Can I pay for Diagnosis for my Misfires?
 

Hi guys,

It has been such a long time and I am honestly getting so sick of my 1988 Mercedes 300TE Misfiring constantly.

Me and my dad have gone through so many things trying to figure this out (he doesn't have a lot of time free to do everything...)

and I just feel this will never be figured out. Fixing it is NO problem! We can do it all..we just can't figure out what the heck the problem is that is causing the misfire!

We have done so far:
* OVP
* Voltage Regulator
* Injector's+Seals (previous owner)
* New Fuses
* Non-Resistor OEM Bosch H9DCO's
* New Bosch Ignition Wires
* Distributor+Cap (previous owners)
* Valve Stem Seals
* Breather Hoses
* I checked for leaky pipes/cracked pipes
* Compression is perfect (1/ 180, 2/ 180, 3/ 185. 4/ 185, 5/ 195, 6/ 190)

Can I just take the car somewhere and have it diagnosed? Do mechanics do this for relatively cheap for like a couple hundred dollars?

I'm on the edge of just buying a new car...but I really don't want to do that. It's embarrassing having other people in the car with me and I avoid it at all costs because the damn thing shakes so much. I've lived with it for 18 months now and I'm drawing the line soon...

Thanks, ps2cho

Have you ever changed the fuel filter?

Check your mixture. If the air/fuel ratio isn't right, it will misfire. Mine is an 88 300TE also. had the same problem.

I have a full oil change every 3000 miles and have changed the fuel filter each time.

Yep we did the mixture and tried all different types of ratios.

I am assuming that this is not a diesel car. You should call some Auto Diagnistic shops and explain you problem and ask what it would cost to find out what is wrong. You do not have to get it repaired by them. They should give you a printout of what they checked and the results.
You also said that the previous owner did somethings. Don't count on that he did a good job or even that it was done (is there paper work on what was done).

He had the receipts for the things he changed. This is the reason why they sold the car to me for $3000 because they put a good $2000-$3000 into parts and the problem still persisted.

If he put that much $ into the car if you can find the problem you should have a good car.
Did he ever take it to an auto diagnostic place?
Engine misses are caused by basic things; wrong fuel mixture (covers air/fuel), wrong timing, no or poor ingition spark and poor compression. What can cause those 4 things to be incorrect can be complicated.
In the old days you were able to check all of these as there was no computer on the car to deal with (and no electronic emission controls either); but now trouble shooting can be a nightmare.
The eingine diagnostic analyzers (that they have in a shop not a hand held one) they have today can even tell you if the compression is bad (they measure the resistance of the spark jumping across the gap high compression = high resistance).
Of course it is your choice. I would at least call a diagnostic center and see what they charge.
Best wishes.

Answer:
 

ShopForum > General Discussion
Good MB Shops
http://www.peachparts.com/shopforum/forumdisplay.php?f=14

Ok got quoted $80 to have it looked at tomorrow morning! So will post back tomorrow afternoon with what happened!

Fingers crossed everybody! I really hope they can figure it out.

There's your problem - you're changing the fuel filter too often. Just kidding - but you are changing it too often - it's a 60,000 mile item.

Sorry your right. I was getting confused with the oil filter I think... I just remember we changed it when we got the car (one of the first things we did). I have another one for a later date.

Ok got it looked at by the local Benz shop...He first adjusted the mixture to the exact place where it should be...He drove it around but ended up not being exact as to where the problem lies.

He put on the notes:
-Test engine found fuel mix to rich
-Adjust fuel mix found kick down
-Cable strut clean and lube cable
-Found rust at Fuel Distributor
-Possible rust inside gas tank

He said in his professional opinion, I should just leave the car alone as it drives fine...it's just the idle that is irratic. But honestly I'm not driving a car that shakes this hard when I pull up to every light.

So you guys think that I should find a nice looking used fuel distributor and replace that first? As for the gas tank, my dad said he can take it into his work and get all the rust off for relatively cheap.

One thing he did while the car was running though...He unscrewed the screws to the Fuel Injectors a little and fluid came out (I am assuming thats the gasoline? Sorry noob)...why did he loosen them? He also was spraying brake cleaner all around the injector lines (I am assuming to check for leaks correct?)

He also said using Costco gas makes the engine rust so use Chevron...I know this isn't the problem...but just wanted to see what you guys also think about that.

I wonder if I will ever be able to get this fixed...

are you sure your motor and transmission mounts are fine?

Yes. The engine is misfiring and it's erratic...it's different every day so it's not the mounts. You can hear it misfiring at idle with the hood up.

He also said using Costco gas makes the engine rust so use Chevron...I know this isn't the problem...what do you guys think about that?

<<Yes. The engine is misfiring and it's erratic...it's different every day so it's not the mounts. You can hear it misfiring at idle with the hood up.>>

Does the engine EVER run smooth at idle, like cold or hot? Or damp days or dry days? Have you tried driving it without the fuel tank cap on? What about misting the plug wires with water in the dark, any external sparks you can cordinate with the misfire? Is the spark plug you mentioned the correct plug for that engine? I know that trying to upgrade plugs, especially Bosch, is NOT a good idea in a Mercedes.

I am betting it is the ignitor, which I believe has a tired capacitor in it.

Good luck, and be sure and let us know what fixes it!

Jim in Phoenix

For the first 5-10 seconds of starting it in the morning it has no misfires...and then it slowly kicks in. After that, there are no correlations between softer/harder misfires. I know before we did the Valve Stem Seals, when the AC was turned on, (aka more engine temperature), it used to misfire harder...but since fixing that, I haven't noticed it shake harder.
It's difficult to say because it differs every day regardless. There is no consistency at all.

Like tonight on the way home from school -- Absolutely beautiful to drive. The power was quick and it felt really responsive. Other days its feels slow to respond and doesn't want to really want to accelerate faster than it has to.

As for the plugs: Yes they are the Bosch H9DCO's. I scowled long and hard for the non-resistor spark plugs (one site claimed to have them but sent me resistor ones(yes very angry when I got them)), until I found mercedesshop had them on special order

You could have it rebuilt . . . or exchanged . . . at "Jaytan". Check MENU#24 toward the bottom for their phone number.

We (Exclusive Motors) sent one to them for rebuilding and it fixed the 'stumbling' in the engine. Prices are reasonable.

Just buying a used one 'could' be ok but it's a crap shoot IMO.

Well I need to have my car in the mean time, so used would be the best option for me. At least if I replaced it with a used...nothing could be worse than I have right now LOL!

I don't understand how he knows that the Fuel Distributor has rust in it...I pulled off the intake and had a look around and I see no rust...?

What I meant was there's two (2) ways . . send yours in to be rebuilt or get a rebuilt one from them w/ your old unit as a core. Prices are on their web site.

I don't think that it has 'rust' in it but they are a 'delicate' machine and get 'plugged' easily. When they plug, the car has a steady miss.

When my 450SL (different car, V8 engine) had an intermittent miss at different speeds, particularly idle, I went through the same process you are determining fuel versus ignition, and after seeing what looked like marginal readings to me on an old Sun LS2000 ignition scope I have, I changed the ballasts and ignition wires on general principle, and then (incorrectly, it turned out) moved on to fuel thinking I had good hot spark on all eight. After quite a bit of head scratching over the fuel injection, I went back and used the old school, old fashioned way of isolating a single cylinder miss and found it was electrical after all. With the car idling, I pulled the plug wires one at a time, listening for whether they changed how it was running. This technique is usually used to isolate whether a single cylinder is completely dead, since the engine will run the same with or without the dead cylinder's ignition wire connected, but in my case I was listening for whether disconnecting some cylinders made it a lot worse while others made it just a little worse. Long story short, I found two different cylinders that made a lot of difference, and then with some horsing around moving whole ignition wires from one cylinder's use to another figured out I had (in my brand new set of factory made to length Bosch replacement ignition wires) not one but two flaky wires. I cut off and remade the plug end on them and the problem was solved. Two morals here. First, if I had taken the car to a shop with a big sensitive ignition scope and a technician who knew how to read it, I am sure the two wire ignition miss would have been visible to a trained eye (even though I couldn't see it on my dim, small LS2000 scope). Second, because my ultimately-ignition-wire fault continued even after changing all the ignition wires, it reminds me that just because a part has been changed doesn't mean it isn't (wasn't) the problem. With other kinds of analysis available, not as many mechanics spend the time to read secondary ignition scopes anymore. Be sure before you rule electrical out entirely that someone has "scoped" the ignition system. A good ignition scope is a good tool for hard to find misses in the right hands. This is the tool "Diesel911" was refering to earlier, and I don't think from your posts that it has necessarily been tried. If you want an idea of what that's all about, look here: http://www.babcox.com/editorial/us/us30224.htm.

Ps2,

I've tracked your car across 3 sites and see no report on your fuel filter condition. Have you determined it's clean or did you remove it and find evidence of tank deposits?

What's the O2 status when out of circuit?

JimF used the term "crap shoot" on the rebuild. He's right, and a proper disclaimer. The car has a troubled history as you've described. Think of what part(s) dates back to the prior owners woes. Things like the F-distrib. do fall in that range but is a guess.

Before ordering a spendy part, you need to recheck the basic stuff. Actual vacuum tests with a gauge. Squirting cans of various products is a method but leaks hide. Fuel pressure readings would be of value.

The O2 sensor is suspicious from contamination how much SeaFoam, Tecroline and other VooDoo chemicals has she drank? Is the EGR valve stuck open? There still are some easy but critical tests.