CO951

I just replaced my AFM, because my Porsche mechanic had done tests and said that it was why my can was running so rich. Now it will only run for about 2 sec, and the mechanic has the whole week off. I'm guessing it may be lean now, because they had done adjustments before to get it so it wouldn't be too rich with the old AFM in it. What can I do? Is there an adjustment I can make? Thanks!

testarossa_td

Sounds like he didn't know what he was doing.....

http://frwilk.com/944dme/afm.htm

Could be many things but the AFM is easy to take care of yourself...as is replacing the O2 sensor,TPS or adjusting the idle screw...

Clarks Garage or this forum should help you...just search.

Jake951

When you say it runs for only 2 seconds, I assume you mean that it starts up and runs for 2 seconds but then dies. If that's the case, then it sounds as though the DME is not getting a signal from the AFM. The DME doesn't need the signal to start up the engine but it does need the AFM signal to continue running. It could be a bad AFM or a bad connection at the plug connecting the harness to the AFM.

CO951

Yes, It starts and then dies quickly. When I get home, I will double check the connection on the AFM, it felt like it was a solid connection, but I'll try again. So there are really no adjustments, if I installed the AFM correctly and it is good, it should run. Correct?

Jake951

There is really nothing to adjust in the AFM. The car should run properly if the AFM and its connections are good (and everything else in the car is good). There is a mixture adjustment on the throttle body but it is intended as an idle mixture adjustment.

If you are running rich everywhere, then a bad O2 sensor is a possible culprit. How old is your O2 sensor? Have you checked it?

Jeremy Himsel

Not quite the correct answer. The adjustment on the t-body of for idle speed, not mixture. The AFM does have a mixture adjustment (used by the factory for emissions tuning with the EG test port) but you shouldn't have to screw with it very much. If you try and start it from a cold state (not warmed up and sitting over night) and it will only run for 2 seconds then the o2 sensor is not an issue either because the DME does not read it until it comes out of closed loop. Hell you could even unplug it if you want. Basically the DME runs off of a preset map until the DME temp sensor (coolant) and the o2 sensor come up to temp.

Next time you try and start it and it dies pull one of the plugs and see if it's wet. I have a feeling you have a bad fuel pressure regulator.

CO951

The O2 was replaced 9mo ago, but the rich problem was worst at WOL and decreased with decrease in throttle. The FPR checked out good 3 weeks ago.

Jeremy - Where is the mixture adjustment? I know it was turned as lean as they could get it, because the car was running so rich with the old AFM. I would like to adjust the mixture so it won't be so lean now that I have a new AFM in it. I am at work tonight, but will double check the AFM connections in the am.

jy951

"the o2 sensor is not an issue either because the DME does not read it until it comes out of closed loop. Hell you could even unplug it if you want. Basically the DME runs off of a preset map until the DME temp sensor (coolant) and the o2 sensor come up to temp."

I thought that the car is in "closed loop mode" under idle and part throttle conditions, thus the DME is looking for feedback from the 02 sensor under these situations. Under WOT (open loop) the DME could care less about 02 sensor feedback because it's operating off "pre-set fuel maps". That's how closed and open loop operation were explained to me by my tech (this was also includes many articles that I've read while tuning my 951 and Audi S4).

From my personal experience, it doesn't take a long time for the O2 sensor to "come up to temp" after starting up my 951, maybe a minute at the longest (under winter conditions); the car runs very rich until the 02 sensor does "comes up to temp" unless the 02 sensor is defective.

jy951

Based on personal experience, I usually adjust fuel pressure to lean out or richen the AFR (I also use MAFterburner -sold by Lindsey Racing). If you have a wideband 02 sensor and AFPR, this is a fairly simple process. I usually let the car idle and adjust fuel pressure (by turning the screw on the AFPR) until my AFR is close to 14.7. I also have a fuel pressure gauge which allows me to be more exact (in adjusting fuel pressure).

But, I have a MAF, larger turbo, and other things that require a pretty good AFR, especially under boost (i'm keeping boost at stock levels for the moment). If you don't have an AFPR maybe someone can tell you how to adjust the AFR w/o using my method. You might want to change the FQS on the DME from the stock setting to get additional fuel also, but folks with larger injectors (like me) usually make that adjustment.

Jeremy Himsel

[QUOTE=jy951 I thought that the car is in "closed loop mode" under idle and part throttle conditions, QUOTE]

Yup you're right, I made a alcoholic typo and I should have said open loop. The o2 sensor does come up to temp fairly quick but it's the DME temp sensor that takes it out of open loop once the coolant temp hits the specific temperature. Either way, if it's dying after two seconds, the 02 sensor is not the primary issue.