Mark in Baltimore

You may be right; I had saved that info from a previous post on here and can't verify the veracity.

timothymoffat

Great thread guys. I've been wanting to do this upgrade for quite some time but was unsure of the stalling issue. My 95 is a late build (04 95) but had the clutch replaced with standard parts when I bought it three years/ 8K miles ago. I think I'll leave well enough alone, heavy flywheel, heavy Speedlines, no VRam, I'm surprised I can get out of my driveway in the slug LOL. My 97 still has the original clutch and although everything seems okay, I'd really like to try this. Thanks for all this info.

nile13

Thanks, Mark. I believe mine is a 674 ECU. Should I try a 679 just for the hell of it?

Actually, I just thought about it. As far as I remember, I have a Bosch 163 chip. So I must have the 213.02 ECU then? I can't pull the seat in a foot of snow outside, but I'll look at my old post when I tried to put a chip in the car. BTW, maybe I should try to install that Autothority chi again to see how it would be regarding stalling. The chip is 01.993.200 and was not completely compatible with my ECU according to Autothotiry. It worked, but cased pinging at higher revs, so i took it out quickly.

I strongly believe that the issue is purely ECU mapping. The '96+ cars must have different fuel delivery maps around idle. They seem to deliver some fuel quickly as the RPMs drop down, the old ECUs do not. Which tells me that someone can remap the older ECUs to deal with stalling issues. To my knowledge noone has done so yet. Talkign to Steve W. confirmed that.

nile13

I would heartily agree. \

My rule of thumb - if it's a street-only '95, do not install LFW. Consider MWF perhaps, if you can still find Andial somewhere or a similar unit. If it's a '96+ car or it's doing track duty, you might want LFW.

Not everything that sounds cool and racy is actually good for a street car.

Geets

So has anyone out there tried this? Is it even possible to do on an OBD-I chip?

nile13

There's this odd confusion going on, I feel, between OBD 1 and OBD 2. The OBD version is completely irrelevant. What's relevant is the fuel mapping in the system's brain.

It so happens that OBD2 is both more "smart" and more restrictive when it comes to changing things. That's why OBD2 cars generally don't have removable chips. However, they can be reprogrammed just as OBD1 can. The logistics of reprogramming are different, but the bottom line is the same - there is an EPROM somewhere that holds information on how much gas to pump through injectors based on the "gas" pedal input and a set of readings from a number of other sensors.

It also so happens that Porsche made a lot of changes between OBD1 and OBD2. Among other things they installed a Varioram system. But I'm certain that the stalling problem is the issue with mapping and is completely external to whether it's OBD1 or OBD2 car.

Just my opinion based on what I understand. I'd love if others chime in with more knowledge and info.

Geets

Mark,

i was actually asking about nile13's post above and if anyone has tried to remap the old ecus to deal with stalling issues. I have done all of the searches and still have not found information on this specific question.

Quote:
Originally Posted by nile13
I strongly believe that the issue is purely ECU mapping. The '96+ cars must have different fuel delivery maps around idle. They seem to deliver some fuel quickly as the RPMs drop down, the old ECUs do not. Which tells me that someone can remap the older ECUs to deal with stalling issues. To my knowledge noone has done so yet. Talkign to Steve W. confirmed that.

Mark in Baltimore

Gotcha. My misunderstanding.

JM993

I think that's right.

However, as I've learned from my v-ram conversion project, Porsche upgraded the ECU during the 95 model year. And, in fact, since then, the part number has been superceeded at least (and probably more than) twice more. One of the upgrades I know was to provide compatibility with the v-ram intake. This is why I was able to make v-ram function with the addition of a chip to my US OBD-I ECU. Knowing Porsche, I'm betting that the later ECUs are better able to compensate for the LWF. Don't you think that it's possible that once they created the LWF for the RS (in 95), that they contemplated owners of "normal" 993s would want to upgrade?

Mike, I'll also bet your car (built 4/94) uses the earliest ECU which could be why you've had so much trouble. For owners with later cars with the problem, as noted by Steve, there's a number of other potential causes of the problem (most noteable vacuum and ICV related).

So for me the question really is (assuming the car is otherwise tip-top), determining what version of the 993 ECU is compatible with the LWF notwithstanding whether the car is OBD-I or OBD-II.

nile13

I would say upfront that I have not had a tremendous amount of stalling. However, it stalls sometimes and it is pretty annoying and can be dangerous on a city street. Thus it's a big concern for me.

The next thing to do (as Steve W. suggested that to me as well) is to check for vacuum leaks. I'd rather not spray the carb cleaner around the engine myself. Is there any other way to check?

The thing to do after that is to adjust the ICV for slightly higher idle.

The last thing and the great one would be to find an ECU solution for all '95 LFW people.

Having said that, I would doubt that Porsche, or any german company, would even contemplate that regular 993 people would be swapping in LFW. The factory, remember, is infallable. They do not make mistakes. If they chose to have DFW in 993s in the first place, they are oblivious to anyone who tries to upgrade it in any way. So, no, I would not believe that they would remap anything in ECUs specifically in response to LFW being available on RS cars. Especially given the fact that RS cars had a different ECU part numbers. However, they did some remapping and it's entirely possible that whatever they did happens to have with LFW stalling.

Now, what would be really interesting is for someone with a clue (not me, certainly ) to compare the fuel maps on, say the old '95 chip, newer '95 chip and, if at all possible, RC ECU chip. It's not difficult to dump the data. It'll take someone who's done it before to actually understand it.

On my end, I can try to put several different chips into my ECU to see what happens. But not before spring

nile13

Just confirmed through some old posts of mine - I have Bosch # 0.261.203.163 ECU. So it's the oldest one for '95s, right?

The question is - which other chips would this ECU work with? Would I be able to swap in a chip from 674 ECU and see what happens?

JM993

That's the early ECU, as I thought.

You could try the later chip but realize that the architecture of your ECU is different than the later ECU.

As to Porsche being infalliable, it's not so much about that, but instead it's about saving money. The one thing I've learned from my v-ram experience is that the later Euro and US OBD-1 manual trans ECUs are the same except for the chip (the early ECUs are identical down to the part number). This makes sense as it's likely cheaper change variables (such as v-ram compatibility) with the chip while using the same ECU.

Again, these are just my theories. Take them for what you think they're worth.

JM993

There's a procedure for checking vacuum in the factory manual. Essentially, you unplug the vacuum line on the fresh air flap and hook up a vacuum gauge. Start the car and rev it a bit to generate vacuum. When you shut the car off, the car should hold the vacuum generated. If it doesn't hold for at least several minutes, you have a leak.

I'll bet ya a number of our friends with stalling problems have a vacuum leak.....

nile13

If I ever get to a mechanic to do a few things that need to be done, I'll have them do a vacuum leak test.

4X4SCHE

I am pretty sure that there is a signal from the climate control to the ECU to tell it that the A/C is turned on. This has the effect of increasing the idle speed to compensate for the A/C compressor load. Many people have said that it does not stall with the A/C turned on. This is why.

When I install a LWF, I plan to hot-wire my ECU so it thinks that the A/C is permanently on. Anyone care to try this first?


John