King James

It's been over 2 years since my Weissach has been on the road. First, it was out of commission as I chased a coolant leak (O-ring under coolant cross-over), then found the WP to be bad and did a TB/WP job...now I've spent the last few months chasing a classic case of "No-Start-itus". I'm grasping at straws now, although may have had a break-through yesterday...
Here's what I've done so far:

Ignition:Fuel:Additional notes:[INDENT]- replaced all vacum lines
- verified injectors are 'clicking' when trying to start
- she wants to start immediately, but just hiccups once or twice and that's it.

Now, here's the discovery from yesterday. Temp II sensor checks out A-OK as far as the meter readings, but just for laughs, I disconnected the Temp II and tried to start...immediately roared to life and raced at high RPMs (simulating a cold start?), eventually settling into a pattern of high revs and then a drop-off, reving back up for a few seconds and dropping off, this went on for a minute or so and I turned it off...My question is this:

The Temp II doesn't appear to be bad, why would disconnecting it suddenly make the engine roar to life? I'm at a loss here (although it looks like I can stop chasing fuel/ignition/timing issues! - it sounded better than it ever has for the minute or so of high revs!)

I'm hoping the brain trust can help me out here...any Ljet pros out there that have experienced this?

Thanks!
King James

SwayBar

I would check the wire continuity with an ohm-meter; the wire(s) could be either broken or shorted.

AO

Have you checked the imfamous "GREEN Wire"?

King James

Wire continuity of the Temp II sensor appears to check out ok (2k ohms between the terminals), that's why I haven't gone back to the Temp II, it seemed to be ok. I was running out of ideas which is why I tried starting it with it disconnected...

Andrew - what is the best method/steps to take to check the 'Green Wire'?

Thanks for the replies...I'm on the hunt!

PorKen

Look for a very large vacuum leak.

Unplugging the TempII makes L-Jet go full rich, which would normally stall the engine. There must be a large air leak that is giving enough air to compensate. The engine races to over 1800 rpm, but the idle switch is on, so the L-Jet thinks you are coasting, and cuts out the injectors until the rpms hit 1200.

King James

Porken - thanks for the insight, I will look again at vacum...what are most likely candidates for a massive air/vacum leak? I have replaced all of the vacum hoses I can find, and haven't found anything disconnected or loose...are there any usual suspects in a case like this?

thanks again for the help!

Podguy

Look at the boot between the valve body and the Plemum. These can get skewed or even crack and leak.

Just saw the same problem on a 79.

Dan the Pod Guy

Tampa 928s

Go get it smoked tested, I had an issue after my intake rebuild and found it by smoking it. Call a few garages that to emmissions and they will have one.

Podguy

You can use a small propane torch too. Start the engine and wave the nozzle of the propane around the intake (unlit of course). If you hear the engine idle speed up then the engine is sucking in and burning the propane. If you detect a difference it should be easy to move the propane torch near and away from the vaccum leak to locate it.

There is a side benefit to the propane test. if you have bad plug wires it is possible for the propane torch to ignite for an ignition spark. I have never seen it happen, but it is possible. Not a big deal since the flame is small and of low temperature.

Do the test in a well ventilated place and you will have no problems. I have a propane torch that connects to a bottle with a hose. This allows the bottom to stay on the ground while I have more control over the torch end. The entire set up is cheap - $20 or so.

Dan the Pod Guy

King James

Porken - This finally saved me! I started looking for a very large vacum leak and finally noticed that the spider air intake had come loose from the throttle body (which apparently is not bolted down to the block and is held steady by the spider intake and AFM). All of the monkeying around w/the AFM (and the fact I did not know the throttle body was loose) must have dislodged it. Reconnected the air intake to the throttle body, reconnected the Temp II sensor and....VROOM, first time in over 2 years. With all of the other upgrades as a result of chasing the no-start, it sounded better than it ever has! Now I need to officially put everything back to gether, get it down off the jack stands and gently work it back into shape (after a bath to clean off a couple of years of garage grime) WOW! I was really beginning to doubt whether or not I would ever be back in business.

3 Cheers for Porken (He should have a bunch of little Porsche emblems on the drivers side door for each time he has fixed/bailed out/ solved someone's problem - he would definitely be a 928 ace!)

KJ is out!

PorKen

Good job! L-Jet is pretty easy to fix/diagnose, once you work with it for a while. Especially if you simplify it, like I did, (in all these posts).

BTW: the J-pipe that the throttle body bolts to is supposed to be held down by three rubber isolators which screw into the block, but they get old and the bolts separate from the rubber.

(3) 928 110 191 00 - bonded rubber buffer