More Questions on MFI

targa911S · 10-27-2003, 05:11 PM

Ok we got the adjustment screw thing solved ,, thanks guys. But here is another part of the story. All of a sudden a few weeks ago, my engine, a 2.2 S, started to idle a little, as Jeremy put it, "lumpy". i knew it wasn't right, so pulled the plugs first and checked out who was and who wasn't. Well #6 wasn't. The plugs and wires are about 6 mos old. Bosch WR8DP. Wires are OEM Beru. I did notice that there was some corrosion (!) inside the wire to plug connector as if moisture had gotten in and was causing the plug to misfire. No tracks down the side of the of the plug though. I cleaned out the connector and used some electrolitic silicon on the plug terminal of a new plug just in case I had a factory dead one. tested the compression 136lbs., every cylinder, not 1 lb of differance between em'. i even checked the guage on that one! Fired it up, checked the timing. Everything seemed OK. It was better but as you all know when you know your car well, you know when it ain't just right. OK so I leaned the idle mix out at the MFI pump and readjusted the idle mix at the throttle bodies. Drove it again today and it still seems too rich and won't idle right. So tonight I pulled #6 again and well there it was again all black ..except the ceramic center. Carbon every where. I took a pic but it's a spark plug so it is really hard to tell in the photo. I'm at a loss. I do have some suspicions though. Still a bad connector at the plug? Injector hung open or just bad. The (the MFI has 99,000 miles on it) Hello Gus! Help me out here
fellas. Any other suggestions?

jeff m · 10-27-2003, 06:46 PM

Could be the beru connector, have you swapped it.
Did you ground a spare plug in lead 6 to see if it's sparking. (quicker than taking out the plug)

How does it drive?
If it drives ok it could actually be lean on idle (and rich on main, normal for MFI) and you could have a lean miss at idle. If you could stick it on a machine to see the co then you would know were you are. If your hydrocarbons are way up, that's unburnt stuff.

Jeff

304065 · 10-28-2003, 04:33 AM

Can you borrow a Gunson Gastester from somebody?

targa911S · 10-28-2003, 04:52 AM

Well Jeff you had the silver bullet on my last inquiry, and I was kinda going down that road myself. I thought I would swap out the #6 connector to say #5 and visa versa to see if the connector is bad first. At speed it runs like a scalded cat. When I first come to a stop it idles OK but then slowly loads up and drops about 300 RPM and starts to lope. If I rev it to clear it's throat it does the same thing although sometimes it straightens out and idles smooth. I cleaned the thermostat washers also thinking that it may not be working properly. As far as the Gunson...well it ain't a tool that everbody has just sitting around, but maybe a trip to Dave White Racing($$$) could shed some light on this if all else fails. I'm just trying to avoid a trip to see DW. It just bothers me that it's only #6 that is not right. #1 thru #5 are perfect, for as much as you can read plugs on unleaded fuel. They certainly aren't like #6. They are clean and proper.

jeff m · 10-28-2003, 03:01 PM

Lots of shops have emmissions testing stuff.
Maybe the place that you use for your daily driver or wifes car.
These things do need to warm up so don't expect instant service.
I use "do you think you could stick my car on the emmissions tester sometime this week" the reply is usually tommrrow at 9.
By going to a non P shop they don't mind doing it and not getting the work. They don't want to work on your car!
If it were my car I would be checking everything before the PUMP.
Is your thermotime switch wired correctly. Do you have weeping cold start.
Read the "MFI check and adjust" and go through as if you are tuning it.
Good luck
Jeff

targa911S · 10-28-2003, 05:01 PM

I stopped by Whites shop today plug in hand. general concensis is either a bad plug wire end or a bad injector. most likely an injector because it's only one cylinder not all of them. i put a new wire and end on #6 and again a new plug. I will drive it tomorrow if it stops raining and then pull #6 again to check. If that fails White told me to bring all my injecters to him and he will check them on his machine. Then we will go on from there. I will keep you all posted. Thanks for all the great advice.

6771911esses · 12-14-2004, 12:14 AM

What condition is are the valves in? If your valves don't seat properly you will never get all the fuel to burn. Guaranteed! Do a leak down and see what's up. MFI and Webers are pretty similar in that they both require excellent heads, i.e. valve jobs, tight throttle shafts and butterflies, in order to synchronize each cylinder. In order to do the latter you have to listen to each stack individually. It's a dark science, but I use a hose and stick it in the stack to listen to the airflow and match all of them to "sound" a like. Never had a problem with my Webers by tuning them this way.

MN

67 911s
70 911s 2.2 MFI
69 911s Targa 2.0 MFI (just sold)
67-73 911s always wanted

Early_S_Man · 01:59 AM

First of all ... those spark plugs are WAY TOO HOT for a 9.8:1 911S engine!!! Bosch W4C or NGK BP7ES would be closer to the right plug ... ditch the Platinums!

Second ... why didn't they put your engine on an ignition analyzer scope like a Sun machine???

It sounds like they are 'shotgunning' the problem, or trying to empty your wallet!

You don't start testing injectors to see if a problem is ignition or fuel related!!!

You need to pay particular attention to the testing sequence on p. 10 of Check, Measure, Adjust ...

If you can't put the engine on a Sun Analyzer [or equivalent] ... then get a KD Tools test spark plug like this:

deoxford · 12-14-2004, 04:55 AM

targa911S
Did you check to see if #6 is getting spark from the distributor, I know you checked the wire but what about the line . Switching it with #5 may have done nothing if it went bad in the distributer.
Hope it helps
Derek

6771911esses · 12-14-2004, 04:55 AM

"So tonight I pulled #6 again and well there it was again all black ..except the ceramic center. Carbon every where."

Is this dry black deposits on the plug or does it look wet and shiny. Dry deposits can be ignition, fuel/air mixture, or bad valves. Wet black and shiny deposits means most probably bad rings (passing oil).

Maybe this can help you eliminate some areas.

Mike