Cold miss/hot miss M117 - PeachParts Mercedes-Benz Forum

MikeTangas · #1 02-26-2002, 08:54 PM

This is on the 560SEL.

I had a very slight miss at cold idle, also noticed after yesterdays highway run I have a miss at hot idle too..

I decided the cold miss was ignition timing. Book shows I can set timing without vacuum to between 3-7 BTC, which should yield 12-14 BTC with vacuum. Soon as I got home from work I disconnected the vacuum line to the EZL and attached my vac gauge and timing light. At cold idle was pulling 15" HG, and timing was about 10 BTC. I adjusted timing without vacuum to 5 BTC (can't get much closer to the split of 3-7), vacuum increased to 16" HG. I reconnected the vacuum to EZL and checked timing, and it is now steady at 13 BTC idle, 44 BTC at 3K rpm. Miss at cold idle is gone. Vac gauge applied to the air pump vac line shows 17" HG at idle.

Now for the hot miss. I want to ask if the miss could be temperature dependent? After running 20 miles yesterday, the temp was only about 40dC (but <50 dC). At less than 50dC, the thermo switches don't open to redirect the vacuum. Could a cold running engine cause the hot idle miss, or could it be a combination of the time being a shade off plus the cold temp? Am I even on the right track?

Thanks.

JohninFla · #2 02-26-2002, 09:39 PM

Last question first: I think your thermostat is failed, open. After 20 miles, you should be above 80C. My car 560SEL runs that anyway. If the engine is not hot enough, it won't run right.

Some other things cause rough idle in older V-8's, like injector seals and leaking air hoses. I have not kept up with what you have replaced on the engine, past the timing chain and guides.

Did you notice a steady miss or just rough idle overall? Could be a bad plug wire end also. Might take some messing around, pulling wires to isolate?

Not much help, I know. Good luck.

MikeTangas · #3 02-26-2002, 10:47 PM

John,

After seeing the low temp at the end of the 20 mile run, I came to the conclusion the t-stat was stuck open or missing. I received my new t-stat and expansion tank cap today (along with my tires and oil pressure sender), and hope to do a coolant flush with new hoses and t-stat this weekend.

The miss at cold idle was erratic, not steady so I ruled out a mechanical miss. Since getting the timing dialed in this afternoon the cold miss seems to be taken care of, I'll wait until I get the engine temp up to par and see how the hot idle is looking.

I guess I was looking for verification of my methodology.

JohninFla · #4 02-27-2002, 12:23 PM

The bad news is you will wish you did the T-stat when you did the timing chain, as you were right there!

Also, I agree with your thinking, but no guarantee that thinking the way I think is a good thing.

Good luck, keep chipping away at it!

stevebfl · #5 02-27-2002, 12:40 PM

Just to confuse the issue, I will mention that the timing is NOT adjustable on 86-on V8s. You are second in two weeks to say they did. I am not sure what is happening but spark is controlled by mapped calculation and a crank position sensor not distributor position.

My first mechanism for locating a single cylinder misfire is to use a 12mm open end wrench to loosen injector lines at the fuel distributor one line at a time (soak up fuel with a rag - not much will come out if done quickly). Feel the contribution of each cylinder as they are killed. This is similar to pulling plug wires without the shocking experience.

Common vac leak can occur down the back side of the motor where the vacuum source for the transmission modulator hooks to intake.

MikeTangas · #6 02-27-2002, 01:24 PM

Not to deny that the timing is electrically controlled, but by disconnecting and plugging the vac line to the EZL I was able to drop the timing to 5BTC at the distributor. I will quantify or qualify, that the timing did not adjust to 5BTC immediately as it would on the 4.5, but after a slight rise in RPMs, when the engine dropped back to idle the timing dropped from 10BTC to 5BTC and stayed steady.

The 117 manual shows distributor timing for both with and without vacuum - with vac is something like 12-14BTC, with out 3-7BTC (both at idle). Based on that I would think there must be some adjustment ability at the distributor. I will check and see if there is an "up to date" notation that I might have missed.

After I put the tires on tonight I'll put the light on her and see if the readings are the same as yesterdays.

I will also check that vac line for the modulator. What kind of vacuum should I be seeing at idle? I thought 17" was doing pretty good.

As always, thanks.

DJNEWK2 · #7 02-27-2002, 03:20 PM

hey Mike,
Sorry to add a stupid question, but did you replace with new wires? Mine has just recently started to idle just a bit rough (not as bad as it was) and I've heard of the engine starting to run a little rough once its warm if the wires are going or gone. I replaced my wires (but they were from another 560 SEL that LOOKED okay and not neccesarily still good) but plan on getting a New set from Fastlane today.My baby runs at about 80C once she's warm. I had a slight cold idle a while back but the cold start valve I replaced pretty much cured that... my $.02

P.S. What kind/size of tire did you decide to go with anyway?

Alan

MikeTangas · #8 02-27-2002, 10:11 PM

Cold this afternoon, no miss. Timing is exactly as it was last night ~13BTC with vacuum to the EZL, 5BTC without. Will wait to see how this are after I do the coolant flush and T-stat this weekend. Going to see if the cool engine temp is causing the miss.

No I didn't do the wires, will look into wires/ends and injectors if the miss is still there after getting up to proper temp.

DJ, I went with the Avid H-4's 215/60/15, almost the same size as the 205/65/15, something like .02MPH difference. Look nice and rode nice this afternoon.

Car is looking much better.

MikeTangas · #9 02-28-2002, 01:18 AM

In my constant quest for learning and bringing this 560 back to the driven world I just couldn't let it rest for the evening (besides, everyone at the house is feeling bunky and hit the rack way early). I read through a number of OVP posts, with one asking about what was causing poor running after getting up to temp, OVP was the suggested remedy.

I went and checked my rather large box of extra parts, and sure enough I had a couple three OVP's in there

. I found one with a build date of 1996, then pulled the OVP from the socket and compared the two. The one in the car "looked" old, had no build date and the flip top was mounted 180* out from the 1996 version. Thought what the hey, replaced the fuse and swapped them out. Then went for a 10 mile drive to get the engine as warm as I could. Got home and the hot idle miss was almost imperceptable, but still there.

Even felt like it was running smoother at speed. I'll admit, I have probably about 50 miles in this car now, not nearly enough to notice subtle improvements, but it sure felt better.

We'll see if the planned work for this weekend cures the last of the miss. Well, I better get ready for the rack myself, gotta go to work so I can continue to feed my habit.

stevebfl · #10 02-28-2002, 08:46 AM

The vacuum is an input to the controller and of course changes the timing. Moving the distributor should not. Other than changing reference resistors where aplicable (or altering the vacuum signal) there is no way to positively afffect timing. I say positively because (for those who think they have) the only thing that moving the distributer does is creat a booster gap by not having the spark occur while pointing at the terminal it is supposed to leave on. This condition will eventually lead to the destruction of a relatively indestructable cap and rotor. It could I suppose look like a timing change as the booster gap could alter idle performance and manifold vacuum thus changing timing. Who knows the controllers on these things just sit there, they never go bad and most of us never even diagnose their strategies. They might have a mapped strategy to alter timing as the secondary kv changes versus manifold vacuum.

The timing IS NOT adjustable.

#11 02-28-2002, 09:41 AM

Steve or Mike: this is going to sound really stupid - but please remember - I work mainly on diesel. I will be doing my rails in my 88 560sel this spring. When the distributor is removed from the car - how do you know how to put it back in in the proper position? To clarify - if I lift the distributor out and I use a bolt or something on the intake manifold as a guide to visually see where, say #1 plug terminal on distributor is and mark this down, then when I put the distributor back in make sure the alignment of the terminal is about the same in relation to the bolt or whatever I eyeballed as a guide. Is this close enough for proper distributor alignment? I hope I am explaining this right. Again - this may sound stupid - how do I know if I put the distributor back in the right position. Injection pump timing and cam timing - no problem - this is new to me.
Thanks - and my apologies for not not knowing something which I have the feeling will be real easy once you know.

stevebfl · #12 02-28-2002, 10:35 AM

The distributor on the V8 has a gear drive. You can put it in with a certain number of combinations (due to the number of gear teeth). I used to mark the "housing to cover" alignment with a scratch or dab of paint. I would not worry where the motor was, I would take a felt pen and mark somewhere the direction the rotor was pointing. Remember that one tooth will change the angle enough that a simple mark will do fine (like I think you are saying).

Since your ask the question I presume your are going to take off the front cover. I would not suggest this unless you have over 300k on the motor. The upper head rails and the tentioning rail are all that are necessary untill the lower right side guide rail wears through well after 300k. If you are taking the cover off I would do everything at TDC.

#13 02-28-2002, 10:49 AM

Thanks Steve - understand now. I am only changing the upper guides like Mike, but I noticed he said he had to remove the distributor to do the driver's side. Hence the question. I must say - diesels are much simpler to work on once you get the hang of them - and no elecronics or elecrical to go wrong!

MikeTangas · #14 02-28-2002, 10:53 AM

Thank you Steve. I thought about what I had seen at the timing light when I moved the distributor. What I decided was, the change I saw was simply the timing settling down to where it should be without vacuum as the engine speed decreased. So from my view it appeared to adjust the timing. And just to keep from ruining a good cap, I will roll her over to TDC this weekend and set the rotor directly on the timing mark at the distributor.

Thanks for clearing that up.

Maurice,if you start with #1 at TDC on a compression stroke, you will see where the rotor points, it should be pointing at a tickmark on the outer edge of the distributor body. Remove one bolt and lift the distributor out. When you roll the chain in and have connected both ends, roll the engine through two complete revolutions (to ensure no piston/valve contact), and finish up at TDC on #1. When you stab the distributor it's a simple matter of setting the distributor in the hole, and meshing the drive gear, if the rotor doesn't point at the tick mark lift slightly and move the rotor in the direction of the mark then set the distributor back down. Easiest distributor I have ever stabbed.

#15 02-28-2002, 11:15 AM

Thanks Mike - We changed the tining chain last year - so all I have to do is the guides. Sounding simplier as time goes on - last year was scared stiff to attempt - now feeling pretty confident. Will post when I start in about 2 months when it gets warmer (Today was -40C with wind chill)

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