1989 300TE stumble/hesitating/hiccup - PeachParts Mercedes-Benz Forum

dka-66 · #1 04-01-2012, 10:51 AM

My 89' 300TE has stumble/hesitation/hiccup (not sure how to actually define it) under hard acceleration, it seems to happen in the 1000 to 2000 RPM range and as far as I can tell it happen happens around 1200 and 1700 RPM........Also, every once in a while under hard acceleration it bogs down but above the 2000 RPM point it will accelerate fine.
It does not seem to make any difference if it is hot or cold, it may be slightly better at the first start of the day.

It has new Beru plugs, Beru wires, distributor cap and had the head off for a head gasket, valve guides, and valve seals.

What would be the best place to start looking? I have found threads for stmbling, hesitation, and hiccups but I cannot find any threads that match what my wagon is doing.

JamesDean · #2 04-02-2012, 11:48 AM

Perhaps its related to fuel quality? or a dirty fuel filter?

fdm_alex · #3 04-05-2012, 01:05 PM

Did you use copper core plugs? Was the base fuel mixture at hot idle reset after the head job?

dka-66 · #4 04-07-2012, 09:00 PM

I use 92 octane Chevron or Shell and recently put in some Techron hoping (but not believing) that it would clear up, The fuel filter is one thing that was on my "to do" list but somehow missed....can't believe I forgot.
I believe the plugs are copper core, I put a empty plug box in my MB file so I would know what to order next time, So I will check it out and get back with the answer.

And finally......NO, I did not reset the base fuel mixture at hot idle after completing the head job. Can you point me to the right place that would go over this procedure? I tried finding information on if there were things that needed to be done once everything was back together. Maybe you (fdm alex) if you have some time, could let me know what I am missing or point me in the right direction? I would be perfectly happy with a list of procedures/jobs that get done after a job like that and I can take it from there with figuring out the rest.

fdm_alex · #5 04-11-2012, 06:31 PM

Sorry, been away a few days here. So, Bosch makes an official tool to set those, but I haven't ever been able to find one outside of the dealers, not even a replica on eBay or anything. It really kind of pisses me off, I'd like to have one very much...

Anyhow, what I have done in the past and had work relatively well is to get a really good digital voltmeter with a fast sampling rate. There is a small round plug on the left fender near the EZL with a screw cover on it, open this and plug one lead to pin 9 and one to chassis ground. with the engine at no load idle and at full operating temp, watch your meter reading. It should roam back and forth from about -.070 to +.070 or close to that. You adjust it from the tower that's between the air intake horn and the fuel distributor, it's a 3mm allen way down in there, and it's spring loaded, so you need to press down in order to turn it and be careful letting it go so you don't lose your wrench down the intake. Adjust it just a little at a time, and blip the throttle between adjustments to even it out. Clockwise makes it richer, counter makes it leaner. You should end up with a smooth idle and instant response to revving it out.

Another, lower tech, way is to get a good but very light magnet (a pocket screwdriver works well) and put it on the throttle plate. Adjust until it runs very well and bogs down if you push down on or pull up on the magnet at all.

Both of these have worked for me in the past, though they aren't perfect, you can get the mixture set pretty close.

fdm_alex · #6 04-12-2012, 10:08 PM

Thought of something else today, it should have hit me right away but somehow it just didn't register... Are you certain that you have the timing correct? I assume you had the cam gear removed when you took off the head, because you kind of have to. If the chain slipped a tooth on the sprocket it would do almost exactly what you have described in the first post.

dka-66 · #7 04-13-2012, 08:28 PM

Sorry for the length of the post, I have a few things to mention. Interesting update, at least I think so. I was out earlier driving to the hardware store and heard a noise that was metallic and thought it might be the water pump (it's new though), a/c, alternator, or something like that...Got out checked and could not find anything wrong so I got it home (a few miles away) and checked, got out a stethoscope and did some more checking and came up with nothing, crawled underneath and there was my crank damper in pieces. So now I get to work on that before I can continue.

I cannot believe I missed (forgot) this detail..... I thought I used the Beru plugs that I read about but it was taking way to long to get them so I bought some Bosch plugs when I put my order in at one of the more popular Benz parts places (not sure which). Turns out that they are Bosch Super Plus, HR 9 DC+. So how much difference would this make?
In reply to the timing, I did have the cam gear removed because I had a newer cam put on...There was some wear on mine and I had read that if it needed replaced it was best to replace it with a cam from a 90's M1003 (not sure which year right now) because they are supposed to be stronger. Not sure how true it is....I just read it on the internet. I did make sure I was at TDC and the cam was lined up properly as well as using the correct bolt holes for the gear.....Now I do have to be honest that my method for finding top dead center was not what the Mercedes program said but I was told by a MB mechanic that it would work perfectly fine, I did the dowel through the plug hole method. I hope I did not mess up by following those directions.