Intermittant Turbo stall

Marshall Deems · 08-18-2001, 11:54 PM

I am a first-time user here and I know that there are some real brains out there. This one may stump you! It has me.
'87 Turbo (37k miles) stalls ocassionally in very embarassing places. Most of the time it recovers on its own, while left in gear, before I come to a complete stop. A couple of times I had to pull into a safe place and mess with it. It has never let me down to where I needed a tow. SYMPTOMS: Cold start no problem however I do not here either of the fuel pumps buzzing with just the ignition on. Car will idle fine after starting. Once or twice I had a hard time starting when cold. It seems that the pumps are working when the engine is running. I feel a vibration in the fuel line. What's weird is that I jiggled the yellow signal relay (square plastic one in the engine compartment)and got intermittant fuel pump buzzing with the ignition on, engine off. It seemed to have a short either in the relay or underneath the relay connector say underneath the aluminum tray that holds the relays. Any way, I purchased a new yellow relay 911-615-118-01 O.E.M. for $85.00. Upon installing the new relay, I heard no sound of pumps even if I jiggled it with the ignition on. I could not get the new relay to show any evidence of a short beneath the aluminum mounting tray. I'm confused because the two relays produce different results from the jiggle test but my stalling problem has not gone away.

One observation is that the tach goes to "0" RPMs at the time of the stall (sounds electric) even when left in gear. All other gauges stay alive. There is one other noise that is evident when the pumps are on. It sounds like a fuel distributor whizzing. Are the pumps supposed to be on when the ignition is on and the engine not running? With either relay,the pumps seem to be on when the engine is running. If there is sufficient pressure left in the lines, will the pumps come on anyway? My wrench told me to replace the green distributor wire. A short in the distributor wire makes sense but what's up with that weird short-like symtom from the jiggle test of the old relay? I will get a book on fuel injection but it won't read like my '67 Bug book! I have read in other threads that fuel pressure should be checked. I'm OK with that but I don't have the tool and the car runs perfect most of the time. If the pressure was messed up, wouldn't the car run poorly or not at all? And why would the RPM gauge go flat if there was a fuel starvation problem? I hope there is a simple answer. Thanks to anyone responding. This is a real brain teaser for me and I REFUSE to stall out again on the freeway (with a nasty appetite) next to a hyper Honda kid ready to be eaten, but gets away.....it's a really bad feeling.

Early_S_Man · 08-19-2001, 12:11 AM

Marshall,

The tach. going to zero is your 'best' clue, as the CDI-unit drives the tach! Either your CDI-unit is losing power, or the green cable or connector is opening-up when the stalling occurs! Try replacing the green cable first, as a power loss will be harder to track down!

------------------
Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

Marshall Deems · 08-19-2001, 02:12 PM

Thanks for the suggestion. I noticed that the green wire disappears up underneath the air cooler. Should I remove the cooler or is there a spade connector somewhere unseen but reachable by hand or pliers?

DJB · 08-20-2001, 04:19 AM

Hi Guys,

I am having a very similar problem in my 86 3.2 cab. The vehicle starts first time, every time and runs fine when she's warm. But cold she is a real *****, she'll stall and splutter unless you keep your foot on the gas at approx 1000rpm.

Similarly, the tacho dips to zero and does not recover - leading to a stall. Today she died in the middle of a roundabout - very safe!

The wrench said she was too rich and adjusted accordinly, however, it is now worse than it was. I am taking it back this week. I'll share the knowledge and suggestions.

David

Ted Stringer · 08-20-2001, 04:43 AM

Beware of the diferent FI systems here.

Marshall, you have the CIS injection and CDI ignition. Very similiar to a 911SC.

David, you have a mototronic FI and ignition system. This is a fully integrated fuel delivery and ignition.

------------------
Ted Stringer
nuke3@juno.com
'84 911 Targa aka pocketrocket

Marshall Deems · 08-21-2001, 12:06 AM

Thanks guys for responding! I have since taken half the engine apart to look for possible causes primarily to trace the green distributor wire. It seems to go diectly to the ignition box. Funny thing that a small portion of the wire insulation was cut away near the plug that goes into the box. The previous owner must have had a reason... perhaps to check the signal from the distributor? I will now remove the mounting plate that holds the relays and the ignition box. I still think that there is a short beneath the yellow relay. I'm sure that someone will mention the fuel pressure from the fuel pump. All I know is that the car runs perfect 99% of the time. It drives me crazy when it acts up. Since the intercooler, air cleaner housing and A/C compressor are removed, it has allowed me to have a better look at all the connections. Everything is intact. I may have to check the continuity of the green wire. When all is said and done, I probably won't know what I did to fix the problem but I'll have a super clean engine. From searching the threads,the cause of the stalling could be just about anything. I just want to avoid buying a whole bunch of stuff. Happy to here from you.

logician · 06-25-2002, 05:29 PM

Hi Marshal,

I'm curious if you ever found the cause of your problem with intermittent stalling. My '86 930 is exhibiting the exact same symptoms -- engine cuts out, tach goes to zero.

I've looked at the schematics, and a likely explanation is either that the yellow relay or the CDI unit is cutting out. The yellow relay supplies power to the CDI. Another possible explanation is that the distributor sensor is bad. In any event, the fact that the tach goes to zero points to a problem with the ignition, and not fuel.

-Juan

dean · 06-26-2002, 04:45 PM

The fuel pumps on CIS cars are not supposed to run with the key on. Only when the flapper get air flow or cranking. Safety issue. If the tach goes dead it's ign.

logician · 06-26-2002, 09:53 PM

Hi,

> The fuel pumps on CIS cars are not supposed
> to run with the key on. Only when the flapper
> get air flow or cranking. Safety issue.

Right, I can see that from the scematics.

> If the tach goes dead it's ign.

Right. Question is what part of the ignition is bad? The delay time relay seems likely. But it could also be CDI unit (I've got a Permatune), or the distributor pickup, or some loose wire in the ignition. I'm curious what experience others might have. It's one of those things where the problem is intermittent, so I can't just take it to my mechanic.

-Juan

dean · 06-27-2002, 04:33 AM

My green dist. wire was butchered by the PO, so I replaced it. $21 or so. I heard Permatunes are junk, I also heard from one guy that his MSD would fail. So I don't know what to tell you. I would call Spermatune and see if they will send you a loaner unit (yea right) or have any ideas

logician · 07-03-2002, 05:56 PM

Hi,

For the record, I wanted to correct the following incorrect statement that I made in an earlier post:

> The yellow relay supplies power to the CDI.

Actually, the yellow relay is for over-boost protection, and cuts power to the fuel pumps. The relay that supplies power to the CDI is part number 930.617.117.01, and is further forward on the relay chassis. The yellow relay is part number 911.615.118.00/01.

-Juan

Marshall Deems · 10-02-2003, 09:27 PM

It has been a long time, but I found the problem to be the magnetic coil inside the distributor. Even a new one was defective. Caused me to go nuts. Anyway, car has been fine since I replaced the defective coil.

obrut · 10-02-2003, 09:47 PM

A mate's 930 did the same thing. It was a little wire in the middle of nowhere that ran to the over boost protection circuit - had to pull the i-cooler to get to it... Another possible related symptom seemed to the be the boost gauge in the tach going funky

You can bridge out the fuel pump relays to get around it until you have it fixed - however, your pumps will run as soon as you turn the key on so the car should be started ASAP.

Cheers - Ryan