Bosch diagnostics results - PeachParts Mercedes-Benz Forum

pentoman · #1 03-21-2007, 06:30 AM

Yesterday we hooked up my car to the my dad's Bosch diagnostic machine. It's amazing what you can do with it! Quite fascinating, I now see how people would've fixed these things back when they were new, its not such a nightmare. It does suddenly make us trying to diagnose problems over the internet via guesswork seem more than a little amateur! It's so well suited to diagnosing issues with these older engines - if you can understand what it's telling you

. Which I can't but luckily my dad can.

No disassembly required, you merely hook up cables measuring battery voltage, current, and spark, plus an exhaust analyser and it does so much with it. For example it can measure each cylinder's contribution to the power output - It cuts out spark to a each cylinder in turn and measures the HydroCarbon output change and RPM drop. It will even measure engine compression to give you an idea of mechanical health. To do this you try to start the engine (it cuts out the spark so it won't start) and it measures current drain at each point during the engine's rotation. This tells you how much effort the starter is putting in to turn the engine over at each point in the engine's rotation = a measure of compression for each cylinder. Well I found it interesting...

This is what we found in less than an hour:

From top-left:
1 secondary (spark?) voltage?
2 primary spark voltage?
3 Combustion time per cylinder in ms
Second row:
4 RPM drop caused by each cylinder being shut off
5 Something similar (can't remember but have instruction manual!)
6 Compression per cylinder, measured in Amps required to turn each cylinder through combustion stroke
Third row
7 Change in HC output for each cylinder that is cut out.

Graphs 4 and 6 tell me that cylinders 1 and 3 are weaker, and I could do with rebuild (which I already knew - top end). I forgot what the rest tells me - anyone care to show off their big brains!?.

It made me realise I have a lot to learn. There's a huge difference between a proper mechanic (or Bosch service centre as this is) and people like me who know how to work a spanner and know what a spark plug and an OVP is...! :p

.

Car is a non catalyst non o2 sensor 2.5-16 by the way

suginami · #2 03-21-2007, 12:22 PM

Steve Brotherton posts here under the username stevebfl, and is the owner of Continental Imports.

He is a Bosch Master technician, and provides Bosch factory service:

http://www.continentalimports.com/ci_home.html

He doesn't post here very often anymore, but if you PM him, he may be able to provide you with some advice.

pentoman · #3 03-22-2007, 06:17 AM

Thanks Paul, I remember the old days when he always posted here, but I shan't bother him, it's more just for general interest than any dire need for a tech...

pentoman · #4 05-10-2007, 05:26 AM

OK dragging this up again.. does knowledge from that graph when combined with my rolling road graph:

give me an idea of what work I should be thinking about on the engine? That ~3500rpm flat spot is very irritating in day to day driving let me tell you!

pentoman · #5 05-15-2007, 05:39 AM

bump.. any thoughts at all on nasty flat spots on a CIS engine? Can poor compression cause it?? Or should I be looking somewhere else?

mailzura · #6 05-17-2007, 01:01 PM

hello! can you help me?
i need this diagnostic theh, wich you have on a picture!
can you write me were to buy this diagnostic tech?
thank you!

pentoman · #7 05-17-2007, 01:36 PM

Hi,

I have replied to your email.. the system is quite old now but is still very expensive and specialised equipment. Try ebay, all I have found is this old auction:

http://cgi.ebay.co.uk/Bosch-Diagnostics-Scan-Tool-engine-analyser-gas-bench_W0QQitemZ180074980771QQihZ008QQcategoryZ30921QQcmdZViewItem

I think you would be best to find a local garage with a similar system? Perhaps they will sell you it!

good luck

Russell