house. When I did, I opened the hood and saw one of the pre-cats(?? Bulbous canister thing right after the exhaust manifold) glowing orange, though the coolant was only up to 65 or so. Engine barely ran, was very reluctant to rev in park. Haven't had a chance to try it again from cold yet.

Could this be indicative of a major exhaust restriction? Could replacing the injectors have caused a change in the A/F ratio enough to exacerbate a problem with the exhaust?

Thanks,
Mark

Just a guess, but I think your cat or pre-cat is gone. Is it original (probably)? How many miles are on the car?

Ever have a cat go? I had one go on my 87 Tbird a looonng time ago. Motor ran fine at idle. Just wouldn't go worth a nickel. Replaced them and problem solved. IIRC, I had about 114,000 mi on it when that happened.

My 87 300CE has 122,200 miles on it and the cat life is one of the things that I always wonder about. That and the timing chain life!

Thanks for the reply. I suspect the same. The car has 199,999.5 miles on it

Not that I would ever advocate such a thing of course, but I wonder how some straight pieces of pipe in their place would affect the running? Don't NA gas engines like some backpressure?

If your plugs are fouling it is due to valve stem seals leaking. Very common.

I hollowed out the precats on my 300TE last year. Can't say I notice a difference. I only did it since they had heated up heavily due to oil consumption via valve stem seals for a long time from the P/O. Sounds same issue as you.

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I agreee with the valve stems seals, especially since the seller daid he had repeated problems with those 2 cylinders. BTDT.

But he still has the problem with the new plugs & injectors in the motor.
The seals should be replaced Heep. Not a big deal. No need to remove the head for that. The seals are very inexpensive, if you are a diyer.
http://catalog.peachparts.com/ShopByVehicle.epc?q=1989-Mercedes--Benz-300e-Engine--Mechanical&yearid=1989%40%401989&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6201%3AED%7C10000013%3AMBC%7C1507%40%40300E&catid=240154%40%40Engine+Mechanical&subcatid=240477@@Valve+Stem+Seal+Kit&mode=PD
If not a good indy will be in the 200-250 range.

I still think you are going to have to address the air/exhaust flow problem, probably in the precat, as discussed. Good luck.

Thanks for the replies - I'll take a look at those valve stem seals. I thought those would leave oily black residue on the plugs instead of powdery black deposits, though?

Post pics of the plugs.

Backpressure is always bad.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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Just pulled the plugs for photos. None of them look particularly good

The engine has not been run since the Tuesday evening drive aforementioned in my first post.

Plug #1 doesn't look too terrible. Slightly wet black.


Plug #2 is very powdery black again.


Plug #3 looks the best, there's actually some non-black metal visible!


Plug #4 doesn't look great. Pretty black but not notably powdery.


Plug #5 looks the worst. Thick powdery black again.


Plug #6 has the most black on it but it's all oily/wet, not powdery.