89 300TE poor performance during warm-up - PeachParts Mercedes-Benz Forum

fdm_alex · #1 04-03-2012, 06:09 PM

Hi. My wagon is doing poorly on warm-up cycle. It lacks all performance between about 15*--80*C. Once the CIS unit shuts off at full warm it runs fine. It isn't the computer, I tried another one in it. I have checked all of the wiring for the temp. switch from switch to CIS to fuel pump relay to EZL, all okay. The switch reads about 290ohm at full warm, I haven't had a chance to check it cold yet.
The mixture is set correctly for warm running, it seems if I set it up rich it will counteract the warm-up problems, but then economy goes way down and such. Not an acceptable fix anyhow. I changed the cold start valve last winter and I assume it's still okay. I checked the other morning and it seemed that it wasn't getting signal at start-up or cold run, I checked the wiring back to the fuel pump relay and also to ground and it's okay.
I'm pretty much stumped and that doesn't happen much. At least it's my car and I don't have a customer biting down my neck for it...

Any help is appreciated,
Alex

mbdoc · #2 04-04-2012, 08:27 AM

That is a somewhat common problem.
IF the secondary ignition system is in GREAT condition..

Then try adding a 300-400 ohm resistor to the coolant temp sensor wire
OR try adjusting the EHA basic setting by 1/6 turn colckwise.

The second step does require removal of the EHA & that means gas will come out,
DO that with rags around & under it and ONLY with a cold engine that is SHUT off,
NOT running!!

fdm_alex · #3 04-04-2012, 02:43 PM

Thanks for the tip mbdoc. All the secondary is new within 12mos., all Bosch. I reset the EHA this morning, seems to have helped some. I will continue to tinker with it tomorrow, feels like it may need a bit more. It's getting harder to tell as the weather gets warmer, doesn't stay in warm-up cycle as long...

fdm_alex · #4 04-05-2012, 02:41 PM

From my understanding of the old CIS-E system (they had pretty much stopped teaching it by the time I went through factory training, but between a service writer who disliked me and going independent I got the immersion style training), and the wiring diagrams for the system, I am basically setting the internal resistance of the EHA by adjusting the screw.
So two questions:
1- Is this assumption correct?
2- If so, is there a good base spec. to set it to with my ohmmeter hooked up?

Thanks again!

ps2cho · #5 04-08-2012, 03:55 AM

Check coolant temperature sensor as MBDoc stated.

Try this first -- disconnect it completely and see if anything changes other than the CEL. My experience on two occasions with the CTS is that it makes piss poor performance cold, but once warm, it makes no difference at all.

I know because I broke the pole on it. The difference was immediately noticeable while I waited for the new one to come in the mail.

Also, what's condition of O2 sensor? Could be sluggish warming up...

fdm_alex · #6 04-11-2012, 06:20 PM

I unplugged the sensor a couple of days ago. If it isn't so cold out that it just plain stalls out, it takes about two minutes of rough running, then it seems to go to default value and run fine all the way through warm-up and into hot cycle. The reason these never matter warm is that the CIS controls essentially shut off once it hits full warm operation. In fact, you can unplug the computer entirely without causing any driveability issue. It will even run better that way if your base mixture is way off. I learned all of that through too much first hand experience...

I was going to add a resistor last weekend, but it turned out I am out of both butane for my iron and flux-core solder, so it will have to wait a bit. I'll certainly post once I get if resolved.