DJet Frustration, Ever play that Whack-A-Mole game at the arcade? Options

[ConeDodger]

Remember that arcade game Whack-A-Mole? You take a hammer and whomp the moles as they come up through the random holes? McMark and jcd914 and me had that kind of day playing Whack-A-Mole with the DJet on Jim's engine (jcd914) in my car...

Recently the engine started running bad. It had a low speed miss and then would go like stink when you got into the advance curve. I have a bunch of new 914 DJet components so I started throwing parts at it. This is a method used by people who aren't mechanics to fix something they don't want to pay a mechanic to figure out and fix. Take a note if you aren't a mechanic - this method is often more expensive then just paying the damned mechanic. So, I replaced the MPS with one that I bought from George at AA a few years back and never really used, I replaced the harness with a Bowlsby harness, I put a resistor in the CHT circuit... Each thing I did made it run better in some ways but often worse in others.
So, I decided that since I was having the Sacramento Porsche Family Reunion today and McMark was coming up, how about having him take a look at it and paying him for his time. Mark was game. He brought his LM 1 Wideband AFR and we methodically went through the tuning process. Here is where the Whack-A-Mole game began. Everything we did would improve it but unmask some other issue. Some things did nothing when they logically should have. We replaced the distributor with a rebuilt one from Rich Bontempi, it ran worse. We discovered that two injectors were not firing. So the distributor was good but the trigger points, which were new by the way, were bad. Swapped in the trigger points from the original distributor and it ran on all cylinders again but still ran bad. Lean, very lean... Then Jim Dupree pulls in the driveway and steps out of his car with an MPS that he pulled off of one of his spares. 30 seconds to plug in the vacuum line and the harness plug and the problem is solved. Turns out the new MPS from AA is bad or badly tuned for the motor. I suspect the later as it will hold vacuum.
So after three hours of Mark's time and lots of parts. The engine - Jim's engine runs very nicely again... Ahhh... the joys of a 30+ year old car (IMG:style_emoticons/default/headbang.gif)

[pbanders]

Good story, and you point out something that I've been harping on recently. Even if everything is right - mechanically, electrically, fuel system, ignition, FI components, hoses, vacuum integrity, etc. - you STILL have to use a CO/AFM meter to verify the idle, part-load, and full-load mixtures, and if they're off, make the appropriate adjustments to the MPS, ECU idle mixture control, or CHT circuit.

I've got two NOS 049 MPS's and two NOS 043 MPS's in my parts store. For each type, the factory adjustment of the full load settings is signficantly different (i.e. 0.2 to 0.3 ms different). I've done some adjustment recently on my MPS and I can tell you that a 0.05 ms change in injection duration for the part-load setting makes a noticable (~0.5%) change in CO. You can't depend on the "factory" settings to get things exactly right.

I'd recommend to anyone who has D-Jet to have at least two, and preferably three MPS's in good condition, with the epoxy carefully removed from the full load stop, and replaced with hot glue gun glue. You'll also need an LCR meter to record your calibrations, and to set the full-load stop position. Take your car to a dyno shop, and using the adjustment info on my page, set your idle (spec), part-load (3.0 to 3.5%), and full-load (5%) mixtures. After you're done, use your LCR meter to record your MPS's calibration curve, and use it later to set up your other MPS's. Re-set your full-load stops with glue gun glue and you should be set for at least 15K miles.

Once you get all of this done, if your warm-up behavior is crappy due to lean mixture during warm-up, get a CHT spacer from Brad Mayeur. I got one, and compared to trying to use ballast resistance with the CHT to fix this problem, it's far more effective. The spacer made a huge difference, my car no longer has the rough idle and surging it previously did, and when the motor is fully warmed-up, it's like the spacer isn't even there. I didn't even have to adjust my setup after I'd installed it.

[detoxcowboy]

Good story, and you point out something that I've been harping on recently. Even if everything is right - mechanically, electrically, fuel system, ignition, FI components, hoses, vacuum integrity, etc. - you STILL have to use a CO/AFM meter to verify the idle, part-load, and full-load mixtures, and if they're off, make the appropriate adjustments to the MPS, ECU idle mixture control, or CHT circuit.

I've got two NOS 049 MPS's and two NOS 043 MPS's in my parts store. For each type, the factory adjustment of the full load settings is signficantly different (i.e. 0.2 to 0.3 ms different). I've done some adjustment recently on my MPS and I can tell you that a 0.05 ms change in injection duration for the part-load setting makes a noticable (~0.5%) change in CO. You can't depend on the "factory" settings to get things exactly right.

I'd recommend to anyone who has D-Jet to have at least two, and preferably three MPS's in good condition, with the epoxy carefully removed from the full load stop, and replaced with hot glue gun glue. You'll also need an LCR meter to record your calibrations, and to set the full-load stop position. Take your car to a dyno shop, and using the adjustment info on my page, set your idle (spec), part-load (3.0 to 3.5%), and full-load (5%) mixtures. After you're done, use your LCR meter to record your MPS's calibration curve, and use it later to set up your other MPS's. Re-set your full-load stops with glue gun glue and you should be set for at least 15K miles.

Once you get all of this done, if your warm-up behavior is crappy due to lean mixture during warm-up, get a CHT spacer from Brad Mayeur. I got one, and compared to trying to use ballast resistance with the CHT to fix this problem, it's far more effective. The spacer made a huge difference, my car no longer has the rough idle and surging it previously did, and when the motor is fully warmed-up, it's like the spacer isn't even there. I didn't even have to adjust my setup after I'd installed it.

PBanders, You have a Parts Store? I would like to see it or hear about it.. Or you mean your personal private parts Stash?

[pbanders]

Personal Parts Stash (PPS)! Every 914 owner should have one!