I would hope that I am not demanding too much from my recently acquired 87 SEL with 129K on the clock. When I bought the car it had a horrible idle. It would pop and sputter w/o any particular rhythm. What I have done thus far are the following:
- Replaced pumps, fuel filter and every single rubber fuel line.
- Removed all injectors and cleaned them with acetone using a pump that I purchased from mercedesource.com. It did work really well. There were all clogged and running acetone revived 7 out of the 8. So I replaced a 1 injector
- I could tell that the ignition wires, rotor and cap were brand new so no changes there.
- I installed brand new spark plugs - Bosch WR9DC +. The car had Champion N9YC spark plugs and 2 Bosch WR9DC+ w/o the cap removed from the electrode connector. So I know, for a fact, that the spark plugs could not have fit the injector and were touching - probably the main cause of the "misfire". I since learned that these are resistor spark plugs and folks recommend not using them even though every single online parts outfit claims it is correct for this vehicle. What gives here??
- I installed fuel pressure gauges in the feed and return lines 95PSI going in (unregulated pressure from fuel pumps) and about 38PSI coming out of the fuel distributor.
The idle improved *dramatically* but not quite to my liking. I did buy another 7 injectors but have not installed them yet.
The video of the improved idle is shown below. It may be hard to tell that is it not perfect but here it is nevertheless.
It is not clear how to edit a post but what I was trying to describe above is that two of the spark plug wires were not hooked to the spark plugs (not injectors) because of fact that the electrode cover had not been removed.
It is hard to tell that the idle isn't exactly right from the video. It sounds high but the tach looks good.
You seem to be at a point where you're just refining, not trying to find a big problem. So I'd suggest getting the proper plugs which are W9DC or DC0. They are very reasonable from the dealer. This might fix the final unevenness but at least you'd have the right plugs in the car. Yes, all the online places say the resistor plug is right but they're wrong.
You might also do the dark test on the wires. Put the car in total darkness and watch for flashes along any of the plug wires or coil wire. Even though they're new.
Definitely into refining mode - no major idle issue. Yes this is my shop in the back of my house.
I just bought NGK BP5ES (7832) and will be installing them tomorrow. I ohmed them out at about 0.3 Ohms. The WD9DC+ ohmed out at 5.4 KOhms. I shall report tomorrow.
I replaced all the spark plugs and I am seeing a marginal improvement. There is definitely a miss. Next step is to hook up my PICO scope and identify the cylinder that has the combustion problem @ idle and go from there.
The gap on the NGKs were all at around 0.037" and I left them alone. I can't imagine going to 0.040 - 0.042 would make much of a difference?
Also I replaced all injectors with Bosch injectors and the idle quality is the same.
I think it is time to pack it in, drive the car and enjoy it for a while before I figure out my next move..... besides, there are other things to do: coolant flush and refill, tranny fluid replacement and rear differential fluid replacement. This should bring the car up-to-snuff and to a daily driver status (I hope!).
I put around 200 miles on the car and the slight, random miss still persists. It looks like I have a weak fan clutch (I got one on order) which forces the engine to run hotter than normal (between 100 - 110C). So, when I come home from work in hot Texas weather with the A/C on and park the car with engine temperature approaching 110C and jump out to put my hand over the exhaust, I detect *PURRFECT*, glassy idle. Just perfect. Like a new car. Better even.
Of course when I let it sit, to cool a bit, the random, less-then-perfect idle returns. Just like herpes. This is idle ONLY. The performance on the highway is absolutely amazing! Any RPM over 1000 makes the car extremely happy!
Now, I ran into this awesomelly juicy, but old thread that several folks have contributed with symptoms *identical* to mine that have done a hell of a lot more parts replacement than I did and still got no relief... except one: replacing the coil fixed his sub-optimal idle. My personal experience with ignition coils on other cars is that if they are marginal, they tend to misbehave/fail with heat. I am just throwing it out there.
What is the protocol on zombie-ing up a thread? Frowned upon? Only 4 years old but its life span may have been 2 years....
That old thread has lots of pages with no resolutions , to keep from chasing ghosts do a compression test .
Also look for vaccum leaks , after that it literally could be anything , run some injector cleaner for a few tanks can't hurt .
I think I failed to mention that I finally went ahead and replaced *all* the injectors with brand new Bosch units from Pelican. My next steps are as follows:
- Smoke test the intake. I do have access to an automotive smoke machine. If that does not reveal anything then:
- Cylinder Compression test
Yes, good point. I have used SeaFoam in the past with fairly good success on my classic carburetor cars. Many years ago, I used Lucas Fuel Injector cleaner on my '77 V12, fuel injected Jaguar and I thought it was the s**t. Very noticeable improvement after 2 - 3 tanks with that stuff in. Is there a fuel injector cleaner that any of you swear by for these engines?
Still suggest that you gap the plugs a bit more. Car runs better when its really hot, lets get the gap there from the start. All things electrical on this car, and if one component isn't working, idle thru the management of the data in the ECU is going to try and compensate with air/fuel/pressure. Complex yet primitive and is 30 year old tech. Since the coil converts so much into usable electricity, it should be changed if it is old. Engine ground straps perfect and clean connections. The insulators at the wire ends get brittle and might also be grounding to the engine so check each end for cracks, even new ones could be that way. Look at the engine running in the dark too, may have some arcs that look impressive but robbing the steadiness of idle. My metal covers were tuned in such a way they were quite close to the flange on my Stainless Steel headers, and the blue light show was pretty erie, simple 1/4 turn of the end cured it. One less stupid thing, the O2 sensor is good for maybe 50k, lots of data going to the ECU as well.
^^Louis makes some great points. I'm leaning towards a vacuum leak, so common in our old engines. A smoke test is simple, cheap, and almost infallible in finding them.
Crack in lines and connectors behave differently depending on rpms and/or temperature. Even a tiny one will cause engine problems.
Assume you're a doctor working with an old man with clogged arteries, everything is suspect... vacuum lines, seals, rubber connectors, breather hoses, the donuts between the upper and lower part of the intake manifold, fuel injectors seals, etc, etc...
I am sure I shall have some updates this weekend. I will add the "checking random sparks in the engine bay in the dark" test. If I end up doing the compression test, I shall re-gap the plugs to 0.042" as previously suggested.
Clean your battery ground and it's connection to the frame , many older cars have dirty and weak grounds , never a bad idea to ground the alternator to the battery ground on the frame .
Also the coil has its own ground , clean it if you ever replace the coil.
So I hooked up the smoke machine in the intake manifold where the vacuum line for the brake booster would normally connect. Besides smoke from the air intake, which is expected, I detected smoke coming from the injector seals for injectors #2, #6 and $7. All injector seals, o-rings, injector holders, air distribution lines and injectors themselves are brand new. Air distribution lines are authentic mercedes parts but the seals, o-rings and injector holdersare OEM from Pelican. I reseated injector #2 and that got rid of the smoke... not so much with #6. Running out of time for tonight.
Would it make sense to seal those seals with some additional material - gasket sealer or something along those lines or did I get a batch of bad seals/o-rings/injector holders?
I did block the air intake so as to better determine the leaks. Essentially the same places - injector seals, including injector #2 seal which I thought was resolved yesterday. This cannot possibly be normal, correct? During engine operation, un-metered air goes into the cylinders creating a lean condition manifesting itself as rough idle. The engine warms up, the plastics expand and seal and that is why I then have perfect idle. It all falls in place. My puzzlement is how could brand new parts be so f***d? Or am I doing something wrong??
You know what they say... an engine is a big air pump. As far as the parts, many brands fail in the rubber department, if they are original MB then installation may be the issue.
At least now you're moving in the right direction.
Yuppers. I switched injector #2 with seal (leaking) with injector #3 (non-leaking) and the leak persists on the injector #2 cavity. So, the natural conclusion is injector holder, injector holder o-ring at the bottom of the injector holder or installation error which carries a higher than normal probability in this particular circumstance.
I am removing / inspecting / reseating everything. Stay tuned.
On injector #2, sure s**t the injector holder o-ring was buggered. Prolly installation error. I compared that o-ring with a set of fresh o-rings I had and realized that the fresh set were a tat smaller and a tat thicker. I replaced all those o-rings. This fixed injector #2 for good. Injector #7? Not so munch.
I swapped #7 with #5, I smoked tested the individual injector holders with the injectors and everything checked out ok. The leak from injector cavity #7 was substantial and f*ing persistent. I blocked off the air hose, the nipples going to the the injector holders.... nothing. A bunch of smoke..... I had flash lights going, reading glasses, the works.
And then it dawned on me..... it is leaking from the mating surface of the lower intake manifold right where the injector is. The intake manifold gasket seemed to be the culprit. I can actually see a small tear protruding from the head/intake manifold mating surface.
This job is done for now.
Once I fix the ABS problem and a freshly discovered SLS pump leak, once I replace the cooling fan clutch and possibly the thermostat I will take the upper and lower intake manifolds and replace the gaskets and donuts and whatever else is lurking down there.... SOB.
That's what I had to do to mine, not difficult or expensive but time consuming.
Protip... take pics and notes as you disassemble, lots of small parts and bolts of different sizes. Good time to replace what I'm sure are rock hard breather hoses lubricate all the throttle connectors, pop the cylinder covers and replace oilers, etc, etc... :grin
Even by fixing just the injector #2 leak, the idle has improved even further!
To give you an idea where this intake manifold gasket tear is, I have the intake off of my 84 SEL. I took a pic of intake #7 to show where the tear is and where the smoke is coming out of.
Add nothing but seats/seals and be sure they are firmly in place. Replace if needed as I get 4 extra due to irregularities like you just said.
Sorry I posted on the phone before refresh. Glad you found your leaking points, and doing all new rubber donuts is best while you are there.
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