CIS Help - 930 cutting out when shifting -

[ZCAT3]

Any other suggestions? I should be able to test the fuel pumps on Monday. There is nothing worse than having a 930 that you can drive as long as you don't use boost -

[beepbeep]

Originally posted by ZCAT3


EDIT: Well that didn't work - just did another test drive and it cut out again. This is getting embarassing. How do I ground a wire that is hot??

If fuel pumps work with this wire unhooked then it's the wrong switch. Do not ground it.

[ZCAT3]

Hmm - I seem to be getting no where with this. I can get a new Hobbs switch for $30, but if the car runs with it disconnected then that does not seem to be the problem. Several mechanics have suggested a vacuum leak, but are confused that the car runs fine at all times other than when I give it moderate boost and then shift.

[beepbeep]

Hmm...on the other hand, there is a certain (unlikely) possibility that switch is only connected to one fuel pump. Arcing is perfectly normal as fuel pump draws lot's of current.

I suggest tracing the wire from the switch. Are you sure that this two-pronged switch (with one of terminals grounded, as far as i can see) is a pressure switch?

You can always measure acros it's terminals with a ohm-meter (with live terminal disconnected). If it's just a switch then resistance should be zero.

[ZCAT3]

Yep - it is Hobbs 10 PSI pressure switch for sure - exactly as shown in the link I listed yesterday. I will check resitance on it as you suggest. I figure this must be a standard deal with the Kokeln IC as there is little doubt that the mounting point of the switch was built into the IC as it cam from Kokeln.

[Porschephd]

The Hobbs switch is part of the andial system. Not the overboost system. The wires going to the unit also are the wrong color. They should be white. That switch trips the Andial or AMG unit to set of the frequency valve. It has nothing to do with the overboost. From the pictures there does not seem to be an overboost switch. I would check the main wiring and relays to the HPXs and I would check the overboost relay as well as the grounded white wire which would have gone to the overboost switch if it was there.

[ZCAT3]

Thanks Stephen - that thought did occur to me this morning - it makes more sense that the andial enrichment is tripped at 10 PSI.

[orac69]

I know this is a very old thread, but does anyone know what the actual fix for this was?

I have a UK model 930, '81, and have the exact same problem.

I have tested / cleaned all the electrics, the fuses and the fuel pump relays have been replaced.

I also have a Kokelyn IC, and I have replaced the original overboost sensor with a brand new one.

A very annoying problem...

My problem too happens mainly on shifting up, but a few times it has also happened when just cuirsing along at 2 or 3000 rpm @ 40mph..

When the problem happens all the rest of the car electrics are fine, radio stays on, dials continue to work - its just like there is no spark - and after 5-10 seconds it just fires back into life.

I have hit the overboost sensor before (faulty EBC) and you really get a "dash in the face". This problem seems to be different though, as it usually happens on up-shifting.

[orac69]

Im still having this problem on my UK '81 - can anyone else suggest anything else ?

Ive replaced and checked just about everything - apart from the Green Dizzy wire - and im not sure that will fix it either as the OP has the same issue and doesnt have one...

Ive just done a 4 day 1000 mile road trip, and the car drove perfectly - APART from just twice on the motorway when up-shifting from 2nd to 3rd (on minimal boost - it cut out for just 3 or 4 seconds) and again from 3rd to 4th - this time it cut out for about 20 seconds which was a nightmare @ 80mph on a busy motorway with no power trying to pull across off the road with cars up my **se...

Distributor - looks good, clean, new.
New plugs
Injectors cleaned and flow checked
New fuel pumps front and rear
New red relays
New fuel filter and accumulator
O/B grounded out.
Brian Leasks adjustable WUR and RPM CSV solenoid.
Grounds checked, new battery
Fuel pump Fuses / wires cleaned
No air / other leaks I can see.
I dont have a yellow relay.

All things considered it SEEMS to be electrical - but where !?! and why does the problem only happen rarely, and why only on up-shift, and not when on max boost when youd expect vibration etc to be at its highest....

[JFairman]

My '87 930 used to just shut off and leave me stranded in the worst places at the worst times. Then it would eventually restart.

Turned out to be the multi pin plug on the speed relay under the driver seat had a poor connection at the overboost sending unit white wire pin and at times vibration would make the fuel pumps run or shut off.

The speed relay is tied into the overboost white wire fuel pump relay ground circuit before it goes to the yellow air flow meter safty and overboost relay. It's also the old school rev limiter that shuts off the fuel pumps by disconnecting the fuel pump relay ground at 7200rpms. Its the aluminum color relay closest to the left side of the car under the driver seat.
The whole obsolete fuel pump relay ground chain wiring design is a nightmare waiting to happen and it will.

If you want a 930 to be more reliable it's best to rewire the fuel pumps without the fuel pump relay ground wire chain from hell.

The origonal alarm system can also disconnect fuel pump relay grounds if it goes haywire. The ecu for that is usually under the cowl on the right side.

There more good information in this thread but some stuff is left out. Yellow Relay from Hell...to finally solving the problem

[orac69]

On my '81 I dont have a speed relay (or anything else actually) under the front seats - and I dont have the yellow relay from hell !

Ive spent a ton of hours going through all the forum posts....

Im not convinced its the alarm either to be honest - its the "only happening on up-shift" but that is the very weird bit...

I could understand it if I was on full boost, masses of vibration / power and it cut out regularly, but at 30mph, no boost, gently up shifting from 2nd to 3rd... Now thats odd...

Thanks for your input though - appreciated