MyE28.com

Is the coding plug in the OBC? Does it affect the tach? How do I check the plug?

Thanks,

Chuck

Is the coding plug in the OBC?

It is on the back of the instrument cluster.

I have seen a coding plug affect the tach. However, only in cases where the tach from a different model has been fitted. (In my case, a 535 tach fitted to my 528e.) If I used the original 528e coding plug, my tach was way off, reving upwards of 6k (shown.) Changing to the coding plug that came with the tach (535) corrected things.

Just a little insight.....

Is the plug that goes into the bottom of the tachometer? Or a different plug?

Thanks,

Chuck

Marked as part #9. Plugs into the back of the cluster, behind the tach.

The best way to check it, is to pull it out (it pulls straight down (you'll have to remove a couple of bulbs). Don't put too much pressure on it, as you'll break the tabs (this is for early clusters with 3 red SI LEDs).

Then, take the number off of it and plug it into RealOEM. It will tell you what it came from.

I had this exact same problem from the time I bought my car. I just had a new in tank pump put in and it fixed all of these problems that were occurring. ie: not redlining, hard start, idle dipping.

I replaced both fuel pumps, in-tank and main. It made no difference to the performance of the car.

Cheers,

Chuck

So try this:

Go out on the road, stop and then do a 0-60 shifting just before the fuel cutoff. Report back the time.

What is the top speed in 1st?

What is the top speed in 2nd?

Manual or auto, refresh our information.

Is the tach needle put on right?

Have you try pulling out the relief relay on the fuse box?

Is the relief relay in the fuse box? or on the side? I replaced all the relays on the side. What does the relief relay do?

Thanks,

Chuck

mercury26 wrote:Is the relief relay in the fuse box? or on the side? I replaced all the relays on the side. What does the relief relay do?

Thanks,

Chuck

Side of the engine bay fuse box, I really don't know, but have the same problem with my car, took it out permanently and my car runs now. Just give it a try...I'll keep my finger X. good luck.

Today, I ran a vacuum test on the engine and it was reading about 14 in/Hg. The manual says that 15-22 is good reading for the engine. I have removed and cleaned the throttle body, replaced intake manifold gaskets and fuel injector seals. The Bentley manual says that a low reading can be due to low compression, incorrect valve timing and incorrect ignition timing. The reading is borderline good, does anyone think this anything to be concerned about? Does anyone know if altitude will affect this measurement?

Also, when I reved the engine with the vacuum meter installed the needle would jump between high and low. Should it stay steady? From the reading of the Bentley manual, it sounded like it might be worn (weak) valve springs, ignition miss or faulty head gasket. Any thoughts on this would be appreciated?

Ok, I have now found my problem. Something in the cluster was bad and causing a misread on the tachometer. I installed a used (but known good) cluster from a later model E28 535i. I picked up the cluster a week or so ago from Ebay. After installing the cluster, I can now easily rev to redline. The only problem with the tachometer in the new unit, the Econometer is very flaky.

I am surprised that this was my problem. As I had replaced the following items in the cluster:

* New OEM mainboard
* Two different SI boards (remanufactured AND Programa)
* Two different tachometers (refurbished and original)
* Two different temp/fuel gauge boards (refurbished and original)

The only thing the same between rebuilding it with every combo imaginable was the speedometer. Would this cause a problem in the cluster?

I am glad that the issue is fixed, but frustrated that it took so long to find the issue. I had suspected that tachometer was misreading based on to intuition. Unfortunately, my tach/dwell meter won't work with electronic ignition. So I had no tool to verify the tach, and had a impossible time finding induction meter for testing the engine speed.

I guess I now need to determine why my Econometer is so flaky, but I am glad the tachometer is reading correctly.

Also, I checked with some folks very familiar with the M30 engine and they verified that the 14 reading for the vaccum is acceptable at altitude.

Lastly, my local shop was correct in their assessment that the rev limiter was kicking in early. The tach was reading incorrectly.

Thanks for everyone's help. Now I get to move on to new projects, rebuilt Paul Burke cylinder head with a Euro Cam, M-Tech springs and E34 big brake upgrade.

Cheers,

Chuck

Perseverance pays off.