ruffy

Bob,
I need to tap your experience in motronic systems.

Recently my car has developed boost creep problems as well as misfiring at about 4k rpm all the way to redline. (mostly in 3rd to 5th)

At first, I thought it might have been a leaking pipe or manifold causing faulty readings... so i had all of those replace. It turns out, one of my intake manifold had a crack in it.

we tested it and yet the car had the same misfiring in the higher rev range

We removed the ecu and replaced it with a standard ecu and found that the car was ok.
Before we removed the old unit, the car was boosting beyond 1.2bar(the the end of the meter) in the higher gears with the old computer.

Clearly, it is a boost related problem. The question is where in the system is the fault?

Electronics are usually a matter of full function or total failure.
I find it hard to believe that the program is malfunctioning as it is not rewritable... right?

There is an odd chance of the vacumn driven actuator failing, however, it would also do the same on the stock computer when we tested it.

Any speculations are most welcomed... this time i'm really stumped.
Ruf won't take the motronic on warranty and i'm fearful that the problem isn't motronic related (there aren't any ways to test the ecu as a stand alone unit is there?)

Please help... I'm really stuck this time

Kevin

superyellowfly;

Have you replaced your spark plugs lately... With are crappy fuel it is a issue. Heavy deposited plugs have been throwing CEL on the 996TT's. The wastegate's are not vacuum but pressure activated. Do you have a crack in your line? There are ways to check the regulator. How is your BOV valve's? It might not be the ECU. You need to get this situation corrected before you break a ring land. The engine is clearly not handling 1.2 bar at higher RPM's...

Jeff 993TT

Along the same lines, I was thinking you may want to check your spark plug wires as well.

viperbob

I am still a little unclear so a couple of questions. When you put in the stock ECU everything was OK?? Was it mis-firing then?? You must have a boost gauge, so what was the boost doing with the stock ECU?

ruffy

kevin,
There is a chance that it is indeed the BOV that is failing at higher sustained boost pressure.
I will take a closer look at it to make sure it has a proper seal before resorting to expensive alternatives.

Jeff,
i was under the impression that spark problems would be apparent all the way through the rev range. Is there anyway to verify this?

Bob,
Ruf did not have a boost gauge with the TT computer. (it seems the delibrately removed this function during the rebuild)
Instead, i had a mechanical line plumbed in directly to measure the boost pressure and rigged it through the side window to get a reading.
When the stock ecu was plugged in, the car had no signs of misfiring.
If i remember correctly, it was .8 constant and spike at 1.1
on the ruf ecu it spiked and held beyond 1.2bar(max reading of the guage).

i hope that helps, please feel free to ask in more detail if it helps

thanks all for the input, i'll make sure i look at all the mitigating factors a little closer.
I've been having problems all year round and will be missing the last trackday before the circuit closes for F1

All the advise is greatly appreciated! Thanks a milion

911/Q45

Bad plugs misfire at higher rpm and load levels.

viperbob

If it is holding boost with your stock ECU, then it sounds more like your BOV. I would check these first.... While you are there, I would still check the lines for your wastegates... Still check the plugs as this could be a combo of a couple of things...

Typically when the ECU goes bad, it just DIES.

special tool

Yeah, you have a mechanical problem. Also - driving your car again with its cracked signal line or the stuck wastegate is not really a good idea. It is not your bypass valve, because a break in that diaphram will net you no boost.
When you say "we", I hope you don't mean some mechanic is advising you to make full power runs bouncing against the mechanical limits of your boost guage when you have no idea to what extent you are overboosting.
The reason that your ignition is being cut is that your ecu IS working properly in light of your mechanical problem - KNOCK.

If I was you, I would first have a look at my wastegate ports, but that is just me.

ruffy

Thanks for all the input, i'll definitely make sure all the possible offending parts are scrutinized.

Please note that when the ecu was swapped out for the standard unit, the car was boosting fine and had no problems with over boost... cept the car was running about 110 horses short.

Any plausible explaination? i fear that the standard unit may not exert enough stress to excerarbate the problem. The worse scenerio would be to order the new unit and then realize that it was something else, seeing that there isn't a real way to test the motronic?

As far as checking the ports, we've already done that plus numerous other visual inspections.

sorry for harping on this subject so long, already i'm suffering withdrawal symptoms from missing my car

special tool

Super - probably just for the much more consevative timing maps alone in the stock box , you won't tap the knock sensor.
You really have to check all your mechanicals. because Ruf probably tuned that thing right up against knock, so any raise in compression or heat, will put you over.
Try race gas, and come up on the gas at 60,70,80 and 90%, in increments - carefully. If that helps, it will narrow it down.

If the mechanicals turn out good, maybe Ruf will back off the timing at a few points, or give it some more gas fo you.

krish

SYF, Are you overboosting? Do you know your boost levels before you had this problem? You might want to get yourself another boost gauge unless you're reading just off the scale on this one to know your exact boost levels. If you are way overboosting then special tool is probably right, your ECU is backing off on the timing as it's detecting knock. Also higher combustion pressures (whcih will result from higher boost levels) impose greater demands on the ignition system which can manifest as misfires.

Can you get her on a rolling road with diagnostic equipment hooked up? That might help.

Have you tried swapping your ECU into someone else's car? I'll volunteer if you can get it out to me.

ruffy

Krish,
Believe it or not, before the conversion my car had a factory electronic boost gauge. After the conversion, that function no longer exists???

Thanks for the offer, I was extremely fortunate to get my hands on a stock unit to use for the moment. The car feels incrediblely slow! and also a little wierd, prob due to the mapping as my cams are ruf speced.

With the stock unit in place, i don't seem to have any problems. I won't exclude other mechanical causes.. until i get the test unit from Ruf to accertain the root cause. (thanks to the various members for suggestions)

Ruf seems to think that motronic units usually function as a on/off switch... it either works or it doesn't. They did mention that occasionally some of the internal circuitary may malfunction causing an assortment of problems. This occurs very very rarely...

H.P.Lieb of Ruf is almost certain that if we cannot detect a mechanical fault in the plumbing, then the only other device that controls boost is the ecu. hence most likely to be the culprit.

In the mean time, Ruf has been kind enough to loan me a dyno-test unit so i'll sit put and wait for it to arrive.
Which means i've missed the last track event before the closing for F1

oh well... you win some you lose some :<
Thanks for the offer for help, it is most appreciated

Also, a heartfelt thanks to all the other members that have chimed in their invaluable experience and time... we'll just have to play the waiting game for now