More MFI Stuff

[deoxford]

I was working the MFI, as I was reading the CMA and I noticed the Mirco switch was never being activated.
I adjusted it , Now when at idie the car now hunts between 1200 and 1500 rpm.
I think that I have it wrong, Does the switch stay pressed when the car is idling?
Or does it only get press briefly when the throttle is going to the idling position?
Also In the CMA , it says to drive the car at 2400 rpm to do the CO test is that correct?

[deoxford]

bump

[deoxford]

One more thing, Man it was fun to drive today, I mean the car really pulls!
And the steering was so tight ,you barely touched the wheel and it went left or right. THe sound was amazing. I have waited two years for that and I can't wait for more!!!!!!

[DonDavis]

I'm in the process of debugging my MFI as well. I took my car in for emissions testing prior to registration and they put it on a dyno. That's where I got my initial CO readings. So to answer your question, yes it will need to be under load for correct readings. I can't advise on your idle question. Sorry. My switch is not connected at all and I'm trying to find which wire and where it is. I do have a backfire at rundown but I'm pretty good at "preventive driving". Was your car backfiring?

Could you take a look and/or take a pic for me? My wiring diagram shows a gray/red stripe wire going to the speed switch but it's MIA at this point.

Also, there's a TON of reference material in the archives. Just have wade through and print out the pertinent stuff. Hopefully, one of the gurus will chime in with some pointers.

[jluetjen]

Yes; The switch should be depressed when the throttles are closed at idle. It's function is basically to tell the injection system that the throttles are closed. If the throttles are closed the fuel is shut off until the RPM's drop to idle speed at which time the flow of fuel resumes. The If your car's idle is hunting between 1200 and 1500, you most likely need to continue through the CMA process. It could be any of the adjustments or combination of them. BTW, is your thermostat connected and working properly also?

[deoxford]

John,
Ok so it should not be hunting between 1200 and 1500.
Yes the thermostat is working a connected properly. That took a week to figure out.
Thanks
DErek

Don,
I will take some pics for you.

[304065]

Derek, here's how it is supposed to work.

Throttle wide open
Engine 6000 RPM
Throttle CLOSED
Microswitch engages (it should be ON when throttles at the stops)
Speed switch reads tach pulses, determines RPM > 1500 AND switch closed
Speed switch energizes solenoid on pump, which cuts off fuel
RPM falls to idle, around 900
Speed switch reads tach pulses, determines RPM <1300 AND switch closed
Speed switch de-energizes solenoid on pump, re-establishing fuel flow

Now, suppose that the microswitch is impropely adjusted, so that it's actuated when the throttles are actually open. When the fuel cuts back in, the engine is going to immediately rev up until the revs go over 1500 RPM, which will cause the speed switch to energize and the revs to fall. Then the fuel cuts in again and the revs rise.

This was explained very well by the Great Roland Kunz, wherever he currently resides!

Hello

Easy check as far i remeber.

Let the engine run and rev it over 2500/min.

Hold the throttle from the enginbay at that rev. Use your left hand and press the switch while the engine is still at over 2500/mn.

Now the enginerev should drop to 800 - 1000 for a sec and then speed up automatically to 1600 - 2000 and fall back again. It will always cycle beetween those marks even if you have full throttle then. ( Don´t try it with more then you need.

Anyway, make sure that switch is working properly and that it closes when the throttles are at the stops. Glad you got the thermostat working, too.

[Jim Richards]

Wow, a reference to an old Roland posting. I, for one, miss his great contributions to the board.

[Zeke]

If your throttle bodies are leaking air due to worn butterfly shafts, it will be hard to get the MFI to behave perfectly.

Does this 'hunting' happen when it's cold, warm or hot? Mine starts to hunt only after the car gets a good work out and is HOT.

[ed martin]

Whatever CMA says goes, that is the bible for MFI. As far as the microswitch question goes, you say the problem started when you hooked it up? Disconnect it and see if it resolves the problem and go from there.

[deoxford]

Zeke,
It does it whan it is warmed up
Derek

[deoxford]

I see I must have a high idle proublem, and the switch is working correctly. If it idles high normal , the switch is just cutting it back as designed?
DErek

[deoxford]

Were is GRady, Sherman?

[jluetjen]

deoxford;
I didn't want to say anything earlier until I had a chance to check my data. But if your engine is idling at 1200-1500, that may be part of your problem right there. The proper idle should be 900 to maybe 1000 RPM. This is why I suggested working through CMA. As I said, the problem most likely is not the micro-switch, but rather some other area. Disconnecting the micro-switch won't get you any closer to solving the problem.

[derek murray]

I had the same thing happen once I got my RPM Transducer functioning. For me, as John suggested, was that the idle was set a little too fast and the linkage needed a new return spring and a good oiling.

Good Luck

[Grady Clay]

deoxford,

Grady is waiting for your CMA report.


Here are some of my notes from one of the threads I linked you to earlier.

The original CMA covers this sequence:
Porsche lists the Check Sequence as:
1) Air cleaner cartridge
2) Compression loss
3) Spark plugs (spark plug connectors)
4) Dwell angle
5) Ignition timing
6) Fuel pressure and flow
7) Injection nozzles
8) Injection timing
9) Correlation
10) Exhaust emission test
a) at part load
b) at idle speed

I would add several other points: 2) includes both cranking compression and cylinder leak test. These tests are best after some spirited highway (DE) driving. 3) Includes wires, cap, rotor and general proper condition of the ignition system. 6) I would also want a new fuel filter and clean the screen in the bottom of the fuel tank. 7) The condition of the nozzles has a large effect at idle and just off idle. 8) If you need to adjust the MFI pump timing, use the opportunity to replace the Gilmer belt and both toothed pulleys. You can save the old ones as road spares. 9) Correlation includes the condition of the throttle bodies. One of the important issues is that all the linkage moves off idle simultaneously.
Proper cam timing and valve adjustment are needed.
If the car has been running rich in cool-cold weather, several oil changes are necessary to get any unburned fuel out of the oil.
You should use fresh gasoline.
Test to see if there is a difference in mixture if the breather hose is disconnected from the air filter.
Depending on the car year, the evaporative emissions control system can, under some circumstances, change the apparent mixture. You should disconnect that during tests.
Oil and soot in the muffler can screw up your mixture measurements. It can take a long time to burn off. An OEM stock exhaust system is necessary.
When you go to test the nozzles, find someone with the Bosch tester and test fluid.



SO - - - Where do you stand in the CMA?

I’m concerned you are going down a path that will leave you stranded.

Best,
Grady

[72doug2,2S]

Mine also hunts when warmed up and I know it's running rich from the black plugs. Is there a video version of CMA? I think it would really help a novice like me.

[deoxford]

Grady,

this is what i have found so far, I am reading the Check Measure Adjust also.
I am looking for the air tool that measure each stack airflow , and Shreman sent me some tools and a CO meter this week.

I will be doing the comprision test this week also
1 I have changed the oil about three times now
2. I cleaned and made sure the Thermostat is working with all new hose also.
3.I noticed the Mico switch was never being ingaged, so i adjust that as well.
4. I noticed the coll start solinio was not sending gas to the stacks.
5. I order point replacements and new caps and rotors and plugs.
6. I did the belt when the engine was out, and th gears look good
I took it fun a very fun drive this weekend.

I will get back to the CMA and work thru it . Because there are no shops do here to take it to that know what they are doing so that leaves me and Pelican. I like the idea of removing the breather hose too.

Thanks for the help , I really had a blast in the car this weekend!!!!!

Also If this does not make sense I had moler surgery today and I am druged amd typing with one eye.

[Shuie]

This is a guess on the high idle, but is the vacuum retard line to the distributor ok?

Derek, I found the missing piece for the gastester. It fell out of the box in my truck. Sorry about that . I can put it in an evelope and send it out there if you havent been able to improvise. I forgot I had a sync tool for the stacks. I can dig that out and send it as well.

If your cold start device is not working, how long does it take you to start the car? I would have to crank mine for a solid 30 seconds before it could get enough fuel to start. The cold start runs off the middle fuse on the engine relay panel. Make sure that fuse is in place. MAKE DOUBLE SURE THAT YOUR COLD START FUEL LINES ARE NOT CRACKED OR MISSING BEFORE YOU HOOK IT BACK AND BLOW FUEL ALL OVER THE ENGINE COMPARTMENT AND THE LIVE FUSE PANEL!

[deoxford]

Sherman,
I did check the fuse and the lines, I replace all of them when it was out.
I think the device is bad, it lets a very little gas out .15 mils (.5 drops). I have on from the 73 I will try.
It does not take to long to start. you have to tap the gas and maybe hold it a little for about 70 seconds and then it is fine.

Thanks agian , I did not try it because I was not sure if you need to drive with it on. THe CMA reads that you have to be doing 2400 under load. Is that how you did it.

I have not done the compresion test yet.

It was a lot of fun to drive Really!!!
I have driven lots of 993's 996' 930 and this was fun,much more feed back!!