King James

Greetings all!

I am still at it with my Weissach, still trying to get it to run correctly after a 2 year sit involving cross-over coolant leak fix / TB&WP replacement. PorKen helped me track down a vacum leak, which, when fixed, resulted in a fairly smooth running situation (until I noticed all of the black smoke/soot coming out of the tailpipe, coupled with red-hot glowing cats) Since then, here is what I've discovered.

With the electrical connector to the AFM disconnected (passenger side, side of the AFM) the running condition is as above, smooth idle, a little rough in the 1000-2000 RPM range, smooths out at higher revs...but is either extremely rich running or raw fuel is getting dumped into the cats, as the smoke/soot/glowing cats condition is the result)

With the electrical connector to the AFM connected, it is a hard start, no idle situation in which if I floor the accelerator, it chug-chug-chugs, then suddenly roars to high RPM rev which is near impossible to maintain, if I feather the gas, lay off the gas, it dies.

I've got a book on order from Amazon on Bosch L-Jet (as the shop manual doesn't appear to deal with testing procedures for the L-Jet / AFM setups, all I can find are LH-Jet diagnostic info!) and my old man is getting his hands on an Oscilliscope, but in the mean-time...HELP!

Can any 928 sages shed any light on what these symptoms indicate? Has anyone experienced this set of running conditions before?

My plan was to get her running in 07 and put some serious, fun miles on her as a reward for a 2 year nightmare of being out of commission. It's September already and I'm still struggling with her!

Thanks in advance!

King James

Bump! - either I have not explained this well or it is something no one out there has run into / an opinion on?!? Come on! Help out a brother!

KJ

DonS

IANAExpert but on my '84 when the plug to the AFM is pulled the car will start but idle VERY badly and not improve with RPMs.

No leaks with the jumbo O-ring at the base of the AFM? FPR's getting vacuum? Fuel pressure at rail? Re-check all vac. lines. Next check is injectors, how old and dirty? Last cleaned and flowed date? Bad O2 sensor? Swap with known good one to check.

Check the 3mm allen AFR adjustment on the AFM - make a note of how many turns (full open ~12 turns?) to close (CW). Closed = rich, Open = lean. This will at least let you know how the AFM is affecting idle mixture.

If you don't have a wideband O2 sensor at least put a voltmeter on the narrow band to see how/what it's reading.

My .02.

Oh, the book has a good L-jet diagnostic section and should help.

mj1pate

There must be experience with Ljet among this community. I would also suggest discretely poking into the Alfa GTV6 forum, for which there is a wealth of Ljet AFM knowledge (http://www.alfabb.com/bb/forums/forumdisplay.php?f=14). Greg Gordon and some other forum addicts have posted extremely detailed info on the dismantling and rebuilding of the (actually simple) AFM. You wil find similar detailed knowledge on the workings of the EMU and sensors there as well. Hope it doesn't come down to this, but good luck.

BW: GTV6s are extremely cool cars, but don't forget where home is and get stuck there.

Mike

King James

Thanks guy(s) for the response. A few answers to your questions Don,

-Fixed a leak w/jumbo O-ring at base of AFM, connection rock solid now.
-FPRs getting vacum? - not sure, how to check?
-Fuel Pressure at rail - have plenty of pressure at rail, w/AFM connector disconnected, runs and revs great (albeit extremely rich/raw fuel dumping into cats)
-Injectors - balanced, blueprinted, cleaned by WitchHunter 2 mos ago
-O2 sensor - Is this the green wire coming through firewall at fuse panel? If so, 1. How do you check, and 2. doesn't this come into play once car is warmed up? My probs are immediate after starting (and continue the same as car stays running)


-Mike - thanks for the info, I'll check the Alpha site...while I love the 928, 2 years of none running frustration may lead me into the arms of another lover...

KJ

PorKen

I swapped in some injectors that had been sitting a while and one or more of them stuck open, which promptly made a huge lake in the muffler-in-place-of-the-cat! I'm suprised I didn't blow up! It burned off in a putrid grey cloud.

I used a 9-volt battery to open and close each injector to unstick them, and ran cleaner in the tank, and they started working again.

DonS

For the moment let's rule out the injectors assuming they're okay.

FPR's - Underneath the air filter between the heads and the firewall are your two FPR's. each one should have a vac. line running to it. Check both the vacuum lines (hold vacuum) and the FPRs (applied vacuum will affect pressure). Also check the "Y" they come from at the base of the throttle body; this is a common leak point.

O2 - In the cockpit passenger side of the center console beneath the dash and close to the floor under the carpet is where the leads come through from the O2 sensor. Should be a three-wire connection going to a big, long connector. Two of the wires are for the heater, third is the signal wire.

Go ahead and disconnect the O2 while your trying to run the problem down since the ECU will want to correct any changes you make if it's still connected.

The O2 is being monitored continuously by the ECU and affects all "normal" driving conditions (idle, cruise, mild accel., etc.). Disconnect and tap the sensor wire to test it's voltage to ground once the engine is running and it's warmed up (usually < 1 minute). It will put out any where from .0 - .9 Volts. Running rich it will probably be reading .75-.9v. If you don't have access to a wideband or analyzer this will at least give you a (VERY) rough indication of any changes that happen while you're diagnosing. Ideal will be fluctuations around the middle .45 - .55 Volts (stoich). The sensor will be throwing fluctuations to the meter so just eyeball the average. Note that since it's a narrow band you can't trust the reading on either end of the scale. It's more like a three-way switch: 0-.45v (lean) -to- .45-.55v (stoich) -to- .55-.95v (rich).

I'd start by disconnecting the O2, plugging the AFM back in, set timing to spec and then start trying to diagnose. Get all the ducks in a row first. This will be your baseline for how the engine is really tuned without the ECU monitoring and correcting anything. When I had this condition is was a little of everything (leaks, AFR, timing, somebody monkeying with the AFM spring tension, etc.). There are only so many causes for a rich condition with an L-jet so it's just running each one of them through diagnosis. Once you've got it in the ballpark or closer the ECU will just clean things up.

I really wish the more knowledgeable people would pick this up. Got more Porken? Viribusunits? BB? Dr. Bob? Rog?

DonS

Oh, and you say you have good fuel pressure; make sure it's not too high. L-jet is substantially less than the more modern Bosch systems. Off the top of my head - 32 psi at idle, 36 nominal.

John Speake

Those trap door AFM often have problems with the wiper and track of the main potentiometer that sits under the black cover. The wiper moves with the flap. Worth removing the cover and using some switch cleaner/lubricant on it.

Also make sure the flap moves smoothly .

Seal the lid down afterwards to prevent an air leak.

DonS

Like John said above.

Has the cover on your AFM been off? See any scratches or markings around the cover? Known good versus testing with a spare? There's quite a few write-ups about how to properly adjust the wiper and spring but do this after testing for other possible causes which are much more likely.

DonS

Too slow today. Sorry for not posting earlier. I also added more detail to post #7 above.

Also check the Temp II sensor on top of the engine. If the ECU doesn't think the engine is ever warming up (via this sensor) it keeps the mixture rich. Measure the resistance at room temperature then put it in boiling water and measure the resistance hot. I can't remember the spec values, maybe someone else will chime in on those so post them here when you get them.

Another possibility is the WOT switch is stuck. This will also cause the ECU to keep it rich. This is the one on the top of the throttle linkage. You should hear it click at about 80%? or so of WOT. If that's okay also check that it's just plain working by measuring the resistance across the terminals at open/close.

Jack Riffle

Check the fuel pressure regulators and dampers carefully. When the diaphrams fail the vacuum lines that operate them will suck raw fuel in. If you pull off the vacuum lines attached to them and find fuel leaking there, you have found your problem. And yes, the WSM have a fairly good troubleshooting section for the L-jet in it. Pull your spark plugs and see if the problem is limited to any one cylinder or if they show rich all across the board. If it's one cylinder only, I would have to go along with a stuck injector. I have never heard of a cold start injector sticking open, but I guess that's possible, and if it did, it would certainly cause your problem. If it failed open, it would allow fuel to constantly be dumped directly into the cylinders and the AFM wouldn't even know it. The more I think about it, I think I would check that cold start injector first. Hope this helps. Good luck and keep us posted.

King James

Gentlemen,

Thanks for the tips and suggestions...I've blocked tomorrow (and the weekend if necessary) to try them. I will report back on what I find, as I want to add to the searchable knowledgebase here for the next person banging their head against the wall !

Thanks again and keep your fingers crossed!

KJ

King James

Looks like I've finally found the problem!
Took off the AFM and removed the black cover on the side to get at the potentiometer, looked pristine, but resistance readings were all over the place as I moved the flap. I'm assuming the correct resistance should be slowly increasing as the flap is opened, no up/down/overload/up, etc...
Can someone corroborate that this is indicative of a bad AFM? Used contact/switch cleaner to no avail, maybe a problem due to flap not being opened/moved for 2 years as she has sat in the garage?

Anybody have a good working AFM they can part with? (in exchange for some greenbacks, of course!)

Good news = hopefully have finally found source of my probs
Bad news = expensive part to replace!

John Speake

The resitance should move smoothly. As your have nothing to loose, try bending the contacts, if possible to a unused part of the black track.