Intermittent engine cutout

I'm having trouble with my '95 GTS where the engine will suddenly quickly cut out and on several times before operating fine. The "check engine" light also comes on and off while this is happening.

Anyone have an idea what's going on? It seems electrical.

I always recommend working on the easy things before diving deeper.  There are three relays that are needed for the engine to run, they are;

XXII EZK Ignition System
XXV LH-Fuel Injection
XXVI Fuel pump

They are all the same part number: 141.951.253.B (note, this is the same P/N as the horn relay which can be substituted in an emergency).

I recommend using special "relay puller pliers" as they can be difficult to remove using standard pliers.  An internet search will yield several choices.

In any Porsche 928 I suggest changing all these relays as the contact points carbon over and resistance increases with age.  Inspect the contact pins for corrosion and clean as necessary.  Also inspect the fuses for corrosion.

Does the check engine light go off by it self, or must it be cleared we a diagnostic tool?  If a diagnostic tool has been used, what trouble does it report?  The Porsche 928 requires a special tool, a Bosch KTS 300 (it was built prior to the OBD standard testers).  A few 928 vendors sell their own tools.

Other areas to check for corrosion are the coil wires and grounds around the car (anywhere brown wires are screwed into the chassis).

If the intermittent cut-out problems continue, common problems include a MAF that is out of calibration, a failing LH fuel injection module.  

I can email you an overview of the fuel and spark system that will help you understand the systems.  Drop me a note at info@electronikrepair.com




 

Thanks for the quick reply, it is very helpful.

I'll look at and/or replace all 3 relays. I cannot find anywhere to purchase the Bosch tool for ready the codes.

The "check engine" light comes on when the problem is occurring but is otherwise off.

I'll let you know how it goes.

 A Quick update. I picked up a relay puller and got all 3 relays out. The contacts looked good and the “on” resistance was about 0.1 ohm for all 3. I have new ones coming tomorrow and will go ahead and replace them.

Good progress.  Failing relays can have resistance increase as they heat up due to the carbon build up on the contact points.

Don't overlook checking all the ground points on the chassis.  There is one behind the central electric (fuse) panel. Take the fasteners loose that hold the panel in place and look behind it.  This diagram indicates the ground points on your 928 GTS.

I got some time this morning and replaced the 3 relays and checked all the ground connections. Thanks for the diagram. They all looked fine.

On a test drive everything seemed fine until I took the RPMs up to 4,000 and held it there. The intermittent cutout occurred again. It happens very fast and usually only lasts 3-5 times before returning to normal and then within 20-30 seconds it does it again. Taking the RPMs up to around 4,000 and then shifting up the problems does not seem to happen. It appears the higher RPMs must be held awhile before the problem occurs. Today, the "check engine" light did not appear to come off and on.

The MAF was replaced in 2013 20,000 miles ago. The engine bay wiring harness was replaced 2014.

What are your suggestions?