89 930/Turbo won't turn over.

[89TRBO]

Some history: A month ago I tried to start my car after 3 days away. Would crank but not turn over. Had it checked out, and the CDI box didn't have spark in one of the outputs. Replaced that with a 6-pin Classic Retrofit CDI+ and the coil with a Parts Classik coil, and voila, she started up beautifully.

No problems for 2 weeks city driving. Took it to the mountains a few days ago, harder driving, some spirited Turbo use as well, warmer weather (28-30 deg. Celsius). Stopped for a rest, let the turbo cool down a bit, shut it down. Started up again, drove a block, then let it idle in neutral as I was looking for something, and the engine shut down.

Then, similar scenario to before: would crank, but not turn over.

Checked the fuel pump relays and fuse to the fuel pumps, all good. Could smell fuel (at least I think?) when I tried to start it and hit the gas a little.

I came back the next morning, was able to start it first try, died after 6-7 seconds. Then the same, would crank, but not turn over.

I have someone who is going to look at it who thinks it may be a relay (yellow relay) in the engine bay, or a DME relay or such under the seat. Any thoughts on this?

[fintstone]

Check the connector to the CDI and make sure a pin has not backed up enough to be intermittent.

[john walker's workshop]

The delayed ignition cut-off relay on the rear panel gets 12V power first, then transfers power to the CD unit. They fail occasionally and then you get no spark. They can be bypassed by removing the relay and jumping the two terminals in the PLUG that are closest to the engine. Make up a jumper with two spade terminals.

[89TRBO]

Is bypassing this relay something that is done regularly (without consequence)?

Originally Posted by john walker's workshop

The delayed ignition cut-off relay on the rear panel gets 12V power first, then transfers power to the CD unit. They fail occasionally and then you get no spark. They can be bypassed by removing the relay and jumping the two terminals in the PLUG that are closest to the engine. Make up a jumper with two spade terminals.

[89TRBO]

Is it possible that the (new CDI) is fried (again) due to heat? It was a fairly spirited drive on a warm/hot day in the mountains and the I was not skimping on turbo usage. I feel like the engine bay gets quite hot with city driving, the CDI area as well, nevermind a drive like that.

The unit/relay in the back are also covered by a big black plastic cover that doesn't seem to be a helpful thing for cooling/airflow I don't think.

Also, the fins above my AC condenser in the whale-tail are fairly flattened (bought it like this) which affects the air flow to the condenser but maybe somewhat the engine bay itself as well?

[Schulisco]

If the engine suddenly gets hotter than usual check the igntion timing and dizzy setup. If the spark comes too late this increases the exhaust temperatures tough. A misadjusted dizzy can also cause start problems.

The CDI box can be destroyed because of a loose ignition cable if the spark cannot jump over on the spark plug. If there's no other "exit" the spark back flaps into the CDI box and breaks it:

https://www-911--hkz-de.translate.goog/Zuendspulen.htm?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

Also check for heat depend vacuum leaks.
Also check the control and system fuel pressures of the CIS system cold and warm/hot and crosscheck them to the factory specs.
Is the fuel pump noisy?
Is the idle rpm as high as usual?

Thomas

[fintstone]

The problem is most likely related to the issue from a month ago...as the symptoms are similar. Start there.

[spuggy]

Originally Posted by 89TRBO

Is bypassing this relay something that is done regularly (without consequence)?

Yup. Like a lot of things on the 930, it seems a little over-engineered.

Many have disabled this (either to simplify or improve reliability by having less to go wrong), or drive 930 transplants without that feature for many years/miles with no issues.

Just allow a reasonable amount of cool-down - eg drive a couple of miles on surface streets without the waste gate open before switching the motor off - and you should be fine.

Run-on from the turbo timer is apparently intended to cope with 2 things;

• cast-iron "hot" side glows cherry-red at full chat, and engine oil (which breaks down over 300F or so) is pumped through it. So it needs flow. Oil coking has been seen on some motor teardowns. Perhaps post-shutdown heat-soak, perhaps inadequate cool-down.
• turbine bearings in a K27 are plain-journal - so float on a film of pressurized oil preventing metal-to-metal contact. However, turbine can achieve speeds of 100's of 1000's of RPM, and inertia means it can continues to rotate for some time... Killing the motor - removing oil supply/pressure - when the turbine is rotating that fast will damage the bearings.

Just don't boost up to the pit lane entrance and cut ignition on a fully-spooled/red-hot Kxx turbo to coast into your bay and you should be fine.

Do a cool-down lap at the track before pulling off. Or drive a mile or so at the speed limit followed by idle for 15-30 seconds before switching off. Works for me - I do this to check oil level anyway.

[89TRBO]

Problem solved! It was the black relay in the rear of the car (big one at bottom left in the photo). It was replaced with a newer version (top left in the photo) and car started up no problem. Yellow relay was working just fine, but I may get spares of both just in case.

Any suggestions on spares/where to purchase?