88 300TE hot misfire help needed.
 

My sons 1988 300TE has a misfire, but only when really hot.
Once the car is moving and above 2000 rpm, I cant feel it... but it maybe there. It only seems to happen at 85/90C reading on the gauge... and only afer that temp is sustained for a while.

Changed the OVP and that cured a stalling issue.
Changed the sparkplugs yesterday, leads, rotor and cap are all recent.
Duty cycle I have varied from about 50% to about 75% without change.
Plan to replace all of the intake vacum hoses soon, and Fuel filter.

Couple of questions....
This car does not have an Air Temp sensor on the intake hose... there is a hole for it but no sensor... is that right?
It also only has one fuel pump, that I can see, There is supposed to be a fuel cooler inline. I read that there was an issue with fuel vaporisation in the line near the engine, that uses the A/C line to cool, but the A/C is not working, at this time.
I also read that the that the twin pump setup was added and cured this.
Anyone have any ideas?

300te
 

on the wagon only the fuel pumps are not mounted together.one of the pumps is mounted further back follow the input line to the pump[ you can see under the cover where the filter is] back towards the rear bumper. david poole e. p. dallas tx.

Merk...are you referrring to an air sensor that attaches to the plastic air intake "snorkel" that goes from the air filter houseing to the front of the car, by the left headlight assembly?

If yes, then no...

What I mean is that the air intake sensor was not used in the W124 until 1990 and on (even though there is a perfectly good "hole" to attach it).

Follow the link below...I once had the same question.

http://www.peachparts.com/shopforum/showthread.php?t=148611

I think that your car has two fuel pumps.

Like the other writer stated, just follow the lines...

Follow the link below...

http://www.performanceproducts4benz.com/Drawings.aspx?bmid=70

Or check these links...

http://mb.braingears.com/124_DISC1/Program/Engine/LHIS/47-0005.pdf

http://mb.braingears.com/124_DISC1/Program/Engine/103/Prog_Repairs/comb1.pdf

http://mb.braingears.com/124_DISC1/Program/Engine/103/Prog_Repairs/comb4.pdf

This lastlink should be particularly helpful in answering your fuel pumpquestion. Read the NOTE on page 5 of 6.

http://mb.braingears.com/124_DISC1/Program/Engine/103/07.3-0266.pdf

Have a good weekend. I am leaving early today to go kayaking with my son. I hope I don't drown...or become a snack for a hungry shark...from a distance, a myopic shark may confuse me with a tasty, chubby seal...

I see from your other post you were not Sharksnaks...:D

I will look for the other pump...
I read your post about the air temp sensor and it was funny cos I read that too before posting!
More later!

Kayaking is fun, when the waters are not too rough. We are planning an excursion to the Channel islands...but I have to improve on my "in-and-out" technique before I go out on more ambitious treks.

No sharks...but a few dolphins.

Update
 

We have the A/C working....
We changed the fuel filter... listened to the two pumps... sounded OK.
We also changed the 2 large vacuum hoses from the Idle Control Valve and the hoses from the inlet manifold to valve cover.

No change... its still runs rough and misfires when hot... the hotter it gets the worse it gets...

What is next?
Check fuel pressure?
Check Spark Coil?
Ideas please!

bad coil?
 

If your ignition coil, has a metal stamped laminated center section, try a new coil. The newer version has a solid cast centerbody. Try swapping with a known good coil if you can, otherwise for 70 bucks, its another thing that wont go south when you least expect it.

Thanks Dave,
Yes, I am looking at the coil next... I dont know what type I have until the boy gets home.
The very fact that it plays up when hot.... when I mean hot, I mean when the underhood temp is up.... if you travel at speed and the engine bay is cooled it doesnt do it so bad.... if I remember correctly!
I planned to try a Ice pack on the coil itself when it is doing it... you know, one of those gel packs... see if taking the coil temp down will make it stop misfiring. That should be an interesting experiment!

Here is a pic of the coil.....
Are these the problematic ones?

http://img.photobucket.com/albums/v2.../dad/CoilE.jpg

Merkey:

I have that same coil. I think I still have the original coil.

The new ones for sale are different, so I plan sometime this week to do the ice pac and see what happens...
When I can pin that boy down that is!:rolleyes:

Well, we did the ice pack thing...
It did seem to improve it slightly, but that could have been a coincidence.
He is keen to buy a new coil.
Since we fixed the A/C it has put a larger thermal load on the cooling, and I feel it has got worse.
If you stp the car for 10 mins, it gets better until the engine is reading 90deg and then it starts again.

300te
 

this is beginning to sound like the flywheel pickup needs replacing.they are known to be affected by heat[and age] should be a single wire plug into the top of the ignition module on inner left fender,with the wire running back towards transmission.if original the cable will be green.let me know. david poole european performance dallas tx.

Thanks for the input David...
Looks like you have experience on this... why would it be the flywheel pickup?
What are the signs of it failing?

I will look at the car... when I see him in the daylight again!:rolleyes:

300te
 

i have seen this pickup go intermittent before.it supplies a signal to the ignition brain to tell it exactly where the engine is so that spark can happen at the correct time or in your case happen at all.i think its time that you find out whether you lose spark or fuel when the car shuts down.now this is tricky because there is a signal called "td" produced by the ignition unit that keeps the fuel pump in after start so you need to check first for spark when the car quits.if you have spark the the culprit could be the fuel pump relay or the absence of a "td" signal to keep it turned on.let me know. david poole european performance dallas tx.